There was a question asked a while ago about using Fmoc-Ser(PO.OBzl)-OH.
There was a response, although it was written in German, saying that
it was nonsense to cleave these peptides for extended time.
I would like to add now that when I started using these, I carried out
a lot of test cleavages for different times and found that some
peptides did cleave in the normal 2-3 hours. BUT there were several
examples, particularly with Thr(PO.OBzl), where 8 hours were required
to COMPLETELY remove the benzyl group. In normal cleavage times
up to 30% benzyl can remain.
So with several phosphate units, i would think it is even more
important to extend cleavage times.
Thank you
Dr G. Bloomberg
Dept. Biochemistry
Medical School
University of Bristol
BRISTOL BS8 1TD
UK