Regioselectivity in the glycosylation of 5-(3-chlorobenzo[b]thien-2-yl)-4H-1,2,4-triazole-3-thiol

Design, selective alkylation and X-ray crystal structure determination of dihydro-indolyl-1,2,4-triazole-3-thione and its 3-benzylsulfanyl analogue as potent anticancer agents

Three sets of substituted indolyl-triazoles were synthesized by the alkylation of 1,2-dihydro-5-(1H-indol-2-yl)-1,2,4-triazole-3-thione with different alkyl halides. The use of pyridine restricted the alkylation to sulfur. Whereas, upon using K₂CO₃, the alkylation exceeded sulfur to one of the remaining triazole nitrogens. The assignment of which nitrogen is alkylated besides sulfur is made for the first time using X-ray analysis of single crystals and 2D NMR which indicated that S-, 2-N-isomers will be preferably formed over the S-, 1-N-isomers. The antiproliferative activity on HEPG-2 and MCF-7 cancer cell lines was tested. The results showed that compound 2a is the most active with an IC50 3.58 μg/mL and 4.53 μg/mL for HEPG-2 and MCF-7 respectively and compound 7 is the least active with an IC₅₀ > 100 μg/mL compared to the standard drug doxorubicin (IC₅₀ 4.0 μg/mL). The interaction of the synthesized compounds with tyrosine kinases, namely, Akt, PI3, and EGFR was also studied using molecular docking simulation to predict their mode of action which will drive future work directions.

Regioselectivity of the alkylation of S-substituted 1,2,4-triazoles with dihaloalkanes

Background

1,2,4-Triazole3-thiones are good scaffolds for preparation of new lead compounds. Their derivatives attracted the attention of chemists due to their wide spectrum of biological activities. Alkylsulfanyl-1,2,4-triazoles have three nucleophilic sites (nitrogens) ready for reaction with electrophiles. Herein, new regioselective isomers were synthesized by the reaction of benzylsulfanyl-1,2,4-triazole with various dihaloalkanes. Regioselectivity was determined by X-ray crystallography and NMR.

Results

Coupling of 3-benzylsufanyl-5-(1H-indolyl)-1,2,4-triazole with dibromomethane, 1,2-dichloroethane, 1,3-dibromopropane and di(bromomethyl)quinoxaline was investigated in the presence of potassium carbonate in acetone. In the case of dibromomethane three different bis(triazolyl)methane isomers (–N¹–CH₂–N¹-4, –N¹–CH₂–N²-5, –N²–CH₂–N²-6) were formed in which the two bromide atoms were replaced by two triazole moieties. Among these isomers the reaction was regioselective towards the –N¹–CH₂–N²-5 isomer due to the steric effect. In the case of 1,3-dibromopropane two compounds were obtained due to the alkylation at N(2) to give 2-(3-bromopropyl)-triazole 8 and alkylation at N(1) was followed by cyclization at the indole nitrogen to form a condensed indolo-triazolo-diazepine 10. Upon alkylation of 3-benzylsufanyl-5-(1H-indolyl)-1,2,4-triazole with di(bromomethyl)quinoxaline, two bis(triazolyl-methyl)quinoxaline isomers were separated and characterized as (–N¹–CH₂–N¹–) 11 and (–N²–CH₂–N²–) 12. Single-crystal X-ray diffraction assisted the elucidation and confirmation of the structures of the isomers. An AM1 theoretical study explained the regioselectivity of the alkylation.

Conclusions

On reacting S-protected 1,2,4-triazoles with various alkylating agents, only N(1) and N(2) attack the electrophilic carbons. N(2) alkylated isomers are preferentially formed.

Electronic supplementary material

The online version of this article (doi:10.1186/s13065-016-0165-0) contains supplementary material, which is available to authorized users.

Synthesis and Antimicrobial Screening of Novel Thioglycosides and Acyclonucleoside Analogs Carrying 1,2,3-Triazole and 1,3,4-Oxadiazole Moieties

The solvent-free 1,3-dipolar cycloaddition reaction of dimethylacetylene dicarboxylate (1) with 2-chlorophenyl azide (2) afforded 1,2,3-triazole diester 3 that upon hydrazinolysis, furnished the corresponding bis-acid hydrazide 4. The treatment of compound 4 with carbon disulfide in a refluxing potassium hydroxide solution furnished the desired bis-1,3,4-oxadiazole-2-thione 5 tethered to a 1,2,3-triazole moiety. The respective SOx-glycosides 9-11 were obtained by glycosylation of bis-oxadiazole 5 with 2,3,4,6-tetra-O-acetyl-α-d-glucopyranosyl bromide (6), 2,3,4,6-tetra-O-acetyl-α-d-galactopyranosyl bromide (7), and 2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-α-d-glucopyranosyl chloride (8) in dry acetone in the presence of Et3N, which acted as a base. However, alkylation of 5 with halogeno-alkanol 12 or 13, chloroglycerol 14, bromoethers 20 or 21, and epichlohydrin 22 in the presence of K2CO3 in DMF yielded the corresponding acyclonucleoside analogs 16-18 and 23-25. The isopropylidenes 19 and acetyl derivatives 26-28 of the products were also prepared. The newly synthesized compounds were characterized by (1)H NMR, (13)C NMR, 2D NMR, and mass spectra. The compounds were screened for their antibacterial and antifungal activities. A number of the tested compounds exhibited significant antimicrobial activity compared to the reference drugs.

Efficient synthesis and antimicrobial activity of some novel S-β-d-glucosides of 5-aryl-1,2,4-triazole-3-thiones derivatives

A series of 3-S-β-d-glucosides-4-arylideneamino-5-aryl-1,2,4-triazoles were rationally designed and synthesized according to the principle of superposition of bioactive substructures by the combination of 1,2,4-triazole, Schiff base and glucosides. The structures of the target compounds have been characterized by (1)H NMR, (13)C NMR, IR, MS and HRMS. All the newly synthesized compounds have been evaluated for their antimicrobial activities in vitro against Staphylococcus aureus (ATCC 6538), Escherichia coli (ATCC 8099) as well as Monilia albican (ATCC 10231). The bioactive assay showed that most of the tested compounds displayed variable inhibitory effects on the growth of the Gram-positive bacterial strain (Staphylococcus aureus), Gram-negative bacterial strains (Escherichia coli) and fungal strains (Monilia albican). All the target compounds exhibited better antifungal activity than antibacterial activity. Especially, compounds 6b, 6c, 6f, 6j, 6k and 6l showed excellent activity against fungus Monilia albican with MIC values of 16 μg/mL.

Revisit to the reaction of o-phenylene diamine with thiosemicarbazide to give benzimidazole-2-thione rather than benzotriazine-2-thione and its glycosylation

Reaction of o-phenylene diamine with thiosemicarbazide did not give benzotriazine-2-thione 2 as reported, although the product was found to be benzimidazole-2-thione 3. Glycosylation of 3 with acetobromo sugars 4a-4b gave the respective thioglycosides 7a-7d in addition to minor products of the nucleosides 8a and 8b, in the case of the gluco- and galacto-analogs, respectively. The regioselectivity of glycosylation reaction has been investigated.

Convenient Synthesis and Antimicrobial Activity of Some Novel Amino Acid Coupled Triazoles

This study describes a promising one-pot synthesis of [2-(5-benzyl-4-phenyl-4H-[1,2,4]triazol-3-thio)-acetyl]-amino acid methyl esters 6a-h and dipeptides 10a-e, which were successfully synthesized starting from amino acid esters 5a-h, 9a-e and azides 4, 8a,b, respectively. On the other hand, azide 4 underwent Curtius rearrangement to the corresponding isocyanate, which subsequently reacted with selected aliphatic amine and/or aniline derivatives to give the corresponding urea derivatives 11 and 12a,b. Reactions of the isocyanate with secondary amines gave amide derivatives 13a,b. The structural elucidation of products is reported and some of the products were also screened for their antimicrobial activity.