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Chlormethiazole definitive binding site ?

Limpet_Chicken

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Oct 13, 2005
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This came up after a PM from an individual curious about getting on it, came to me with a few questions, but appeared to think it more or less alpha1 selective, but AFAIK, it isn't. Just did some digging, and found some data specifically stating that the binding site was separate from bicucculline, and akin to that of picrotoxin.

Bicucculline is alpha1-selective, or at least has affinity for a1 type BZD receptors does it not? and in a paper on loreclezole, it stated that it (chlormethiazole) displaced neither GABA, muscimol, nor bicucculline from their respective binding sites in a competitive binding assay. But stated that it was competitive with the alkyl-bicyclophosphorothionate convulsants. I'm not overly familar with these, at least, not to the extent of knowing their molecular mode of action, only that they are potent GABAa antagonists.

One paper, this one
http://sci-hub.tw/10.1016/0014-2999(89)90242-2

Suggests that it might act at a unique binding site, and specifically states that this is different from the barbiturate binding site. I'd always been under the impression that the barbiturate site of GABAaRs was synonymous with the picrotoxin-labeled binding site, and that the two were competitive ligands vs one another.

Yet the paper quoted, it states that chlormethiazole did not affect the binding time of tritiated flunitrazepam enhanced via (3H)pentobarbital. Although it did display some displacement of (3H)flunitrazepam, although this looks odd, given the typical therapeutic dose of chlormethiazole when used as a hypnotic, some
(125-185 uMol), it doesn't ACT like a benzo site ligand, and it's sensitivity to displacement by picrotoxin or dihydropicrotoxinin suggest that it isn't. Subjectively, it doesn't feel a damn bit like a benzo, more like a very, very clean barbiturate (using as subjective comparators, barbital, various benzos, nitrazepam,diazepam, lorazepam, loprazolam and a fair few others.), and besides, a benzo OD is most unlikely to be lethal, chlormethiazole is meant to be pretty good at knocking people off.

The quoted paper shows it's doing some rather weird shit, when it comes to interacting with tert-butylbicyclophosphorothionate (one of the 'cage convulsants', a potent GABAa antagonist)

Whereas pentobarbital inhibited the binding Bmax of TBPS, it did very little to alter the dissociation constant of TBPS, when used alone, compared control, substrate being rat synaptosomes, whereas chlormethiazole, whereas chlormethiazole significantly increased the dissociation constant of TBPS whilst the Bmax was left almost unaltered.

What the devil is going on here? The conclusion was that the barb site, benzo site, orthosteric (muscimol) and neurosteroid binding sites are not the target. And that it alters TBPS binding not by taking up binding sites, but by modulating the Kd of the antagonist ligand. Which suggests an allosteric ligand does it not (in the case of chlormethiazole) but induction of direct uptake of radiolabelled chloride ions suggests something like a channel opener, no?
 
There are a vast number of papers that discuss the cascade effects that are attributed to clomethiazole but if you look at the various ethynylhydroxyl (and carbamate derivatives) and ethynylhalides, you can see that you have a PERFECT training set. Take a look at:

DOI: 10.1097/00008877-199809000-00001
DOI: 10.1016/j.ejphar.2005.02.036
DOI: 10.1111/j.1476-5381.1989.tb16893.x
doi.org/10.1038/sj.bjp.0703398
doi.org/10.1016/S0028-3908(01)00052-1
doi.org/10.1111/bph.12454
DOI: 10.1021/jm300353r
doi.org/10.1016/0165-6147(92)90142

It's hard to find a paper that directly tests clomethiazole (or homologue) so the above are of differential value. Barbs & clomethiazole substitute for benzos but not the reverse. We know the oxazole-ring homologue (US 3401172) is equipotent (by mmol dose) & the imidazole homologue is known. This really is one for CHARMM. I mean, it's free and you can just leave it chugging away in the background. Try overlaying Brallobarbital, Butallylonal and so on (that -Br increases potency a lot so may be like your 'bromethiazole'. Consider that barbs are disubstituted because any monosubstituted compounds are unstable. That lipophilic pocket must be BIG. I seem to recall a barb that has a 5,5-cycloalkyl rather than disubstitution.

Of course, a lot of work has been done in Japan and more recently China... so worth looking. I warn you, they try to make the title obscure as possible.....
 
What do you mean by cascade effects? I have to confess molecular modeling is not a strong point of mine. I can see where things overlay, but otherwise thats my limit.

Currently I can't install the software unfortunately, I'm running on a fucking fucked laptop that has no working screen and a broken HD. Using a linux installation CD to boot, so I can get online, but thats more or less the limit of it's capability, hooked up to an external screen. I haven't the cash for a replacement atm.

I'll read the papers, thanks a ton mate.

What do you think of the way it increases the dissociation constant of TBPS?

And if you are more familiar with cage convulsants than I, what more can you tell me of them.

I'm aware of the activity of the oxazole, didn't know of the imidazole. Thanks for the inspiration there.

Only ones I've tried, are chlormethiazole, the unsubstituted alcohol intermediate, as I'd read it spoken of as possessing activity (its far, far, far less potent) and 'bromethiazole' (I'm not willing to try 'iodomethiazole' due to the excellent leaving group properties, nor of course an azido moiety, given it'd almost certainly be an irreversible ligand, although I'd love to try preparing the aforementioned azide, and see just what ligands it totally prevents, at a saturation-binding concentration in recombinant GABAaRs, from binding, with barbiturates and picrotoxin being first choices)

Cyanomethiazole, after of course careful and long-separated small dose increases, to test for toxicity, given some nitriles are toxic, and the tri- and difluoromethyl homologs are the next obvious candidates for testing, as well as nitromethiazole, and possibly the pentafluorosulfanyl homolog.

After all, any improvement on this drug has to be a good thing. The original is THE best medically-used depressant that I've ever had. Ever.

I'd imagine the barb-chlormethiazole or bromethiazole (best thing I can come up with to call it, since it isn't used medically, but it just seemed obvious to me that when the intermediate alcohol is there, ready to end up as chlormethiazole, why not at least taste the brominated homolog) Just one of those things that happens when you get a drug user, an autistic knowledge-junkie, a chemist with a similar autie-driven taste for the hobby, and the creativity of a spazz, and put them all together in the same individual. Things happen, sometimes obvious, sometimes out there, but always intriguing=D)

That they would substitute incompletely for barbs. Afterall, barbiturates are quite potent AMPA antagonists, with an unusually long washout period in context of electrophysiological studies via E.g patch-clamp or cell clamp assay. IIRC binding within the clamshell of AMPARs, in a manner not dissimilar to glutamate, but they stick there for a fair long time, interfering with glutamate binding)

I know data may be hard to find, given it's such an oooooold drug, it practically has reptillian, feathered relatives. Most of them being doctors who still script it. Although dangerous in OD, and most people preferring to rx benzos, got to admit, it's one of those oldschool wallbanger drugs that deserved very much to survive the general cull of such medicaments.

True, a terminal alkyl halide isn't exactly a choice moiety for a rx drug, but hey, several years and I don't have a third eye, or a double-sized five foot long cock yet=D
No tail or tentacles to speak of... (sadly, I'd love a tail=D, that'd look SO hot on me!)
 
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