The pink color is most likely due to oxidation of tryptophan. EDT or other
reducing agent should be present in the cocktail during TFA cleavage.
Anita Hong
AnaSpec, Inc.
2149 O'Toole Avenue, Suite F
San Jose, CA 95131
(408)452-5055 (phone)
(408)452-5059 (fax)
e-mail: service@anaspec.com
home-page: www.anaspec.com
-----Original Message-----
From: KNIERMAN MICHAEL D <KNIERMAN_MICHAEL_D@Lilly.Com>
To: Recipients of ABRF List <abrf@aecom.yu.edu>
Date: Thursday, March 12, 1998 8:49 AM
Subject: Re: PEPTIDE SYNTHESIS
>Frank,
>
>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
>
>