Why drug development is hard #34 — designer hallucinogens

NBOMe (2-(4-Bromo-2,5-dimethoxyphenyl)-N-[(2-methoxyphenyl) methyl]ethanamine to you) is a potent hallucinogen, a member of the phenylethylamine series of hallucinogens.  Well that’s the same as saying the current Intel chips are a member of the Intel class of starting with the 8080. https://psychonautwiki.org/wiki/25B-NBOMe has the structure, but I count 2 methoxy groups and a bromine on the phenyl group and a methoxy benzyl group making the amine group a secondary amine.

How anyone came up with the structure will remain unknown to me as it was part of a PhD thesis written in 2003 — unfortunately in German —Ralf Heim (February 28, 2010). “Synthese und Pharmakologie potenter 5-HT2A-Rezeptoragonisten mit N-2-Methoxybenzyl-Partialstruktur. Entwicklung eines neuen Struktur-Wirkungskonzepts.” (in German). diss.fu-berlin.de. Retrieved 2013-05-10.

Like other hallucinogens (LSD, mescaline, psilocin) NBOMe binds to the 2A variety of serotonin receptor (aka 5HT2A — at least 16 serotonin receptors are known) and acts like LSD as an agonist.

Which brings me to Cell vol. 182 pp. 1574 – 1588 ’20 — https://www.cell.com/cell/fulltext/S0092-8674(20)31066-7, probably behind a paywall.  Which has beautiful cryoEM structures of 5HT2A bound to LSD, NBOMe and methiothepin, an inverse agonist.  To get pictures they had to stabilize the structure with a single chain variable fragment of an antibody (something that always makes me wonder how physiologic the structure obtained actually is).

Why use NBOMe as an example of how hard drug discovery is?  Well the binding site of LSD to 5HT2A is well known, and the paper has some beautiful pictures of LSD snuggled between the 7 transmembrane segments of 5HT2A.  What is remarkable about NBOMe is that it lies in the binding site in a completely different orientation.  Moreover NBOMe fits in a previously undescribed pocket between transmembrane segments #3 and #6 (TM3, TM6).  Actually I think NBOMe actually produces the pocket.

So even if you know the target of your drug (5HT2A) and how another drug hits the target you’re aiming for, this doesn’t help you in designing a newer and more potent drug.