Non-fluorescent chlorophyll catabolites NCCs

Scheme 1. Overview of chlorophyll breakdown in senescent higher plants (2). The chlorophylls (Chi a, la (R = CH3) or Chi b, lb (R = CH=0) are degraded via pheophorbide a (Pheo a, 5a), red chlorophyll catabolite (RCC, 11), the primary fluorescent chlorophyll catabolites (pFCCs, 10) to non-fluorescent chlorophyll catabolites (NCCs), such as //v-NCC-1 (2, also called RP-14)...

The fluorescent chlorophyll catabolites, such as pFCC (10), were observed not to accumulate during chlorophyll breakdown in senescent leaves (24). The indicated further transformation of the FCC chro-mophore to those of non-fluorescent chlorophyll catabolites (NCCs) was suggested to possibly be the result of a non-enzymic isomerization (56, 62). In analogy to the results of studies on the tautomerization chemistry of a range of hydro-porphinoids (91), the isomerization of the chromo-phore of FCCs into that of NCCs was judged to be rather favorable, thermodynamically. The complete de-conjugation of the four pyrrolic units, characteristic of the tetrapyrrolic NCCs, thus may occur in the course of natural chlorophyll breakdown under rather mild and, possibly, even without catalysis by (an) enzyme(s) (56). 

Scheme 12. Constitution of non-fluorescent chlorophyll catabolites (NCCs) from higher...

FIGURE 4.1.1 Possible chlorophyll degradation pathways in plant tissues or in processed foods. Pheophorbide a monooxygenase is specific for pheophorbide a. RCC = red chlorophyll catabolite. FCC = fluorescent chlorophyll catabolite. NCC = non-fluorescent chlorophyll catabolite. 

Colourless, non-fluorescent Chl-catabolites (NCCs) have meanwhile been observed to accumulate in a variety of senescent vascular plants (1, 2, 3, 4, 5, 36, 48, 49, 50, 51, 52, 53, 54, 55, 56). All of them feature an annealed cyclopentanone unit, substituted by a carboxylate or methoxycarbonyl function (1), a hallmark of the natural chlorophyll derivatives (61). The molecular constitution of the NCCs revealed an intriguing and specific oxygenolytic ring-opening reaction at the a-meso position (rather than at the 8-meso carbon) of the chlorin macrocycle with retention of the a-meso carbon as a formyl group (1). 

---