Regioselective synthesis of kojic acid esters by Bacillus subtilis protease.

The lipophilicity of kojic acid [5-hydroxy-2-(hydroxymethyl)-4H-pyran-4-one] was improved by esterifying kojic acid with either divinyl adipate, vinyl hexanoate, vinyl octanoate or vinyl decanoate using protease from Bacillus subtilis for 7 d. 1H-NMR and 13C-NMR showed that the primary hydroxyl group at the C-7 position of kojic acid was regioselectively esterified to afford 7-O-vinyl adipoyl kojic acid, 7-O-hexanoyl kojic acid, 7-O-octanoyl kojic acid and 7-O-decanoyl kojic acid (13-27% yield). The kojic acid esters had radical scavenging activities, inhibited tyrosinase activity and was biodegradable.