抄録
Two diastereomers (6 and 7) of the cyclic tautomer of cyclo-L-propyl-L-tryptophyl (5) have been prepared by dissolving 5 in 85% phosphoric acid or trifluoroacetic acid. The stable isomer (6) was obtained in 89% yield on the acid treatment of 5 at room temperature. Cyclic tautomers (15 and 17) of the related 2, 5-piperazinediones (14 and 16) have also been prepared. Hydroxylation of the N-acetyl cyclic tautomers (8 and 9) with lead tetraacetate in trifluoroacetic acid followed by methylation gave the 8- and 9-methoxy derivatives (18, 19, 21, and 22) in moderate yields. The 9-methoxy derivative (22) was the major product of the oxidation of 9. On the other hand, oxidation of 5 in trifluoroacetic acid with lead tetraacetate followed by reduction with zinc gave the 8-hydroxy derivative (28) selectively in good yield via the cyclic tautomer (26) and the quinoneimine (27).
