Novel isochroman-triazoles and thiadiazole hybrids: Design, synthesis and antimicrobial activity

In this study, new isochroman-triazole (6a-e) and thiadiazole (7a-e) conjugates were obtained by heterocyclization of isochromanyl thiosemicarbazides (5a-e) under basic and acidic catalysis respectively. The latter were obtained by the treatment of corresponding acetohydrazide (4) with suitably substituted phenylisothiocyanates. The acetohydrazide (4) is accessible from methyl 2-(6,7,8-trimethoxy-1-methyl-3,4-dihydro-1H-isochromen-1-yl)acetate (3) obtainable by oxa-Pictet-Spengler reaction of 2-(3,4,5-trimethoxyphenyl)ethanol (2) with methyl acetoacetate in the presence of p-TsOH. The isochromanyl triazoles (6a-e) and isochromanyl thiadiazoles (7a-e) were screened for their in vitro antibacterial activity against four bacterial strains and were found to exhibit moderate to good activity toward the tested microorganisms, compared to ampicillin, the standard drug. In vitro antifungal activity was also determined against four fungal strains using fluconazole as standard and the most active compounds were identified in each case.