Message-Id: <QQbyph26614.199701151323@relay5.UU.NET>
Date: Wed, 15 Jan 97 15:22 +0200
From: "Leah" <uunet!leah@mail.uu.net>
Subject: Re: pepsyn
To: Recipients of ABRF List <abrf@aecom.yu.edu>
Responding to the message of Tue, 14 Jan 1997 12:43:02 -0500
from Leah Efron<vms.huji.ac.il>
>
Dear Pat:
The low TFA concentration in HPLC can't deprotect the CBZ group. If you
sure that you use N-Z-Pyroglutamate, that the problem may be the opening
some of the ring N-Z-Pyroglutamate.I know that, the ring of Pyroglutamic
acide can be opening by ethanolic hidrochloric acide with simultanieously
esterification of the g-carbocsil group.So if this is the problem, Ithink,
may be by changing the HPLC solvent you can solved it.
Leah Efron
vms.huji.ac.il
> 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.?
>