Pepsyn
Frank (frank.ward@kcl.ac.uk)
Wed, 11 Mar 1998 16:54:16 -0500 (EST)
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