Re: PepSyn: cyclization methods

Matteo Villain (villain@uab.edu)
Tue, 01 Jun 1999 18:46:57 -0500

A further possibility, if you can afford the introduction of a D/E at the
C-terminus , is the cyclization on the resin. This is done using this three a.a.
connected to the resin by the side chain and with the COOH protected by the Allyl
group. This can be removed with Pd, and you can do the ciclization with the N
terminal with PyAOP/DIEA. Perseptive sells this resins(Peg-Ps), with a substitution
of ~0.2mmoles/g.
I did it with different 9 mer, with an efficiency of ~95%, but two of them gave me
the head to tail dimer, and there was nothing to do, I guess a very favorable
conformation.
With some 12 mer the fraction of dimer increased, but you could still get ~ 50%.
Longer, a disaster.

Is really a neat approach.
Good luck
Matteo

Steven.Johnson@biomeasure.com wrote:

> 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

--
Matteo Villain                   E-mail : villain@uab.edu
Research Associate               Phone  : 205 934 3032
University of Alabama            Fax    : 205 934 1446
Birmingham
35294, USA