Synthesis of tryptophan-dehydrobutyrine diketopiperazines and analogues

Condensation of N-1-methyl-cyclo-Trp-Gly and aldehydes in basic media was studied to confirm the structure of the natural product TDD (N-methyl-Tryptophan Dehydrobutyrine Diketopiperazine, 1) and to prepare analogues with potential activity as GST (Glutathione-S-Transferase) inhibitors. This strategy was successful for 1,4-diacetyl-cyclo-Trp-Gly but it did not work for N-4-acetyl, N-1-methyl-cyclo-Trp-Gly derivatives. Pyrolytic cyclization of N-Boc-L-Thr-N-methyl-L-Trp methyl ester gave the Z-isomer of N-methyltryptophan dehydrobutyrine diketopiperazine, which was previously supposed to be the natural product. However, by comparison of melting points and pectroscopic data with those of 1, we conclude that the proposed structure for TDD must be corrected. (C) 1999 Elsevier Science Ltd. All rights reserved.