Methyl-4,5-dioxo-4,5-secopheophorbidate

Scheme 7. Partial synthesis of the elusive red chlorophyll catabolite (RCC, 11) from pheophorbide a (5a). Photo-oxygenolysis of Cd-methyl-pheophorbidate a (Cd-13) gave Cd-methyl-4,5-dioxo-4,5-secopheophorbidate a (14) (besides a trace of the isomeric Cd-methyl-19,20-dioxo-19,20-seco-pheophorbidate, Cd-15) reduction of 14 with sodium borohydride and metal extrusion with dilute aqueous acid provided mcthyl-4,5-dioxo-4,5-seco-pheophorbidate 16 in good yield partial hydrolysis of the red diester 16 with pig liver esterase was regio-selective and produced red chlorophyll catabolite 11 (RCC)...

The cadmium 4,5-dioxo-4,5-seco-pheophorbidate 14 was reduced with sodium borohydride and demetallated with dilute aqueous acid to provide methyl-4,5-dioxo-4,5-secopheophorbidate 16 in about 72% yield. The UV/Vis-spectrum of the weakly fluorescing red diester 16 has prominent absorbance maxima near 500 and 316nm (1). The diester 16 was spectroscopically identified (76) with the methylation product (compound 32a, see Scheme 16) of the diacid 9 from the green alga C. protothecoides (78). Regioselective, partial hydrolysis of the diester 16 with pig liver esterase occurred practically exclusively at the propionic acid side chain and produced the red chlorophyll catabolite 11 (RCC,... 

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