On-Resin Acetamidomethyl (Acm) Removal and Disulfide Formation in Cysteinyl Peptides Using N-Chlorosuccinimide (NCS) in the Presence of Other Cys-Protecting Groups

Acetamidomethyl (Acm)-protected cysteine derivatives are essential components of multi-disulfide synthesis, particularly due to the availability of multimodal removal conditions for Acm protection. Most of these removal conditions are harsh and are commonly used to remove Acm protection at the last step of regioselective synthesis of a multi-disulfide, implying that the removal of Acm is performed in the absence of other Cys thiol protections. In this context, <i>N</i>-chlorosuccinimide (NCS)-mediated removal of Acm and concomitant disulfide bridge formation provides a fast and reliable way to synthesize multi-disulfides. In the present study, we demonstrate that NCS-mediated Acm removal and disulfide bond formation can be performed in the presence of other commonly used Cys thiol protections. Interestingly, Acm can be removed with NCS without affecting the Trt group, which is also removed with I₂. Later, we successfully employ the NCS-based Acm removal method in the synthesis of multi-disulfide peptides like α-conotoxin SI.