SYNTHESIS OF THE NEW IMMUNOSTIMULATING AGENT PIDOTIMOD (3-L-PYROGLUTAMYL-L-THIAZOLIDINE-4-CARBOXYLIC ACID) LABELED WITH C-14 ISOTOPE AND S-35 ISOTOPE

3-L-Pyroglutamyl-L-thiazolidine-4-carboxylic acid (Pidotimod), a new immunostimulating agent, has been prepared labelled with C-14 and S-35 isotopes starting from L-[U-C-14]-glutamic acid 5 and L-[S-35]-cysteine hydrochloride 6, respectively. In the first synthesis, L-[U-C-14]-5 is converted into L-[U-C-14]-pyroglutamic acid 2, which was reacted with ethyl L-thiazolidine-4-carboxylate 3 to afford the ester 4, in turn hydrolyzed to [C-14]-Pidotimod 1. In the second synthesis, L-[S-35]-6 reacted with formaldehyde to give L-[S-35]-thiazolidine-4-carboxylic acid 7, which was coupled with the activated ester of pyroglutamic acid, compound 8, to afford [S-35]-Pidotimod 1. The total activity of [C-14]-Pidotimod was 1.2 mCi (specific activity 5.52 mCi/mmol) and that of [S-35]-Pidotimod was 1.0 mCi (specific activity 9.43 mCi/mmol).