Discovery Process of Enlicitide, a Highly Engineered Macrocyclic Peptide Therapeutic, through Issue-Driven Fragment-Based Synthetic Assembly and SAR

Herein, we report the discovery process of enlicitide (MK-0616, compound 18), an orally active macrocyclic peptide therapeutic against PCSK9 for LDL-C reduction. To overcome development bottlenecks in a prior lead (compound 1a) in a timely manner (sulfur oxidation liability, low solubility, azido potential manufacturing hazard, and alkene isomeric complexity), we deployed a novel scalable solution-phase modular fragment assembly (North/East/South/West/tail), which allowed us to accelerate the design-make-test-analyze (DMTA) cycle and preclinical profiling. Design solutions were quickly validated through this approach (a northern lactam staple, an N-benzylamide southern spacer, an RCM-derived cross-link in conjunction with solvent-exposed motifs to modulate solubility) and delivered compounds with low picomolar potency, improved solubility, stability, and PK from which enlicitide (MK-0616, compound 18) was selected for clinical progression. This modular strategy may act as a template to accelerate late-stage issue-driven SAR in highly engineered macrocyclic peptides.