A novel and convenient conversion of chlorins to phytoporphyrins during the modification of chlorophyll derivatives

Detection of 132-carboxy-chlorin produced by the in vitro BciC enzymatic hydrolysis of zinc chlorophyllide

Green photosynthetic bacteria with an efficient light-harvesting system contain special chlorophyll molecules, called bacteriochlorophylls c, d, e, in their main antennae. In the biosynthetic pathway, a BciC enzyme is proposed to catalyze the hydrolysis of the C13²-methoxycarbonyl group of chlorophyllide a, but the resulting C13²-carboxy group has not been detected yet because it is spontaneously removed due to the instability of the β-keto-carboxylic acid. In this study, the in vitro BciC enzymatic reactions of zinc methyl (13¹R/S)-hydroxy-mesochlorophyllides a were examined and a carboxylic acid possessing the C13²S-OH was first observed as the hydrolyzed product of the C13²-COOCH₃.

Facile Synthesis of 131-Oxo-porphyrins Possessing Reactive 3-Vinyl or 3-Formyl Group, Protochlorophyll-a/dDerivatives by 17,18-Dehydrogenation of Chlorins

Methyl protopyropheophorbides-a/d were prepared by modification of readily available chlorophyll-a. The key step was oxidation of 131-oxo-chlorin to the corresponding porphyrin, and 2,3-dichloro-5,6-dicyano-p-benzoquinone was effective for 17,18-dehydrogenation. A reduction in oxidation potential of the chlorin was necessary for the oxidation. Facile oxidation was achieved by insertion of zinc as the central metal, reduction of the 13-carbonyl group and/or aggregation by high concentration. The synthetic 131-oxo-porphyrins had vinyl and formyl groups at the 3-position. These groups were very reactive in the molecule and selectively converted to other functional groups.