Hydrolysis products of flavins (isoalloxazines)

Hydrolysis of the flavin (5) with Triton B gave the 4a-spirohydantoin (6) as the major product together with, among other products, the imidazo[4,5-b]quinoxaline (7). Formation of such products indicates that nucleophilic attack by hydroxide ion on the flavin ring had occurred preferentially at the 10a-position.