Improved Synthesis of a Macrocyclic Peptide-Like C5aR Antagonist for Intravenous Applications

A multigram scale synthetic procedure for the preparation of a complex and polar macrocyclic peptidic C5aR antagonist is described. The route was developed through improvements to an initial small-scale research synthesis and hinged on optimized solid-phase peptide synthesis featuring an early side chain decoration, a highly efficient off-resin macrolactamization, and global deprotection steps. These improvements resulted in a reduction in off-resin peptide manipulations and ultimately to a 6-fold increase in overall yield from 2-chlorotrityl-bound intermediate SP-7c.