Meso porphyrin side chains

Because of the occurrence of isomers, the synthesis from pyrroles is only useful for porphyrins with eight identical /8-pyrrolic and four identical methine bridge substituents. Famous examples are the syntheses of chloroform-soluble /8-octaethyl-porphyrin and meso-tetraphenylporphyrin which have been used in innumerable studies on porphyrin reactivity (K.M. Smith, 1975). Porphyrins with four long meso-alkyl side-chains can be obtained by use of analogous reactions. These porphyrins have melting points below 100 °C and are readily soluble in petroleum ether. Sulfonation of olefinic double bonds leads to highly charged, water soluble porphyrins (J.-H. Fuhrhop, 197 ). 

Porphyrins are formally derived from the porphin (1) nucleus by substitution of some or all peripheral positions with various side chains. In the classical system of nomenclature T, introduced by H. Fischer,Sc the peripheral /5-pyrrolic positions are numbered front 1 to 8 and the methine positions (also named meso positions) between the pyrrole rings are designated a, //, y, and 5. The rings are lettered clockwise A, B, C, and D. The classical nomenclature was in the past more and more displaced by a nomenclature which numbers all the carbon... 

Several other research groups are actively contributing in this field of CcO model chemistry. Naruta et al. have reported tris(2-pyridylmethyl)amine Cu complex-linked iron meso-tetra-phenylporphyrin derivatives and well-characterized Fe—(O2)—Cu species that are similar to [( L)Fe -(0 )-Cu ]+ (Structure (7)). A CcO model developed by Casella and co-workers is a natural porphyrin derivative, in which a polybenziimidazole residue for the Cu coordination site is attached to the propionic acid side chain of the deuteroporphyrin. A new class of picket porphyrin, bearing covalently linked, axially placed tris(heterocycle) chelates for a copper ion, has been synthesized and characterized by Wilson and co-workers. ... 

Fig. 3.20 Reduction of porphyrins to give chlorins. None of these methods can be applied without protection of reducible side chains (e.g. vinyl). Also, there is no selectivity for which pyrrole ring is reduced unless there are bulky substituents on adjacent meso-carbons.

It should be noted that in some cases cartoon representations of the porphyrins will be used due to the increasing complexity of the systems as we go on in the discussion. These are subsequently introduced in the course of the sections. In many cases the side chains on the j8-pyrrole positions or the substituents on the meso-phenyl groups have been omitted (which may not explicitly be mentioned) as their role is primarily related to solubility control, and the reader is referred to the original literature for full structmal details. 

Protoporphyrin-IX (36). FT C n.m.r. was used to good advantage to investigate the biosynthetic origin of the meso-carbons of protoporphyrin-IX methyl ester (36). Initially, the C chemical shifts of a series of porphyrins at natural abundance were determined. These resonances are tabulated in Table 17. The assignment of the sharp side-chain signals was made by comparison within the spectra of the four model porphyrins (36), (37), (38), and (39)... 

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