B. Krautler et al., BREAKDOWN OF CHLOROPHYLL - PARTIAL SYNTHESIS OF A PUTATIVE INTERMEDIARY CATABOLITE - PRELIMINARY COMMUNICATION, Helvetica Chimica Acta, 80(5), 1997, pp. 1355-1362
The partial synthesis of 10,22-dihydro-4,5-dioxo-4,5-secopheophorbide
a (1) from pheophorbide a methyl ester (2) is described. A regioselect
ive, photooxygenolytic reaction of (pheophorbidato a methyl ester)cadm
ium(II) (3) provides the entry to the crucial 4,5-secoporphinoid struc
ture in form of the (10,22-dihydro-4,5-dioxo-4,5-secopheophorbidato a
methyl ester)cadmium(II) (4). The hydride reduction of this 4,5-dioxo-
4,5-secophytoporphyrin ester occurs selectively at the 'eastern' meso-
position to lead (after demetallation) to 10,22-dihydro-4,5-dioxo-4,5-
secopheophorbide a methyl ester (5). This oxobilin-carbaldehyde has th
e structure assigned earlier to an ester of an isolation form of the r
ed pigment(s) from Chlorella protothecoides. Hydrolysis of the propano
ate ester function of 5, selectively catalyzed by pig liver esterase,
then yields the title compound 1. The red tetrapyrrole 1 may represent
an intermediary chlorophyll catabolite in degreening plants.