Side-Chain Oxygenation of Pregnanes

Preparation of 17,20-bis-oxygenated pregnanes by side-chain oxygenation of pregnanes... 

IV. Side-Chain Oxygenation of Pregnanes / 162 17-Mono-oxygenated pregnanes / 162... 

A monograph concerned with the configurations and conformations of corticosteroids provides detailed information particularly on mass spectra and and n.m.r., and discusses side-chain conformations of corticosteroids both with and without C-18 oxygen functions the relationships between biological activity and conformation are discussed. The structural features and conformations compatible with anaesthetic activity in pregnane derivatives have also been reviewed. ... 

The A ° -21-oxygenated pregnanes, on hydride reduction, give the 21-alcohols, which are important intermediates for the construction of the complete cortical side-chain (see below). 

The composition of the C(ao)-alcohol mixture derived from a pregnan 20-one can be explained qualitatively in similar terms. The side-chain conformations available to the adsorbed side chain in the half-reduced state will differ depending upon whether a metal-oxygen or metal-carbon bond is in-... 

It seems necessary to accept an intermediate species with either zwitterionic or closely related character. The most recent proposal [2gg] invokes the known conformational features of the pregnan-20 0ne side-chain (p. 12). The individual steps are considered to be (i) formation of the i7a-bromoenolate anion (21) with the side-chain in its most stable conformation (ii) rotation about the C i7) C(20) bond to minimise dipole interactions between the i7a-Br and 20-oxygen substituents 22 (iii) expulsion of Br , perhaps assisted by the anti-perlplanar -0 entity to give the unsaturated epoxide (23) or its valence tautomer, the zwitterion 24) (iv) cyclopropanone ring closure and (v) base-promoted rupture to give the Favorskii product. 

Adrenal corticosteroids, adrenocorticoids, corticosteroids, corticoids, cortins an important group of steroid hormones, formed in the adrenal cortex in response to adrenocorticotropic hormone [ACTH, Corticotropin (see)]. A.c. are structurally related to pregnane (see Steroids) they contain a carboxyl group with a neighboring a,p-unsaturated bond in ring A, a ketol side chain in position 17, and other oxygen functions, particularly in positions 11,17,21 and 18. 

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