Abstract
The reaction of β-lipoic acid with acetic anhydride under mild conditions yielded an unknown product which liberated acetic acid by hydrolysis with NaOH. The product showed almost the same microbiological activity for Streptococcus faecalis 10C1 and Corynebacterium bovis as α-lipoic acid and β-lipoic acid. The results of ultraviolet and infrared spectrophotometry and other tests confirmed the identity of the acetylated product with an acetoxy derivative of α-lipoic acid, the formation mechanism of which is thought to be analogous to that of Pummerer reaction. Deuterium exchange studies revealed the possibility of a proton attracted to the carbon adjacent to the sulfoxide group in β-lipoic acid. A possible steric hindrance caused by the bulky alkyl side chain would support that 8-C-acetoxylipoic acid is derived from β-lipoic acid having 8-sulfoxide structure. Associated with the competitive inhibitory effect of 8-C-methyllipoic acid, the results obtained in this experiment may suggest the possible reactivity at the C-8 position of β-lipoic acid which may play an unknown role in biological systems.
