Central Chirality and Axial Chirality Recognition of the Enantioselective Antibodies to Herbicide Metolachlor

Enantioselective antibodies have emerged as efficient tools in the field of chiral chemical detection and separation. However, it is complicated to obtain a highly stereoselective antibody due to the unclear recognition mechanism. In this study, the hapten of metolachlor was synthesized and enantio-separated. The absolute configuration of the four haptens obtained was identified by the computed and experimental electronic circular dichroism comparison. Five polyclonal antibodies against the Rac-metolachlor and its enantiomers were generated by immunization. The cross-activity of all the 5 antibodies with 44 structural analogues, including metolachlor enantiomers, was tested. It demonstrated that antibodies have higher specificity to recognize central chirality than axial chirality. Especially, αRR-MET-Ab exhibited excellent specificity and stereoselectivity. Accordingly, 3D-QSAR models were constructed and revealed that paired stereoisomers exhibited opposite interactions with the antibodies. It is the first time that the antibodies against four stereoisomers were prepared and analyzed, which will be conducive to the rational design of the stereoselective antibodies.

Chiral Heterometallic Cu8Ln4 Complexes with Enantiopure Schiff Base Ligands: Synthesis, Structural, Spectroscopic and Magnetic Studies

The enantiomerically pure Schiff base ligands H2L-S and H2L-R yield chiral heterometallic dodecanuclear complexes of the form [Cu8Ln4(OH)8(OMe)4(O2CBut)8(L-S or L-R)4(H2O)4] where LnIII = Gd (1S), Tb (2S), Dy (3S, 3R), Ho (4S, 4R), Er (5S) or Y (6S, 6R) and H2L = (S or R)-2-{[(1-hydroxypropan-2-yl)imino]methyl}-6-methoxyphenol. The complexes are isomorphous and crystallize in the non-centrosymmetric polar space group C2 in enantiomeric conformation. The chirality of the Schiff base ligands originates from the respective S- or R- enantiomer of 2-aminopropan-1-ol, is imparted to the complexes and to the crystals that belong to non-centrosymmetric space group. The chirality and enantiomeric conformation of all complexes are retained in dmso solutions as confirmed by Circular Dichroism spectra which consist of mirror images, expected for enantiomeric pairs. All complexes consist of four distorted cubane-like subunits [Cu2Ln2(m3-OH)2(m3-OMe)(m3-OR)], which share the LnIII ions and result in a cyclic distorted tetragonal arrangement; each edge of the {LnIII4} quadrilateral is occupied by two m-OH- ions that further bridge to a CuII ion. Magnetic susceptibility measurements revealed ferromagnetic interactions for 3S with LnIII = Dy and antiferromagnetic interactions for all other complexes. AC susceptibility data of 3S under 1 kOe external dc field indicate slow magnetic relaxation phenomena below 2 K.

Pharmaceutical Residues in Edible Oysters along the Coasts of the East and South China Seas and Associated Health Risks to Humans and Wildlife

The investigation of pharmaceuticals as emerging contaminants in marine biota has been insufficient. In this study, we examined the presence of 51 pharmaceuticals in edible oysters along the coasts of the East and South China Seas. Only nine pharmaceuticals were detected. The mean concentrations of all measured pharmaceuticals in oysters per site ranged from 0.804 to 15.1 ng g-1 of dry weight, with antihistamines being the most common. Brompheniramine and promethazine were identified in biota samples for the first time. Although no significant health risks to humans were identified through consumption of oysters, 100-1000 times higher health risks were observed for wildlife like water birds, seasnails, and starfishes. Specifically, sea snails that primarily feed on oysters were found to be at risk of exposure to ciprofloxacin, brompheniramine, and promethazine. These high risks could be attributed to the monotonous diet habits and relatively limited food sources of these organisms. Furthermore, taking chirality into consideration, chlorpheniramine in the oysters was enriched by the S-enantiomer, with a relative potency 1.1-1.3 times higher when chlorpheniramine was considered as a racemate. Overall, this study highlights the prevalence of antihistamines in seafood and underscores the importance of studying enantioselectivities of pharmaceuticals in health risk assessments.

Enantioselective metabolism of fenpropathrin enantiomers by carboxyl/choline esterase 6 in Tetranychus cinnabarinus

BACKGROUND

Tetranychus cinnabarinus is a polyphagous pest mite commonly found in agriculture. As an excellent acaricide, fenpropathrin (FEN) is frequently used to control T. cinnabarinus in agriculture. However, commercial FEN is a racemate with two enantiomers, R-FEN and S-FEN. Considering that investigations on the metabolism of FEN by T. cinnabarinus are based on racemate FEN, it is important to investigate the enantioselective metabolism of FEN in T. cinnabarinus.

RESULTS

S-FEN was more toxic to T. cinnabarinus than R-FEN by more than 68.8-fold. Moreover, the synergist bioassay revealed that carboxylesterase and cytochrome P450 were the primary enzymes engaged in the detoxification of FEN in T. cinnabarinus, with carboxylesterase playing a leading role. Seven genes were substantially different after the induction of S-FEN and R-FEN. TcCCE06 was screened and selected as a key gene that related to FEN metabolism in T. cinnabarinus. The metabolic results showed that the recombinant TcCCE06 effectively metabolized 32.1% of the R-FEN and 13.8% of the S-FEN within 4 h of incubation. Moreover, R-FEN was demonstrated to have a higher affinity for the TcCCE06 protein than S-FEN based on molecular docking.

CONCLUSION

Our results indicated that TcCCE06 mediates the enantioselective metabolism of FEN in T. cinnabarinus. Our findings will contribute to a more comprehensive understanding of the mechanisms underlying the differential toxicity of the FEN enantiomers against T. cinnabarinus. Furthermore, they also provide a new perspective for the development of enantiomer-enriched acaricides with higher activity and lower pesticide dosage and pollution risks. © 2023 Society of Chemical Industry.

An enantioselective study of β-cyclodextrin and ionic liquid-β-cyclodextrin towards propranolol enantiomers by molecular dynamic simulations

In this study, the enantioselectivity of β-cyclodextrin and its derivatives towards propranolol enantiomers are investigated by molecular dynamic (MD) simulations. β-cyclodextrin (β-CD) have previously been shown to be able to recognize propranolol (PRP) enantiomers. To improve upon the enantioselectivity of β-cyclodextrin, we propose the use of an ionic-liquid-modified-β-cyclodextrin (β-CD-IL). β-CD-IL was found to be able to complex R and S propranolol enantiomers with differing binding energies. The molecular docking study reveals that the ionic liquid chain attached to the β-CD molecule has significant interaction with propranolol. The formation of the most stable complex occurred between (S)-β-CD-IL and (S)-propranolol with an energy of -5.80 kcal/mol. This is attributed to the formation of a hydrogen bond between the oxygen of the propranolol and the hydrogen on the primary rim of the (S)-β-CD-IL cavity. This interaction is not detected in other complexes. The root mean-squared fluctuation (RMSF) value indicates that the NH group is the most flexible molecular fragment, followed by the aromatic group. Also of note, the formation of a complex between pristine β-CD and (S)-propranolol is the least favorable.

Molecular properties, structure and chiral resolution of secondary metabolites from the leaves of Viburnum chingii

A chemical investigation of leaves of Viburnum chingii afforded eleven compounds, including one undescribed lignan (1), a pair of known phenylpropanoid enantiomers (2a/2b), and eight known lignans (3-10). Their structures were elucidated by detailed spectroscopic and comparative literature data analysis. The absolute configurations of compounds 1 was determined by comparing the experimental ECD data with the calculated values. The compounds 2a/2b were separated successfully by a chiral chromatographic column. In addition, the acetylcholinesterase (AChE) inhibitory activities of described compounds were evaluated.

Pharmacokinetics of d- and l-norfenfluramine following their administration as individual enantiomers in rats

The effect of fenfluramine and norfenfluramine enantiomers in rodent seizure models and their correlation with the pharmacokinetics of d- and l-fenfluramine in rats have been reported recently. To complement these findings, we investigated the pharmacokinetics of d- and l- norfenfluramine in rat plasma and brain. Sprague-Dawley rats were injected intraperitoneally with 20 mg/kg and 1 mg/kg l- norfenfluramine. A 1 mg/kg dose of d-norfenfluramine was used because higher doses caused severe toxicity. The concentration of each enantiomer in plasma and brain was determined at different time points by liquid chromatography/mass spectrometry. Pharmacokinetic parameters were compared between norfenfluramine enantiomers, and with those reported previously for fenfluramine enantiomers after a 20 mg/kg, i.p., dose. All enantiomers were absorbed rapidly and eliminated, with half-lives ranging from 0.9 h (l-fenfluramine) to 6.1 h (l- norfenfluramine, 20 mg/kg) in plasma, and from 3.6 h (d-fenfluramine) to 8.0 h (l-fenfluramine) in brain. Brain-to-plasma concentration ratios ranged from 15.4 (d-fenfluramine) to 27.6 (d-norfenfluramine), indicating extensive brain penetration. The fraction of d- and l-fenfluramine metabolized to norfenfluramine was estimated to be close to unity. This work is part of ongoing investigations to determine the potential value of developing enantiomerically pure l-fenfluramine or l-norfenfluramine as follow-up compounds to the marketed racemic fenfluramine.

[Chiral capillary gas chromatography for the separation of the enantiomers of 4-chloromethyl-2,2-dimethyl-1,3-dioxolane]

Chiral compounds play an important role in the pharmaceutical industry owing to their unique biological activities. The enantiomers must be separated because they can exhibit different pharmacological activities. Thus, the development of chiral separation methods is essential to determine the purity of enantiomers. 4-Chloromethyl-2,2-dimethyl-1,3-dioxolane is an important chiral pharmaceutical intermediate. In this context, a method based on chiral capillary gas chromatography was established for the separation and determination of the enantiomers of 4-chloromethyl-2,2-dimethyl-1,3-dioxolane. The separation of (R)- and (S)-4-chloromethyl-2,2-dimethyl-1,3-dioxolane was initially investigated using two conventional stationary-phase capillary columns: SH-I-5Sil MS and SH-WAX. The stationary phase of SH-I-5Sil MS consisted of 5% phenyl and 95% polymethylsiloxane, whereas the stationary phase of SH-WAX consisted of 100% crosslinked polyethylene glycol. Neither of the columns exhibited chiral selectivity, so they both were unable to separate the enantiomers of 4-chloromethyl-2,2-dimethyl-1,3-dioxolane. Subsequently, the separation of (R)- and (S)-4-chloromethyl-2,2-dimethyl-1,3-dioxolane was investigated using four chiral columns: Rt-bDEXm, Rt-bDEXsm, Rt-bDEXse, and InertCap CHIRAMIX. Among the chiral columns, Rt-bDEXse, which used a stationary phase composed of 2,3-di-O-ethyl-6-O-tert-butyl dimethylsilyl β-cyclodextrin added to 14% cyanopropyl phenyl and 86% dimethyl polysiloxane, achieved the best separation of (R)- and (S)-4-chloromethyl-2,2-dimethyl-1,3-dioxolane. Thus, this column was selected as the analytical column for further method optimization. Detection was performed using a hydrogen flame ionization detector. The effects of various gas chromatographic parameters, such as linear velocity, initial column temperature, column heating rate, and solvent type, on the separation of (R)- and (S)-4-chloromethyl-2,2-dimethyl-1,3-dioxolane were investigated. The optimal chromatographic conditions included a linear velocity of 70 cm/s, an initial column temperature of 70 ℃, and a column heating rate of 2.0 ℃/min. The final column oven temperature was 150 ℃. Methanol, ethanol, ethyl acetate, n-hexane, dichloromethane, and dimethyl sulfoxide were selected as solvents. The results showed that dimethyl sulfoxide interfered with the peaks of the target compounds, whereas the other solvents had no significant effect on the peak shape and separation of (R)- and (S)-4-chloromethyl-2,2-dimethyl-1,3-dioxolane. Methanol was finally selected as the solvent in this study. Further experiments revealed that (R)- and (S)-4-chloromethyl-2,2-dimethyl-1,3-dioxolane could be rapidly separated within 10 min, with a resolution greater than 1.5. A good linear relationship was observed in the range of 0.5-50.0 mg/L, with a linear correlation coefficient greater than 0.998. The limits of detection for (R)- and (S)-4-chloromethyl-2,2-dimethyl-1,3-dioxolane were 0.07 and 0.08 mg/L, respectively, and the corresponding limits of quantification were 0.22 and 0.25 mg/L, respectively. Spiked recovery tests were performed at three spiked levels of 0.5, 2.0, and 10.0 mg/L using methanol as the blank to determine the accuracy of the proposed method. The recoveries for (R)- and (S)-4-chloromethyl-2,2-dimethyl-1,3-dioxolane were 94.0%-99.1% and 96.0%-98.8%, respectively, with relative standard deviations (RSDs) of 1.26%-4.87% and 1.51%-4.46%, respectively. The established method is efficient and reliable; thus, it can serve as a reference for the separation of the enantiomers of 4-chloromethyl-2,2-dimethyl-1,3-dioxolane. It can also potentially be applied to evaluate the enantiomeric purity of other chiral compounds in the pharmaceutical industry and produce chiral drugs and other related compounds.

Nature-Inspired Chiral Structures: Fabrication Methods and Multifaceted Applications

Diverse chiral structures observed in nature find applications across various domains, including engineering, chemistry, and medicine. Particularly notable is the optical activity inherent in chiral structures, which has emerged prominently in the field of optics. This phenomenon has led to a wide range of applications, encompassing optical components, catalysts, sensors, and therapeutic interventions. This review summarizes the imitations and applications of naturally occurring chiral structures. Methods for replicating chiral architectures found in nature have evolved with specific research goals. This review primarily focuses on a top-down approach and provides a summary of recent research advancements. In the latter part of this review, we will engage in discussions regarding the diverse array of applications resulting from imitating chiral structures, from the optical activity in photonic crystals to applications spanning light-emitting devices. Furthermore, we will delve into the applications of biorecognition and therapeutic methodologies, comprehensively examining and deliberating upon the multifaceted utility of chiral structures.

A Direct Analysis of β-N-methylamino-l-alanine Enantiomers and Isomers and Its Application to Cyanobacteria and Marine Mollusks

Of the wide variety of toxic compounds produced by cyanobacteria, the neurotoxic amino acid β-N-methylamino-l-alanine (BMAA) has attracted attention as a result of its association with chronic human neurodegenerative diseases such as ALS and Alzheimer's. Consequently, specific detection methods are required to assess the presence of BMAA and its isomers in environmental and clinical materials, including cyanobacteria and mollusks. Although the separation of isomers such as β-amino-N-methylalanine (BAMA), N-(2-aminoethyl)glycine (AEG) and 2,4-diaminobutyric acid (DAB) from BMAA has been demonstrated during routine analysis, a further compounding factor is the potential presence of enantiomers for some of these isomers. Current analytical methods for BMAA mostly do not discriminate between enantiomers, and the chiral configuration of BMAA in cyanobacteria is still largely unexplored. To understand the potential for the occurrence of D-BMAA in cyanobacteria, a chiral UPLC-MS/MS method was developed to separate BMAA enantiomers and isomers and to determine the enantiomeric configuration of endogenous free BMAA in a marine Lyngbya mat and two mussel reference materials. After extraction, purification and derivatization with N-(4-nitrophenoxycarbonyl)-l-phenylalanine 2-methoxyethyl ester ((S)-NIFE), both L- and D-BMAA were identified as free amino acids in cyanobacterial materials, whereas only L-BMAA was identified in mussel tissues. The finding of D-BMAA in biological environmental materials raises questions concerning the source and role of BMAA enantiomers in neurological disease.

New benzofuran neolignans with neuroprotective activity from Phyllanthodendron breynioides

A pair of undescribed dihydrobenzofuran neolignan enantiomers, (+/-)-phybrenan A (1a/1b), two new benzofuran neolignans, phybrenan B and C (2 and 3), along with four known neolignans (4 - 7) were obtained from the plants of Phyllanthodendron breynioides P. T. Li. The planar structures of all isolates were demonstrated by the analysis of detailed spectroscopic evidence (NMR, HRMS, and IR), and the absolute configurations of novel neolignans were elucidated by combined calculated and experimental ECD data analysis. The neuroprotective activities of all benzofuran neolignans against sodium nitroprusside (SNP)-induced cell death were examined in rat pheochromocytoma PC12 cells. The results exhibited that three compounds (4 - 6) possessed remarkable neuroprotective activities at 10 µM, better than the positive drug edaravone.

Enantiomeric Complexes Based on Ruthenium(III) and 2,2'-Biimidazole: X-ray Structure and Magnetic Properties

We have prepared and characterized two Ru(III) compounds based on the 2,2'-biimidazole (H2biim) ligand, namely, a single complex of formula cis-[RuCl2(H2biim)2]Cl·4H2O (1) and a racemic mixture of formula {cis-[RuCl2(H2biim)2]Cl}2·4H2O (2), which contains 50% of Ru(III) complex 1. Both compounds crystallize in the monoclinic system with space groups C2 and P21 for 1 and 2, respectively. These complexes exhibit the metal ion bonded to four nitrogen atoms from two H2biim molecules and two chloride ions, which balance part of the positive charges in a distorted octahedral geometry. Significant differences are observed in their crystal packing, which leads to the observation of differences in their respective magnetic behaviors. Despite having imidazole rings in both compounds, π-π stacking interactions occur only in the crystal structure of 2, and the shortest intermolecular Ru···Ru separation in 2 is consequently shorter than that in 1. Variable-temperature dc magnetic susceptibility measurements performed on polycrystalline samples of 1 and 2 reveal different magnetic behaviors at low temperatures: while 1 behaves pretty much as a magnetically isolated mononuclear Ru(III) complex with S = 1/2, 2 exhibits the behavior of an antiferromagnetically coupled system with S = 0 and a maximum in the magnetic susceptibility curve at approximately 3.0 K.

The Phenomenon of Self-Induced Diastereomeric Anisochrony and Its Implications in NMR Spectroscopy

Nuclear magnetic resonance (NMR) spectroscopy is an analytical technique largely applied in the analysis of discrimination processes involving enantiomeric substrates and chiral agents, which can interact with the analyte either via covalent bonding or via formation of diastereomeric solvates. However, enantiodiscrimination has been observed, in some cases, even in the absence of any additional chiral selector. The reasons behind this phenomenon must be found in the capability of some chiral substrates to interact with themselves by forming diastereomeric solvates in solution that can generate nonequivalences in the NMR spectra of enantiomerically enriched mixtures. As a result, differentiation of enantiomers is observed, thus allowing the quantification of the enantiomeric composition of the mixture under investigation. The tendency of certain substrates to self-aggregate and to generate diastereomeric adducts in solution can be defined as Self-Induced Diastereomeric Anisochrony (SIDA), but other acronyms have been used to refer to this phenomenon. In the present work, an overview of SIDA processes investigated via NMR spectroscopy will be provided, with a particular emphasis on the nature of the substrates involved, on the interaction mechanisms at the basis of the phenomenon, and on theoretical treatments proposed in the literature to explain them.

A New Essential Oil from the Native Andean Species Nectandra laurel Klotzsch ex Nees of Southern Ecuador: Chemical and Enantioselective Analyses

The leaves of Nectandra laurel Klotzsch ex Nees, belonging to the family, Lauraceae, were collected in the province of Loja (Ecuador), dried, and analytically steam-distilled. An unprecedented essential oil was obtained, with a 0.03% yield by weight of dry plant material. The volatile fraction was submitted to qualitative (GC-MS) and quantitative (GC-FID) chemical analysis, on two orthogonal stationary phases. Seventy-eight compounds were detected and quantified on at least one column. The essential oil was dominated by sesquiterpene hydrocarbons (53.0-53.8% on the non-polar and polar stationary phase, respectively), followed by oxygenated sesquiterpenoids (18.9-19.0%). A third group was constituted by metabolites of other origins, mainly aliphatic compounds, apparently derived from the acetate pathway (11.7-8.5%). The major components of the EO (≥3.0% with at least one column) were δ-selinene (30.5-28.8%), δ-cadinene (5.4-6.4%), epi-α-cadinol (4.9-5.2%), an undetermined compound with a molecular weight of 204 (3.4-4.2%), α-pinene (3.3-2.9%), and α-cadinol (2.9-3.0%). Finally, the essential oil was submitted to enantioselective analysis, on two β-cyclodextrin-based chiral selectors, determining the enantiomeric distribution of seven chiral terpenes. Among them, (1R,5R)-(+)-α-pinene, (1R,5R)-(+)-β-pinene, and (R)-(-)-α-phellandrene were enantiomerically pure, whereas camphene, borneol, α-copaene, and α-terpineol were present as scalemic mixtures.

A New Leaf Essential Oil from Endemic Gynoxys laurifolia (Kunth) Cass. of Southern Ecuador: Chemical and Enantioselective Analyses

The fresh leaves of Gynoxys laurifolia (Kunth) Cass. (Asteraceae), collected in the province of Loja (Ecuador), were submitted to steam distillation, producing an essential oil with a yield of 0.02% by weight. This volatile fraction, described here for the first time, was submitted to qualitative (GC-MS) and quantitative (GC-FID) chemical analyses, on two orthogonal columns (non-polar and polar stationary phase). A total of 90 components, corresponding to 95.9-95.0% by weight on the non-polar and polar stationary phase, respectively, were detected and quantified with at least one column. Major constituents (≥3%) were: germacrene D (18.9-18.0%), (E)-β-caryophyllene (13.2-15.0%), α-pinene (11.0-10.3%), β-pinene (4.5-4.4%), β-phellandrene (4.0-3.0%), bicyclogermacrene (4.0-3.0%), and bakkenolide A (3.2-3.4%). This essential oil was dominated by sesquiterpene hydrocarbons (about 45%), followed by monoterpene hydrocarbons (about 25-30%). This research was complemented with the enantioselective analysis of some common chiral terpenes, carried out through 2,3-diethyl-6-tert-butyldimethylsilyl-β-cyclodextrin and 2,3-diacetyl-6-tert-butyldimethylsilyl-β-cyclodextrin as stationary phase chiral selectors. As a result, (1S,5S)-(-)-β-pinene, (R)-(-)-α-phellandrene, (R)-(-)-β-phellandrene, (S)-(-)-limonene, (S)-(+)-linalyl acetate, and (S)-(-)-germacrene D were observed as enantiomerically pure compounds, whereas α-pinene, linalool, terpinene-4-ol, and α-terpineol were present as scalemic mixtures. Finally, sabinene was practically racemic. Due to plant wildness and the relatively low distillation yield, no industrial applications can be identified, in the first instance for this essential oil. The focus of the present study is therefore academic.

Structurally diverse lignans from Solanum lyratum: chemical evidence for their acetylcholinease inhibitory activity

A chemical investigation of Solanum lyratum Thumb. (Solanace) afforded two new lignans (1b and 3) and eleven known lignan analogues (1a, 2a/2b and 4-11). Compounds 1a/1b and 2a/2b were separated as two pairs of enantiomers by chiral high-performance liquid chromatography (HPLC). Their structures were elucidated by detailed spectroscopic and comparative literature data analysis. The absolute configurations of compounds 1a/1b and 2a/2b were determined by comparing the experimental ECD data with the calculated values. All compounds were evaluated for their acetylcholinesterase (AChE) inhibitory activity. Notably, compared to the positive control, compounds 4 and 9 showed obvious AChE inhibition with their IC50 values of 1.30 ± 0.25 and 0.89 ± 0.04 μM, respectively. In addition, the possible interaction between acetylcholinesterase and the active compounds was also investigated by molecular docking.

The Role of Functional Groups in Tuning the Self-Assembly Modes and Physical Properties of Multicomponent Gels

We have analyzed the nature and role of functional groups on the self-assembly modes and the physical properties of multicomponent gels with structurally similar individual components. The gelation properties of individual and mixed enantiomeric compounds of biphenyl bis-(amides) of alanine (BPA) or phenylalanine (BPP) methyl ester were analyzed in various solvent/solvent mixtures. Multicomponent gels were formed by mixing the enantiomeric BPP compounds at a lower concentration, but a higher concentration was required for mixed alanine-based BPA gels. The comparison of the mechanical strength of the individual and mixed BPP compounds indicated that the mixed BPP gels displayed enhanced mechanical strength (∼2-fold increase) in p-xylene, but a weaker gel was observed in DMSO/water. However, a reverse trend was observed for BPA gels, indicating the role of functional groups in the gel network formation. X-ray diffraction analysis of the gelator and the xerogels in the solid state confirmed the formation of co-assembled networks in mixed enantiomeric gels. The stability of the gels towards anions was evaluated by analyzing the anion induced stimuli-responsive properties. These results indicate the effective modeling of the functional groups of the individual components could lead to multicomponent gels with tunable properties.

Sex- and enantiospecific differences in the formation rate of hydroxyeicosatetraenoic acids in rat organs

Hydroxyeicosatetraenoic acids (HETEs) are hydroxylated arachidonic acid (AA) metabolites that are classified into midchain, subterminal, and terminal HETEs. Hydroxylation results in the formation of R and S enantiomers for each HETE, except for 20-HETE. HETEs have multiple physiological and pathological effects. Several studies have demonstrated sex-specific differences in AA metabolism in different organs. In this study, microsomes from the heart, liver, kidney, lung, intestine, and brain of adult male and female Sprague-Dawley rats were isolated and incubated with AA. Thereafter, the enantiomers of all HETEs were analyzed by liquid chromatography-tandem mass spectrometry. We found significant sex- and enantiospecific differences in the formation levels of different HETEs in all organs. The majority of HETEs, especially midchain HETEs and 20-HETE, showed significantly higher formation rates in male organs. In the liver, the R enantiomer of several HETEs showed a higher formation rate than the corresponding S enantiomer (e.g., 8-, 9-, and 16-HETE). On the other hand, the brain and small intestine demonstrated a higher abundance of the S enantiomer. 19(S)-HETE was more abundant than 19(R)-HETE in all organs except the kidney. Elucidating sex-specific differences in HETE levels provides interesting insights into their physiological and pathophysiological roles and their possible implications for different diseases.

Innovative insight into the mechanism of enantioselective skin permeation for chiral drugs

OBJECTIVES

A profound comprehension of the molecular mechanisms underpinning the enantioselective transdermal permeation of chiral drugs is critical in the design and assessment of transdermal preparations. The primary objective of this study is to investigate the distinct skin permeation behaviors exhibited by enantiomers of non-steroidal anti-inflammatory drugs (NSAIDs) and elucidate the intricate molecular mechanism at play.

METHODS

In vitro and in vivo transdermal permeation studies of chiral NSAIDs were performed using transdermal patch and solution system. Chiral interaction between NSAIDs enantiomers and synthesized chiral ceramide present in the skin was characterized to clarify the different transdermal behaviors.

RESULTS

The S-enantiomers of NSAIDs exhibited higher permeability through the skin than R-enantiomer in vitro (1.5-fold) and in vivo (2.0-fold), which was attributed to a stronger interaction between S-enantiomer and ceramide caused by more favorable spatial conformations. S-enantiomer required lower activation energy (24.4 kJ/mol) and Gibbs energy (43.3 kJ/mol), which was favorable in forming the H-bond with ceramide in the skin, resulting in more permeation.

CONCLUSION

This research furnished an innovative comprehension of the molecular underpinnings governing the enantioselective permeation of drug enantiomers through the skin, fostering the minimization of undesired enantiomer ingestion (distomers) and amplifying therapeutic efficiency.

Dissimilar effects of stereoisomers and racemic hydroxychloroquine on Ca2+ oscillations in human induced pluripotent stem cell-derived cardiomyocytes

All currently employed pharmaceutical formulations of hydroxychloroquine (HCQ) sulfate are a racemate, consisting of equal parts mixture of two stereoisomers: R(-)HCQ and S(+)HCQ sulfates. The aims of the current study were first, to obtain and characterize pure HCQ enantiomers. The separation and purification of free base HCQ enantiomers from the racemate form were performed using semi-preparative chiral high-performance liquid chromatography. Second, we compared the pharmacological properties of both optical isomers and racemic mixture on the intracellular Ca2+ oscillations employing an in vitro model of human cardiomyocytes derived from induced pluripotent stem cells (iPSCs). The results of the pharmacological investigations indicate that the racemic and pure stereoisomer forms of HCQ sulfate exhibited a dose-dependent inhibition of spontaneous Ca2+ oscillations (as measured from their frequency and Ca2+ peak widths) in cardiomyocytes 5-45 min following exposure. In addition, the concentration-response relationships for all three compounds indicated that the rank order of potency (IC50 ) was R(-)HCQ >racemic HCQ >S(+)HCQ for the frequency of the Ca2+ oscillations and width of Ca2+ peaks for all time points examined. These studies indicate that both R(-) and S(+) stereoisomers exhibit differing pharmacological actions on hiPSC cardiomyocytes, with the former effecting a greater potency on cell Ca2+ handling.

Enantiomeric Separation and Degradation of Benoxacor Enantiomers in Horticultural Soil by Normal-Phase and Reversed-Phase High Performance Liquid Chromatography

The separation of benoxacor enantiomers on six commercial chiral columns was investigated by high-performance liquid chromatography (HPLC) under normal-phase and reversed-phase conditions. The mobile phases included hexane/ethanol, hexane/isopropanol, acetonitrile/water, and methanol/water. The effects of the chiral stationary phases (CSPs), temperature, and mobile phase composition and ratio on the separation of benoxacor enantiomers were examined. Under normal-phase conditions, the two benoxacor enantiomers were completely separated on Chiralpak AD, Chiralpak IC, Lux Cellulose-1, and Lux Cellulose-3 columns and partially separated on a Lux Cellulose-2 column. Under reversed-phase conditions, benoxacor enantiomers were completely separated on a Lux Cellulose-3 column and partially separated on Chiralpak IC and Lux Cellulose-1 columns. Normal-phase HPLC performed better than reversed-phase HPLC for the separation of benoxacor enantiomers. As the column temperature increased from 10 °C to 4 °C, the enthalpy (ΔH) and entropy (ΔS) results indicated that the resolution was strongly affected by the temperature and that the lowest temperature did not always produce the best resolution. An optimized separation method on the Lux Cellulose-3 column was used to investigate the stability of benoxacor enantiomers in solvents and the degradation of benoxacor enantiomers in three types of horticultural soil. Benoxacor enantiomers were stable, and degradation or racemization were not observed in methanol, ethanol, isopropanol, acetonitrile, hexane, or water (pH = 4.0, 7.0, and 9.0). In three horticultural soils, the degradation rate of S-benoxacor was faster than that of R-benoxacor, resulting in soil enrichment with R-benoxacor. The results of this study will help to improve the risk assessment of enantiomer levels of benoxacor in the environment.

Enantioseparation Membranes: Research Status, Challenges, and Trends

The purity of enantiomers plays a critical role in human health and safety. Enantioseparation is an effective way and necessary process to obtain pure chiral compounds. Enantiomer membrane separation is a new chiral resolution technique, which has the potential for industrialization. This paper mainly summarizes the research status of enantioseparation membranes including membrane materials, preparation methods, factors affecting membrane properties, and separation mechanisms. In addition, the key problems and challenges to be solved in the research of enantioseparation membranes are analyzed. Last but not least, the future development trend of the chiral membrane is expected.

Neurosteroids as stress modulators and neurotherapeutics: lessons from the retina

Neurosteroids are rapidly emerging as important new therapies in neuropsychiatry, with one such agent, brexanolone, already approved for treatment of postpartum depression, and others on the horizon. These steroids have unique properties, including neuroprotective effects that could benefit a wide range of brain illnesses including depression, anxiety, epilepsy, and neurodegeneration. Over the past 25 years, our group has developed ex vivo rodent models to examine factors contributing to several forms of neurodegeneration in the retina. In the course of this work, we have developed a model of acute closed angle glaucoma that involves incubation of ex vivo retinas under hyperbaric conditions and results in neuronal and axonal changes that mimic glaucoma. We have used this model to determine neuroprotective mechanisms that could have therapeutic implications. In particular, we have focused on the role of both endogenous and exogenous neurosteroids in modulating the effects of acute high pressure. Endogenous allopregnanolone, a major stress-activated neurosteroid in the brain and retina, helps to prevent severe pressure-induced retinal excitotoxicity but is unable to protect against degenerative changes in ganglion cells and their axons under hyperbaric conditions. However, exogenous allopregnanolone, at a pharmacological concentration, completely preserves retinal structure and does so by combined effects on gamma-aminobutyric acid type A receptors and stimulation of the cellular process of macroautophagy. Surprisingly, the enantiomer of allopregnanolone, which is inactive at gamma-aminobutyric acid type A receptors, is equally retinoprotective and acts primarily via autophagy. Both enantiomers are also equally effective in preserving retinal structure and function in an in vivo glaucoma model. These studies in the retina have important implications for the ongoing development of allopregnanolone and other neurosteroids as therapeutics for neuropsychiatric illnesses.

Synthesis, insecticidal activity, and ensembled docking of nitroguanidines bearing S- and R-proline

BACKGROUND

The amino acids R- and S-proline were used to synthesize novel neonicotinoid derivatives that, after being characterized by ¹ H, DEPTQ 135, and HRMS-QTOF, were evaluated for use as insecticides against Galleria mellonella (caterpillar), Sitophilus zeamais, Xylosandrus morigerus, Xyleborus affinis, and Xyleborus ferrugineus.

RESULTS

Comparisons of biological activity and absolute configuration showed that the R enantiomer had excellent and outstanding insecticidal activity against the insects tested, with up to 100% mortality after 12 h compared with dinotefuran at the same concentration.

CONCLUSIONS

The results suggest that compound R6 is an excellent lead enantiopure insecticide for future development in the field of crop protection. Furthermore, intermolecular interactions between nicotinic acetylcholine receptors and the R enantiomer displays a lower score which mean a higher affinity to the nAChR receptor and the π-π interactions are more stable than the S derivative. © 2023 Society of Chemical Industry.

A greener pathway to enantiopurity: mechanochemical deracemization through abrasive grinding

We report the first case of mechanochemical deracemization by using liquid-assisted abrasive grinding. The target molecule is a precursor of Paclobutrazol, an important fungicide and plant growth inhibitor. Using mechanochemical deracemization, we are even able to transform a 10% ee scalemic mixture of this latter in an enantioenriched product of 97% ee in a couple of hours. This is substantially shorter compared to solution-based deracemization methodologies. The present paper thus introduces an efficient and greener process to enantiopure material.

A Group-Theoretic Approach to the Origin of Chirality-Induced Spin-Selectivity in Nonmagnetic Molecular Junctions

Spin-orbit coupling gives rise to a range of spin-charge interconversion phenomena in nonmagnetic systems where certain spatial symmetries are reduced or absent. Chirality-induced spin-selectivity (CISS), a term that generically refers to a spin-dependent electron transfer in nonmagnetic chiral systems, is one such case, appearing in a variety of seemingly unrelated situations ranging from inorganic materials to molecular devices. In particular, the origin of CISS in molecular junctions is a matter of an intense current debate. Here, we derive a set of geometrical conditions for this effect to appear, hinting at the fundamental role of symmetries beyond otherwise relevant quantitative issues. Our approach, which draws on the use of point-group symmetries within the scattering formalism for transport, shows that electrode symmetries are as important as those of the molecule when it comes to the emergence of a spin-polarization and, by extension, to the possible appearance of CISS. It turns out that standalone metallic nanocontacts can exhibit spin-polarization when relative rotations which reduce the symmetry are introduced. As a corollary, molecular junctions with achiral molecules can also exhibit spin-polarization along the direction of transport, provided that the whole junction is chiral in a specific way. This formalism also allows the prediction of qualitative changes of the spin-polarization upon substitution of a chiral molecule in the junction with its enantiomeric partner. Quantum transport calculations based on density functional theory corroborate all of our predictions and provide further quantitative insight within the single-particle framework.

Molecular Origins of Chiral Amplification on an Achiral Surface: 2D Monolayers of Aspartic Acid on Cu(111)

Recent experiments have demonstrated an intriguing phenomenon in which adsorption of a nonracemic mixture of aspartic acid (Asp) enantiomers onto an achiral Cu(111) metal surface leads to autoamplification of surface enantiomeric excess, ee_s, to values well above those of the impinging gas mixtures, ee_g. This is particularly interesting because it demonstrates that a slightly nonracemic mixture of enantiomers can be further purified simply by adsorption onto an achiral surface. In this work, we seek a deeper understanding of this phenomena and apply scanning tunneling microscopy to image the overlayer structures formed by mixed monolayers of d- and l-Asp on Cu(111) over the full range of surface enantiomeric excess; ee_s = -1 (pure l-Asp) through ee_s = 0 (racemic dl-Asp) to ee_s = 1 (pure d-Asp). Both enantiomers of three chiral monolayer structures are observed. One is a conglomerate (enantiomerically pure), another is a racemate (equimolar mixture of d- and l-Asp); however, the third structure accommodates both enantiomers in a 2:1 ratio. Such solid phases of enantiomer mixtures with nonracemic composition are rare in 3D crystals of enantiomers. We argue that, in 2D, the formation of chiral defects in a lattice of one enantiomer is easier than in 3D, simply because the stress associated with the chiral defect in a 2D monolayer of the opposite enantiomer can be dissipated by strain into the space above the surface.

Chemical Composition and Biological Activities of Essential Oils from Origanum vulgare Genotypes Belonging to the Carvacrol and Thymol Chemotypes

The remarkable biological activities of oregano essential oils (EOs) have recently prompted a host of studies aimed at exploring their potential innovative applications in the food and pharmaceutical industries. The chemical composition and biological activities of EOs from two Origanum vulgare genotypes, widely cultivated in Sicily and not previously studied for their biological properties, were characterized. Plants of the two genotypes, belonging to the carvacrol (CAR) and thymol (THY) chemotypes and grown in different cultivation environments, were considered for this study. The chemical profiles, including the determination of enantiomeric distribution, of the EOs, obtained by hydrodistillation from dried leaves and flowers, were investigated by GC-MS. Biological activity was evaluated as antimicrobial properties against different pathogen indicator strains, while intestinal barrier integrity, reduction in pathogen adhesion and anti-inflammatory actions were assayed in the intestinal Caco-2 cell line. The chemical profile of the CAR genotype was less complex and characterized by higher levels of the most active compound, i.e., carvacrol, when compared to the THY genotype. The enantiomeric distribution of chiral constituents did not vary across genotypes, while being markedly different from that observed in Origanum vulgare genotypes from other geographical origins. In general, all EOs showed high antimicrobial activity, both in vitro and in a food matrix challenge test. Representative EOs from the two genotypes resulted not altering epithelial monolayer sealing only for concentrations lower than 0.02%, were able to reduce the adhesion of selected pathogens, but did not exert relevant anti-inflammatory effects. These results suggest their potential use as control agents against a wide spectrum of foodborne pathogens.

Separation and determination of triadimefon and its metabolites triadimenol enantiomers in fruit puree by supercritical fluid chromatography

A method was established for the separation and determination of triadimefon and its metabolite triadimenol enantiomer residues in major complementary fruit puree for infants and young children (banana puree, pineapple puree, and grape puree) by supercritical fluid chromatography. After the samples were extracted with acetonitrile and purified with a solid phase extraction cartridge, Acquity Trefoil CEL2 chiral chromatographic column was adopted for separation, and gradient elution was conducted at the flow rate of 1.0 ml/min under the mobile phase of supercritical carbon dioxide - 0.5% ammonia methanol, the detection wavelength was 220 nm and quantification was conducted with the external standard method. The limits of quantitation of triadimefon and triadimenol enantiomers were both 0.05 mg/kg, the linear ranges were 0.5-50 mg/L, and the linear correlation coefficients were greater than 0.9993. The recoveries in the spiked samples at 0.05, 0.2, and 3.0 mg/kg were from 80.1 to 106%, and the relative standard deviation reached 3.3-7.6%. The method is efficient, rapid, reproducible, and environmentally friendly, enabling accurate analysis of pesticide enantiomers, which can detect the enantiomer residues of triadimefon and its metabolite triadimenol in major complementary fruit puree for infants and young children.

Stairway to Stereoisomers: Engineering Short- and Medium-Chain Ketoreductases To Produce Chiral Alcohols

The short- and medium-chain dehydrogenase/reductase superfamilies are responsible for most chiral alcohol production in laboratories and industries. In nature, they participate in diverse roles such as detoxification, housekeeping, secondary metabolite production, and catalysis of several chemicals with commercial and environmental significance. As a result, they are used in industries to create biopolymers, active pharmaceutical intermediates (APIs), and are also used as components of modular enzymes like polyketide synthases for fabricating bioactive molecules. Consequently, random, semi-rational and rational engineering have helped transform these enzymes into product-oriented efficient catalysts. The rise of newer synthetic chemicals and their enantiopure counterparts has proved challenging, and engineering them has been the subject of numerous studies. However, they are frequently limited to the synthesis of a single chiral alcohol. The study attempts to defragment and describe hotspots of engineering short- and medium-chain dehydrogenases/reductases for the production of chiral synthons.

Enantioselectivity of chiral dihydromyricetin in multicomponent solid solutions regulated by subtle structural mutation

Multicomponent crystals of a chiral drug with non-chiral components have attracted increasing attention in the application of enantiomer purification and regulation of the physicochemical properties of crystalline materials. Crystalline solid solutions provide opportunities for fine-tuning material properties because of continuously adjustable component stoichiometry ratios. The synthesis, crystal structure, thermodynamics and solid-state enantioselectivity of a series of multicomponent crystals of chiral dihydromyricetin (DMY) with caffeine (CAF) or theophylline (THE) were investigated and the results reveal how the subtle change of molecular structure of the coformer dictates the enantiomer selectivity in multicomponent cocrystals. A series of multicomponent cocrystal solvates of chiral DMY with CAF and THE were synthesized by the slurry cocrystallization method in acetonitrile. Although most racemic mixtures crystallize as racemic compounds or conglomerates, both DMY-CAF and DMY-THE crystallize as chiral solid solutions, unveiled by pseudo-binary melt phase diagrams and pseudo-ternary solution phase diagrams. Crystal structures of Rac-DMY-CAF, R,R-DMY-CAF, Rac-DMY-THE and R,R-DMY-THE are reported for the first time via single-crystal X-ray diffraction, displaying two distinct types of solid solution differing in mixing scale of enantiomers spanning several orders of magnitude. Surprisingly, this remarkable impact on enantiomer discrimination was simply achieved by the reduction of a methyl group of CAF to the THE coformer, which was further rationalized from their crystal structures and intermolecular interactions. Collectively, this work has demonstrated that a subtle change in the molecular structure of a coformer can regulate enantioselectivity in crystalline materials, guiding the purification of chiral racemic compounds via the cocrystallization method and the design of solid-solution crystalline materials.

[Meroterpenoids from Rhododendron nivale]

To elucidate the chemical material basis of Rhododendron nivale, this study comprehensively used various chromatographic techniques to isolate and obtain five new meroterpenoid enantiomers(1a/1b-5a/5b) from the ethyl acetate extract of R. nivale. A variety of spectral analytical methods, such as high-resolution mass spectrometry(HRMS), nuclear magnetic resonance spectroscopy(NMR), and infrared(IR) spectrum, were used to evaluate the structure, combined with the measurement and calculation of electronic circular dichroism(ECD). The new compounds 1a/1b-4a/4b were named as(±)-nivalones A-B(1a/1b-2a/2b) and(±)-nivalnoids C-D(3a/3b-4a/4b), along with one known enantiomer(±)-anthoponoid G(5a/5b). Human neuroblastoma cells(SH-SY5Y cells) induced by hydrogen peroxide(H_2O_2) were used as oxidative stress models to evaluate the protective activity of the isolated compounds against oxidative damage to nerve cells. It was found that compounds 2a and 3a had a certain protective effect on nerve cells against H_2O_2-induced oxidative damage at concentrations of 50 μmol·L~(-1), which increased the cell survival rate from 44.02%±2.30% to 67.82%±1.12% and 62.20%±1.87%, respectively. Other compounds did not show a significant ability to protect cells from oxidative damage. These findings enrich the chemical constituents of R. nivale and provide valuable information for identifying the structure of its meroterpenoids.

A New Essential Oil from the Leaves of Gynoxys rugulosa Muschl. (Asteraceae) Growing in Southern Ecuador: Chemical and Enantioselective Analyses

An essential oil, distilled from the leaves of the Andean species Gynoxys rugulosa Muschl., is described in the present study for the first time. The chemical composition was qualitatively and quantitatively determined by GC-MS and GC-FID, respectively. On the one hand, the qualitative composition was obtained by comparing the mass spectrum and the linear retention index of each component with data from literature. On the other hand, the quantitative composition was determined by calculating the relative response factor of each constituent, according to its combustion enthalpy. Both analyses were carried out with two orthogonal columns of nonpolar and polar stationary phases. A total of 112 compounds were detected and quantified with at least one column, corresponding to 87.3-93.0% of the whole oil mass. Among the 112 detected components, 103 were identified. The main constituents were α-pinene (5.3-6.0%), (E)-β-caryophyllene (2.4-2.8%), α-humulene (3.0-3.2%), germacrene D (4.9-6.5%), δ-cadinene (2.2-2.3%), caryophyllene oxide (1.6-2.2%), α-cadinol (3.8-4.4%), 1-nonadecanol (1.7-1.9%), 1-eicosanol (0.9-1.2%), n-tricosane (3.3-3.4%), 1-heneicosanol (4.5-5.8%), n-pentacosane (5.8-7.1%), 1-tricosanol (4.0-4.5%), and n-heptacosane (3.0-3.5%). Furthermore, an enantioselective analysis was carried out on the essential oil, by means of two cyclodextrin-based capillary columns. The enantiomers of α-pinene, β-pinene, sabinene, α-phellandrene, β-phellandrene, linalool, α-copaene, terpinen-4-ol, α-terpineol, and germacrene D were detected, and the respective enantiomeric excess was calculated.

The Mechanism of Enantioselective Neurosteroid Actions on GABAA Receptors

The neurosteroid allopregnanolone (ALLO) and pregnanolone (PREG), are equally effective positive allosteric modulators (PAMs) of GABAA receptors. Interestingly, the PAM effects of ALLO are strongly enantioselective, whereas those of PREG are not. This study was aimed at determining the basis for this difference in enantioselectivity. The oocyte electrophysiology studies showed that ent-ALLO potentiates GABA-elicited currents in α1β3 GABAA receptors with lower potency and efficacy than ALLO, PREG or ent-PREG. The small PAM effect of ent-ALLO was prevented by the α1(Q242L) mutation in the intersubunit neurosteroid binding site between the β3 and α1 subunits. Consistent with this result, neurosteroid analogue photolabeling with mass spectrometric readout, showed that ent-ALLO binds weakly to the β3-α1 intersubunit binding site in comparison to ALLO, PREG and ent-PREG. Rigid body docking predicted that ent-ALLO binds in the intersubunit site with a preferred orientation 180° different than ALLO, PREG or ent-PREG, potentially explaining its weak binding and effect. Photolabeling studies did not identify differences between ALLO and ent-ALLO binding to the α1 or β3 intrasubunit binding sites that also mediate neurosteroid modulation of GABAA receptors. The results demonstrate that differential binding of ent-ALLO and ent-PREG to the β3-α1 intersubunit site accounts for the difference in enantioselectivity between ALLO and PREG.

Efficient resolution of 4-chlormandelic acid enantiomers using lipase@UiO-67(Zr) zirconium-organic frameworks in organic solvent

A new biocatalyst PCL@UiO-67(Zr) was successfully synthesized by immobilized lipases on metal-organic frameworks (MOFs) materials. Compare with free lipases, zirconium foundation organic framework material UiO-67(Zr) modification on immobilized lipases Pseudomonas cepacia lipase (PCL) great boosts their enantioselectivity in the kinetic resolution racemic 4-chloro-mandelic acid (4-ClMA) on the organic solvent. The acquired bio-composite PCL@UiO-67(Zr) was fully characterized by powder X-ray diffraction (PXRD), Fourier transform infrared (FT-IR) spectroscopy, N₂ adsorption-desorption isotherm and aperture distribution map, and scanning electron microscopy (SEM). The catalytic performance of PCL@UiO-67(Zr), such as temperature, reaction time, and lipase quantity, were deeply explored. The experiment results showed resolution racemic 4-ClMA optimum conditions that 20 mmol/L of (R, S)-4-chloromandelic acid, 120 mmol/L vinyl acetate, 30-mg immobilized lipases PCL@UiO-67(Zr), 2 mL of MTBE, 500 rpm, and under the 55°C reaction 18 h. In this optimum conditions, c and ee_p could reach up to 47.6% and 98.7%, respectively.

Development and validation of a novel chiral chromatographic method for separation of lenalidomide enantiomers in human plasma

Lenalidomide (LND) is an analogue of thalidomide that is second generation immunomodulatory drugs (IMiDs). LND contains asymmetric carbon atom and exist R and S enantiomer. S (-) form of enantiomer are considered to be more potent and biologically active in tumor cell. It is available in racemic form for clinical use. The study aims to develop and validate enantiomer separation of LND in human plasma. The chromatographic enantiomeric separation was achieved on a Daicel-CSP, Chiralpack IA 4.6 × 250 mm_5 μm. The mobile phase was constituted in combination of methanol:glacial acetic acid at a concentration of 499.50 ml: 50 μl. UV wavelength detection was 220 nm. The RSD% for all validation parameters was found to be within the acceptable limit. The chiral chromatographic (chiral stationary phase-high-performance liquid chromatography [CSP-HPLC]) method developed and validated for the quantitative estimation of LND enantiomers S (-) and R (+) in human plasma sample is accurate, precise, robust, stable and selective.

Comparative metabolism and tolerability of racemic primaquine and its enantiomers in human volunteers during 7-day administration

Primaquine (PQ) is an 8-aminoquinoline antimalarial, active against dormant Plasmodium vivax hypnozoites and P. falciparum mature gametocytes. PQ is currently used for P. vivax radical cure and prevention of malaria transmission. PQ is a racemic drug and since the metabolism and pharmacology of PQ's enantiomers have been shown to be divergent, the objectives of this study were to evaluate the comparative tolerability and metabolism of PQ with respect to its two enantiomers in human volunteers in a 7 days' treatment schedule. Fifteen subjects with normal glucose-6-phosphate dehydrogenase (G6PDn) completed four arms, receiving each of the treatments, once daily for 7 days, in a crossover fashion, with a 7-14 days washout period in between: R-(-) enantiomer (RPQ) 22.5 mg; S-(+) enantiomer (SPQ) 22.5 mg; racemic PQ (RSPQ) 45 mg, and placebo. Volunteers were monitored for any adverse events (AEs) during the study period. PQ and metabolites were quantified in plasma and red blood cells (RBCs) by UHPLC-UV-MS/MS. Plasma PQ was significantly higher in SPQ treatment group than for RPQ. Carboxy-primaquine, a major plasma metabolite, was much higher in the RPQ treated group than SPQ; primaquine carbamoyl glucuronide, another major plasma metabolite, was derived only from SPQ. The ortho-quinone metabolites were also detected and showed differences for the two enantiomers in a similar pattern to the parent drugs. Both enantiomers and racemic PQ were well tolerated in G6PDn subjects with the 7 days regimen; three subjects showed mild AEs which did not require any intervention or discontinuation of the drug. The most consistent changes in G6PDn subjects were a gradual increase in methemoglobin and bilirubin, but these were not clinically important. However, the bilirubin increase suggests mild progressive damage to a small fraction of red cells. PQ enantiomers were also individually administered to two G6PD deficient (G6PDd) subjects, one heterozygous female and one hemizygous male. These G6PDd subjects showed similar results with the two enantiomers, but the responses in the hemizygous male were more pronounced. These studies suggest that although the metabolism profiles of individual PQ enantiomers are markedly different, they did not show significant differences in the safety and tolerability in G6PDn subjects.

Stereoselective Synthesis of Flavonoids: A Brief Overview

Stereoselective synthesis has been emerging as a resourceful tool because it enables the obtaining of compounds with biological interest and high enantiomeric purity. Flavonoids are natural products with several biological activities. Owing to their biological potential and aiming to achieve enantiomerically pure forms, several methodologies of stereoselective synthesis have been implemented. Those approaches encompass stereoselective chalcone epoxidation, Sharpless asymmetric dihydroxylation, Mitsunobu reaction, and the cycloaddition of 1,4-benzoquinone. Chiral auxiliaries, organo-, organometallic, and biocatalysis, as well as the chiral pool approach were also employed with the goal of obtaining chiral bioactive flavonoids with a high enantiomeric ratio. Additionally, the employment of the Diels-Alder reaction based on the stereodivergent reaction on a racemic mixture strategy or using catalyst complexes to synthesise pure enantiomers of flavonoids was reported. Furthermore, biomimetic pathways displayed another approach as illustrated by the asymmetric coupling of 2-hydroxychalcones driven by visible light. Recently, an asymmetric transfer hydrogen-dynamic kinetic resolution was also applied to synthesise (R,R)-cis-alcohols which, in turn, would be used as building blocks for the stereoselective synthesis of flavonoids.

Chiral Inversion of Pharmaceutical Drugs - Mini Review

2-Arylpropionic acid nonsteroidal anti-inflammatory drugs (NSAIDs) provide one of the most demonstrated pharmaceutical examples of chiral inversion. Chiral inversion depends on various factors (viz. biological-, solvent-, light-, temperature-induced, etc.) and the energy barrier associated with the stereogenic element present in the chiral molecule. The pharmacological properties of chiral drugs depend on the activity of one enantiomer or both the enantiomers targeting different biological targets. Consequently, chiral inversion can alter the biological activities of the pharmaceutical drug. Hence a better understanding of chiral inversion, factors facilitating such inversion, and the tools employed to determine chiral inversion are of great significance from a pharmacological and toxicological perspective.

Development of a capillary electrophoretic method for determination of ketorolac enantiomers in human plasma using cationic β-cyclodextrin derivative as a chiral selector

A novel approach for the separation of ketorolac enantiomers by capillary electrophoresis is presented. A cationic β-cyclodextrin derivative based on imidazole was synthesized and used as a chiral selector in the background electrolyte. The influence of pH and ionic strength of background electrolyte, as well as cationic β-cyclodextrin derivative concentration on the resolution of ketorolac enantiomers, was investigated. The highest value of the resolution for ketorolac enantiomers was 1.46 when the background electrolyte consisted of 25 mM NaH₂ PO₄ (pH 6.4) with 1 mM 1-butyl-3-β-cyclodextrinimidazolium tosylate. Additionally, the possibilities of cationic derivatives for the separation of ketoprofen enantiomers were shown (peak resolution 1.06). The two-step preconcentration mode was developed to reduce the limit of detection of individual enantiomers. The proposed approach was successfully applied to determine ketorolac enantiomers in tablet "Ketorol express" and human plasma. The calibration range of ketorolac enantiomers for plasma samples was 0.25-2.50 μg/ml with coefficients of determination ≥ 0.99. The relative standard deviation both of the peak area and migration time was less than 15%, as well as the accuracy ranged from 90.1% to 110.2% for both analytes. The limits of detection were 44 and 55 ng/ml for R- and S-ketorolac. The quantity of ketorolac in plasma was verified with high-performance liquid chromatography.

The Synthesis and Absolute Configuration of Enantiomeric Pure (R)- and (S)-3-(piperidin-3-yl)-1H-Indole Derivatives

This article describes the synthesis of new chiral 3-(piperidin-3-yl)-1H-indole derivatives (R)-10a-c and (S)-11a-c from the corresponding diastereomers: (3R, 2R) and (3S, 2R)-2-[3-(1H-indol-3-yl)-1-piperidyl]-2-phenyl-acetamides (3R, 2R)-4a, (3R, 2R)-6b, (3R, 2R)-8c and (3S, 2R)-5a, (3S, 2R)-7b, (3S, 2R)-9c. Diastereomers were obtained by N-alkylation of derivatives of racemic 3-(piperidin-3-yl)-1H-indoles 1a-c using (S)-2-(4-toluenesulfonyloxy)-phenylacetic amide (S)-II. The same method was applied to obtain (3R, 2S)-methyl-2-[3-(1H-indole-3-yl)-1-piperidyl]-2-phenylacetate (3R, 2S)-2a and (3S, 2S)-methyl-2-[3-(1H-indole-3-yl)-1-piperidyl]-2-phenylacetate (3S, 2S)-3a diastereomers by treating amine 1a with (R)-2-(4-toluenesulfonyloxy)-phenylacetic acid methylester (R)-I. Systematic studies via single crystal X-ray crystallography were used to determine the molecular structure of the racemates 1a-c and the absolute configuration of the enantiomers. The solid racemates 1b and 1c were "true racemates" crystallizing in a centrosymmetric space group, while 1a formed a racemic conglomerate of homoenantiomeric crystals. The absolute configuration was determined for the enantiomeric pairs (R)-10a/(S)-11a, (R)-10b/(S)-11b, and (R)-12c/(S)-13c, as well as for (3S,2S)-3a. Spectra of ¹H, ¹³CNMR, HPLC, and HRMS for diastereomers and enantiomers were consistent with the determined structures.

Silica Immobilised Chloro- and Amido-Derivatives of Eremomycine as Chiral Stationary Phases for the Enantioseparation of Amino Acids by Reversed-Phase Liquid Chromatography

Macrocyclic glycopeptide antibiotics immobilized on silica are one of the effective classes of stationary phases for chiral recognition and HPLC separation of a wide range of optically active compounds. Enantioselectivity primarily depends on the chemical structure of the chiral ligand, immobilization chemistry, and separation conditions. In the present work, three new chiral stationary phases (CSPs) based on macrocyclic antibiotic eremomycin were prepared and investigated for enantioseparation of amino acids. Two eremomycin derivatives, including simple non-substituted amide and bulky adamantyl amide, provided important information on the role of the carboxylic group in the eremomycin structure in the chiral recognition mechanism concerning amino acid optical isomers. One more CSP having a chlorine atom in the same position elucidates the role of the first aromatic ring in the eremomycin structure as a crucial point for chiral recognition. CSP with immobilized chloreremomycin was the most successful among the phases prepared in this work. It was additionally investigated under various separation conditions, including the type and content of the organic solvent in the eluent, the effects of different additives, and the concentration and pH of the buffer. Importantly, an efficient enantioselective separation of amino acids was achieved with pure water as the eluent.

Polymyxin Stereochemistry and Its Role in Antibacterial Activity and Outer Membrane Disruption

With increasing rates of resistance toward commonly used antibiotics, especially among Gram-negative bacteria, there is renewed interested in polymyxins. Polymyxins are lipopeptide antibiotics with potent anti-Gram-negative activity and are generally believed to target lipid A, the lipopolysaccharide (LPS) anchor found in the outer membrane of Gram-negative bacteria. To characterize the stereochemical aspects of their mechanism(s) of action, we synthesized the full enantiomers of polymyxin B and the polymyxin B nonapeptide (PMBN). Both compounds were compared with the natural compounds in biological and biophysical assays, revealing strongly reduced antibacterial activity for the enantiomeric species. The enantiomeric compounds also exhibit reduced LPS binding, lower outer membrane (OM) permeabilization, and loss of synergetic potential. These findings provide new insights into the stereochemical requirements underlying the mechanisms of action of polymyxin B and PMBN.

Evaluation of Chiral Organosulfur Compounds on Their Activity against the Malaria Parasite Plasmodium falciparum

Malaria is one of the deadliest tropical diseases, especially causing havoc in children under the age of five in Africa. Although the disease is treatable, the rapid development of drug resistant parasites against frontline drugs requires the search for novel antimalarials. In this study, we tested a series of organosulfur compounds from our internal library for their antiplasmodial effect against Plasmodium falciparum asexual and sexual blood stages. Some active compounds were also obtained in enantiomerically pure form and tested individually against asexual blood stages of the parasite to compare their activity. Out of the 23 tested compounds, 7 compounds (1, 2, 5, 9, 15, 16, and 17) exhibited high antimalarial activity, with IC₅₀ values in the range from 2.2 ± 0.64 to 5.2 ± 1.95 µM, while the other compounds showed moderate to very low activity. The most active compounds also exhibited high activity against the chloroquine-resistant strain, reduced gametocyte development and were not toxic to non-infected red blood cells and Hela cells, as well as the hematopoietic HEL cell line at concentrations below 50 µM. To determine if the enantiomers of the active compounds display different antimalarial activity, enantiomers of two of the active compounds were separated and their antimalarial activity compared. The results show a higher activity of the (-) enantiomers as compared to their (+) counterparts. Our combined data indicate that organosulfur compounds could be exploited as antimalarial drugs and enantiomers of the active compounds may represent a good starting point for the design of novel drugs to target malaria.

[A pair of enantiomeric sesquiterpenoids from florets of Carthamus tinctorius]

This study investigated the chemical components from the florets of Carthamus tinctorius. Five compounds were isolated from C. tinctorius by column chromatography with silica gel and toyopearl HW-40 F, preparative thin-layer chromatography(TLC), and semi-preparative reverse phased high performance liquid chromatography(RP-HPLC). Their structures were identified by mass spectrometry(MS), one-dimension nuclear magnetic resonance(1 D-NMR), two-dimension nuclear magnetic resonance(2 D-NMR), and single-crystal X-ray diffraction as(-)-(2S,3S,5S,7S,10R)-eudesma-4(15)-en-2,3,11-triol(1 a),(+)-(2R,3R,5R,7R,10S)-eudesma-4(15)-en-2,3,11-triol(1 b), rosin(2),(+)-syringaresinol(3), and(E)-1-(4'-hydroxyphenyl)-but-1-en-3-one(4). Compounds 1 a and 1 b are a pair of enantiomeric sesquiterpenoids. Compound 1 a is a new eudesmene and is named(-)-plucheol A. Compound 1 a at 100 μmol·L~(-1) showed significant antioxidant activity against ABTS~(+·) and DPPH·, with the scavenging rates of 30.98%±4.17% and 27.52%±1.24%, respectively, while compound 1 b was inactive. In addition, compounds 1 a and 1 b showed no obvious anti-inflammatory activity.

Two Pairs of 7,7'-Cyclolignan Enantiomers with Anti-Inflammatory Activities from Perilla frutescens

Perilla frutescens (L.) Britt. (Labiatae), a medicinal plant, has been widely used for the therapy of multiple diseases since about 1800 years ago. It has been demonstrated that the extracts of P. frutescens exert significant anti-inflammatory effects. In this research, two pairs of 7,7′-cyclolignan enantiomers, possessing a cyclobutane moiety, (+)/(−)-perfrancin [(+)/(−)-1] and (+)/(−)-magnosalin [(+)/(−)-2], were separated from P. frutescens leaves. The present study achieved the chiral separation and determined the absolute configuration of (±)-1 and (±)-2. Compounds (+)-1 and (−)-1 have notable anti-inflammatory effects by reducing the secretion of pro-inflammatory factors (NO, TNF-α and IL-6) and the expression of pro-inflammatory mediators (iNOS and COX-2). These findings indicate that cyclolignans are effective substances of P. frutescens with anti-inflammatory activity. The present study partially elucidates the mechanisms underlying the effects of P. frutescens.

Essential Oil Compositions of Pinus Species (P. contorta Subsp. contorta, P. ponderosa var. ponderosa, and P. flexilis); Enantiomeric Distribution of Terpenoids in Pinus Species

Pinus species are important in traditional medicine throughout their ranges, and pine essential oils are of interest in aromatherapy and as topical treatments. In this work, the leaf (needle) essential oils of Pinus ponderosa var. ponderosa and Pinus contorta subsp. contorta from Oregon and Pinus flexilis growing in Idaho, have been obtained by hydrodistillation and analyzed by gas chromatographic techniques. The leaf essential oil of P. ponderosa was dominated by β-pinene (21.5-55.3%), methyl chavicol (8.5-41.5%), α-pinene (3.6-9.6%), δ-3-carene (3.6-6.2%), and α-terpineol (1.4-5.3%). The major components of P. contorta essential oil were β-phellandrene (23.8%), terpinen-4-ol (11.0%). The essential oil of P. flexilis was dominated by α-pinene (37.1%), β-pinene (21.9%), bornyl acetate (12.8%), and camphene (8.5%). Chiral gas chromatography revealed the enantiomeric ratios of α-pinene and limonene to be variable, but (-)-β-pinene predominated in Pinus essential oils.

Evaluating the Utility of Temporal Compression in High-Resolution Traveling Wave-Based Cyclic Ion Mobility Separations

Ion mobility spectrometry coupled to mass spectrometry (IMS-MS) is slowly becoming a more integral part in omics-based workflows. With the recent technological advancements in IMS-MS instrumentation, particularly those involving traveling wave-based separations, ultralong pathlengths have become readily available in commercial platforms (e.g., Select Series Cyclic IMS from Waters Corporation and MOBIE from MOBILion). However, a tradeoff exists in such ultralong pathlength separations: increasing peak-to-peak resolution at the cost of lower signal intensities and thus poorer sensitivity of measurements. Herein, we explore the utility of temporal compression, where ions are compressed in the time domain, following high-resolution cyclic ion mobility spectrometry-mass spectrometry-based separations on a commercially available, unmodified platform. We assessed temporal compression in the context of various separations including those of reverse sequence peptide isomers, chiral noncovalent complexes, and isotopologues. From our results, we demonstrated that temporal compression improves IMS peak intensities by up to a factor of 4 while only losing ∼5 to 10% of peak-to-peak resolution. Additionally, the improvement in peak quality and signal-to-noise ratio was evident when comparing IMS-MS separations with and without a temporal compression step performed. Temporal compression can readily be implemented in existing traveling wave-based IMS-MS platforms, and our initial proof-of-concept demonstration shows its promise as a tool for improving peak shapes and peak intensities without sacrificing losses in resolution.

A validated chiral chromatographic method for the enantiomeric separation of acalabrutinib

Acalabrutinib is aided in the treatment of various cancers, which acts by inhibiting Bruton tyrosine kinase. Acalabrutinib belongs to the imidazopyrazine class consisting of a chiral carbon, resulting in two enantiomers. Currently, no methods exist for the separation and quantification of these enantiomers. A novel and selective enantiomeric chromatographic technique has been established to estimate the enantiomeric purity of acalabrutinib. Chiral separation was carried out on an immobilized amylose-based chiral stationary phase with methyl tert-butyl ether/ethanol/ethylenediamine (60:40:0.1% v/v) mixture as a mobile phase. The total runtime is 20 min, and the resolution (R_s ) between the enantiomers was more than 2.5. The detection and quantification thresholds for the R-enantiomer were 0.06 and 0.2 μg mL^-1 , respectively, for a test concentration of acalabrutinib (1000 μg mL^-1 ). The linearity of the technique for the R-enantiomer was excellent (R²  > 0.999) over the range from the limit of quantification to 0.3%. Recovery of the R-enantiomer was ranged from 95% to 102%, indicating the greater accuracy of the technique. For a 48-h research period, the drug was shown to be stable.

A new pair of cytotoxic enantiomeric isoprenylated chromone derivatives from Pestalotiopsis sp

A new pair of enantiomeric isoprenylated chromone derivatives, (±)-pestaloficiol X [(±)-1], along with a known compound pestaloficiol J (2), were isolated from the plant endophytic fungus Pestalotiopsis sp. The racemic mixture 1 was separated through chiral HPLC. The structures of new compounds (±)-1 were elucidated on the basis of extensive spectroscopic data and their absolute configurations were further configured through computational analysis of their electronic circular dichroism (ECD) spectra. Compound (+)-1 showed significant inhibitory potency against HL-60 and HEP-3B cell lines, with IC₅₀ values of 1.35 ± 0.15 and 3.70 ± 0.33 μM, respectively, while compound (-)-1 showed significant inhibitory potency against HL-60 and HEP-3B cell lines, with IC₅₀ values of 2.39 ± 0.26 and 2.99 ± 0.35 μM, respectively.