High resolution NMR detects diastereomers, but you need an expert to
interprete the spectra. HPLC often works, but not always. Polarimetry
is not the method for peptides, because optical rotation depends on
concentration of peptide in the sample which is subject to another
analysis. Threrefore, the errors from the two analyses would be
multiplied. I have heard about AAA on chiral phases but have never
seen anyone who used it. In my cinical opinion, for most research
there is no difference which substance is used at all, so it's better
to forget about racemization and present HPLC and mass spec. If you
are producing a pharmaceutical compound, it makes a difference but you
would have resources to study the compound and develop analytical
methods.
On 31/07/2000, fperini@unmc.edu wrote:
> I have been spending a good deal of deal trying to get an universal
> procedure,and I
> found out that no matter which method I tried,it does not work all the
> time.
> If the method is relatively small,and I will not be pinned down on size,a
> reverse phase HPLC separation will do the job.If you can get same
> column,conditions,etc.as the initial
> run,it should work when combined with amino acid analysis.Once,I got a
> peptide which gave
> baseline resolution of two peaks of identical size.I found out that the
> researcher
> synthesized the derivatives,using the D,L-amino acid.
> To prove the amount of D-amino acid is not so easy.I have seen
> publications,and I tried
> the procedures.They work for only a few amino acids.Probably,the best
> method is that of
> N.Nimura and T.Kinoshita,J.Chromat.,vol.352,169-177(1986).It relies on the
> reaction of
> primary amino acids with 0-phtaldehyde(OPA),in presence of sulfur compound
> which is usually
> the L-form.A ternary compound is formed,and it is possible to separate a
> complex with
> L-amino acid from D-amino acid,by the fact that there is a L-L and D-L
> form.The authors and
> Ihave been using N-acetyl-L-cysteine,although other sulfur compounds have
> been used.
> It is a precolumn derivatization and detection is fluorometric.I do not
> think that any
> other physico-chemical method will work.
Vladimir Titov
Bokiron Ltd., Moscow, Russia
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