Herewith a belated answer to your frustration.
It is known that carbodiimide reacts with hydroxysuccinimide, 3 mols in
fact, to give the succinimidyl ester of
succinimidyloxycarbonyl-beta-alanine. Your activated esters were thus
prepared using carbodiimide, and not properly purified, and this is the
contaminant. In addition, this compound is an acylating agent, that can
react with added amine nucleophiles, thus contaminating your target
molecules with beta-alanyl-substituted side-products. See page 191 of Vol 5
of The Peptides [Gross & Meienhofer, eds. 1983]. There are two references
(1965, 1968) there to the original demonstration of this side reaction.
Complain to your supplier. They must be using too much HONSu in their
preprative reactions
Regards. Leo Benoiton.
At 09:53 PM 98/2/22 +0100, you wrote:
>Hi all knowledgeble people!
>
>I have a problem with amino acid derivatives in the form of succinimide
>esters, as they often contain some beta-alanine, sometimes up to 3 %.
>The method of analysis I use is quite standard post-column
>derivatization on a Biotronik (Eppendorf) instrument.
>
>At first I attributed this effect to the hydrolysis procedure i.e. that
>beta-alanine forms somehow in the analysis, but now I to have confirmed
>that the impurity is present in the samples from the start. That
>indicates that the manufacturing process of the derivative is
>responsible, or maybe a degradation process. What puzzles me is that not
>all samples of Su esters (comparing different batches and manufacturers)
>contain beta-alanine.
>
>Does anyone have any suggestions about what is happening?
>
>Aleksander Swietlow
>Polypeptide Laboratories (Sweden) AB
>email: aleksander.swietlow@ebox.tninet.se
>
>
N. Leo Benoiton
Department of Biochemistry
University of Ottawa
Ottawa, Ontario, Canada K1H 8M5
Tel: 613 562 5800, Ext. 8216
Fax: 613 562 5440
eMail: benoiton@uottawa.ca