Message-Id: <199701142006.PAA12341@chem.bu.edu>
Date: Tue, 14 Jan 1997 15:23:55 +0000
From: laursen@bu.edu (Richard Laursen)
Subject: Re: pepsyn
To: Recipients of ABRF List <abrf@aecom.yu.edu>
Not very likely. The CBZ group is normally stable to 100% TFA ar r.t.,
though it will cleave it at about 70oC. That is for N-Cbz amino acids. On
the other hand if you have N-Cbz-pyroglu, then the Cbz group is on an amide
and could be a lot more labile. But that would explain maybe one extra
peak, not 6 to 10. Were the masses of these extra peaks greater or lower
than the expected mass? If they are lower, could they be the [M + nH+]
peaks (this seems too obvious) or just garbage peaks that one often sees at
masses <500. I don't have much experience with ESI-MS, but there are
plenty of experts out there that do and may have better ideas.
Richard Laursen
>Dear colleagues:
>
>We are doing small molecule organic synthesis in our cominatorial
>lab. We recently made some compounds which involve amide bond
>formation using N-Z-Pyroglutamate as an acid monomer coupled with
>various amines. Analytical HPLC of these samples exhibit high purity
>(generally >90%). However, after having run these samples on HPLC, I
>did ESI-MS on them the following day and some of them have 6, 8, 10
>major ions that show up. My question is this. Is it possible that
>the low TFA concentration in my HPLC solvents (0.05%) was sufficient
>to chew up the CBZ group as the samples sat overnight at r.t.?
>
>Thanks,
>Pat Wesdock
>wesdocp@war.wyeth.com
Richard A. Laursen
Department of Chemistry
Boston University
590 Commonwealth Ave.
Boston, MA 02215
Tel (617) 353-2491; FAX (617) 353-6466
email: <laursen@bu.edu>