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Author: Subject: Alpha-hydroxy acid from alpha-aminoacid
jarynth
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[*] posted on 8-9-2008 at 12:23
Alpha-hydroxy acid from alpha-aminoacid


As a follow-up to the MSG thread

https://sciencemadness.org/talk/viewthread.php?tid=9105

I was speculating about the hydroxylative deamination of glutamic acid (and other alpha-aminoacids). The interest lies in keeping the carboxylic group in the first position, unlike what happens during oxidation to alpha-ketoglutaric acid (and analogs), to get alpha-hydroxyglutaric acid (etc). Unfortunately I know of no general method of getting alcohols from amines except via diazotization. Is this even feasible alpha to a carboxylic group? Also, what's the influence of the side chain?
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Klute
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[*] posted on 8-9-2008 at 12:48


Yes, i think amino acids diazotize well enough. There was a preparation of 2-bromo/chloro ethyl propanoate by diazotation of the corresponding amino acid ethyl etser IIRC.

You should be able to make the alcohol, but you might get traces of chloride if you use dil. HCl as the acid.




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tapira1
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[*] posted on 8-9-2008 at 13:48
alpha-OHacids from Aminoacids


Yes, you can do that by diazotization. Have seen examples where you loose some optical purity (i.e. you have some epimerization of your chiral center).
Below you will find a reference; think that you do not need an expensive nitrate such as AgNO3.
Additional ref: (10) Urban, F. J.; Moore, B. S. J. Heterocycl. Chem. 1992, 29, 431. (do not have access to the Journal)

[Edited on 8-9-2008 by tapira1]

[Edited on 8-9-2008 by tapira1]

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tapira1
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[*] posted on 8-9-2008 at 14:08
acetoxy acids from aminoacids


Sorry to post twice; attached is a procedure yielding acetoxyacids from aminoacids.

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sonogashira
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[*] posted on 8-9-2008 at 14:12


I'm guessing that H2SO4 and NaNO2 will go the job. HBr and NaNO2 gives the bromide via the cyclic intermediate (OH of CO2H displaces N2+) because Br is nuclephilic but if a non-nucleophilic counterion is used(sulfate/hydrogensulfate) then surely hydrolysis will take place to give the racemized product.
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tapira1
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[*] posted on 8-9-2008 at 14:13
Last one on hydroxyacids


I apologize; wont post anymore in order to avoid being observed by the Mod. Just found this one; the supplementary material is free I suppose and it has two alternatives towards the target. Next time will try to prepara a rar file.

MOD. Forgive me please. I should have hit "post reply" and clicked on "new topic". Please move, if possible, or delete.

[Edited on 8-9-2008 by tapira1]
<sub>Edit by Nicodem: The mess was corrected and the orphan threads merged.</sub>

[Edited on 10/9/2008 by Nicodem]

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tapira1
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[*] posted on 8-9-2008 at 14:18
Keep following the thread....


It is not as simple as Sonogashira points it out. The assistance given by the carboxyl group helps mantaining (at least in part" the stereochemistry in the product; otherwise you would get racemic products always. Please check other references posted on the subject (an compare stereochemistry in the product Vs. stereochem in the starting material).
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sonogashira
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[*] posted on 8-9-2008 at 14:24


Sorry, you're absolutely right. There'll be retention of stereochemistry (2 x Sn2).
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[*] posted on 10-9-2008 at 22:21


An interesting side product of this nifty diazotization/deamination reaction, is the generation of deadly oxides of nitrogen. This is mentioned in passing, in the procedures that are detailed in Organic Synthesis.

They suggest things like gas masks, a good fume hood, and using a water aspirator etc. to entrain the toxic gases.

What precautions have you taken when running this reaction?

Will bubbling these gases through a strong sodium hydroxide solution, effectively neutralize them?
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jarynth
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[*] posted on 11-9-2008 at 06:17


Bah, I never bother to read the notes in OrgSyn. But being concerned about the environment, I connected the vent pipe from the flask directly to my left nostril :P

Seriously though, sodium carbonate generaly suffices for catching the nitrogen oxides. This is a rather benign reaction compared to nitrations, etc. The diazotization itself does not produce nitrogen oxides; these are caused by the excess of nitrous acid the solution.

[Edited on 11-9-2008 by jarynth]

[Edited on 11-9-2008 by jarynth]
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