Acid catalyzed intramolecular attack of β‐phenylthioureido group on amide function. Parallel formation of thiodihydrouracil and 4‐iminothiodihydrouracil. Different pathways in the Edman degradation reaction in the formation of six‐ versus five‐membered cyclic intermediates
Abstract:Contrary to the cleavage of a-phenylthioureido peptides 1 proceeding through intermediate 2-anilinothiazolinone 2, the b-analog cis-2-(3-phenylthioureido)cyclopentane-carboxamide 5 forms transiently 4-imino-2-thioxopyrimidine 6. Monitoring amide cyclization and hydrolysis of iminopyrimidine 6 in acid by UV showed that an equilibrium between 5 and 6 was reached followed by slower conversion of both compounds into 2-oxo-4-thioxopyrimidine 7. Both processes were characterized by isosbestic points, the first due t… Show more
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