Synthesis, characterization and biological evaluation of 1,2,4-triazole-3-thiones derived from homochiral aminoacids

In our effort to develop new homochiral compounds endowed with an effective and broad spectrum agent that might be used for treatment of viral infection, here we designed the combination of chiral N-sulfonylated α-amino acid moiety with a 1,2,4-triazole-3-thione nucleus in one frame. The compounds having either (R) or (S) configuration at the chiral center in the side chain of 1,2,4-triazole-3-thione were synthesized from D-phenylalanine methyl ester and L-phenylalanine ethyl ester, respectively. Chiral benzenesulfonamides as starting materials (1a-1b) were obtained from D-phenylalanine methyl ester and L-phenylalanine ethyl ester in reaction with benzenesulfonyl chloride. Then the ester moiety of these chiral compounds were converted to the hydrazide derivatives (2a-2b) after treatment with 98% hydrazinemonohydrate in methanol (for 1a) or in ethanol (for 1b). (R)-1-[2-(benzene sulfonamido)-3-phenylpropanoyl]-4-substitutedthiosemicarbazides (3a-15a) and (S)-1-[2-(benzenesulfonamido)-3-phenylpropanoyl]-4-substitutedthiosemicarbazides (3b-15b) were synthesized by condensing the acid hydrazide (2a-2b) with commercially available isothiocyanates in methanol. In the last step, homochiral thiosemicarbazides were cyclized into their corresponding (R)-5-[1-(benzene sulfonamido)-2-phenylethyl]-4-substituted-2,4-dihydro-3H-1,2,4-triazole-3-thiones (16a-28a) and (S)-5-[1-(benzenesulfonamido)-2-phenylethyl]-4-substituted-2,4-dihydro-3H-1,2,4-triazole-3-thiones (16b-28b) in the presence of aqueous 2N sodium hydroxide. A series of new chiral 4,5-substituted-1,2,4-triazole-3-thiones (16a-28a and 16b-28b) in good yields (54-83%) and high enantiopurity after recrystallization from ethanol were obtained. The chemical structures of the all compounds were elucidated by the combination of UV-Vis, IR, 1HNMR, 13C NMR, 2D NMR (HETCOR), MS spectral data, and elemental analysis. All compounds were tested in vitro antiviral activity against a broad variety of DNA and RNA viruses and in vitro cytostatic activity against murine leukemia (L1210), human T-lymphocyte (CEM) and human cervix carcinoma (HeLa) cell lines. Although, enantiopure 1,2,4-triazole-3-thione analogs in (R) configuration emerged as promising anti-influenza A H1N1 subtype in Madin Darby canine kidney cell cultures (MDCK), their enantiomers exhibited no activity. Especially, compounds 18a, 21a, 22a, 23a and 24a (EC50: 6.5, 6.1, 2.4, 1.6, 1.7 µM, respectively) had excellent activity against influenza A H1N1 subtype compared to reference drug ribavirin (EC50: 8.0 µM). Several compounds have been found to inhibit proliferation of L1210, CEM and HeLa cell cultures with IC50 in the 12-53 µM range. Compound 5a and 27a in (R) configuration were the most active compounds (IC50: 12-22 µM for 5a and IC50: 19-23 µM for 27a).