Oxidation of 3‐hydroxykynurenine. A reexamination

The oxidation mixture of 3‐hydroxykynurenine (1), treated with aqueous acetic anhydride and, subsequently, with acidic methanol, yields the 1‐hydroxy‐3‐carbomethoxy‐5‐methoxy‐11‐(β‐aspartoyl‐N‐acetyl‐methyl ester)pyrido[3,2‐a]phenoxazine (5), the 1‐hydroxy‐11‐(β‐aspartoyl‐N‐acetyl‐methyl ester)‐5.H‐pyrido[3,2‐a]‐phenoxazin‐5‐one (6), the 1‐methoxy‐11‐(β‐aspartoyl‐N‐acetyl‐methyl ester)‐5H‐pyrido[3,2‐a]phenoxazin‐5‐one (6a), the l,5‐dimethoxy‐11‐(β‐aspartoyl‐N‐acetyl‐methyl ester)pyrido[3,2‐a]phenoxazine (7) and the 1‐methyl‐1(1′‐[11‐(β‐aspartoyl‐methyl esterimino)]ethenyl)ketal‐1H,5H‐pyrido[3,2‐a]phenoxazin‐5‐one (8). A probable scheme, for the compound formation, is reported.