Yes, HOBt is effective in preventing the condition
that you are experiencing. It operates under a
similar mechanism as the prevention of racimization in
that it acts like an acid to the organic base(I'm
assuming you're using DIEA or NMM) preventing the
abstraction of the alpha proton that leads to
racimization.
In your case, HOBt will act as an acid to prevent the
elimination of water from the sidechain of the amino
acid which forms a nitrile functionality (in the case
of Asn) which in turn is open to attack by the
piperidine forming your aspartimide/piperidide
impurity.
But, one has to ask the question...why are you doing
FMOC chemistry using Asn without sidechain protection
(as amides are not reactive to coupling as the
terminal amines, makes sense, but leaves you open to
other problems like you're experiencing) when the
simplest solution is to buy your Asn as
FMOC-Asn(Trt)-OH and avoid the problem all together?
That too, works well.
Regards,
Steven Johnson, B.S. Chem.
Research Associate
Biomeasure, Inc.
--- Ben_Van_Der_Perre@innogenetics.com wrote:
> I wanted to know if anybody has some experience in
> using
> Hobt for suppressing aspartimide/piperidide
> formation in
> combination with 2%piperidine/2%DBU in DMF?
> I know of the Hmb AA's but I am looking for a
> cheaper
> alternative.
>
> Thanks
>
>
> Ben Van der Perre
> benvdp@innogenetics.be
>
>
>
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