John R. Proudfoot

Application of selenosulfonation to marine sterol synthesis. Preparation of 24,28-dehydroaplysterol, xestosterol and ostreasterol from a common acetylenic intermediate

Abstract The title compounds were synthesized from a readily available steroidal acetylene by a protocol employing selenosulfonation, introduction of the appropriate side chain at C-24 via an alkyl selenocuprate, and reductive desulfonylation.

Minor and trace sterols in marine invertebrates 53: Further novel marine sterols resulting from triple and quadruple biomethylation of the cholesterol side-chain ☆

The isolation and structure elucidation of nine new trace sterols with highly branched side chains from a Pseudaxinyssa species from the Australian Great Barrier Reef are described.

Biosynthetic studies of marine lipids. 6. Evidence for an unprecedented biomethylation pathway in the biosynthesis of the cyclopropyl-containing marine sterol, petrosterol

Abstract Petrosterol, an unusual cyclopropane-containing marine sponge sterol, is shown, unexpectedly, to be derived by SAM biomethylation of 24-methylenecholesterol via a ccunplex rearrangement process.

Minor and trace sterols in marine invertebrates 48. The isolation, structure elucidation and synthesis of 23(R),24(R)-methylenecholesterol.

Abstract The isolation, structure determination and synthesis of 23(R),24(R)-methylene-cholesterol—a possible biosynthetic precursor of brassicasterol—is described.

Minor and trace sterols from marine invertebrates 56. Novel coprostanols from the marine sponge petrosia ficiformis

Twelve stanols possessing the rare 5 beta-dihydro nucleus have been isolated from the marine sponge Petrosia ficiformis. These stanols have not previously been encountered in any samples of P. ficiformis which we have examined and appear to be the result of bacterial metabolism of the endogenous sponge sterols.

Synthesis and stereochemistry of 23,24-dihydrocalysterol: implications for marine sterols of a unified biosynthetic scheme involving protonated cyclopropanes

The partial synthesis of the marine cyclopropyl-sterol dihydrocalysterol (1), which has allowed the confirmation of the originally postulated absolute stereochemistry around the cyclopropane ring, is described. The firm knowledge of this stereochemistry and that of the other marine sterols petrosterol (7), dehydroaplysterol (21), ficisterol (22), nicasterol (8), and hebesterol (23) has allowed us to construct a unified biosynthetic scheme for these sterols of diverse side-chain structure. Our central postulate, that the intermediate in sterol side biomethylation may be described in terms of a protonated cyclopropane species [i.e. protonated dihydrocalysterol (1)], enables us to interrelate the absolute stereochemistries of the above sterols and predict the biosynthetic origin of the side-chain carbon atoms.

Molecular Complexity and Retrosynthesis

An atom-environment complexity measure, CA, to assess local changes in complexity during synthetic transformations is described. The complexity measure is based on applying Shannons equation to the number and diversity of paths up to two bonds in length emanating from an atom node. The method requires no explicit accounting for bond type, stereochemistry, ring membership, symmetry, or molecular size. CA varies with expectation across a number of basic reaction examples and may identify the key disconnections to guide retrosynthesis.

Biosynthesis of three cyclopropene-containing sterols in the sponge Calyx niceaensis

As shown by a series of radiolabelling experiments in the sponge Calyx niceaensis, the cyclopropane sterol dihydrocalysterol (3), itself a metabolic product of 24-methylenecholesterol (1), undergoes formal cis-dehydrogenation to the cyclopropene 24H-isocalysterol (6).