Enlicitide decanoate (Merck's MK-0616) is the highest-profile oral cyclic peptide drug program in late-stage development outside the GLP-1 class. The molecule is a macrocyclic peptide designed to inhibit PCSK9, the protease that down-regulates the LDL receptor and which has become a validated target for hyperlipidemia following the success of monoclonal antibody PCSK9 inhibitors (evolocumab, alirocumab). Where the existing approved drugs require injection, enlicitide is dosed orally as a pill, a development that has potential to widen the PCSK9-inhibition addressable market by orders of magnitude.
Merck submitted enlicitide's New Drug Application in 2026 based on the Phase 3 CORALreef program, which read out positive results across CORALreef HeFH, CORALreef AddOn, and CORALreef Lipids. The drug achieved approximately 50-60% LDL reduction depending on dose and patient subgroup. Approval would make enlicitide one of the first oral cyclic peptides to reach market for a major cardiovascular indication and would validate the macrocyclic peptide modality as a competitor to small-molecule and monoclonal-antibody drug classes.
The broader context: the June 2026 C&EN feature drawing on CAS Content Collection data documented the cyclic peptide patenting surge from 2020 through April 2026, with Bicycle Therapeutics and Bristol Myers Squibb among the most active corporate filers. Cyclic and macrocyclic peptides are projected to grow from $1.22B in 2024 to $4.76B by 2030 at 21.44% CAGR, with enlicitide cited as the oral-pill proof point. Stories tagged here track the FDA review timeline, CORALreef program data, and how the molecule's commercial trajectory affects the macrocyclic peptide modality more broadly. See [[merck]], [[cyclic-peptide]], [[macrocyclic-peptide]], and [[pcsk9]] for adjacent threads.
A Chemical & Engineering News feature published in June 2026, drawing on data from the CAS Content Collection, documented the cyclic-peptide patenting surge over 2020 to April 2026. Chinese universities are the top filers globally on cyclic peptides. Outside China, US universities lead. Among corporates, Bicycle Therapeutics and Bristol Myers Squibb were called out for sustained patent activity covering cancer, infectious, inflammatory, and autoimmune disease indications. The article frames cyclic peptides as bridging the small-molecule and biologic divide: enhanced conformational rigidity, elimination of unstable terminal residues, and improved metabolic stability are the structural advantages that allow some cyclic peptides to be dosed orally. Merck's enlicitide decanoate (MK-0616, oral PCSK9 macrocyclic peptide for hyperlipidemia) was cited as the proof point for oral-pill cyclic-peptide drug development; an enlicitide NDA submission was underway as of mid-2026. The broader market backdrop: macrocyclic and stapled peptides are projected to grow from $1.22 billion in 2024 to $4.76 billion by 2030 at a 21.44% CAGR, driven mostly by oncology pipelines and the macrocyclic deal flow that includes the Unnatural Products-Novartis $1.7-1.8B cardiovascular pact (February 2026), Biogen-Dayra $50M+ immunology pact (November 2025), and the Parabilis Helicon platform (Regeneron $2.3B collaboration, June 10 $670M record IPO).
Joelle Pelletier's perspective in Science (volume 392, pages 582-583, published online May 8) accompanies the Merck enlicitide biocatalytic synthesis paper and frames the enzyme-cascade route — engineered enzymes plus chromatography-free crystallization to cut step count by more than half — as a template that goes well beyond enlicitide. The piece argues that the limiting step for oral macrocyclic peptide therapeutics has been the manufacturing cost of multi-step protected-residue chemistry, not pharmacology or pharmacokinetics; biocatalysis collapses the cost curve and unlocks a pipeline of oral peptides at large molecular weights that have been quietly stuck in preclinical or Phase 1 economics. The framing matters as enlicitide (oral PCSK9 inhibitor with 57% LDL-C reduction at 24 weeks) heads toward NDA filing.
Merck scientists published in Science a convergent biocatalytic synthesis of enlicitide decanoate, an investigational oral PCSK9 inhibitor and macrocyclic peptide. A tailored suite of engineered enzymes catalyzes selective peptide fragment formation, coupling, and macrocyclization in a protecting-group-free sequence; combined with chromatography-free crystallizations, the route reduces step count by more than half versus prior state-of-the-art methods. Enlicitide is in Phase 3 (CORALreef, with –55.8% LDL-C reported earlier in 2026) and would be the first oral PCSK9 inhibitor if approved. The paper matters beyond enlicitide: protein-engineering-led cascades shift the cost basis for any large macrocyclic peptide program facing peptide-CDMO bottlenecks.