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Of the porphyrinoid structures occurring in nature the most
important and most widespread are the red blood pigment heme (1),
the green pigment of plant photosynthesis chlorophyll a (2), the
bacterial photo- synthetic pigment bacteriochlorophyll a (3), and
the "antipernicious" red pigment vitamin BJ2 (4). The basic
function of these cofactors are determined by the incorporation of
the different metal ions into the macrotetracycles. The different
oxidation levels of the macrocyclic ligand system regulate the fine
tuning of these functions. The final adaptation of the cofactors to
their special molecular environments in the cell compartments is
effected by variation of the substitution patterns of the
chromophores. HCO,C 3 CO,Phytyl 2 Heme Chlorophyll a CONH, CONH, ~
H,NOC 1 , CONH, /I(Y N~ 3 4 Bacteriochlorophyll a Vitamin B" HO
References, pp. 42-51 Naturally Occurring Cyclic Tetrapyrroles 3
Until the mid-1970s the four classic cyclic tetrapyrrolic
structures with their porphyrin, chi orin, bacteriochlorin, and
corrin skeletons were almost the only representatives in the class
of porphyrinoid natural products (1-10). Although other partially
reduced porphyrins were conceivable, none of these partially
saturated porphyrinoid structures had hitherto been found in
nature.
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