Abstract
Unidentified six biologically active lipoic acid-like substances showing varing Rf values on paper chromatogram with a solvent of n-butanol saturated with 0.5N ammonium hydroxide beside α- and β-lipoic acids were detected in human urine. Main activities on the bioautogram were observed on the spots corresponded to Rf 0.02 and 0.12 which responded to Corynebacterium bovis, but not Streptococcus faecalis and were tentatively named as S_1-and S_2-compounds, respectively. These substances were partly soluble in organic solvents such as ethylacetate and butanol, but hardly soluble in chloroform and benzene at acidic pH. They were easily convertable to α-lipoic acid responsible for Streptococcus faecalis by acid hydrolysis. The uriary excretion of ^<35>S-metabolic compounds by rats was investigated following intraperitoneal injection of 20 mg/kg of DL-lipoic acid-^<35>S. About 80% of radioactivity was recovered in 24hr urine. The radioactivities on radioautogram were observed on the spots corresponding to the microbiological growth, but the amounts of radioactivity appearing on radioautogram were considerably larger than those of the microbiologically active substances on bioautogram. This suggested that ^<35>S-metabolic compounds excreted in rat urine contained the biologically inactive metabolite of lipoic acid-^<35>S.
