Iodoresiniferatoxin
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| Other names
5-Iodoresiniferatoxin
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3D model (Jmol)
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PubChem CID
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| Properties | |
| C37H39IO9 | |
| Molar mass | 754.61 g·mol−1 |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Iodoresiniferatoxin (I-RTX) is a strong competitive antagonist of the Transient Receptor Potential Vanilloid 1 (TRPV1) receptor. I-RTX is derived from resiniferatoxin (RTX).
I-RTX is an iodinated form of resiniferatoxin, which is produced by the Moroccan succulent Euphorbia resinifera. I-RTX is iodinated at the 5-position and is therefore also called 5-iodoresiniferatoxin.
I-RTX can be prepared from RTX by electrophilic aromatic substitution. Iodide substitutes the 5-position.
Iodination of RTX at the 5-position changes the toxin from an TRPV1-receptor agonist into an TRPV1-receptor antagonist, with only a little lower affinity for TRPV1 than RTX.
As RTX, I-RTX belongs to the daphnane family of molecules.
The substance is soluble in DMSO and in ethanol.
Binding of I-RTX is dependent upon temperature and pH value, as has been shown in research with HEK 293 cells expressing TRPV1. The optimal pH value is around 7.8 to 8.0 and binding increases markedly with temperature up to 37 °C and then decreases at higher temperatures.
Initially, iodoresiniferatoxin was thought to be a competitive antagonist of the TRPV1 receptor with high affinity (Kd = 4.3 ± 0.9 nM to HEK 293/VR1 and Kd = 4.2 ± 1.0 nM to rat spinal cord membranes), but recent research indicated also partial transient agonistic characteristics in the thermoregulatory system in mice, especially in higher concentrations ranging from 1 to 30 µM.
The TRPV1 receptor encodes a protein of 838 amino acids forming a calcium-permeable channel that is activated by capsaicin but also by noxious heat and low extracellular pH. TRPV1 receptors are expressed in many systems in the central and peripheral nervous system, and have a particularly important role in signal conduction in afferent pain pathways.
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