Synthesis and quantitative structure-activity relationship analysis of N-triiodoallyl- and N-iodopropargylazoles. New antifungal agents

Late-stage diversification of bacterial natural products through biocatalysis

Bacterial natural products (BNPs) are very important sources of leads for drug development and chemical novelty. The possibility to perform late-stage diversification of BNPs using biocatalysis is an attractive alternative route other than total chemical synthesis or metal complexation reactions. Although biocatalysis is gaining popularity as a green chemistry methodology, a vast majority of orphan sequenced genomic data related to metabolic pathways for BNP biosynthesis and its tailoring enzymes are underexplored. In this review, we report a systematic overview of biotransformations of 21 molecules, which include derivatization by halogenation, esterification, reduction, oxidation, alkylation and nitration reactions, as well as degradation products as their sub-derivatives. These BNPs were grouped based on their biological activities into antibacterial (5), antifungal (5), anticancer (5), immunosuppressive (2) and quorum sensing modulating (4) compounds. This study summarized 73 derivatives and 16 degradation sub-derivatives originating from 12 BNPs. The highest number of biocatalytic reactions was observed for drugs that are already in clinical use: 28 reactions for the antibacterial drug vancomycin, followed by 18 reactions reported for the immunosuppressive drug rapamycin. The most common biocatalysts include oxidoreductases, transferases, lipases, isomerases and haloperoxidases. This review highlights biocatalytic routes for the late-stage diversification reactions of BNPs, which potentially help to recognize the structural optimizations of bioactive scaffolds for the generation of new biomolecules, eventually leading to drug development.

Antifungal Activity of Fibrate-Based Compounds and Substituted Pyrroles That Inhibit the Enzyme 3-Hydroxy-methyl-glutaryl-CoA Reductase of Candida glabrata (CgHMGR), Thus Decreasing Yeast Viability and Ergosterol Synthesis

Due to the emergence of multidrug-resistant strains of yeasts belonging to the Candida genus, there is an urgent need to discover antifungal agents directed at alternative molecular targets. The aim of the current study was to evaluate the capacity of three different series of synthetic compounds to inhibit the Candida glabrata enzyme denominated 3-hydroxy-methyl-glutaryl-CoA reductase and thus affect ergosterol synthesis and yeast viability. Compounds 1c (α-asarone-related) and 5b (with a pyrrolic core) were selected as the best antifungal candidates among over 20 synthetic compounds studied. Both inhibited the growth of fluconazole-resistant and fluconazole-susceptible C. glabrata strains. A yeast growth rescue experiment based on the addition of exogenous ergosterol showed that the compounds act by inhibiting the mevalonate synthesis pathway. A greater recovery of yeast growth occurred for the C. glabrata 43 fluconazole-resistant (versus fluconazole-susceptible) strain and after treatment with 1c (versus 5b). Given that the compounds decreased the concentration of ergosterol in the yeast strains, they probably target ergosterol synthesis. According to the docking analysis, the inhibitory effect of 1c and 5b could possibly be mediated by their interaction with the amino acid residues of the catalytic site of the enzyme. Since 1c displayed higher binding energy than α-asarone and 5b, it is the best candidate for further research, which should include structural modifications to increase its specificity and potency. The derivatives could then be examined with in vivo animal models using a therapeutic dose. IMPORTANCE Within the context of the COVID-19 pandemic, there is currently an epidemiological alert in health care services due to outbreaks of Candida auris, Candida glabrata, and other fungal species multiresistant to conventional antifungals. Therefore, it is important to propose alternative molecular targets, as well as new antifungals. The three series of synthetic compounds herein designed and synthesized are inhibitors of ergosterol synthesis in yeasts. Of the more than 20 compounds studied, two were selected as the best antifungal candidates. These compounds were able to inhibit the growth and synthesis of ergosterol in C. glabrata strains, whether susceptible or resistant to fluconazole. The rational design of antifungal compounds derived from clinical drugs (statins, fibrates, etc.) has many advantages. Future studies are needed to modify the structure of the two present test compounds to obtain safer and less toxic antifungals. Moreover, it is important to carry out a more in-depth mechanistic approach.

Benzofuroxan Derivatives as Potent Agents against Multidrug-Resistant Mycobacterium tuberculosis

Tuberculosis (TB) is currently the leading cause of death related to infectious diseases worldwide, as reported by the World Health Organization. Moreover, the increasing number of multidrug-resistant tuberculosis (MDR-TB) cases has alarmed health agencies, warranting extensive efforts to discover novel drugs that are effective and also safe. In this study, 23 new compounds were synthesized and evaluated in vitro against the drug-resistant strains of M. tuberculosis. The compound 6-((3-fluoro-4-thiomorpholinophenyl)carbamoyl)benzo[c][1,2,5]oxadiazole 1-N-oxide (5 b) was particularly remarkable in this regard as it demonstrated MIC₉₀ values below 0.28 μM against all the MDR strains evaluated, thus suggesting that this compound might have a different mechanism of action. Benzofuroxans are an attractive new class of anti-TB agents, exemplified by compound 5 b, with excellent potency against the replicating and drug-resistant strains of M. tuberculosis.

Recent Progress in the Synthesis of Pyrroles

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Pyrrole derivatives are nitrogen-containing heterocyclic compounds and widely distributed in a large number of natural and non-natural compounds. These compounds possess a broad spectrum of biological activities such as anti-infammatory, antiviral, antitumor, antifungal, and antibacterial activities. Besides their biological activity, pyrrole derivatives have also been applied in various areas such as dyes, conducting polymers, organic semiconductors.

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Due to such a wide range of applicability, access to this class of compounds has attracted intensive research interest. Various established synthetic methods such as Paal-Knorr, Huisgen, and Hantzsch have been modified and improved. In addition, numerous novel methods for pyrrole synthesis have been discovered. This review will focus on considerable studies on the synthesis of pyrroles, which date back from 2014.

Expanding the SAR of Nontoxic Antiplasmodial Indolyl-3-ethanone Ethers and Thioethers

Despite major strides in reducing Plasmodium falciparum infections, this parasite still accounts for roughly half a million annual deaths. This problem is compounded by the decreased efficacy of artemisinin combination therapies. Therefore, the development and optimisation of novel antimalarial chemotypes is critical. In this study, we describe our strategic approach to optimise a class of previously reported antimalarials, resulting in the discovery of 1-(5-chloro-1H-indol-3-yl)-2-[(4-cyanophenyl)thio]ethanone (13) and 1-(5-chloro-1H-indol-3-yl)-2-[(4-nitrophenyl)thio]ethanone (14), whose activity was equipotent to that of chloroquine against the P. falciparum 3D7 strain. Furthermore, these compounds were found to be nontoxic to HeLa cells as well as being non-haemolytic to uninfected red blood cells. Intriguingly, several of our most promising compounds were found to be less active against the isogenic NF54 strain, highlighting possible issues with long-term dependability of malarial strains. Finally compound 14 displayed similar activity against both the NF54 and K1 strains, suggesting that it inhibits a pathway that is uncompromised by K1 resistance.

Nitropyrrole natural products: isolation, biosynthesis and total synthesis

A review of the isolation, biological activity, biosynthesis and chemical synthesis of nitropyrrole-containing natural products reported to date, including the pyrrolomycins, heronapyrroles and nitropyrrolins.

Synthesis and antifungal activity of 5-iodo-1,4-disubstituted-1,2,3-triazole derivatives as pyruvate dehydrogenase complex E1 inhibitors

To identify new antifungal lead compound based on inhibitors of pyruvate dehydrogenase complex E1, a series of 5-iodo-1,4-disubstituted-1,2,3-triazole derivatives 3 were prepared and evaluated for their Escherichia coli PDHc-E1 inhibitory activity and antifungal activity. The in vitro bioassay for the PDHc-E1 inhibition indicated all the compounds exhibited significant inhibition against E. coli PDHc-E1 (IC50<21μM), special compound 3g showed the most potent inhibitory activity (IC50=4.21±0.11μM) and was demonstrated to act as a competitive inhibitor of PDHc-E1. Meanwhile, inhibitor 3g exhibited very good enzyme-selective inhibition of PDHc-E1 between pig heart and E. coli. The assay of antifungal activity showed compounds 3e, 3g, and 3n exhibited fair to good activity against Rhizoctonia solani and Botrytis cinerea even at 12.5μg/mL. Especially compound 3n (EC50=5.4μg/mL; EC90=21.1μg/mL) exhibited almost 5.50 times inhibitory potency against B. cinerea than that of pyrimethanil (EC50=29.6μg/mL; EC90=113.4μg/mL). Therefore, in this study, compound 3n was found to be a novel lead compound for further optimization to find more potent antifungal compounds as microbial PDHc-E1 inhibitors.

A practical and general ipso iodination of arylboronic acids using N-iodomorpholinium iodide (NIMI) as a novel iodinating agent: mild and regioselective synthesis of aryliodides

A mild and efficient protocol for the ipso-iodination of aryl boronic acids using N-iodomorpholinium iodide (NIMI) generated in situ from morpholine and molecular iodine as a novel iodinating agent has been developed.

Pyrrole: a resourceful small molecule in key medicinal hetero-aromatics

Pyrrole is widely known as a biologically active scaffold which possesses a diverse nature of activities.

Synthesis and biological evaluation of novel N-substituted 1H-dibenzo[a,c]carbazole derivatives of dehydroabietic acid as potential antimicrobial agents

A series of new N-substituted 1H-dibenzo[a,c]carbazole derivatives were synthesized from dehydroabietic acid, and their structures were characterized by IR, (1)H NMR and HRMS spectral data. All compounds were evaluated for their antibacterial and antifungal activities against four bacteria (Bacillus subtilis, Staphylococcus aureus, Escherichia coli and Pseudomonas fluorescens) and three fungi (Candida albicans, Candida tropicalis and Aspergillus niger) by serial dilution technique. Some of the synthesized compounds displayed pronounced antimicrobial activity against tested strains with low MIC values ranging from 0.9 to 15.6μg/ml. Among them, compounds 6j and 6r exhibited potent inhibitory activity comparable to reference drugs amikacin and ketoconazole.

Synthesis and evaluation of novel 4-nitropyrrole-based 1,3,4-oxadiazole derivatives as antimicrobial and anti-tubercular agents

We report synthesis and antimicrobial evaluation of 42 novel 4-nitropyrrole-based 1,3,4-oxadiazoles. The synthesized molecules were evaluated for anti-bacterial, anti-fungal and anti-tubercular activities. Promisingly, most of the compounds showed equal or more potency than standard ciprofloxacin against Staphylococcus aureus, Bacillus subtilis and Escherichia coli. Compound 5e exhibited highest anti-tubercular activity (0.46 μg/mL) close to that of standard Isoniazid (0.40 μg/mL). Equal antifungal activity (1.56 μg/mL) compared to standard Amphotericin-B was shown by most of the compounds. All the N-methylated compounds showed more potent to equal activity against MSSA (MIC 0.39-1.56 μg/mL) and MRSA (MIC 0.78-1.56 μg/mL). All compounds were tested for mammalian cell toxicity using VERO cell line and were found to be non-toxic.

Molecular energetics of alkyl pyrrolecarboxylates: calorimetric and computational study

The pyrrole subunit plays an important role in material science as the building block of polypyrroles, an important representative class of conducting polymers, which found widely applications in the area of new materials due to their chemical, thermal, and electrical properties associated with their easiness and low cost of production, making them especially promising for commercial applications. The energetic characterization of this kind of molecules provides information concerning stability, reactivity, and biodegrability of chemical compounds in environment being, for example, helpful in choosing the most adequate method for their elimination by converting the waste into harmless compounds or even decreasing the production of toxic substances in industrial processes. This work reports a combination of calorimetric and computational determinations of several alkyl pyrrolecarboxylates (alkyl = methyl or ethyl) whose main purpose is the calculation of their standard (p° = 0.1 MPa) molar enthalpies of formation, in the gaseous phase, at T = 298.15 K. Experimentally, for methyl 1-pyrrolecarboxylate (M1PC), methyl 2-pyrrolecarboxylate (M2PC), and ethyl 2-pyrrolecarboxylate (E2PC), these values were derived from the standard (p° = 0.1 MPa) molar enthalpies of formation, in the condensed phase, ΔfHm° (cr,l), at T = 298.15 K, obtained by static bomb combustion calorimetry, and from the standard molar enthalpies of phase transition, Δcr,l(g)Hm°, at T = 298.15 K, determined by high-temperature Calvet microcalorimetry. Standard ab initio molecular calculations, at the G3(MP2)//B3LYP level, were performed, and the standard enthalpies of formation of these three compounds were estimated. A very good agreement between the calculated and the experimental data was obtained. Thereby, we have extended these calculations to other alkyl pyrrolecarboxylates, namely, ethyl 1-pyrrolecarboxylate (E1PC), methyl 3-pyrrolecarboxylate (M3PC), and ethyl 3-pyrrolecarboxylate (E3PC), whose study was not performed experimentally. The computational analysis, at the B3LYP/6-31G(d) level of theory, of the six molecules allowed a detailed inspection and a better knowledge about their molecular structure and geometrical parameters.

Bipolar molecules with high triplet energies: synthesis, photophysical, and structural properties

This article sheds new light on the interplay of electronic and conformational effects in luminescent bipolar molecules. A series of carbazole/1,3,4-oxadiazole hybrid molecules is described in which the optoelectronic properties are systematically varied by substituent effects which tune the intramolecular torsion angles. The synthesis, photophysical properties, cyclic voltammetric data, X-ray crystal structures, and DFT calculations are presented. Excited state intramolecular charge transfer (ICT) is observed from the donor carbazole/2,7-dimethoxycarbazole to the acceptor phenyl/diphenyloxadiazole moieties. Introducing more bulky substituents onto the diphenyloxadiazole fragment systematically increases the singlet and triplet energy levels (E(S) and E(T)) and blue shifts the absorption and emission bands. The triplet excited state is located mostly on the oxadiazole unit. The introduction of 2,7-dimethoxy substituents onto the carbazole moiety lowers the value of E(S), although E(T) is unaffected, which means that the singlet-triplet gap is reduced (for 7bE(S) - E(T) = 0.61 eV). A strategy has been established for achieving unusually high triplet levels for bipolar molecules (E(T) = 2.64-2.78 eV at 14 K) while at the same time limiting the increase in the singlet energy.

Tandem regioselective synthesis of tetrazoles and related heterocycles using iodine

A one-pot, tandem process has been developed for the synthesis of a library of tetrazoles from aryl isothiocyanates. Condensation of aryl isothiocyanates with ammonia, and aryl amines (R-NH(2)) provided mono, 1,3-disubstituted symmetrical and unsymmetrical thioureas, which on desulfurization with molecular iodine (I(2)) led to formation of the corresponding heterocumulene (cyanamides or carbodiimides). The in situ generated heterocumulene on subsequent treatment with sodium azide at room temperature gave corresponding tetrazoles. The product regioselectivity for unsymmetrical 1,3-disubstituted thioureas was found to be correlated with the basicities (pK(a)'s) of the parent amines attached to the thiourea. Aryl-sec-alkyl unsymmetrical thioureas gave thioamido guanidino products rather than the 5-aminotetrazoles produced by HgCl(2) mediation of the reaction. Bis-thioureas derived from aryl isothiocyanates and hydrazine gave thiadiazoles exclusively.

Molecular Assemblies from Imidazolyl-Containing Haloalkenes and Haloalkynes: Competition between Halogen and Hydrogen Bonding

The structural characterization of molecular assemblies constructed from imidazolyl-containing haloalkenes and haloalkynes is reported. 1-(3-Iodopropargyl)imidazole (2) and 1-(2,3,3-triiodoallyl)imidazole (5) were synthesized from 1-propargylimidazole (1). In the solid state, these wholly organic modules self-assemble through N...I halogen-bonding interactions, thus giving rise to polymeric chains. The N...I interaction observed in 2 (d(N...I)=2.717 A, angle-spherical C(sp)-I...N=175.8 degrees) is quite strong relative to previously reported data. The N...I interaction in 5 (d(N...I)=2.901 A, angle-spherical C(sp2)-I...N=173.6 degrees) is weaker, in accordance with the order C(sp)-X<--base>C(sp2)-X<--base. Compound 5 was found to give a 1:1 cocrystal 4 with morpholinium iodide (6). In the X-ray crystal studies of 4, N...I halogen-bonding interactions similar to those observed in 5 were shown not to be present, as the arrangement of the molecules is governed by two interwoven hydrogen-bonding networks. The first network involves N-H...O interactions between nearby morpholinium cations, and the second network is based on N-H...N hydrogen bonding between morpholinium cations and imidazolyl groups. Both hydrogen-bonding schemes are charge-assisted. Halogen bonding is not completely wiped out, however, as the triiodoalkene fragment forms a halogen bond with an iodide anion in its vicinity (d(I...I)=3.470 A, angle-spherical C(sp2)-I...I=170.7 degrees). X-ray crystal studies of 6 show a completely different arrangement from that observed in 4, namely, N-H...O interactions are not present. In crystalline 6, morpholinium cations are interconnected through C-H...O bridges (d(H...O)=2.521 and 2.676 A), and the NH2+ groups interact with nearby iodide anions (d(H...I)=2.633 and 2.698 A).

Oxidation of substituted toluenes with molecular oxygen in the presence of N,N',N' '-trihydroxyisocyanuric acid as a key catalyst

N,N',N' '-Trihydroxyisocianuric acid (THICA) was found to be a very efficient catalyst for the oxidation of alkylbenzenes with dioxygen. Thus, a variety of meta- and para-substituted toluenes bearing an electron-withdrawing substituent such as cyanotoluene, chlorotoluene, and toluic acid under O(2) (1 atm) in the presence of THICA (5 mol %) and Co(OAc)(2) (0.5 mol %) at 100 degrees C were smoothly oxidized to the corresponding benzoic acids in almost quantitative yields. The aerobic oxidation of toluene by THICA was compared with that by N-hydroxyphthalimide. p-Xylene was efficiently oxidized by THICA to telephthalic acid in high yield (over 95%) under mild conditions.

Prediction of complement-inhibitory activity of benzamidines using topological and geometric parameters

A hierarchical approach to quantitative structure-activity relationship (QSAR) modeling has been used to estimate the complement-inhibitory potency of 105 benzamidines. This hierarchical approach uses topostructural, topochemical, and geometric parameters in a stepwise fashion to build increasingly more complex models. The results show that topostructural indices alone, specifically I(D), predict inhibitory potency reasonably well. The addition of topochemical and geometrical parameters to the set of descriptors provides only marginal improvement in predictive power. However, when taken alone, the geometric parameter (3D)W provides a more stable model than the topostructural one.

Computer automated structure evaluation of antifungal 1-vinylimidazoles, 1,2-disubstituted propenones, and azolylpropanolones

The Computer Automated Structure Evaluation (CASE) program has been applied to a series of 1-vinylimidazoles, 1,2-disubstituted propenones, and azolylpropanolones exhibiting in vitro antifungal properties. Relevant molecular fragments were obtained for activity against the fungal strains Candida albicans, Aspergillus fumigatus, and Trichophyton asteroides. Fragments were utilized as descriptors to derive quantitative structure-activity relationships (QSAR) within each respective biological endpoint. A high degree of correlation was observed between fragments derived from C. albicans and A. fumigatus. The relevant activating and inactivating fragments from each of the respective biological endpoints analyzed are discussed.