First total synthesis of xestobergsterol A and active structural analogues of the xestobergsterols
作者:Michael E Jung、Ted W Johnson
DOI:10.1016/s0040-4020(00)01086-3
日期:2001.2
The novel pentacyclic polyhydroxylated sterol, xestobergsterol A la, a strong inhibitor of histamine release from rat mast cells induced by anti-IgE, has been synthesized in 24 steps and good overall yield From stigmasterol 7. The Breslow remote functionalization process has been extended to several more highly functionalized steroid derivatives, especially those with oxygen functionality in the B-ring. The key steps of the synthesis of xestobergsterol A la and its analogues, 7-deoxyxestobergsterol A Id and 16,23-seco-23-deoxyxestobergsterol A 73, are the Breslow remote functionalization of oxygenated steroids and for compounds la and Id, a novel base-catalyzed epimerization-aldol condensation of a dione to give the desired CD-cis ring structure of the xestobergsterols. Thus the known alcohol 75, prepared from stigmasterol 7, was taken to the tetraacetate 107 which was then converted via a Breslow remote functionalization into the alkene aldehyde 114 which was transformed in 5 steps to xestobergsterol A la. Testing of the synthetic materials showed that the two analogues, 7-deoxyxestobergsterol A Ib and 16,23-seco-23-deoxyxestobergsterol A 73, are also potent inhibitors of histamine release with ICS, values (IC50 500 nM and 750 nM, respectively) being only 1015 times less than that of xestobergsterol A itself (50 nM). (C) 2001 Elsevier Science Ltd. All rights reserved.
Synthesis of 7-Deoxyxestobergsterol A, a Novel Pentacyclic Steroid of the Xestobergsterol Class<sup>1</sup>
作者:Michael E. Jung、Ted W. Johnson
DOI:10.1021/ja9733189
日期:1997.12.17
pentacyclic steroids with a cis C/Dringjunction which are powerful inhibitors of histamine release. 3 Three years later, another member of this novel class, xestobergsterol C, 1c, was isolated and the original stereochemistry proposed for C23 was corrected. 4 Another inhibitor of histamine release is contignasterol, 2, which has a similar structure but is missing the additional E ring. 5 To date,