Synthesis of disulfide‐bridged fragments of ω‐conotoxins GVIA and MVIIA

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 ω‐conotoxins GVIA and MVIIA.