S-S Cleavage of Stable 1,2-Dithiolanes with Carbon Nucleophiles as Model for Enzyme Reductive Acylation of Lipoic Acid

Abstract

Coenzyme lipoic acid is bound covalently to pyruvate and 2-oxoglutarate dehydrogenase complexes and reductively acylated by the “active aldehydes” bound to thiamine diphosphate in Krebs cycle^[1]. The mechanism for these acylations is controversial; redox and carbanion mechanisms have been proposed^[2]. Owing to the intrinsic ring strain, 1,2-dithiolanes 2 have the polymerizability preventing the studies on their reactivity towards carbon nucleophiles 1. We found substituents on the dithiolane ring reduced the polymerizability; 4,4-diethyl- and 4,4-pentamethylene-1,2-dithiolanes do not polymerize and are suitable to the model study^[3]. The substituent effect was discussed in terms of the ceiling temperature Tc.