Synthesis and Characterization of the R27S Genetic Variant of Insulin-like Peptide 5

We report the synthesis and in vitro bioactivity assessment for an insulin-like peptide 5 (INSL5) analogue that was recently discovered as a genetic mutation in an Amish population. The mutation was associated with improved metabolic status, and receptor-based antagonism was proposed as a potential mechanism for the altered phenotype. We determined the specific peptide analogue to be fully potent and of maximal efficacy at the human relaxin family peptide receptor 4 (RXFP4), suggesting an alternative basis for the observed effect. In preparation of this synthetically challenging hormone, we have introduced several improvements such as implementation of isoacyl chemistry for high-efficiency preparation of INSL5 B-chain and selective intramolecular A6-11 disulfide formation as a first step in sequential disulfide assembly.