Dear Krystyna,
I have had best luck using PyBroP
(bromo-tris-pyrrolidino-phosphonium hexafluorophosphate) (available
from Novabiochem or Advanced ChemTech) for coupling N-methyl amino
acids. HATU (so far available only from PE Biosystems) also works
well in some instances. You may also want to use double couplings
and extended coupling times for the difficult couplings between
N-methyl amino acids. The worst coupling with which I have had
experience was N-methyl valine to N-methyl valine. In this case,
even using PyBroP did not give complete coupling. I use a Milligen
Biosearch 9050 synthesizer for my work, so I can not give any advice
on the best conditions for the 433A.
Best wishes,
Dan Brune
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