Similarities and differences in the structure−activity relationships of capsaicin and resiniferatoxin analogues

Walpole, Christopher S J, Bevan, Stuart, Bloomfield, Graham, Breckenridge, Robin, James, Iain F, Ritchie, Timothy, Szallasi, Arpad, Winter, Janet and Wrigglesworth, Roger (1996) Similarities and differences in the structure−activity relationships of capsaicin and resiniferatoxin analogues. Journal of Medicinal Chemistry, 39 (15). pp. 2939-2952. ISSN 0022-2623

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Structure−activity relationships in analogues of the irritant natural product capsaicin have previously been rationalized by subdivision of the molecule into three structural regions (A, B, and C). The hypothesis that resiniferatoxin (RTX), which is a high-potency ligand for the same receptor and which has superficial structural similarities with capsaicin, could be analogously subdivided has been investigated. The effects of making parallel changes in the two structural series have been studied in a cellular functional assay which is predictive of analgesic activity. Parallel structural changes in the two series lead to markedly different consequences on biological activity; the 3- and 4-position aryl substituents (corresponding to the capsaicin ‘A-region') which are strictly required for activity in capsaicin analogues are not important in RTX analogues. The homovanillyl C-20 ester group in RTX (corresponding to the capsaicin ‘B-region') is more potent than the corresponding amide, in contrast to the capsaicin analogues. Structural variations to the diterpene moiety suggest that the functionalized 5-membered diterpene ring of RTX is an important structural determinant for high potency. Modeling studies indicate that the 3D position of the α-hydroxy ketone moiety in the 5-membered ring is markedly different in the phorbol (inactive) analogues and RTX (active) series. This difference appears to be due to the influence of the strained ortho ester group in RTX, which acts as a local conformational constraint. The reduced activity of an analogue substituted in this region and the inactivity of a simplified analogue in which this unit is entirely removed support this conclusion.

Item Type: Article
Schools and Departments: School of Life Sciences > Chemistry
Subjects: Q Science > QD Chemistry
Depositing User: Tom Gittoes
Date Deposited: 01 Jun 2015 14:42
Last Modified: 01 Jun 2015 14:42
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