Formation of Thioxopyrrolidines and Dithiocarbamates from 4-Methylthio-3-butenyl Isothiocyanates, the Pungent Principle of Radish, in Aqueous Media.

Reaction products of 4-methylthio-3-butenyl isothiocyanate (MTBI), the radish pungent principle, in aqueous media were identified and their antimicrobial activities were examined. A rapid degradation of MTBI in aqueous media afforded a mixture of 3-(hydroxy)methylene-2-thioxopyrrolidine (1), (Z)-3-(methylthio)-methylene-2-thioxopyrrolidine (2), its (E)-isomer (3), methyl 4-methylthiobutyldithiocarbamate (4), methyl (Z)-4-methylthio-3-butenyldithiocarbarnaie (5), and its (E)-isomer (6). The products 1, 2, and 3 were detected at all pHs examined, while 4, 5, and 6 were formed at pH over 6.0. The formation of 4 from 6 was accompanied by an oxidation of methanethiol released from MTBI in aqueous media. Antimicrobial activities of 2 and 3 against all microbes examined were much lower than that of 1, which had MICs ranging from 50 to 400 μg/ml. As for 4, 5, and 6, antifungal activities were comparable to that of 1, but little antibacterial activities were observed. The antimicrobial activities of the six products were considered to be far lower than that of MTBI.