Abstract
When α-lipoic acid in chloroform was oxidized with 5 molar ratio of t-butyl hydroperoxide for 2 days at 38℃, an unidentified lipoic acid derivative (X) was detected at Rf 0.90 on the paper chromatogram using 2.8% aq. ammonia saturated n-butanol as a developing agent. The zone corresponding to X was extracted with methanol and the extract was purified by paperor thin layer chromatography. X was obtained as a yellow oily substance in about 5% yield. It was positive to KCN・nitroprusside reagent and exerted an inhibitory effect on Streptococcus faecalis 10 C1. Its spectrum indicates that X is t-butyl ester of lipoic acid sulfone. Free acid (Y) was obtained by hydrolysis of X in ca. 4% yield. The infrared spectrum of Y was essentially identical with that of α-lipoic acid except that the peaks assignable to a sulfone group were observed at 1310 cm^<-1> (ν_<as>SO_2) and 1140 cm^<-1> (ν_sSO_2) . Its elementary analysis value corresponded to that of monosulfone. Y showed an inhibitory effect on Stc. faecalis 10 C1 with a 50% inhibition index of about 100.
