I believe DPPA has been recommended because it is the most
racemization-proof. You correctly noticed that a diluted solution is
better for cyclization (simply, the molecule has more chances to meet
itself than another molecule), so the process is slow and racemization
may really compete. If your peptide C-ends with Gly or Pro, it doesn't
matter of course. But you still can expect many surprises...
Vladimir
On 12/08/2000, Richard F. Cook wrote:
> Dear ABRFers,
> I need some advice or references on what you think are the best ways to
> make a head to tail cyclized peptide 5mer and 6 mer?
>>From my own reading, it seems that a good way is to synthesize the peptide
> and cleave it from acid sensitive resin with only the NH2-terminus and the
> COOH-terminus free...then cyclize....then deprotect the side chains and
> purify the correct product. I've read that highly diluted peptide favors
> the cyclized product over polymers.
> However, I'm confused by all the cyclic reagents in the literature. Many
> people seem to use DPPA which seems to take 5 days at -20 C where as other
> labs like to use HBTU, DCC, DIEA or HOBT etc. etc. ....which may take only
> an hour.
> Can I get a reality check on what is currently the most reliable procedure?
> Thanks,
> Dick
Vladimir Titov
Bokiron Ltd., Moscow, Russia
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