Structural biochemistry. 17. Synthesis of tryptophan dipeptides

Boc-Trp-Leu hydrazide has been found to significantly inhibit growth of the L-1210 and P388 murine lymphocytic leukemias. A series of related tryptophan dipeptides were prepared and found to be devoid of such activity. The tryptophan dipeptides were most conveniently obtained employing the DCCI-NHS peptide bond-forming procedure.

On the interaction between flavin-adenine rings and between flavin-indole rings by X-ray structural studies

Two crystal structures of 7,8-dimethylisoalloxazine-10-acetic acid:adenine-9-ylethylamine(1:1)hepatahydrate and 7,8-dimethylisoalloxazine-10-acetic acid:L-tryptophan methylester(1:1)heptahydrate complexes were determined as models for the flavin-adenine and flavin-indole interactions, respectively. In the former complex, both molecules were connected by Hoogsteen-type hydrogen bonds between the pyrimidinoid portion of flavin and the adenine, in addition to the normal stacking of both aromatic rings. On the other hand, parallel stackings and intermolecular vertical spacings less than the normal van der Waals separation distance were observed between the flavin and indole rings of the latter complex, indicative of the pi D-pi A charge-transfer interaction in their ground states. Comparing with the X-ray findings of related complexes, we discussed the interaction modes between flavin and adenine rings and between flavin and indole rings.