e-52862 e-52862 e-52862, also known as sigma-1 receptor antagonist (s1a, s1ra), as well as mr-309, is a selective sigma-1 receptor antagonist, with a reported binding affinity of ki = 17.0 ± 7.0 nm, selective over the sigma-2 receptor and against a panel of other 170 receptors, enzymes, transporters and ion channels. in preclinical studies, s1ra has demonstrated efficacy in relieving neuropathic pain and pain in other sensitizing conditions, associated with an improvement of the emotional negative state. e-52862clinical dataother namess1a; s1ra; mr-309identifiers iupac name 4-(2-((5-methyl-1-(naphthalen-2-yl)-1h-pyrazol-3-yl)oxy)ethyl)morpholine cas number878141-96-9chemspider28641653uniizw18dsd1h4chemblchembl2170062chemical and physical dataformulac20h23n3o2molar mass337.423 g·mol−13d model (jsmol)interactive image smiles cc1=cc(occn2ccocc2)=nn1c1=cc=c2c=cc=cc2=c1 inchi inchi=1s/c20h23n3o2/c1-16-14-20(25-13-10-22-8-11-24-12-9-22)21-23(16)19-7-6-17-4-2-3-5-18(17)15-19/h2-7,14-15h,8-13h2,1h3key:dgpgxhrhnryvdh-uhfffaoysa-n s1ra is being developed by esteve for the treatment of neuropathic pain and the potentiation of opioid analgesia and has successfully completed phase i clinical trials showing good safety and tolerability, and a pharmacokinetic profile compatible with once a day oral administration. phase ii clinical trials are currently underway, making s1ra the first selective sigma-1 receptor antagonist evaluated in humans for these conditions.