Amidation of arabinoglucuronoxylans to modulate their flow behavior

Arabinoglucuronoxylans obtained from the exudate of Cercidium praecox (Brea gum) were subjected to an amidation reaction to modulate their flow behavior to obtain a product with similar behavior to gum Arabic. The amidation reaction of the uronic acids present in this exudate was studied using the 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS) system with the aim of maximizing product yield and minimizing by-product. An analysis of the significant factors involved in the reaction was carried out and a response surface methodology was conducted to optimize the stoichiometry of the reagents used. It was possible to obtain models for predicting the degree of amidation (DA) of arabinoglucuronoxylans and the formation of by-products. The formation of a secondary product derived from the amino acid β-alanine which has not been reported previously in the reaction with polysaccharides, was described. The flow behavior of an amidated product (DA = 52 %) was determined, showing a pseudoplastic behavior and a decreased Newtonian viscosity (η0 = 36.2 Pa s) at the lowest shear rate range with respect to native product solution (η0 = 115 Pa s). Amidated arabinoglucuronoxylans had a flow behavior more similar to that of gum Arabic.

On the importance of being amidated: Analysis of the role of the conserved C-terminal amide of amylin in amyloid formation and cytotoxicity

The polypeptide hormone Amylin (also known as islet amyloid polypeptide) plays a role in regulation of glucose metabolism, but forms pancreatic islet amyloid deposits in type 2 diabetes. The process of islet amyloid formation contributes to β-cell dysfunction and the development of the disease. Amylin is produced as a pro-from and undergoes processing prior to secretion. The mature hormone contains an amidated C-terminus. Analysis of an alignment of vertebrate amylin sequences reveals that the processing signal for amidation is strictly conserved. Furthermore, the enzyme responsible for C-terminal amidation is found in all of these organisms. Comparison of the physiologically relevant amidated form to a variant with a free C-terminus (Amylin-COO-) shows that replacement of the C-terminal amide with a carboxylate slows, but does not prevent amyloid formation. Pre-fibrillar species produced by both variants are toxic to cultured β-cells, although hAmylin-COO- is moderately less so. Amyloid fibrils produced by either peptide are not toxic. Prior work (ACS Pharmacol. Translational. Sci. 1, 132-49 (2018)) shows that Amylin- COO- exhibits a 58-fold reduction in activation of the Amylin1 receptor and 20-fold reduction in activation of the Amylin3 receptor. Thus, hAmylin-COO- exhibits significant toxicity, but significantly reduced activity and offers a reagent for studies which aim to decouple hAmylin's toxic effects from its activity. The different behaviours of free and C-terminal amidated Amylin should be considered when designing systems to produce the polypeptide recombinantly.

Design, synthesis and evaluation of novel deferasirox derivatives with high antifungal potency in vitro and in vivo

Here we designed and synthesized 58 deferasirox derivatives with the aim of discovering novel antifungal agents. Most compounds exhibited moderate to excellent in vitro antifungal activities against Cryptococcus neoformans H99 with MIC values ranging from 0.25 μg/mL to 16 μg/mL, including ten compounds with MIC values less than 1 μg/mL that were further screened against an additional six pathogenic fungi. This class of compounds showed high potency against Candida glabrata with MIC values ranging from <0.125 μg/mL to 1 μg/mL. We identified that compound 54 has high potency against 14 strains of Candida glabrata spp. and Cryptococcus spp. with MIC values ranging from <0.125 μg/mL to 1 μg/mL. In addition, compound 54 significantly reduced the CFU in a mouse model of disseminated infection with Cryptococcus neoformans H99 at a dose of 10 mg/kg, which is comparable to FLC. Further investigations on compound 54 are currently in progress.

Amide-decorated carbon dots as sensitive and selective probes for fluorescence enhancement detection of cadmium ion

As highly toxic metal ions, cadmium ions (Cd2+) are prevalent in varying concentrations around the world. The establishment of an accurate and effective method for Cd2+ determination with high sensitivity and selectivity is of particular concern. The present work fabricated a fluorescence chemosensor for the detection of Cd2+ based on functionalized carbon dots (CDs), which were hydrothermally prepared using amidated hyperbranched-polyethyleneimine (HPEI). As investigated by FTIR, NMR, and XPS, the stably grafted amide groups endowed the CDs with thermosensitivity and high cloud point due to the change in hydrophilic-hydrophobic behaviors. The CDs chemosensor with optimal amidation degree exhibited high sensitivity, selectivity, and stability in the determination of Cd2+ from various water environments. Notably, the fluorescence intensity enhanced with the increase of Cd2+ concentration, originating from the improved structure rigidity caused by the interactions between grafted amides and Cd2+. These impressive features made the CDs not only sensitive to detecting Cd2+ in low-concentration solutions with a limit of detection of 3.41 nM (the lowest known value for Cd2+ detection) but also accurate for the quantification in high-concentration solutions with a detectable Cd2+ concentration of 6.0 × 10-2 M. Owing to the broad detection range, the CDs developed in present work show great potential applications in various scenarios.

Investigating the antimicrobial activity, cytotoxicity, and action mechanism of acylated and amidated derivatives of AurH1 antifungal peptide

BACKGROUND

The increasing growth of microbial resistance threatens the health of human societies. Therefore, the discovery and design of new antibiotics seem necessary. Today, antimicrobial peptides (AMPs) are receiving attention due to their unique properties. In our previous studies, exclusive antifungal effects of AurH1, which is a truncated and modified form of Aurein1.2, were synthesized. In this study, AurH1 antifungal peptide was synthesized into acylated (Ac-AurH1) and amidated (AurH1-NH2) derivatives, and their antifungal activity, cytotoxicity, anticancer activity, hemolytic effects were investigated. Finally, the time- of killing, the action mechanism of amidated and acylated peptides, and the effects of salts and human serum on their antimicrobial potency were determined. All the results obtained about these peptides were compared with the AurH1 without chemical modifications.

RESULTS

The results showed that amidation at the C-terminal of AurH1 compared to acylation at the N-terminal of it can improve the antifungal properties and cytotoxicity of AurH1. The results showed that AurH1 amidation can maintain the antifungal activity of this peptide in the culture medium containing specific dilutions of human serum compared to the intact AurH1. Also, the amidation of the C-terminal of AurH1 could not affect the mechanism of action and its time -of killing.

CONCLUSION

As a result, the amidation of the C-terminal of the AurH1 is a suitable strategy to improve its antifungal properties and cytotoxicity. This modification can enhance its properties for animal studies.

Non-activated Esters as Reactive Handles in Direct Post-Polymerization Modification

Non-activated esters are prominently featured functional groups in polymer science, as ester functional monomers display great structural diversity and excellent compatibility with a wide range of polymerization mechanisms. Yet, their direct use as a reactive handle in post-polymerization modification has been typically avoided due to their low reactivity, which impairs the quantitative conversion typically desired in post-polymerization modification reactions. While activated ester approaches are a well-established alternative, the modification of non-activated esters remains a synthetic and economically valuable opportunity. In this review, we discuss past and recent efforts in the utilization of non-activated ester groups as a reactive handle to facilitate transesterification and aminolysis/amidation reactions, and the potential of the developed methodologies in the context of macromolecular engineering.

Gelling properties of lysine-amidated citrus pectins: The key role of pH in both amidation and gelation

The amidation of pectin by amino acids has been widely applied due to its safety and excellent gelling properties. This study systematically examined the effects of pH on the gelling properties of lysine-amidated pectin during amidation and gelation. Pectin was amidated over the range of pH 4-10, and the amidated pectin obtained at pH 10 showed the highest degree of amidation (DA, 27.0 %) due to the de-esterification, electrostatic attraction, and the stretching state of pectin. Moreover, it also exhibited the best gelling properties due to its greater numbers of calcium-binding regions (carboxyl groups) and hydrogen bond donors (amide groups). During gelation, the gel strength of CP (Lys 10) at pH 3-10 first increased and then decreased, with the highest gel strength at pH 8, which was due to the deprotonation of carboxyl groups, protonation of amino groups, and β-elimination. These results show that pH plays a key role in both amidation and gelation, with distinct mechanisms, and would provide a basis for the preparation of amidated pectins with excellent gelling properties. This will facilitate their application in the food industry.

Optimization of antimicrobial peptides for the application against biocorrosive bacteria

Microbiologically influenced corrosion is a common problem in the industrial field due to the deterioration of metals in the presence of various microorganisms, in particular sulfate-reducing bacteria (SRB) and sulfur-oxidizing bacteria (SOB). A common method to reduce microbiologically influenced corrosion is the application of biocides. The limited number of suitable biocides and the resulting development of resistance, high dosage, and high application rate hinder an effective application. An environmentally friendly alternative could be the application of antimicrobial peptides (AMP), which have already been established in the field of medical devices for a while. Here, the successful treatment of different AMPs against 3 SRB and 1 SOB was demonstrated. The peptide L5K5W was favored due to its broad activity, high stability, and simple structure resulting in low synthesis costs. An alanine scan showed that substitution of leucine with tryptophan increased the activity of this peptide twofold compared to the original peptide against D. vulgaris, the main representative of SRB. Additional optimization of this modified peptide through changes in amino acid composition and lipidations significantly increased the effectiveness, finally resulting in a minimum inhibitory concentration (MIC) of 15.63 μg/mL against Desulfovibrio vulgaris. Even against the marine SRB Desulfovibrio indonesiensis with a required salt concentration of min. 2%, an activity of the peptides can be observed (MIC: 31.25 μg/mL). The peptides also remained stable and active for 7 days in the supernatant of the bacterial culture. KEY POINTS: • Antimicrobial peptides provide an alternative to combat biocorrosive bacteria. • Optimization of the peptide sequence leads to a significant increase in activity. • The investigated peptides exhibit high stability, both in the medium and in the bacterial supernatant.

Formation and Loading of a (2S)-2-ethylmalonamyl Starter Unit in the Assembly Line of Polyketide-Nonribosomal Peptide Hybrid Sanglifehrin A

Sanglifehrin A (SFA) is a spirolactam-conjugated, 22-membered macrolide with remarkable immunosuppressive and antiviral activities. This macrolide is a result of a hybrid polyketide synthase (PKS)-nonribosomal peptide synthetase (NRPS) assembly line that utilizes (2S)-2-ethylmalonamyl as a starter unit. Here, we report that the formation and loading of this starter unit in the SFA assembly line involve two unusual enzymatic reactions that occur on a discrete acyl carrier protein (ACP), SfaO. An amide synthetase, SfaP, catalyzes the amidation of (2S)-2-ethylmalonyl in a SfaO-dependent manner. Then, a b-ketoacyl-ACP synthase III-like protein, SfaN, transfers resultant (2S)-2-ethylmalonamyl from SfaO onto the loading ACP domain of the hybrid PKS-NRPS assembly line to prime SFA biosynthesis. Both SfaP and SfaN display promiscuous activities. This study furthers the appreciation of assembly line chemistry, as a new paradigm for unusual building block formation and incorporation is provided.

Nickel-Catalyzed Site-Selective Intermolecular C(sp3 )-H Amidation

A nickel-catalyzed site-selective intermolecular amidation of saturated C(sp³ )-H bonds is reported. This mild protocol exhibits a predictable reactivity pattern to incorporate amide functions at C(sp³ )-H sites adjacent to nitrogen and oxygen atoms in either cyclic or acyclic frameworks, thus offering a complementary reactivity profile to existing oxidative-type processes or metal-catalyzed C(sp³ )-N bond-forming reactions operating via two-electron manifolds.

Mechanistic Understanding of KOtBu-Mediated Direct Amidation of Esters with Anilines: An Experimental Study and Computational Approach

A sustainable and cost-effective protocol has been reported for the synthesis of amide bonds from unactivated esters and non-nucleophilic amines promoted by potassium tert -butoxide under aerobic conditions. The reaction proceeds under relatively mild conditions, encompassing wide substrate scope. A combined experimental and quantum chemical study has been performed to shed light on the mechanism, which implied that a radical pathway is operating for the present protocol.

Cilia-derived vesicles: An ancient route for intercellular communication

Extracellular vesicles (EVs) provide a mechanism for intercellular communication that transports complex signals in membrane delimited structures between cells, tissues and organisms. Cells secrete EVs of various subtypes defined by the pathway leading to release and by the pathological condition of the cell. Cilia are evolutionarily conserved organelles that can act as sensory structures surveilling the extracellular environment. Here we discuss the secretory functions of cilia and their biological implications. Studies in multiple species - from the nematode Caenorhabditis elegans and the chlorophyte alga Chlamydomonas reinhardtii to mammals - have revealed that cilia shed bioactive EVs (ciliary EVs or ectosomes) by outward budding of the ciliary membrane. The content of ciliary EVs is distinct from that of other vesicles released by cells. Peptides regulate numerous aspects of metazoan physiology and development through evolutionarily conserved mechanisms. Intriguingly, cilia-derived vesicles have recently been found to mediate peptidergic signaling. C. reinhardtii releases the peptide α-amidating enzyme (PAM), bioactive amidated products and components of the peptidergic signaling machinery in ciliary EVs in a developmentally regulated manner. Considering the origin of cilia in early eukaryotes, it is likely that release of peptidergic signals in ciliary EVs represents an alternative and ancient mode of regulated secretion that cells can utilize in the absence of dedicated secretory granules.

Mapping Dual-Base-Enabled Nickel-Catalyzed Aryl Amidations: Application in the Synthesis of 4-Quinolones

The C-N cross-coupling of (hetero)aryl (pseudo)halides with NH substrates employing nickel catalysts and organic amine bases represents an emergent strategy for the sustainable synthesis of (hetero)anilines. However, unlike protocols that rely on photoredox/electrochemical/reductant methods within Ni^I/III cycles, the reaction steps that comprise a putative Ni^0/II C-N cross-coupling cycle for a thermally promoted catalyst system using organic amine base have not been elucidated. Here we disclose an efficient new nickel-catalyzed protocol for the C-N cross-coupling of amides and 2'-(pseudo)halide-substituted acetophenones, for the first time where the (pseudo)halide is chloride or sulfonate, which makes use of the commercial bisphosphine ligand PAd2-DalPhos (L4) in combination with an organic amine base/halide scavenger, leading to 4-quinolones. Room-temperature stoichiometric experiments involving isolated Ni^{0, I, and II} species support a Ni^0/II pathway, where the combined action of DBU/NaTFA allows for room-temperature amide cross-couplings.

Direct Access to Amides from Nitro-Compounds via Aminocarbonylation and Amidation Reactions: A Minireview

The ubiquity of the amide bond in functional molecules including proteins, natural products, pharmaceuticals, agrochemicals and materials provides impetus to design and develop newer strategies for the generation of this linkage. Owing to growing awareness about sustainability and development of benign strategies, the traditional route of synthesis of amides via reaction between carboxylic acids and amines in the presence of stoichiometric amount of coupling reagents is tagged to be harsh and wasteful. In one of the unconventional routes, nitro compounds are used directly as amine surrogates for preparing amides mostly via aminocarbonylation and amidation reactions. Typically, such processes involves nitroarenes owing to their propensity to transform into nitroso, hydroxylamine, diazo, hydrazine or aniline intermediates in situ under the influence of suitable catalyst or oxidant. This short review provides the comprehensive overview of these reactions including insight into the scope and their mechanisms.

Semi-synthesis of hybrid ulvan-kappa-carrabiose polysaccharides and evaluation of their cytotoxic and anticoagulant effects

In this study we described the synthesis of a hybrid polysaccharide harboring moieties of ulvan and kappa-carrabiose. Alkylamines (1,3-diaminopropane and 1,6-diaminohexane) were selectively inserted into β-D-GlcAp and α-L-IdoAp units in the ulvan structure via an amide bond formation producing ulvan-amide derivatives F-DAP (N% = 1.77; M_w = 208 kg mol^-1) and F-DAH (N% = 1.77; M_w = 202 kg mol^-1), which were reacted with kappa-carrabiose via reductive amination to produce hybrid ulvan-kappa-carrabiose polysaccharides F-DAP-Kb (N% = 1.56; M_w = 206 kg mol^-1) and F-DAH-Kb (N% = 1.16; M_w = 200 kg mol^-1). All the ulvan derivatives were characterized by ¹H and ¹³C NMR spectroscopy and did not show cytotoxicity against human dermal fibroblasts (HDFa) at the concentrations of 25, 100, and 500 μg mL^-1, neither anticoagulant properties at the range of 10-150 μg mL^-1. Therefore, the ulvan-amide derivatives and the hybrid ulvan-kappa-carrabiose polysaccharides showed good biocompatibility in vitro, presenting as worthy candidates for tailoring scaffolds for biomedical applications.

Catalytic and non-catalytic amidation of carboxylic acid substrates

The present review offers an apt summary of amide bond formation with carboxylic acid substrates by taking advantage of several methods. Carboxamides can be regarded as a substantial part of organic and medicinal chemistry due to their utility in synthesizing peptides, lactams, and more than 25% of familiar drugs. Moreover, they play a leading role in the synthesis of bioactive products with anticancer, antifungal, and antibacterial properties. The data are arranged based on the type and amount of reagents used to conduct amidation and are also divided into the following categories: catalytic amidation of carboxylic acids, non-catalytic amidation, and transamidation.

Effect of the acyl-group length on the chemoselectivity of the lipase-catalyzed acylation of propranolol-a computational study

The selective N-acylation of 1,2-amino alcohols has been proposed to occur through the proton shuttle mechanism. However, the O-acetylation of propranolol catalyzed by Candida antarctica lipase B is an exception. We investigated the relation between the chemoselectivity of this reaction and the acyl group length. For this purpose, we compared the acyl groups: ethanoyl, butanoyl, octanoyl, and hexadecanoyl. We studied the Michaelis complexes between serine-acylated Candida antarctica lipase B and propranolol, employing a computational approach that involved sampling Michaelis complex conformations through ensemble docking plus consensus scoring and molecular dynamics simulations. The conformations were then classified as near attack conformations for acylation of the amino or hydroxy group. The relative populations of these two classes of conformations were found to be consistent with the experimentally observed chemoselective O-acetylation. We predict that increasing the length of the hydrocarbon chain of the acyl group will cause O-acylation to be unfavorable with respect to N-acylation. The nucleophilic attack of propranolol to the acylated lipase was found to be more favorable through the classical mechanism when compared with the proton shuttle mechanism.

Performance and multi-scale investigation on the phase miscibility of poly(lactic acid)/amided silica nanocomposites

In this work, amino-functionalized nano-SiO₂ (m@g-SiO₂) was synthesized through coupling reaction on the surface of nano-SiO₂. Moreover, the optimum preparation conditions of m@g-SiO₂ were selected via orthogonal experiments as follows: reaction temperature of 80 °C, reaction time of 8 h, the mass ratio of stearic acid, N,N'‑carbonyldiimidazole, imidazole hydrochloride and g-SiO₂ of 0.5:0.7:0.7:1. Fourier transform infrared spectroscopy, static angle measurement and X-ray photoelectron spectroscopy unanimously confirmed the formation of m@g-SiO₂. Furthermore, poly(lactic acid)(PLA)/m@g-SiO₂ nanocomposites was prepared with m@g-SiO₂ as fillers to improve the comprehensive performance of PLA. Then, the mechanical properties and crystallization behavior of PLA/m@g-SiO₂ nanocomposites were studied, which showed that the impact strength and elongation-at-break of PLA/m@g-SiO₂ (0.3 wt%) nanocomposites were increased by 78.05% and 1148%, respectively, and its crystallinity was increased by 26.46%. Simultaneously, thermal gravimetric analysis indicated that the thermal stability of PLA/m@g-SiO₂ nanocomposites was improved. Eventually, the multi-scale investigation on the phase miscibility of PLA/m@g-SiO₂ nanocomposites was probed by rheological behaviors analysis and the molecular dynamics simulations, which confirmed that surface modification of SiO₂ greatly enhanced the interaction energy and miscibility between the filler and PLA bulk.

Synthesis of amide derivatives for electron deficient amines and functionalized carboxylic acids using EDC and DMAP and a catalytic amount of HOBt as the coupling reagents

A convenient protocol for amide bond formation for electron deficient amines and carboxylic acids is described. Amide coupling of aniline derivatives has been investigated with a number of reagents under a variety of reaction conditions. The use of 1 equivalent of EDC and 1 equivalent of DMAP, catalytic amount of HOBt and DIPEA provided the best results. This method is amenable to the synthesis of a range of functionalized amide derivatives with electron deficient and unreactive amines.

PAM haploinsufficiency does not accelerate the development of diet- and human IAPP-induced diabetes in mice

AIMS/HYPOTHESIS

Peptide hormones are first synthesised as larger, inactive precursors that are converted to their active forms by endopeptidase cleavage and post-translational modifications, such as amidation. Recent, large-scale genome-wide studies have suggested that two coding variants of the amidating enzyme, peptidylglycine α-amidating monooxygenase (PAM), are associated with impaired insulin secretion and increased type 2 diabetes risk. We aimed to elucidate the role of PAM in modulating beta cell peptide amidation, beta cell function and the development of diabetes.

METHODS

PAM transcript and protein levels were analysed in mouse islets following induction of endoplasmic reticulum (ER) or cytokine stress, and PAM expression patterns were examined in human islets. To study whether haploinsufficiency of PAM accelerates the development of diabetes, Pam^+/- and Pam^+/+ mice were fed a low-fat diet (LFD) or high-fat diet (HFD) and glucose homeostasis was assessed. Since aggregates of the PAM substrate human islet amyloid polypeptide (hIAPP) lead to islet inflammation and beta cell failure, we also investigated whether PAM haploinsufficiency accelerated hIAPP-induced diabetes and islet amyloid formation in Pam^+/- and Pam^+/+ mice with beta cell expression of hIAPP.

RESULTS

Immunostaining revealed high expression of PAM in alpha, beta and delta cells in human pancreatic islets. Pam mRNA and PAM protein expression were reduced in mouse islets following administration of an HFD, and in isolated islets following induction of ER stress with thapsigargin, or cytokine stress with IL-1β, IFN-γ and TFN-α. Despite Pam^+/- only having 50% PAM expression and enzyme activity as compared with Pam^+/+ mice, glucose tolerance and body mass composition were comparable in the two models. After 24 weeks of HFD, both Pam^+/- and Pam^+/+ mice had insulin resistance and impaired glucose tolerance, but no differences in glucose tolerance, insulin sensitivity or plasma insulin levels were observed in PAM haploinsufficient mice. Islet amyloid formation and beta cell function were also similar in Pam^+/- and Pam^+/+ mice with beta cell expression of hIAPP.

CONCLUSIONS/INTERPRETATION

Haploinsufficiency of PAM in mice does not accelerate the development of diet-induced obesity or hIAPP transgene-induced diabetes.

Synthesis of Branched Peptides via a Side-Chain Benzyl Ester

Branched peptide as an attractive mimic of natural peptide is widely used in structural design of functional or therapeutic peptides, to improve their biological activity, stability, and pharmacokinetic properties. In this protocol, we employ a function group of side-chain benzyl ester as the precursor of hydrazide, which could be conveniently used to assemble a branch peptide by native chemical ligation or direct amidation. This method is convergent and efficient, and facilitates the synthesis and application of branched peptides.

Ciliary and cytoskeletal functions of an ancient monooxygenase essential for bioactive amidated peptide synthesis

Many secreted peptides used for cell-cell communication require conversion of a C-terminal glycine to an amide for bioactivity. This reaction is catalyzed only by the integral membrane protein peptidylglycine α-amidating monooxygenase (PAM). PAM has been highly conserved and is found throughout the metazoa; PAM-like sequences are also present in choanoflagellates, filastereans, unicellular and colonial chlorophyte green algae, dinoflagellates and haptophytes. Recent studies have revealed that in addition to playing a key role in peptidergic signaling, PAM also regulates ciliogenesis in vertebrates, planaria and chlorophyte algae, and is required for the stability of actin-based microvilli. Here we briefly introduce the basic principles involved in ciliogenesis, the sequential reactions catalyzed by PAM and the trafficking of PAM through the secretory and endocytic pathways. We then discuss the multi-faceted roles this enzyme plays in the formation and maintenance of cytoskeleton-based cellular protrusions and propose models for how PAM protein and amidating activity might contribute to ciliogenesis. Finally, we consider why some ciliated organisms lack PAM, and discuss the potential ramifications of ciliary localized PAM for the endocrine features commonly observed in patients with ciliopathies.

Amidation Strategy for Final-Step α-Hydroxytropolone Diversification

α-Hydroxytropolones (αHTs) are excellent metalloenzyme-inhibiting fragments that have been the basis for the development of potent inhibitors of various therapeutically important enzymes. The following manuscript describes a final-step amidation approach for αHT diversification. The method takes advantage of a scalable, chromatography-free synthesis of a carboxylic acid-appended αHT, and in the present manuscript we describe the synthesis of eight amide-containing αHTs, three of which we envision using as chemical probes. We expect that the general strategy will find widespread usage in both chemical biology and medicinal chemistry studies on αHTs.

Identification of Sialic Acid Linkages on Intact Glycopeptides via Differential Chemical Modification Using IntactGIG-HILIC

Mass spectrometric analysis of intact glycopeptides can reveal detailed information about glycosite, glycan structural features, and their heterogeneity. Sialyl glycopeptides can be positively, negatively, or neutrally charged depending on pH of their buffer solution and ionization conditions. To detect sialoglycopeptides, a negative-ion mode mass spectrometry may be applied with a minimal loss of sialic acids, although the positively charged or neutral glycopeptides may be excluded. Alternatively, the sialyl glycopeptides can be identified using positive-ion mode analysis by doping a high concentration of sodium salts to the analytes. Although manipulation of unmodified sialoglycopeptides can be useful for analysis of samples, less than optimal ionization, facile loss of sialyl and unfavorable ionization of accompanying non-sialyl peptides make such strategies suboptimal. Currently available chemical derivatization methods, while stabilizing for sialic acid, mask sialic acid linkage configuration. Here, we report the development of a novel approach to neutralize sialic acids via sequentially chemical modification that also reveals their linkage configuration, often an important determinant in biological function. This method utilizes several components to facilitate glycopeptide identification. These include the following: solid phase derivatization, enhanced ionization of sialoglycopeptides, differentiation of sialic acid linkage, and enrichment of the modified glycopeptides by hydrophilic interaction liquid chromatography. This technology can be used as a tool for quantitative analysis of protein sialylation in diseases with determination of sialic acid linkage configuration. Graphical Abstract ᅟ.

Facile ring opening reaction of oxazolone enables efficient amidation for aminoisobutyric acid

4,4-Dimethyloxazolones derived from N-protected aminoisobutyric acid (AIB) are particularly known as poor electrophiles due to the steric hindrance around the carbonyl and not employed as useful intermediates for amidation whereas numerous examples have been reported to support the utility of other oxazolones in amidation. AIB is an important and strategical synthon in medicinal chemistry but the peptide bond formation of the N-protected urethane derivatives of AIB is known to be often unproductive due to the rapid formation of the stable 4,4-dimethyloxazolone via an intramolecular cyclization. We discovered that the 4,4-dimethyloxazolone of an AIB urethane is in fact an excellent electrophile that enables efficient amidation even with weakly reactive nucleophiles. The 4,4-dimethyloxazolone can be stored in a pure form and used as a reagent offering an efficient and convenient synthetic tool for generating AIB-peptide analogs.

Peptide identifications and false discovery rates using different mass spectrometry platforms

Characterization of endogenous neuropeptides produced from post-translational proteolytic processing of precursor proteins is a demanding task. A variety of complex prohormone processing steps generate molecular diversity from neuropeptide prohormones, making in silico neuropeptide discovery difficult. In addition, the wide range of endogenous peptide concentrations as well as significant peptide complexity further challenge the structural characterization of neuropeptides. Liquid chromatography-mass spectrometry (MS), performed in conjunction with bioinformatics, allows for high-throughput characterization of peptides. Mass analyzers and molecular dissociation techniques render specific characteristics to the acquired data and thus, influence the analysis of the MS data using bioinformatic algorithms for follow-up peptide identification. Here we evaluated the efficacy of several distinct peptidomic workflows using two mass spectrometers, the Thermo Orbitrap Fusion Tribrid and Bruker Impact HD UHR-QqTOF, for confident peptide discovery and characterization. We compared the results in several categories, including the numbers of identified peptides, full-length mature neuropeptides among all identifications, and precursor proteins mapped by the identified peptides. We also characterized the peptide false discovery rate (FDR) based on the occurrence of amidation, a known post-translational modification (PTM) that has been shown to require the presence of a C-terminal glycine. Thus, amidation events without a preceding glycine were considered false-positive amidation assignments. We compared the FDR calculated by the search engine used here to the minimum FDR estimated via false amidation assignments. The search engine severely underestimated the rate of false PTM assignments among the identified peptides, regardless of the specific MS platform used.

Identification of a moronecidin-like antimicrobial peptide in the venomous fish Pterois volitans: Functional and structural study of pteroicidin-α

The present study characterizes for the first time an antimicrobial peptide in lionfish (Pterois volitans), a venomous fish. Using a peptidomic approach, we identified a mature piscidin in lionfish and called it pteroicidin-α. We detected an amidated form (pteroicidin-α- CONH₂) and a non-amidated form (pteroicidin-α-COOH), and then performed their functional and structural study. Interestingly, the two peptides displayed different antibacterial and hemolytic activity levels. Pteroicidin-α-CONH₂ was bactericidal on human pathogens like Staphylococcus aureus or Escherichia coli, as well as on the fish pathogen Aeromonas salmonicida, while pteroicidin-α-COOH only inhibited their growth. Furthermore, the two peptides induced hemolysis of red blood cells from different vertebrates, namely humans, sea bass and lesser-spotted dogfish. Hemolysis occurred with low concentrations of pteroicidin-α-CONH₂, indicating greater toxicity of the amidated form. Circular dichroism analysis showed that both peptides adopted a helical conformation, yet with a greater α-helix content in pteroicidin-α-CONH₂. Overall, these results suggest that amidation strongly influences pteroicidin-α by modifying its structure and its physico-chemical characteristics and by increasing its hemolytic activity.

Kinetic commitment in the catalysis of glutamine synthesis by GS1 from Arabidopsis using 14N/15N and solvent isotope effects

Glutamine synthetase (GS, EC 6.3.1.2) catalyzes the production of glutamine from glutamate, ammonium and ATP. Although being essential in plants for N assimilation and recycling, kinetic commitments and transition states of the reaction have not been clearly established yet. Here, we examined ¹²C/¹³C, ¹⁴N/¹⁵N and H₂O/D₂O isotope effects in Arabidopsis GS1 catalysis and compared to the prokaryotic (Escherichia coli) enzyme. A¹⁴N/¹⁵N isotope effect (¹⁵V/K ≈ 1.015, with respect to substrate NH₄⁺) was observed in the prokaryotic enzyme, indicating that ammonium utilization (deprotonation and/or amidation) was partially rate-limiting. In the plant enzyme, the isotope effect was inverse (¹⁵V/K = 0.965), suggesting that the reaction intermediate is involved in an amidation-deamidation equilibrium favoring ¹⁵N. There was no ¹²C/¹³C kinetic isotope effect (¹³V/K = 1.000), suggesting that the amidation step of the catalytic cycle involves a transition state with minimal alteration of overall force constants at the C-5 carbon. Surprisingly, the solvent isotope effect was found to be inverse, that is, with a higher turn-over rate in heavy water (^DV ≈ 0.5), showing that restructuration of the active site due to displacement of H₂O by D₂O facilitates the processing of intermediates.

Green synthesis of biocompatiable chitosan-graphene oxide hybrid nanosheet by ultrasonication method

Ultrasound-induced synthesis of chitosan-modified nano-scale graphene oxide (CS-NGO) hybrid nanosheets, which has great potential pharmaceutical applications, in supercritical CO2 without catalyst was presented for the first time. The preparation process does not require organic solvent and post-processing, and CO2 easily escapes from the product. The morphology and structure of the CS-NGO, characterized using scanning electron microscopy, transmission electron microscopy, infrared spectroscopy, X-ray photoelectron spectroscopy and thermogravimetric analysis, confirms that it was combined via the amide linkage, and had excellent dispersibility and stability toward acidic and physiological aqueous solution, which implies that it could be used as a drug-carrier. The sonication power played a crucial role in inducing forming amidation, and the conversion rate increased with the sonication time. The mechanism of this reaction was explained.

Enhancing hyaluronan pseudoplasticity via 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride-mediated conjugation with short alkyl moieties

Hyaluronan (HA) is widely used in the clinical practice and in biomedical research. Through chemical modification, HA shear-thinning properties, essential for injectability and additive manufacturing, can be optimized. In this study, we employed 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMTMM) for grafting propylamine and butylamine to HA. A parametric study was performed to identify the optimal reaction conditions. Results showed that DMTMM amidation gives reproducible and accurate control over a range of degrees of substitution (DS) from 1% to 50% and proved reliable to tune viscoelasticity. At DS=3.0% for HA-propylamine and 3.7% for HA-butylamine a maximum for storage modulus and pseudoplasticity was found, whereas above or below this DS, rheological features go back to baseline values of pristine HA. Due to their singular rheological profiles, these derivatives are valuable biomaterials candidates for preparing bioinks and hydrogels for drug delivery and regenerative medicine.

C-terminal amidation of PACAP-38 and PACAP-27 is dispensable for biological activity at the PAC1 receptor

PACAP-27 and PACAP-38 are the exclusive physiological ligands for the mammalian PAC1 receptor. The role of C-terminal amidation of these ligands at that receptor was examined in neuroendocrine cells expressing the PAC1 receptor endogenously and in non-neuroendocrine cells in which the human and rat PAC1 receptors were expressed from stable single-copy genes driven by the CMV promoter, providing stoichiometrically appropriate levels of this Gs-coupled GPCR in order to examine the potency and intrinsic activity of PACAP ligands and their des-amidated congeners. We found that replacement of the C-terminal glycine residues of PACAP-27 and -38 with a free acid; or extension of either peptide with the two to three amino acids normally found at these positions in PACAP processing intermediates in vivo following endoproteolytic cleavage and after exoproteolytic trimming and glycine-directed amidated, were equivalent in potency to the fully processed peptides in a variety of cell-based assays. These included real-time monitoring of cyclic AMP generation in both NS-1 neuroendocrine cells and non-neuroendocrine HEK293 cells; PKA-dependent gene activation in HEK293 cells; and neuritogenesis and cell growth arrest in NS-1 cells. The specific implications for the role of amidation in arming of secretin-related neuropeptides for biological function, and the general implications for neuropeptide-based delivery in the context of gene therapy, are discussed.

Mechanistic investigation of palladium-catalyzed amidation of aryl halides

A mechanistic investigation using Becke3LYP density functional theory (DFT) was carried out on the palladium-catalyzed amidition of bromobenzene and (t)Bu-isocyanide. The whole catalytic cycle consists of five steps: oxidative addition, migratory insertion, anion exchange, reductive elimination, and hydrogen migration. The rate-determining step is oxidative addition, with a small Gibbs free energy of 14.6 kcal mol(-1). In the migratory insertion step, (t)Bu-isocyanide provides an important source of carboxy and amino groups to establish the amide group. For anion exchange, path 1a is suggested as the most favorable pathway with the help of the base, and water provides a source of oxygen which is perfectly in line with experimental observations. Finally, in the hydrogen migration step, we illustrate that the six-membered ring path is energetically favored due to the assisting influence of water. In addition, our calculations indicate that using dimethyl sulfoxide as a solvent does not change the rate-determining step.

Early eukaryotic origins for cilia-associated bioactive peptide-amidating activity

Ciliary axonemes and basal bodies were present in the last eukaryotic common ancestor and play crucial roles in sensing and responding to environmental cues. Peptidergic signaling, generally considered a metazoan innovation, is essential for organismal development and homeostasis. Peptidylglycine α-amidating monooxygenase (PAM) is crucial for the last step of bioactive peptide biosynthesis. However, identification of a complete PAM-like gene in green algal genomes suggests ancient evolutionary roots for bioactive peptide signaling. We demonstrate that the Chlamydomonas reinhardtii PAM gene encodes an active peptide-amidating enzyme (CrPAM) that shares key structural and functional features with the mammalian enzyme, indicating that components of the peptide biosynthetic pathway predate multicellularity. In addition to its secretory pathway localization, CrPAM localizes to cilia and tightly associates with the axonemal superstructure, revealing a new axonemal enzyme activity. This localization pattern is conserved in mammals, with PAM present in both motile and immotile sensory cilia. The conserved ciliary localization of PAM adds to the known signaling capabilities of the eukaryotic cilium and provides a potential mechanistic link between peptidergic signaling and endocrine abnormalities commonly observed in ciliopathies.

Synthesis of Nocistatin C-terminal and it's Amide Derivatives as an Opioid Peptide

A new biological active hexapeptide of C-terminal of nocistatin, contains Glu-Gln-Lys-Gln-Leu-Gln sequence was synthesized according to solid phase peptide synthesis on the surface of 2-chloro tritylchloride resin and using fmoc-protected amino acids in the presence of TBTU (O-(Benzotriazol-1-yl)-N,N,N',N'-tetramethyl uranium tetrafluoroborate) as a coupling reagent. Then, amidation of the C-terminus of peptides was carried out using NH₄Cl and alkyl ammonium chloride (RNH₃Cl) in the presence of TBTU and a tertiary amine (DIPEA) as the base at room temperature in good to high yields. Cleavage of the desired peptides from the surface of the resin after the addition of TFA (1%) provided the protected peptides. All of the products were purified using preparative HPLC and structures were assigned according to MALDI-mass spectrometry data.

Lipase-catalyzed synthesis of palmitanilide: Kinetic model and antimicrobial activity study

Enzymatic syntheses of fatty acid anilides are important owing to their wide range of industrial applications in detergents, shampoo, cosmetics, and surfactant formulations. The amidation reaction of Mucor miehei lipase Lipozyme IM20 was investigated for direct amidation of triacylglycerol in organic solvents. The process parameters (reaction temperature, substrate molar ratio, enzyme amount) were optimized to achieve the highest yield of anilide. The maximum yield of palmitanilide (88.9%) was achieved after 24 h of reaction at 40 °C at an enzyme concentration of 1.4% (70 mg). Kinetics of lipase-catalyzed amidation of aniline with tripalmitin has been investigated. The reaction rate could be described in terms of the Michaelis-Menten equation with a Ping-Pong Bi-Bi mechanism and competitive inhibition by both the substrates. The kinetic constants were estimated by using non-linear regression method using enzyme kinetic modules. The enzyme operational stability study showed that Lipozyme IM20 retained 38.1% of the initial activity for the synthesis of palmitanilide (even after repeated use for 48 h). Palmitanilide, a fatty acid amide, exhibited potent antimicrobial activity toward Bacillus cereus.

Investigating triazine-based modification of hyaluronan using statistical designs

Hyaluronan (HA) and its derivatives have been extensively researched for many biomedical applications. To precisely tailor the property of HA by derivatizing it to a pre-determined extent is challenging, yet critical. In this paper, we used 2-chloro-4,6-dimethoxy-1,3,5-triazine (CDMT) and N-methylmorpholine (NMM) to derivatize HA via a triazine-based coupling reaction. Using a fractional factorial (FF) design, we observed that water content in the solvent, and molar ratios of CDMT and NaHCO3 to the carboxylate were the significant factors controlling the derivatization. We investigated how the effect of each factor changes as reaction conditions change. Moreover, by altering the amount of CDMT and NaHCO3, we developed a cubic regression model for precise control of the extent of derivatization using a response surface methodology (RSM) with a D-optimal design. No spurious peaks were detected by (1)H NMR spectrum and only 10% decrease of molecular weight of the derivatized HA was determined by GPC. The HA with 6% modification was relatively biocompatible up to 15 mg/mL.

The Effective Synthesis of N-(Arylalkyl)-1-R-4-hydroxy-2,2-dioxo- 1H-2λ(6),1-benzothiazine-3-carboxamides as Promising Analgesics of a New Chemical Class

A new, effective preparative method has been proposed and the synthesis of a series of N-(arylalkyl)-1-R-4-hydroxy-2,2-dioxo-1H-2λ(6),1-benzothiazine-3-car-boxamides has been carried out. It has been shown that amidation of alkyl 1-R-4-hydroxy-2,2-dioxo-1H-2λ(6),1-benzothiazine-3-carboxylates with arylalkyl-amines in boiling xylene proceeds with good yield and purity to the corresponding N-(arylalkyl)-amides. However, the presence of water in the reaction mixture has been shown to cause the formation of specific impurities: N-(arylalkyl)-1-R-2,2-dioxo-1H-2λ(6),1-benzothiazin-4-amines. According to the results of the pharmacological studies, powerful analgesics have been found among the substances synthesized.

New functionalized mercaptoundecahydrododecaborate derivatives for potential application in boron neutron capture therapy: synthesis, characterization and dynamic visualization in cells

A series of mercaptoundecahydrododecaborate (B12H11SH(2-), BSH) bearing mono- and dicarboxyalkyl derivatives was prepared, characterized, and their reactivity towards amidation and esterification in DMF was evaluated. Symmetrical alkylation of BSH was achieved by treatment with primary haloalkyl carboxylic acids in aqueous acetonitrile to produce S,S-bis(carboxyalkyl)sulfonium-undecahydro-closo-dodecaborate tetramethylammonium salts. Unsymmetrically substituted sulfonium salts were obtained through a similar treatment of cyanoethylthioether-undecahydro-closo-dodecaborate tetramethylammonium salt with haloalkyl carboxylic acid. Selective removal of the remaining cyanoethyl group upon treatment with tetramethylammonium hydroxide yielded S-carboxyalkyl-thioether-undecahydro-closo-dodecaborate ditetramethylammonium salts. N,N'-dicyclohexylcarbodiimide (DCC) activated amidation of S,S-bis(carboxyalkyl)sulfonium-undecahydro-closo-dodecaborate or S-carboxyalkyl-thioether-undecahydro-closo-dodecaborate tetramethylammonium salts with propargylamine provided the opportunity to install terminal acetylene groups for further conjugation. These compounds acted as powerful building blocks for the synthesis of a broad range of 1,4-disubstituted 1,2,3-triazole products in high yields, utilizing the Cu(I)-mediated click cycloaddition reaction. The synthesis of BSH-lipid with a two-tailed moiety was also achieved, by esterification of S,S-bis(carboxyethyl)sulfoniumundecahydro-closo-dodecaborate(1-) tetramethylammonium salt with 1,2-O-distearoyl-sn-3-glycerol, which may prove useful in the liposomal boron delivery system. The bio-compatibility of the azide-alkyne click reaction was then utilized by performing this reaction in cell culture. The distribution of BSH in HeLa cells could be visualized by treating the cells first with a BSH-alkyne compound and then with Alexa Fluor 488(®) azide dye. The BSH-dye conjugate, which did not wash out, revealed the distribution of boron in the HeLa cells. Cytotoxicity assays of these BSH derivatives revealed that the synthesized BSH-conjugated triazoles possessed low cytotoxicity in HeLa cancer cells. Of these compounds, BSH conjugated triazole 15 induced a significant increase in the level of boron accumulation in HeLa cells.

N-(5-Mercapto-1,3,4-Thiadiazol-2-yl)-2-Phenylacetamide Derivatives: Synthesis and In-vitro Cytotoxicity Evaluation as Potential Anticancer Agents

A new series of N-(5-Mercapto-1,3,4-thiadiazol-2-yl)-2-phenylacetamide derivatives (3a-3j) were synthesized via an amidation reaction using EDC and HOBt in acetonitrile solvent at room temperature condition. Chemical structures were characterized by (1)H NMR, IR and MS spectroscopic methods and related melting points were also determined. The anticancer activity was evaluated using MTT procedure in-vitro. All compounds were tested against SKNMC (Neuroblastoma), HT-29 (Colon cancer) and PC3 (Prostate cancer) cell lines. According to the toxicological data, none of the synthesized derivatives exerted superior activity than doxorubicin as reference drug. Derivatives with Ortho chlorine (compound 3d), meta methoxy (compound 3h) and meta fluorine (compound 3b) substituents on the phenyl ring exhibited the best cytotoxic activity against SKNMC (IC50 = 4.5 ± 0.035 µM), HT-29 (IC50 = 3.1 ± 0.030 µM) and PC3 (IC50 = 12.6 ± 0.302 µM) cell lines respectively.

The profile of bile acids and their sulfate metabolites in human urine and serum

The role of sulfation in ameliorating the hepatotoxicity of bile acids (BAs) in humans remains unknown due to the lack of proper analytical methods to quantify individual BAs and their sulfate metabolites in biological tissues and fluids. To this end, a simple and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and validated to characterize the detailed BA profile in human urine and serum. The limit of quantification was 1ng/mL and baseline separation of all analytes was achieved within in a run time of 32min. The method was validated over the dynamic range of 1-1000ng/mL. The LC-MS/MS method was more accurate, precise, and selective than the commercially available kits for the quantification of sulfated and unsulfated BAs, and the indirect quantification of individual sulfated BAs after solvolysis. The LC-MS/MS method was applied to characterize the BA profile in urine and serum of healthy subjects. Thirty three percent of serum BAs were sulfated, whereas 89% of urinary BAs existed in the sulfate form, indicating the role of sulfation in enhancing the urinary excretion of BAs. The percentage of sulfation of individual BAs increased with the decrease in the number of hydroxyl groups indicating the role of sulfation in the detoxification of the more hydrophobic and toxic BA species. Eighty percent of urinary BAs and 55% of serum BAs were present in the glycine-amidated form, whereas 8% of urinary BAs and 13% of serum BAs existed in the taurine-amidated form.

Diagnosis in bile acid-CoA: Amino acid N-acyltransferase deficiency

Cholate-CoA ligase (CCL) and bile acid-CoA: amino acid N-acyltransferase (BAAT) sequentially mediate bile-acid amidation. Defects can cause intrahepatic cholestasis. Distinction has required gene sequencing. We assessed potential clinical utility of immunostaining of liver for CCL and BAAT. Using commercially available antibodies against BAAT and CCL, we immunostained liver from an infant with jaundice, deficiency of amidated bile acids, and transcription-terminating mutation in BAAT. CCL was normally expressed. BAAT expression was not detected. Immunostaining may facilitate diagnosis in bile-acid amidation defects.