Simmonds RG. Tupper DE. Harris JR.  Synthesis of disulfide-bridged fragments of omega-conotoxins GVIA and MVIIA. Use of Npys as a protecting/activating group for cysteine in Fmoc syntheses.  International Journal of Peptide & Protein Research. 43(4):363-6, 1994.
Summary
The 3-nitro-2-pyridinesulphenyl (Npys) moiety is finding increasing utility as a protecting-activating group for cysteine, particularly in the synthesis of cyclic and unsymmetrical disulfides using the Boc strategy. This chemistry has been extended to peptides assembled by the Fmoc strategy. N-Terminal Cys(Npys) is introduced via Boc-Cys(Npys)-OPfp. Non-N-terminal Cys(Npys) is incorporated by reacting a resin-bound, fully protected Cys(Acm) peptide with NpysCl. This approach has been applied to the synthesis of four disulfide-bridged fragments of omega-conotoxins GVIA and MVIIA.
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