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Subject: RE: Re[2]: Peptides
Date: Thu, 24 Feb 2000 10:22:54 -0500
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Vladimir: You indicate big improvement on the quenching technique; I agree.
Quench your I2/HOAc/Cys(Acm) cyclizations by adding Dowex 1-X8 (Biorad).
Swell the resin in H2O before using. You can add as much as you like and
simply decant/wash or filter to work up the reaction. The reaction goes
colorless immediately and negative to starch indicating the oxidation
potential is now zero. This is scaleable and has worked on as large as 20mg
and as little as 10ug of peptide.
Thiosulfate, bisulfite and dithionite reactions can get tricky in the quench
and destroy all that you've worked to create.
David H. Singleton
Scientist
Pfizer Central Research
PO Box 8118-101
Eastern Point Road
Groton, CT 06340
-----Original Message-----
From: Steven Johnson [mailto:labswine@yahoo.com]
Sent: Thursday, February 24, 2000 7:54 AM
To: Recipients of ABRF List
Subject: Re: Re[2]: Peptides
Good points Vladimir...
My apologies...I forgot to add that at the end of the
cyclization, (HPLC confirming no more linear left) to
quench the unreacted I2 with a 2% aqueous
sodiumthiosulfate solution to a zero response by
starch paper.
Mea culpa...
Regards,
Steven Johnson
Research Associate, B.S.Chem
Process Development
Biomeasure, Inc.
--- Vladimir Titov <vmtitov@aha.ru> wrote:
> A few comments:
>
> On 23/02/2000, Steven Johnson wrote:
>
> > You can quite easily do a solution cyclization.
> Start
> > by using Acm protected Cystine. Then, after
> cleavage
> > and isolation, make a 2mg/mL solution in 4%AcOH.
> Warm
> > to about 45C
>
> Heating is not necessary; it is better to run the
> reaction some longer
>
> > , and hit it (dropwise until the yellow
> > colour persists) with a 20mg/mL I2 in methanol
> > solution calculated to your quantity of peptide at
> a
> > 1.5 molar ratio. You can follow the cyclization
> by
> > HPLC (disappearance of starting material).
>
> We recently observed a strange effect on an HPLC
> column (elution of
> large peaks with r.t. close to the product analyze
> but the area and
> width about three times higher than normal) after an
> analysis of
> iodine containing mixture. I am not sure it was
> because of iodine,
> but... The column was Luna C18(2) from Phenomenex.
>
> > When done,
> > you can purify and desalt your peptide by HPLC.
>
> It is better to remove excess iodine before work-up.
> Recently we found
> it is well absorbed by stirol-DVB resins (we use
> Dowex).
>
>
>
>
>
> Vladimir Titov
>
> Bokiron Ltd., Moscow, Russia
>
> vmtitov@aha.ru
>
>
>
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