Copper(I)-Catalyzed Synthesis of Azoles. DFT Study Predicts Unprecedented Reactivity and Intermediates

Huisgen's 1,3-dipolar cycloadditions become nonconcerted when copper(I) acetylides react with azides and nitrile oxides, providing ready access to 1,4-disubstituted 1,2,3-triazoles and 3,4-disubstituted isoxazoles, respectively. The process is highly reliable and exhibits an unusually wide scope with respect to both components. Computational studies revealed a stepwise mechanism involving unprecedented metallacycle intermediates, which appear to be common for a variety of dipoles.

1,2,3-Triazole-[2',5'-bis-O-(tert-butyldimethylsilyl)-beta-D- ribofuranosyl]-3'-spiro-5"-(4"-amino-1",2"-oxathiole 2",2"-dioxide) (TSAO) analogues: synthesis and anti-HIV-1 activity

Several 4- or 5-monosubsituted and 4,5-disubstituted 1,2,3-triazole analogues of the anti-HIV-1 lead compound [1-[2',5'-bis-O-(tert-butyldimethylsilyl)-beta-D- ribofuranosyl]thymine]-3'-spiro-5"-(4"-amino-1",2"-oxathiole 2",2"-dioxide) (TSAO-T) have been prepared and evaluated as inhibitors of HIV-1-induced cytopathicity. These analogues have been prepared by 1,3-diplar cycloaddition of [2,5-bis-O-(tert-butyldimethylsilyl)-beta-D-ribofuranosyl]- 3-spiro-5'-(4'-amino- and 4'-(N-acetylamino)-1',2'-oxathiole 2',2'-dioxide) (TSAO) azides to various substituted acetylenes. Several 4- and 5-substituted 1,2,3-triazole-TSAO analogues proved superior to the unsubstituted derivative by 1-2 orders of magnitude. In particular the 5-substituted amido-, (methylamido)-, and (dimethylamido)-1,2,3-triazole derivatives of TSAO were endowed with potent anti-HIV-1 activity (50% effective concentration: 0.056-0.52 microM). They show a similar resistance spectrum as previously noted for TSAO-T and related derivatives.

An Efficient Route to Well-Defined Macrocyclic Polymers via “Click” Cyclization

Polystyrene macrocycles have been prepared from ATRP precursors by modification of the terminal bromide to an azide, followed by "click" cyclization with a pendant alkyne from the initiator. This route offers exceptional control over the size and polydispersity of the macrocyclic polymers, as well as providing tolerance to a number of functional groups.

Medicinal attributes of 1,2,3-triazoles: Current developments

1,2,3-Triazoles are important five-membered heterocyclic scaffold due to their extensive biological activities. This framework can be readily obtained in good to excellent yields on the multigram scale through click chemistry via reaction of aryl/alkyl halides, alkynes and NaN₃ under ambient conditions. It has been an emerging area of interest for many researchers throughout the globe owing to its immense pharmacological scope. The present work aims to summarize the current approaches adopted for the synthesis of the 1,2,3-triazole and medicinal significance of these architectures as a lead structure for the discovery of drug molecules such as COX-1/COX-2 inhibitors (celecoxib, pyrazofurin), HIV protease inhibitors, CB1 cannabinoid receptor antagonist and much more which are in the pipeline of clinical trials. The emphasis has been given on the major advancements in the medicinal prospectus of this pharmacophore for the period during 2008-2016.

Copper−Diamine-Catalyzed N-Arylation of Pyrroles, Pyrazoles, Indazoles, Imidazoles, and Triazoles

This paper details the copper-catalyzed N-arylation of pi-excessive nitrogen heterocycles. The coupling of either aryl iodides or aryl bromides with common nitrogen heterocycles (pyrroles, pyrazoles, indazoles, imidazoles, and triazoles) was successfully performed in good yield with catalysts derived from diamine ligands and CuI. General conditions were found that tolerate functional groups such as aldehydes, ketones, alcohols, primary amines, and nitriles on the aryl halide or heterocycle. Hindered aryl halides or heterocycles were also found to be suitable substrates using the conditions reported herein.

A potent and highly selective inhibitor of human alpha-1,3-fucosyltransferase via click chemistry

Potent inhibitors of fucosyltransferases, and glycosyltransferases in general, have been elusive due to the inherent barriers surrounding the family of glycosyltransfer reactions. The problems of weak substrate affinity and low catalytic proficiency of fucosyltransferase was offset by recruiting additional binding features, in this case hydrophobic interactions, to produce a high affinity inhibitor, 24, with Ki = 62 nM. The molecule was identified from a GDP-triazole library of 85 compounds, which was produced by the Cu(I)-catalyzed [2 + 3] cycloaddition reaction between azide and acetylene reactants, followed by in situ screening without product isolation.

Crystalline 1H-1,2,3-triazol-5-ylidenes: new stable mesoionic carbenes (MICs)

Until recently, the availability of neutral carbon-based κ1C ligands was limited to carbon monoxide, isocyanides, and carbenes. Compared to phosphorus-based ligands, carbenes tend to bind more strongly to metal centers, avoiding the necessity for the use of excess ligand in catalytic reactions. The corresponding complexes are often less sensitive to air and moisture, and are remarkably resistant to oxidation.[1 ] As the robustness of carbene complexes is largely due to the presence of strong carbon–metal bonds, other types of carbon-based ligands are highly desirable. It is noteworthy that, although complexes between a carbene and a transition metal have been known for a long time,[2 ] the recent developments in their application in catalysis[3 ] have been greatly facilitated by the availability of carbenes that are stable enough to be bottled.[4 ,5 ] Moreover, carbenes, especially imidazol-2-ylidenes I [4c ] and 1,2,4-triazol-5-ylidenes II ,[4e ] are also excellent organocatalysts (Scheme 1 ).[6 ]

Studies on 1,2,3-triazoles. 13. (Piperazinylalkoxy) [1]benzopyrano[2,3-d]-1,2,3-triazol-9(1H)-ones with combined H1-antihistamine and mast cell stabilizing properties

Several N-benzylpiperazino derivatives of [1]benzopyrano[2,3-d]-1,2,3-triazol-9(1H)-one and its 5-methyl homologue have been prepared and evaluated for H1-antihistamine activity on guinea pig ileum. The most potent compounds were also evaluated for their ability to stabilize mast cells in the rat passive peritoneal anaphylaxis (PPA) system and were shown to inhibit histamine release at concentrations below those required to inhibit extravasation, suggesting that this might be relevant to their antianaphylactic activity in this system. The compound tested with the most potent H1-antihistamine activity was 6-[3-[4-(4-chlorobenzyl)-1-piperazinyl]propoxy][1]benzopyrano[2,3- d]-1,2,3-triazol-9(1H)-one, 28, which had a pA2 of 9.1 against histamine on guinea pig ileum, comparable to that of mepyramine, and inhibited histamine release in the rat PPA system with an IC50 value of 5.4 X 10(-6) M.

Design of 5-(3,5-di-tert-butyl-4-hydroxyphenyl)-1,3,4-thiadiazoles, -1,3,4-oxadiazoles, and -1,2,4-triazoles as orally-active, nonulcerogenic antiinflammatory agents

To discover dual inhibitors of 5-lipoxygenase (LO) and cyclooxygenase (CO) with improved pharmacokinetic properties, we have designed and synthesized series of 1,2,4-triazole, 1,3,4-oxadiazole, and 1,3,4-thiadiazole di-tert-butylphenol derivatives which exhibit a wide range of log P (2.3 to > 4) and pKa (5.5-12) values. From this work 5-[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]-1,3,4-thiadiazole-2(3H)- thione, choline salt (12a, CI-986) was found to be a potent inhibitor of 5-LO (IC50 = 2.8 microM) and CO (IC50 = 0.8 microM), orally active in rat models of inflammation and nonulcerogenic.

4-Amino[1,2,4]triazolo[4,3-a]quinoxalines. A novel class of potent adenosine receptor antagonists and potential rapid-onset antidepressants

A series of 4-amino[1,2,4]triazolo[4,3-a]quinoxalines has been prepared. Many compounds from this class reduce immobility in Porsolt's behavioral despair model in rats upon acute administration and may therefore have therapeutic potential as novel and rapid acting antidepressant agents. Optimal activity in this test is associated with hydrogen, CF3, or small alkyl groups in the 1-position, with NH2, NH-acetyl, or amines substituted with small alkyl groups in the 4-position, and with hydrogen or 8-halogen substituents in the aromatic ring. Furthermore, many of these 4-amino[1,2,4]triazolo[4,3-a]quinoxalines bind avidly, and in some cases very selectively, to adenosine A1 and A2 receptors. A1 affinity of these compounds was measured by their inhibition of tritiated CHA (N6-cyclohexyladenosine) binding in rat cerebral cortex membranes and A2 affinity by their inhibition of tritiated NECA (5'-(N-ethylcarbamoyl)adenosine) binding to rat striatal homogenate in the presence of cold N6-cyclopentyladenosine. Structure-activity relationship (SAR) studies show that best A1 affinity is associated with ethyl, CF3, or C2F5 in the 1-position, NH-iPr or NH-cycloalkyl in the 4-position, and with an 8-chloro substituent. Affinity at the A2 receptor is mostly dependent on the presence of an NH2 group in the 4-position and is enhanced by phenyl, CF3, or ethyl in the 1-position. The most selective A1 ligand by a factor of greater than 3000 is 121 (CP-68,247; 8-chloro-4-(cyclohexyl-amino)-1- (trifluoromethyl)[1,2,4]triazolo[4,3-a]quinoxaline) with an IC50 of 28 nM at the A1 receptor. The most potent A2 ligand is 128 (CP-66,713; 4-amino-8-chloro-1- phenyl[1,2,4]triazolo[4,3-a]quinoxaline) with an IC50 of 21 nM at the A2 receptor and a 13-fold selectivity for this receptor. Representatives from this series appear to act as antagonists at both A1 and A2 receptors since they antagonize the inhibiting action of CHA on norepinephrine-stimulated cAMP formation in fat cells and they decrease cAMP accumulation induced by adenosine in limbic forebrain slices. Thus certain members of this 4-amino[1,2,4]triazolo[4,3-a]quinoxaline series are among the most potent and A1 or A2 selective non-xanthine adenosine antagonists known.

New bis-aminomercaptotriazoles and bis-triazolothiadiazoles as possible anticancer agents

A series of bis-phenoxyacetic acids 2 were prepared starting from corresponding unsubstituted/substituted 1,4-quinols 1. The fusion of bis-phenoxyacetic acids 2 with thiocarbohydrazide gave the corresponding bis-[4-amino-5-mercapto-1,2,4-triazol-3-yl-methyleneoxy]phenylenes (3) in a one pot reaction. The reaction of bis-triazoles 3 with various reagents afforded N-bridged heterocycles 4-6 in good yields. The newly synthesised compounds were screened for their anticancer activity against a panel of 60 cell lines derived from seven cancer types namely, lung, colon, melanoma, renal, ovarian, CNS and leukemia. Some of the tested compounds showed promising anticancer properties.

One-Pot Synthesis of 1,4-Disubstituted 1,2,3-Triazoles from In Situ Generated Azides

[reaction: see text] 1,4-Disubstituted 1,2,3-triazoles are obtained in excellent yields by a convenient one-pot procedure from a variety of readily available aromatic and aliphatic halides without isolation of potentially unstable organic azide intermediates.

A heterocyclic peptide nanotube

An open-ended hollow tubular structure is designed based on hydrogen-bond-directed self-assembly of a chimeric cyclic peptide subunit comprised of alternating alpha- and epsilon-amino acids. The design features a novel 1,4-disubstituted-1,2,3-triazole epsilon-amino acid and its utility as a peptide backbone substitute. The N-Fmoc-protected epsilon-amino acid was synthesized in high yield and optical purity in three steps from readily available starting materials and was employed in solid-phase peptide synthesis to afford the desired cyclic peptide structure. The cyclic peptide self-assembly has been studied in solution by (1)H NMR and mass spectrometry and the resulting tubular ensemble characterized in the solid state by X-ray crystallography.

"Click to chelate": synthesis and installation of metal chelates into biomolecules in a single step

Click chemistry has been employed for the assembly of novel and efficient triazole-based multidentate chelating systems while simultaneously attaching them to molecules of biological interest. The "click-to-chelate" approach offers a powerful new tool for the modification of (bio)molecules with metal chelators for potential diagnostic and therapeutic applications.

1-Acylthiosemicarbazides, 1,2,4-triazole-5(4H)-thiones, 1,3,4-thiadiazoles and hydrazones containing 5-methyl-2-benzoxazolinones: synthesis, analgesic-anti-inflammatory and antimicrobial activities

Acetic acid hydrazide containing 5-methyl-2-benzoxazolinone (4) was synthesized by the condensation of 2-(5-methyl-2-benzoxazolinone-3-yl)acetate with hydrazine hydrate. Thiosemicarbazide derivatives (5a-5d) were afforded by the reaction of corresponding compound 4 with substituted isothiocyanates. The cyclization of compounds 5a-5d in the presence of triethylamine resulted in the formation of compounds 6a-6d containing 1,2,4-triazole ring. On the other hand, the treatment of compounds 5a-5d with orthophosphoric acid caused the conversion of side chain of compounds 5a-5d into 1,3,4-thiadiazole ring: thus, compounds 7a-7c were obtained. The treatment of compound 4 with aromatic aldehydes resulted in the formation of arylidene hydrazides as cis-trans conformers (8a-8e). The structures of the compounds were elucidated by spectral and elemental analysis. While most compounds were exhibiting high activity in the analgesic-anti-inflammatory field, most of them were found to be inactive against bacteria and fungi.

Synthesis, characterization and biological studies of Co(II), Ni(II), Cu(II) and Zn(II) complexes with bidentate Schiff bases derived by heterocyclic ketone

A series of metal complexes of Co(II), Ni(II), Cu(II) and Zn(II) have been synthesized with newly prepared biologically active ligands. These ligands were prepared by the condensation of 4-amino-5-mercapto-3-methyl-s-triazole (AMMT), 4-Amino-3-ethyl-5-mercapto-s-triazole (AEMT) with 2-acetylpyridine. The structure of the complexes have been proposed by elemental analyses, spectroscopic data i.e. IR, 1H NMR, electronic and magnetic measurements. Thermal studies of the complexes are also reported. Antibacterial activities of 10 complexes have been studied in vitro. Heterocyclic bidentate Schiff bases were associated with substantially higher antibacterial activities than some commercial antibiotics.

Synthesis and anticonvulsant activity of new 2-substituted-5- [2-(2-fluorophenoxy)phenyl]-1,3,4-oxadiazoles and 1,2,4-triazoles

A series of new 2-substituted-5-[2-(2-fluorophenoxy)phenyl]-1,3,4-oxadiazoles has been synthesized and screened for their anticonvulsant activities. Compound 3 shows considerable anticonvulsant activity both in PTZ and MES models. It seems that this effect is mediated by benzodiazepine receptors and other unknown mechanism, respectively.

Identification of 4-substituted 1,2,3-triazoles as novel oxazolidinone antibacterial agents with reduced activity against monoamine oxidase A

Oxazolidinones represent a new and promising class of antibacterial agents. Current research in this area is mainly concentrated on improving the safety profile and the antibacterial spectrum. Many oxazolidinones, including linezolid (marketed as Zyvox), are inhibitors of monoamine oxidase A (MAO-A), which presents an undesired side effect. Recently, it was found that the 1,2,3-triazole is a good replacement for the conventional acetamide functionality found in oxazolidinones. We now disclose the finding that 1,2,3-triazoles bearing a substituent like methyl, small substituted methyl, bromo, or a linear (sp-hybridized) group at the 4 position (compounds such as 5, 16, 19, and 21) are good antibacterials with reduced or no activity, within the detection limit of the assay, against MAO-A. The results are especially promising for the development of oxazolidinones with an improved safety profile. The MAO-A SAR can be rationalized on the basis of docking studies to a MAO-A/MAO-B homology model.

1,2,3-Triazoles as peptide bond isosteres: synthesis and biological evaluation of cyclotetrapeptide mimics

Since the discovery of Cu(I)-catalysed click chemistry, the field of peptidomimetics has expanded to include 1,4-connected 1,2,3-triazoles as useful peptide bond isosteres. Here, we report the synthesis of triazole-containing analogues of the naturally occurring tyrosinase inhibitor cyclo-[Pro-Val-Pro-Tyr] and show that the analogues retain enzyme inhibitory activity, demonstrating the effectiveness of a 1,4-connected 1,2,3-triazole as a trans peptide bond isostere.

A platform for the discovery of new macrolide antibiotics

The chemical modification of structurally complex fermentation products, a process known as semisynthesis, has been an important tool in the discovery and manufacture of antibiotics for the treatment of various infectious diseases. However, many of the therapeutics obtained in this way are no longer effective, because bacterial resistance to these compounds has developed. Here we present a practical, fully synthetic route to macrolide antibiotics by the convergent assembly of simple chemical building blocks, enabling the synthesis of diverse structures not accessible by traditional semisynthetic approaches. More than 300 new macrolide antibiotic candidates, as well as the clinical candidate solithromycin, have been synthesized using our convergent approach. Evaluation of these compounds against a panel of pathogenic bacteria revealed that the majority of these structures had antibiotic activity, some efficacious against strains resistant to macrolides in current use. The chemistry we describe here provides a platform for the discovery of new macrolide antibiotics and may also serve as the basis for their manufacture.

An efficient synthesis of achiral and chiral 1,2,4-triazolium salts: bench stable precursors for N-heterocyclic carbenes

[reaction: see text] The promising utility of triazolyl N-heterocyclic carbene catalysts in umpolung aldehyde chemistry requires a straightforward reliable synthesis from readily available materials. Herein, we describe the synthesis of a variety of triazolyl N-heterocyclic carbene precursors. The reactions commence from commercially available amino acids and proceed in 44-68% overall yields. The N-heterocyclic salts are air-stable crystalline solids that can be stored with no special precaution and can generate the active catalyst when treated with an appropriate base.