Sciencemadness Discussion Board

TRPV1 Related Chemicals

PainKilla - 27-1-2007 at 09:34

TRPV1 Related Chemicals

Transient receptor potential vanilloid type 1 channels are very interesting receptors which are legal for us amateur scientists to experiment with. These channels were formerly known as VR1, and are the receptors upon which capsaicin and its analogues exhibit their "sensation of pain" producing properties.

The class of molecules that are agonists and antagonists are all (AFAIK) based on vanillamide skeletons. The more complex molecules (resiniferatoxin and related) are a bit difficult to build, but the simpler ones are relatively easy to construct.

There has been a good amount of research done on these compounds, and a number of agonists (pretty much all based on elongating or substituting the long carbon chain of capsaicin) as well as antagonists (some iodo-vanillamides are potent antagonists see: J Pharmacol Exp Ther (2005) 312: 561-70. ) have been synthesized.

So that being said, these are a nice, potent, and fun-to-play-with class of molecules. It would be interesting to make an inverse agonist... no more pain :) .

Some more info on capsaicin and analogues can be found here:

http://www.homesteadcollective.org/mpg/science/majorcap.shtm...

As a general route to synthesis I propose the following... please give any suggestions/comments…

[Edited on 23-1-2008 by PainKilla]

Levi - 27-1-2007 at 09:55

=/ Your post makes me feel stupid. I have absolutely no idea what you're talking about although the picture seems pretty straight forward. The link you provided talks a lot about chille pepper derivatives which along with your mention of pain receptors I gather that this is probably something like oleoresin/pepper spray. Would you mind posting the names of the reagents in the picture for those of us without a Ph.D. and no previous experience with "vanillamide skeletons?"
I'm also unclear as to whether this is an extraction and isolation or a synthesis from scratch. Sounds fun to mess with--goggles are a must :D

PainKilla - 27-1-2007 at 10:14

The synthesis is from scratch and starts with vanillin which is commonly available OTC (or online anyway). This is reacted with hydroxylamine (NH2OH) to form the aldoxime, which is then reduced with magnesium and ammonium formate (HCOONH4) to vanillamine. This is then coupled with a long chained carboxylic acid (RCOOH) in order to form the vanillamide.

The molecule synthesized would be a very potent pain-producing molecule, like pepper spray, but think about 10 fold stronger (pepper spray is 1-2M scovilles... the pure compound is in the range of 10-20M). Goggles... you better be wearing a full face respirator to the say the least :) . Not all of the TRPV1 agonists are pain-producing from what I understand, though I don't have any experience with them.

I am actually still in high-school. I just took the advice of some of the elder members and spent a long time reading :) . I have to admit though, my organic chemistry knowledge as far as mechanisms and such is still limited, but college is only a few months away...

EDIT: By the way, does anyone know if the proper prefix for vanillin type molecules is vanillyl- or vanill- ? I seem to find both in literature and it's quite confusing...

[Edited on 27-1-2007 by PainKilla]

Ozone - 27-1-2007 at 10:23

This is a great topic.

Step 1: Vanillin (can be had from vanilla flavoring, lignin, etc.), definitely OTC. Is solvated in water using b-cyclodextrin (harder to find, but by no means controlled). To this is added 2 mol/eq of sodium cyanoborohydride (NaBH3 will do also, but the rxn need be retooled for a different, non-nucleophillic organic solvent). Through this is bubbled NH3(g) until the mixture has increased in weight commensurate to a slight molal excess. This should yield 4-(1-aminoethyl)-2-methoxyphenol.

Step 2: Form the amide you desire from the carboxylic acid of your choice, or, from the acyl chloride.

The structure-activity seems effected by changing carbon number and/or hybridization in three primary areas:
a) the hydrocarbon tail on the end
b) the hydrogenation of the double bond and the cis-trans isomerism (cis is not found in the natural product, which is unusual).
c) The length of the carbon tethering the vanillamide to the double bond.

For simple starters we could shorten the tether, try to make a cis version, remove or shorten the tail (or try a polar substituent). What does methylating the 4-hydroxyl do to it (does it work)?

Remember to wash your hands before using the bathroom!

O3

Ozone - 27-1-2007 at 10:31

How do we test it? It seems like these compounds could easily be rendered (unwittingly or not) quite irritating, if not vessicating, or toxic. It seems that a set of testing parameters should be set up beforehand so that products could be, at least empirically, assayed (and more reproducible and scientifically valid). Say, a 1 mm or 1uL spot on fore-arm skin for irritation, before, say, tasting a 1:50,000 (or more) dilution? Side products, say, 2,3-dihydroxy vanillalyl derivatives might be bad (see urushiol in Toxicodendron).

Just a cautious thought,

O3

PainKilla - 27-1-2007 at 11:05

These references (from Mike's Pepper Garden Page) would be of interest... local university does not have access unfortunately.
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Govindarajan, V. S. and M. N. Sathyanarayana. "Capsicum - Production, Technology, Chemistry, and Quality. Part V. Impact on Physiology, Pharmacology, Nutrition, and Metabolism; Structure, Pungency, Pain, and Desensitization Sequences". Food Science and Nutrition. Vol 29, Issue 6. 1991. pp. 435-474.

Krajewska, A. M. and J. J. Powers. "Sensory Properties of Naturally Occurring Capsaicinoids". Journal of Food Science. Vol 53, No 3. 1988. pp. 902-905.
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As far as structure-activity goes, it seems that with the straight chain analogues (octanoic-dodecanoic), the longer the chain, the more potent it is, in SCU. Olvanil (vanillamide of oleac acid) is supposed to be 10x as potent, but not pungent (I am not sure exactly how pungency is defined though). Also interesting, Olvanil interacts with the endocannabinoid system, inhibiting reuptake of anandamide, which I am sure would be interesting to test with other CB1 agonists :) . (FEBS Letters 436 (1998) 449-454)

There is a lot of literature I have to sort through, but I will probably do this as my research topic for AP Bio since we need to choose something soon... anyway, lots of interactions... I am attaching a large overview of capsaicin analogues. I didn't get a chance to read it yet though.

As far as testing goes, I think that what you said would be a good idea, and I'll read through some more journals and see how it is done there. I think that serial dilution to something like 50,000 ought to work great. I don't think that any of the vanillamide based compounds are toxic, at least to the point of tasting diluted solutions. I don't think its physically possible to eat the pure material :) .

EDIT: Ozone, that's a nice route... if only I could obtain hydrides... :*(

[Edited on 27-1-2007 by PainKilla]

Attachment: Vanilloids - Analogs of Capsaicin with Antinociceptive and Antiinflammatory Activity.pdf (1.2MB)
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Nicodem - 27-1-2007 at 11:18

Quote:
Originally posted by PainKilla
The synthesis is from scratch and starts with vanillin which is commonly available OTC (or online anyway). This is reacted with hydroxylamine (NH2OH) to form the aldoxime, which is then reduced with magnesium and ammonium formate (HCOONH4) to vanillamine. This is then coupled with a long chained carboxylic acid (RCOOH) in order to form the vanillamide.

The starting compound in your scheme is not vanillin. You depicted 3-hydroxy-4-methoxybenzaldehyde while vanillin is 4-hydroxy-3-methoxybenzaldehyde.
Besides this, the reference methods are applicable. So would have been several other methods for oxime reduction and amide formation. However, one needs to keep in mind that vanillin and all its phenolic derivatives are weak acids (pKa about 10) and thus all the work-up procedures must be modified properly (no washings with bases stronger than NaHCO3, etc.).

PainKilla - 27-1-2007 at 11:27

Thanks Nicodem... I always mess up some "small" thing :mad:. Changing...

Sergei_Eisenstein - 29-1-2007 at 12:00

You can make vanillylamine from vanillin and formamide in ~50% yield using the Leuckart reaction. Make an amide with pelargonic acid and don't forget to wash your hands before you go to the toilet.

Sauron - 29-1-2007 at 19:04

Some people are extremely allergic to pepper and paprika. One of my friends, a Berkeley physicist, has to carry epinephrin injectors and has to carefully instruct restaurants, airlines, hotels etc that he can't tolerate ANY pepper or paprika in his diet. He still gets caught out occasionally, and has to use the epi. Else he goes into anaphylatic shock.

He would be most interested in any news regarding antagonists I expect.

BTW there's an experimental irritant agent (riot control agent) in the same general cla,, although it is alkyl not aetl.

Pelargonic morpholide. That is, the Pelargonic acid amide with morpholine. This suggests to me that amides of your phenolic carboxylic acids with morpholine might be strongly agonistic.

Ozone - 29-1-2007 at 19:19

@Sauron, I was wondering how long it would take for you to check this one out!

The trouble with capaicinoids is that there are three possible zones for modification (calculate the factorials for that matrix of experiments and it becomes quite ambitious). I would start first with seeing if activity totally tanks if you methylate the 4 hydroxyl. I fit does not...then it is not the main attraction. Following this, a polar group on the end will not seat into the receptor properly, and may, in fact, bind it up (via steric interference when connected to a site adjacent to the pocket.

I would avoid demethylating the 3-methoxyl as I see the potential for, at the minimum, cardiac toxicity or vessication. Once the active end (if it is only the one) is known, we can start playing with substituents and the tether chain length.

Of interest also, might be extending the tether connecting the hydroxyl to the benzene ring.

It's getting late and I'm tired so, anyone know, off-hand, the donor-receptor interaction for capsaicin? How about ferulic acid sec-butyl amide for an antagonist? Morpholine would provide the lone pair we would need for hydrogen bonding...

Brainstorming,

O3

longimanus - 30-1-2007 at 07:21

Quote:
He would be most interested in any news regarding antagonists I expect.
TRPV1 antagonists would not help in that case. The reason for the allergia and the anaphylactic shock (if capsaicin is the actual cause) is that the compound acts as a hapten (incomplete antigen) - binds to some of the normal proteins in the organism thus turnig it into antigen; followed by activation of eosinophyls and release of histamine, serotonin and who knows what else.

About that demethylation thing - the phenolic groups in OLDA (N-oleoyldopamine) are not methylated but it still remains nearly as active as olvanil.