Re: PepSyn: cyclization methods

Steven.Johnson@biomeasure.com
Tue, 1 Jun 1999 12:04:18 +0100

Kathy,

There are several methods to do head to tail cyclizations. Each of
us has our favorites.

I've done them using PyAOP/DIEA in DMF at about 1mg/mL...then strip off
the DMF (with a couple of solvent chases of hexanes) and precipitate
with ether after the cyclization. And like Igor Rodionov states in his
reply, a higher concentration may lead to end to end coupling of two
fragments or more...which according to Le-Chatlier (probably
mis-spelled) could happen to some small extent anyway.

When you get to the more complex peptides, you will want to
cleave them as protected fragments from chlor-trityl resin using
DCM/Trifluoroethanol/AcOH at 70/20/10 for two hours. Then strip
to an oil/residue, redissolve your fragment in DCM and do an
aqueous extraction with saturated bicarbonate followed by brine
and dry over mag or sodium sulfate to dry. Restrip and
precipitate. This workup is to get rid of residual AcOH which
would react with your activators and end up capping some of your
peptide with an Ac group on the N-terminus.

Then do your cyclization...monitor it by HPLC..your activators
should blow off in the injection peak...your cyclic will have a
different rttn. time from your product.

Next, deprotect the cyclized peptide, with the cocktail of your
choosing depending on your sequence, and precipitate.

A really, REALLY, really good reference is the back of the
NovaBiochem catalog. It'll tell you just about all you need to
know.

Good Luck,
Steven Johnson
Steven.Johnson@Biomeasure.com


______________________________ Reply Separator _________________________________
Subject: PepSyn: cyclization methods
Author: schegg@med.unr.edu at Internet
Date: 5/28/99 12:03 PM


Hi All,

I would love some advice on head-to-tail cyclization methods for small synthetic
peptides.I am in the process of synthesizing my first cyclic peptide. This
particular peptide is very simple, a pentaGly, but I will be soon be
synthesizing more complex cyclic peptides. The peptide is currently on a
chlorotrityl resin. I am planning to cleave the peptide from the resin and then
cyclize, but I suppose I could try on-resin methods of cyclization.

Could you please enlighten me as to the most effective current cyclization
methods. Thank you in advance.

Kathy Schegg
University of Nevada, Reno
schegg@med.unr.edu
(775) 784-4058
(775) 784-1419 Fax