Bacteriochlorins, photosynthesis

Chls and all tetrapyrroles are heteroaromatic compounds and the aromatic character of the underlying tetrapyrrole moiety and the reactivity of the functional groups in the side chains govern their chemistry. Three different classes of tetrapyrroles, differentiated by their oxidation level, occur in nature porphyrins (11, e.g. hemes), chlorins (12, e.g. chls) and bacteriochlorins (13, e.g. bchls). As a cyclic tetrapyrrole with a fused five-membered ring, the overall reactivity of chi is that of a standard phytochlorin 7. Such compounds are capable of coordinating almost any known metal with the core nitrogen atoms. Together with the conformational flexibility of the macrocycle and the variability of its side chains, this accounts for their unique role in photosynthesis and applications ... 

The only representative of this class of compounds that is not involved in bacterial photosynthesis is the recently discovered tolyporphin 20. The unusual tolyporphin occurs in the Pacific cyanophyte tolypothrix nodosa. The substitution pattern, especially the tetrahydropyran moieties of the bacteriochlorin, is unique among naturally occurring... 

The only naturally occurring bacteriochlorin that is not involved in photosynthesis is the tolyporphin 131 isolated by Prinsep et from the blue-green alga Tolypothrix nodosa. This compound, which enhances the cytotoxicity of adriamycin or vinblastine in SK-VLB cells at doses as low as 1 pg/ml, is characterized as a multidrug resistance-... 

The bacteriochlorin structural type is formally derived from the porphyrin by saturation of two peripheral double bonds in opposite pyrrole rings. The term bacteriochlorin originates from the bacterio-chlorophylls, which are widespread as pigments in bacterial photosynthesis (i, 13, 27a). 

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