CYCLIZATIONS OF TRYPTOPHANS - IV - CYCLIZATION OF N-B-ACYL-L-TRYPTOPHANAMIDES

Three derivatives of tryptophanamide, N-b-methoxycarbonyl-L-tryptophan amide (2a), N-b-acetyl-L-tryptohanamide (2b), and N-b-trifluoroacetyl- L-tryptophanamide (2c), have been prepared and their reaction with tri fluoroacetic acid investigated. The structure of the diastereomeric py rroloindoles 6a and 7a formed from 2a on cyclisation was established t hrough crystal structure determination of 7a and NMR experiments. In t he case of 2b two diastereomeric dimers 8a and 9b were isolated with s maller amounts of two related lactams 11 and 12. From 2c diastereomeri c dimers 8c and 9c were found in addition to a small amount of an arom atic biindole 10c. The change from cyclisation to dimerisation is corr elated with the decrease in side chain nucleophilicity from 2a to 2c. The stereochemistry of the products was determined by NOE results in c ombination with CD spectra and Cotton effects.