Synthesis of protected norcysteines for SPPS compatible with Fmoc strategy

We report the synthesis of racemic Alloc-Ncy(Tmob)–OH, the resolution of its methyl ester and demonstrate its application to form a norcystine bridge in octreotide-amide using the Fmoc strategy on solid phase. N-Alloc and S-Tmob protections of norcysteine (Ncy) were found to be a preferred choice for Fmoc strategy over three other protected norcysteines synthesized, that is, Fmoc-Ncy(tBu)–OH, Alloc-Ncy(tBu)–OH, and Alloc-Ncy(Trt)–OH.