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Jennifer,
I would tend to agree with Gottfried but, I have not
had very good luck with the Ekathiox resin. I found
it to be very sequence dependent as far as time to
cyclize (a few hours to a few days...) and very
expensive.
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, 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). When done,
you can purify and desalt your peptide by HPLC. You
may want to purify it first...depends on how clean it
is at the outset.
This has worked quite well for me.
Yes, you can do your biotinylation first on the resin
then cleave. If you want to do a head to tail type
cyclization, maybe try a Lys(Dde) at the N terminus,
biotinylate the terminal amine, then deprotect the
episilon amine so's it'll be free to cyclize after
cleavage. The back of the Novabiochem catalog is a
VERY useful tool for synthetic strategies for
peptides.
Good Luck.
Regards,
Steven Johnson
Research Associate, B.S. Chem.
Process Development
Biomeasure, Inc.
--- Jennifer Woodman
<Jennifer_Woodman@dfci.harvard.edu> wrote:
> Hello,
> I was wondering if anyone out there could offer some
> advice on cyclic peptides. We are currently working
> on a project that involves making a cyclic peptide
> in which either the C or N terminus would be
> biotinylated. My concerns are:
>
> I believe I will need the free amine group to
> cyclize the peptide and therefore will not have a
> free amine group to biotinlate.
>
> In addition, both the C and N terminus have a
> Cysteine. We were thinking that we might be able to
> cyclize the peptide by forming a disulfide bond
> between the two ends. That way, we might be able to
> use the free amine to biotinylate. If this is a
> possibility, how do we selectively have the single
> peptide form a disulfide bond between its two ends
> rather than having a chain formation.
>
> I thank you for any advice,
>
> Jen
>
>
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