Syntheses of chlorins from unsymmetrically substituted iron porphyrins

Abstract

Mesohemin (1), deuterohemin (2), protohemin (3), 6,7-dipropylmesohemin (22), 1 -(2-carboxyethyl)meso-tetraphenylhemin (30), coprohemin-II (23), 2-acetyldeuterohemin (40), 2,4-diacetyldeuterohemin (41), and phyllohemin (51) were reduced to chlorins using sodium in isopentyl alcohol. Analytical and semi-preparative h.p.l.c. were used for separation, purification, and quantitation of isomers, which were then identified using ¹H n.m.r. and mass spectroscopy. In the case of the mesochlorins (6), (8), (10), and (12), the ring-,D reduced product, (10), was identified by comparison with an authentic sample prepared from rhodochlorin dimethyl ester (14). The results cast doubt on some previous claims that reduction of unsymmetrical hemins gives only one, or at most two chlorin products, but they also elaborate the electronic and steric factors which control selectivity of reduction.