Inhibitory Activities of Blasticidin S Derivatives on Aflatoxin Production by Aspergillus Flavus

Blasticidin S (BcS) is a protein synthesis inhibitor which shows strong growth inhibitory activity against a number of microorganisms. However, BcS inhibited aflatoxin production by Aspergillus flavus without affecting its growth. In order to obtain information about the structure–activity relationship of BcS as an aflatoxin production inhibitor, BcS derivatives were prepared and their aflatoxin production inhibitory activities were evaluated. Among five derivatives, blasticidin S carboxymethyl ester, deaminohydroxyblasticidin S, and pyrimidinoblasticidin S showed inhibitory activity, while the others did not. The IC(50) value for aflatoxin production of the carboxymethyl ester derivative was one-fifth of that of BcS although their antimicrobial activities were almost the same. These results indicate that the inhibitory activity of BcS against aflatoxin production was enhanced by esterification of its carboxyl group and that the carboxymethyl ester derivative might be more suitable for practical use than BcS because of the specificity of the carboxymethyl ester derivative, which inhibited aflatoxin production more than BcS.