The synthesis and biological activity of thiolcarnitine and its thiolesters

Acetyl‐D,L‐thiolcarnitine was synthesized by the acid‐catalyzed addition of thiolacetic acid to 4‐trimethylammonio‐2‐butenoic acid. Acetyl‐D,L‐thiolcarnitine was the precursor of D,L‐thilcarnitine, which was prepared by base hydrolysis. Thiolcarnitine significantly enriched in the L‐isomer was prepared from acetyl‐D,L‐thiolcarnitine using carnitine acetyltransferase as the resolving agent. The C2, C8 and C16 carnitine thiolesters were obtained by acylating thiolcarnitine with the corresponding N‐hydroxysuccinimide esters. As a substrate for carnitine acetyltransferase, acetylthiolcarnitine gave the same kinetic constants as did acetylcarnitine; on the other hand, thiolcarnitine and carnitine gave the same Km but the Vmax with thiolcarnitine was less than 5% of the value obtained with carnitine. With thiolcarnitine and acetylthiolcarnitine as reactants, the measured Keq, at 30 C and pH 7.0, for the reaction catalyzed by carnitine acetyltransferase (see below) was 4.6±.1. acetylthiolcarnitine+CoA—acetyl‐CoA+thiolcarnitine