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Updated: Jun 18, 2026

Intracerebroventricular Treatment with Resiniferatoxin and Pain Tests in Mice
Published on: September 2, 2020
Structure-activity relationships of the ultrapotent vanilloid resiniferatoxin (RTX): The side chain benzylic
Giovanni Appendino1, Abdellah Ech-Chahad, Alberto Minassi
1Dipartimento di Scienze Chimiche, Alimentari, Farmaceutiche e Farmacologiche, Università del Piemonte Orientale, Via Bovio 6, 28100 Novara, Italy. appendino@pharm.unipmn.it
Abstract:
The side chain benzylic methylene is a critical element for the vanilloid activity of resiniferatoxin (2a, RTX), and introduction of branching, oxygen functions, or isosteric substitution at this center proved detrimental, with a decrease of potency of 2-3 orders of magnitude compared to the natural product. Conversely, only a modest erosion of activity was observed upon alpha-methylation and alpha-methylenation of the side chain. Surprisingly, introduction of an iodine atom in the guaiacyl moiety of the oxygen isoster 2h led to an unexpected and remarkable (>1000-fold) increase of potency, affording 2i, a compound that outperforms RTX in terms of vanilloid agonism and represents the first one-digit picomolar ligand of a TRP channel discovered to date.
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