Compatibility of the S-(3-nitro-2-pyridinesulfenyl) protecting group with DCC/HOBt coupling chemistry.

Two recent reports on the partial lability of the 3-nitro-2-pyridinesulfenyl (Npys) thiol protecting group towards 1-hydroxy-benzotriazole (HOBt) have prompted a rechecking of the chemical behavior of this group. Using both soluble and polymer-bound forms of Cys(Npys) as test materials, the complete stability of this protection against HOBt has now been definitively established, and its compatibility with Boc-benzyl-based solid-phase synthesis strategies has been clearly confirmed by stability assays against a wide range of reagents, as well as by the successful synthesis of several Cys(Npys)-containing peptides.