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Bridging the opioid-agonist/NMDAR-antagonist gap

dexedrone

Greenlighter
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Nov 24, 2019
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I recently read a study suggesting that a great many opioids are, as it turns out, also NMDAR antagonists, but at a level too low to be qualitatively obvious. Further, NMDAR antagonists, nonselective or otherwise, appear to do a decent job of blocking tolerance development in certain classes of opioids. There's also a huge amount of literature on adjunct therapy involving NMDAR antagonists and opioid analgesics. In short, there's probably significant use for a dual-action opioid/NMDAR analgesic.

I'm interested in this from a primarily medicinal standpoint. Frankly "opioids you can take for ages at consistently low-ish doses" sound kinda scary to me. Nonetheless, I thought you all might find the topic of interest.

Notable relevant compounds, from left: 2-OXO-PCE (eticyclidone, anesthetic disso), Bromadol (potent opioid), Tramadol (low-potency opioid).
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It's clear that an aryclyclohexylamine backbone is capable of opioid activity. It's worth noting that alternate 3/meta placement of the bromine (or chlorine) does not negate opioidergic effects of Bromadol analogs. Tacking a methoxyl moiety on R3 of 2-OXO-PCE should produce an active NMDAR compound (MXE). It appears, based on a piddly sample of 2 arycyclohexylamine-ish opioids, that having some steric bulk off the 3/4 positions may be important to opioid activity.

MXE was hypothesized by its designer to hit the MOR (mu opioid receptor). It was later discovered that it does not have any appreciable activity at that site. Looking at the two compounds above, there may be a good reason for this; steric bulk on the ortho position of the cyclohexane ring, or in that general vicinity. The Bromadol has an N,N-Dimethyl group, and the Tramadol has a hydroxyl group, plus an N,N-DImethyl group that would probably spend a bit of time in that general vicinity (but not most of the time).

Perhaps N-methylating MXE would produce the long-sought-after (non-PCP-mania-inducing) MOR/NMDAR activity combo?
 
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wikipedia lists a very low affinity for tramadol and desmethyltramadol as nmda antagonists. at least when orally taken tramadol doesnt reveal its activity as such, whereas its clearly felt with o-dsmt.

mxe is not an opioid, but 3-HO-PCP is one of those mixed nmda antagonists/µ-agonists.

finally, bromadol doesnt seem to have activity as a nmda antagonist.
 
wikipedia lists a very low affinity for tramadol and desmethyltramadol as nmda antagonists. at least when orally taken tramadol doesnt reveal its activity as such, whereas its clearly felt with o-dsmt.

mxe is not an opioid, but 3-HO-PCP is one of those mixed nmda antagonists/µ-agonists.

finally, bromadol doesnt seem to have activity as a nmda antagonist.

Not surprised regarding bromadol; it's got a massive phenethyl substitution, which appears to increase MOR but not NMDAR binding.

Regarding 3-HO-PCP, you're right; we do have a few compounds that do have clinically relevant activity at both NMDAR and MOR, but 3-HO-PCP is...a very stimulating drug, like PCP. I'm more interested in a classically anesthetic opioid, with effects similar to a mixture of morphine and ketamine; the side-effects profile and psychomimetic effects would probably be pretty significantly reduced.
 
Would ciramadol or cebraopadol fit the bill? The former is structurally related to tramadol, Angel Dust, and Effexor . . . Grünenthal came up with a bunch of tramadol/tapentadol-like benzenoid opioids and Upjohn, Wyeth, Allen & Hambury's and American Cyanamid did some as well, and I think this research also dovetailed into the research on benzamide opioids at Upjohn in the 1970s amongst other things.
 
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Cebranopadol is currently in stage 3 medical trials as of 2014 i think. So it will be introduced in a matter of years. It has very high affinity to MOR but abuse is limited by its high affinity to the KOR receptor- making it a hallucinogene(an unpleasant one at that) at higher doses
 
Cebranopadol is currently in stage 3 medical trials as of 2014 i think. So it will be introduced in a matter of years. It has very high affinity to MOR but abuse is limited by its high affinity to the KOR receptor- making it a hallucinogene(an unpleasant one at that) at higher doses
Yuck lol

I think the 4-methyl group on the toluene moiety may be limiting NMDAR activity, as it's not mentioned on the wiki page and there are no such substitutions on the predominating arycyclohexylamine dissos.

The dextroisomer of methadone is both a mu agonist and NMDA blocker at the same dose range. Some believe it can cause cardiac arrhythmias similar to loperamide, unfortunately.

Nice username. Also, I've heard this, regarding NMDAR activity, after I made my original post. Too bad about the arrythmias.
 
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