It has been some years since I have made peptides, but I do remember pink
and red peptide cleavage products. The color would also carry through the
HPLC purification and turn the purified dry product a pink tint (this was
only from the dark red cleavage products). The resin you mentioned, rink
amide, seems to ring a bell that this coloration only occurred when I used
this resin. I believe that this is related to the linker coming off the
resin. If I remember correctly the MALDI analysis of these products was at
correct mass indicating the major product was OK.
Mike Knierman
knierman@lilly.com
>
>Dear Frank,
>It looks like the clour is from impurities, because the peptide should be
>white. I suggest to run the product on HPLC diode array, set your
detector
>wavelength to 215 and 450 nm, and look at the chromatogram you get.
>
>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