DP
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l-alanine to the racemate
I have some l-alanine that I would like to convert to dl-alanine. What's a good method to do so?
[Edited on 2-8-2005 by DP]
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chemoleo
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From peptide synthesis I know that with the Boc coupling methods, the application of TFA (trifluoroacetic acid) to the growing peptide chain causes
racemisation.
So, possibly, incubating your L-alanine for i.e. 24 hours in pure 95% TFA (the conc. usually employed) might do the job. I have no idea about the
mechanism, however. Probably some imine formation (HN=C(CH3)COOH), which subsequently hydrolyses again.
This should be a hint nonetheless, I am sure there's something on google.
Never Stop to Begin, and Never Begin to Stop...
Tolerance is good. But not with the intolerant! (Wilhelm Busch)
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Polverone
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The simplest method I've seen is heating the amino acid in acetic acid with a catalytic amount of aldehyde. The yields are high (85-96%) and no
byproducts could be detected by the authors.
<b><A HREF="http://www.sciencemadness.org/scipics/jo00154a019.pdf">Method for the racemization of optically active amino
acids</A></b>
Shigeki Yamada, Chikara Hongo, Ryuzo Yoshioka, Ichiro Chibata;
<i>J. Org. Chem.</i>; 1983; <i>48</i>(6); 843-846.
[Edited on 8-2-2005 by Polverone]
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Sergei_Eisenstein
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| Quote: | | I have no idea about the mechanism, however. Probably some imine formation (HN=C(CH3)COOH), which subsequently hydrolyses again.
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There are a few variations on the main theme, but they all come down to the same thing: react the amine with something so enolization can occur. Amino
acids usually are not present as their enol, which means they cannot be racemized as such. By reacting the amine with e.g. acetic anhydride, you make
it an amide and the enol form can be formed. Liberation of the amino acid is not hard.
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DP
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Sweet! Nice article.... exactly what I needed. I wish I could get some TFA.
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