Abstract
Oxygenation of tryptophan analogues, 2-(3-indolyl) acetic acid (1), 3-(3-indolyl) propionic acid (2), N-benzoyl-L-tryptophan (3), N-tert-butoxycarbonyl-L-tryptophan (4), and N-benzoyl-L-tryptophan n-butylamide (5), with potassium superoxide (KO2) in dimethyl sulfoxide have been studied. In the case of 1, the major products were 2-formylaminobenzoic acid (25. 3%) and 2'-formylaminoacetophenone (18. 0%), which were produced by the secondary oxidation of 3-(2-formylaminophenyl)-3-oxopropinoic acid. The reaction of 2 with O2 - afforded 4-(2-formylaminophenyl)-4-oxobutanoic acid as the major product (43. 3%), and 2-(3-dioxindolyl) acetic acid (14. 5%) was also obtained. The reaction of 3 and 4 afforded 2-benzoylamino-4-(2-formylaminophenyl)-4-oxobutanoic acid (42. 1%) and 2-tert-butoxycarbonylamino-4-(2-formylaminophenyl)-4-oxobutanoic acid (95. 7%) as the major products, respectively. In the case of 3, 1-benzoyl-2-carboxy-3a-hydroxy-1, 2, 3, 3a, 8, 8a-hexahydropyrrolo[2, 3-b]indole (27. 4%) was also obtained. Unlike 3 and 4, the reaction of 5 mainly afforded N-n-butyl-2-benzoylamino-3-(3-dioxindolyl)propanamide (15) (52. 4%). We found that 1-n-butyl-2-oxo-3-benzoylamino-4a-hydroxy-1, 2, 3, 4, 4a, 9, 9a-heptahydropyrido[2, 3-b]indole is a precursor of 15. A similar difference in the reactivity between 3, 4, and 5 was also observed for two tryptophan-containing dipeptides, N-acetyl-glycyl-L-tryptophan and N-acetyl-L-tryptophyl-glycine.
