Abstract
1. Irradiation of an equimolar mixture of hydroxyethylthiamine (HET) and α-lipoic acid in acidic ethanol with an ultraviolet ray lamp yielded an unidentified condensation product having various properties of both thiamine and lipoic acid.
2. The unidentified compound, tentatively named “Compound X” was obtained as an amorphous white powder (decomposition point 192°). Incorporation of the hydroxyethyl group of HET into “Compound X” was demonstrated by tracer studies using HET-hydroxyethyl-C14. Determination of free SH-group with 5, 5′-dithio-bis-(2-nitrobenzoate) reagent revealed the presence of one mole of SH per mole of “Compound X”. The result of elementary analysis of its HCl salt was consistent with a formula, C22H35O4N4S3-HCl. The compound is expected to correspond with the postulated intermediate in the acetyl transfer reaction from “active acetaldehyde” to lipoic acid proposed by Ingraham et al.
3. “Compound X” served as an acetyl donor in pyruvate dehydrogenation complex systems of E. coli as well as of pig heart muscle.
