16 ピロール-1,2-ジカルボイミドの合成

抄録

The authors have reported previously that a fluoresoent compound, tentatively named as f_2' was isolated from the urine of patients with rheumatoid arthritis specifically and its structure was elucidated to be pyrrole-1,2-dicarboimide (2) on the basis of its chemical and physical properties. This report deals with the synthesis of (2) from both pyrroles and L-proline. Carbonyl group was easily introduced at ring nitrogen of methyl pyrrole-2-carboxylate (4) by treating with potassium alkoxide and then ethyl chlorocarbonate or a large excess of phosgene in toluene giving diester (5) or di-N-pyrryl ketone (8), respectively, but they faced to several difficulties in the case of pyrrole-2-carbamide (10). While ammonolysis of the diester (5) or of the ketone (8) resulted bond cleavage between ring nitrogen and carbonyl group, however, preliminary experiment with the amide (10) and acetyl chloride revealed that pyridine was the best solvent and catalyst, and pyrolysis of the resultant ester-amide (13a) brought about ring closure to form the target imide (2) being identified with f_2'. Dehydrogenation of L-proline hydantoin (16) with paradium charcol in p-cymene at reflux afforded the pyrrole compound (2) in poor yield, too.