good luck,
Ron KASHER.
On Wed, 11 Mar 1998 mbgbb@seqnet.dl.ac.uk wrote:
>
> Dear ABRF
> I have a question concerning an unusual peptide product. I
> recently made a peptide amide (Rink amide MBHA resin) - sequence:
> QQYNNWPP which upon cleavage with TFA (+ water, phenol,
> triisopropylsilane scavengers) gave a rather dark colour. After the addition of
> cold ether the peptide product went a marvellous shade of bright purple.
> Following dissolution in water the product changed colour once again (a rose
> red colour). I know that colour changes can occur with certain difficult
> peptide sequences but I wondered whether anyone knows the precise reason
> for this colour change. The trp and pro residues were unprotected, the gln and
> asn residues protected with trt, and the tyr residue protected with tBu. I
> suspect that during the cleavage step one of these sidechain protecting groups
> has bound the trp sidechain but I'd like to know more.
> Best wishes
>
> Frank Ward
> King's college London
> Kensington
> UK
>
>
> Dear Frank
>
> I have seen similar things although not quite as colorful! Could be a few
> things:- Your phenol may have degraded (it would be some sort of pink
> colour, probably pale) 2) Some of the linker may have cleaved but not
> very much 3) Some of the trp may have got modified, again it wouldnot
> need much. You could try using Trp (Boc).
>
> Graham Bloomberg
> Dept Biochemistry
> Medical School
> University of Bristol
> Bristol BS8 1TD
> 01179-293205
> G.B.Bloomberg@bristol.ac.uk
>
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Ron Kasher
Department of Organic Chemistry
The Hebrew University of Jerusalem
Jerusalem, 91904 Israel.
Tel: 972-2-658 6181
Fax: 972-2-658 5345
e-mail: ronk@cc.huji.ac.il