carrying out Fmoc-SPPS and incorporation of your single cysteine as
Cys(Npys) seems to be a good solution to your problem. Then, you may treat
final peptide-resin with an excess of Boc-Cys(H)-OH prior to final
cleavage:
-----Cys(Npys)------resin + Boc-Cys(H)-OH ---->
----Cys(Boc-Cys-OH)----resin + Npys-H
You may also use the alternative approach:
-----Cys(SBu-t)------resin + Bu3P ---->
----Cys(H)----resin + Boc-Cys(Npys)-OH---->
----Cys(Boc-Cys-OH)----resin + Npys-H
Both of this routes imply that your sequence will survive during cleavage
in absence of thiol scavengers.
Some ideas and details on the related procedures you may find in:
Drijfhout, J.W. et al. Int. J. Pept. Prot. Res. 1988, v.32, pp.161-166
Matsueda, R. et al. Chem. Lett. 1982, pp.921-924.
Kindest regards,
Igor
Laboratory of Peptide Chemistry
Branch of Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry
Pushchino, Moscow Region
142292, Russian Federation
E-mail: <rodionov@fibkh.serpukhov.su> or <Igor_Rodionov@iname.com>
Fax: (0967)-79-05-27
Phones: (0967) 73 54 42; private: (0967) 73 58 26