Porphyrin, steroid-linked

Figure 8 Structure of a lipid bilayer vesicle including a steroid-linked picket-fence porphyrin [202], Reproduced from J. Org. Chem., 53, 3891 (1988) by permission of the American Chemical Society...

Computational studies followed by molecular modeling were performed on a variety of fullerene-porphyrin dyads that contained either flexible polyether or rigid steroid linkers as well as on doubly linked cyclophane-like C60-porphyrin [212]. Not surprisingly those studies confirmed that the attractive van der Waals interactions between porphyrin and C60 units cause these dyads to adopt unusual conformations in order to get together in close proximity. 

Pantothenic acid has a central role in energy-yielding metabolism as the functional moiety of coenzyme A (CoA), in the biosynthesis of fatty acids as the prosthetic group of acyl carrier protein, and through its role in CoA in the mitochondrial elongation of fatty acids the biosynthesis of steroids, porphyrins, and acetylcholine and other acyl transfer reactions, including postsynthetic acylation of proteins. Perhaps 4% of all known enzymes utilize CoA derivatives. CoA is also bound by disulfide links to protein cysteine residues in sporulating bacteria, where it may be involved with heat resistance of the spores, and in mitochondrial proteins, where it seems to be involved in the assembly of active cytochrome c oxidase and ATP synthetase complexes. 

Work from a different laboratory focuses on the synthesis and photophysical properties of Ceo-based porphyrin dyads with a variety of linkers [367-371], These include new types of flexible polyether linkers (30) [367, 368], rigid steroid linkers [370] as well as novel doubly linked porphyrins [369, 371], which provide the means for a parachute-shaped dyad (e.g., ZnP-Ceo (29) and H2P-C60 (28)). In both para-... 

The term half-space concisely represents the region in space, either above or below a flat molecular moiety. Stereotopic or paired half-spaces are separated by a surface that may or may not be planar. The alternative term molecular face is more descriptive of a given molecular structure. Two stereotopic molecular faces are separated by a surface that is assumed to coincide with the plane of a finite, flat molecular framework. We use molecular face, in preference to half-space, as it is intimately linked to the term facioselectivity. Ring systems in carbohydrates, heterocyclic bases, steroids, porphyrins (see refs. 129(a), 129(b) above) are also said to have molecular faces, albeit in a generalized sense. 

We produced metalloporphyrins 30 carrying iron or manganese atoms and with four cyclodextrins linked to the porphyrins, and saw that they could catalyticaUy direct oxidation of hydrophobicaUy doubly boimd substrates. Then we showed that the system would hydroxylate a bound steroid 31 with complete selectivity for the C-6 equatorial hydrogen, producing the 6-q -hydroxy steroid 32 (Fig. 1.18). ° By adding some fluorine atoms to this system in catalyst 33 to stabilize the catalyst against self-oxidation, we greatly improved the catalytic turnovers. 

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