Cyclisations of tryptophans. IV. Cyclisation of Nb-Acyl-L-tryptophanamides
Three derivatives of tryptophanamide, Nb-methoxycarbonyl-L-tryptophanamide (2a), Nb-acetyl-L-tryptohanamide (2b), and Nb-trifluoroacetyl-L-tryptophanamide (2c), have been prepared and their reaction with trifluoroacetic acid investigated. The structure of the diastereomeric pyrroloindoles 6a and 7a formed from 2a on cyclisation was established through crystal structure determination of 7a and NMR experiments. In the case of 2b two diastereomeric dimers 8a and 9b were isolated with smaller amounts of two related lactams 11 and 12. From 2c diastereomeric dimers 8c and 9c were found in addition to a small amount of an aromatic biindole 10c. The change from cyclisation to dimerisation is correlated with the decrease in side chain nucleophilicity from 2a to 2c. The stereochemistry of the products was determined by NOE results in combination with CD spectra and Cotton effects. Acta Chemica.
Holst, Pia Bachmann,Anthoni, Uffe,Christophersen, Carsten,Larsen, Sine,Nielsen, Per Halfdan,Pueschl, Ask
p. 683 - 693
(2007/10/03)
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