Chugai Pharmaceutical scientists reported in Organic Process Research and Development ↗ a convergent 24-step liquid-phase synthesis of LUNA18 (development name paluratide) that delivers kilogram-scale GMP material at more than 98.5 percent purity and over 30 percent overall yield. The achievement landed at TIDES USA 2026 in Boston (May 11-14) as the featured chemistry presentation. The relevance runs further than the molecule itself. LUNA18 is the lead oral cyclic-peptide KRAS inhibitor, which is the most-watched intersection of oncology and the peptide therapeutics field, and a 24-step kilogram-scale GMP route is the first proof that this drug class has tractable manufacturing economics rather than aspirational ones.
The molecule. LUNA18 is an N-alkyl-rich cyclic undecapeptide. It binds the inactive state of KRAS, NRAS, and HRAS (all three RAS family GTPases), plus their oncogenic mutant variants, by occupying the protein-protein interaction surface that RAS-GEFs (guanine nucleotide exchange factors) need in order to flip RAS from the GDP-bound inactive state into the GTP-bound active state. Block the flip and the downstream signaling pathway (RAF, MEK, ERK) that drives proliferation in RAS-mutant tumors does not turn on. The pan-RAS coverage is unusual. KRAS inhibitors approved or in late-stage development to date (sotorasib, adagrasib, divarasib, glecirasib, the rest of the G12C and emerging G12D class) target specific oncogenic mutants, leaving the other RAS isoforms untouched. LUNA18's binding mode reaches all three RAS proteins and both wildtype and mutant forms, which would in principle extend the addressable patient population substantially while raising a different selectivity question about wildtype-RAS toxicity in normal tissues.
The chemistry context. Oral cyclic peptides large enough to engage protein-protein interaction surfaces (roughly 1,200 to 2,000 daltons, with non-natural amino acids and N-methylation for membrane permeability) have been a frustrated drug-design frontier for two decades. The molecules exist and bind their targets in preclinical models, but the synthesis required to make them at the scale and cost a Phase 3 program needs has historically run through too many low-yield steps with too much chromatography. The Chugai route is the answer to that bottleneck for LUNA18 specifically. Twenty-four steps with greater than 30 percent overall yield is the kind of process-chemistry number that lets the company plan Phase 3 supply, contract manufacturing, and commercial inventory in concrete terms rather than as a CDMO risk overhang. It joins Merck's biocatalytic enlicitide cascade ↗ covered last week as the second large-pharma macrocyclic peptide chemistry advance to land in two weeks. Different chemistry (Chugai's liquid-phase convergent route, Merck's engineered-enzyme cascade) is converging on the same answer for the same problem.
The drug-class context. LUNA18 sits at the leading edge of what the field calls the oral-cyclic-peptide-against-intracellular-targets thesis. The thesis says that the molecular weight band antibodies cannot reach and small molecules cannot selectively engage (most of the protein-protein interaction surfaces in cell biology) becomes accessible if the chemistry of cyclization, N-methylation, and conformational restriction is engineered well enough to produce oral bioavailability. Bicycle Therapeutics is advancing the bicyclic-peptide architecture, where two short cyclic loops are constrained on a central scaffold. Circle Pharma is advancing macrocyclic peptide derivatives optimized for KRAS and beta-catenin. Unnatural Products is advancing platform-scale generation of non-natural amino acid cyclic peptides. LUNA18 is the most-clinically-advanced expression of the thesis, with Phase 1 monotherapy and combination-with-cetuximab dose escalation underway and 21 to 47 percent oral bioavailability without special formulation tricks.
The KRAS-oral question matters at the patient-population level. Sotorasib (Lumakras) and adagrasib (Krazati) are KRAS G12C inhibitors approved for the small subset of lung and colorectal cancer patients with that specific mutation, roughly 13 percent of non-small-cell lung cancer and 3 to 4 percent of colorectal cancer. The G12D-targeting follow-ons (Revolution Medicines' RMC-9805, BridgeBio's BBO-8520) extend coverage to another large mutation subset but still narrow. Pan-RAS coverage, if LUNA18 achieves the selectivity profile preclinical data suggested, would cover essentially all RAS-driven tumors, which is roughly 30 percent of all human cancers including the most clinically intractable (pancreatic, where KRAS mutations approach 90 percent of cases, and the harder-to-treat colorectal and lung mutation subsets). The wildtype-RAS toxicity question is the gating clinical safety signal that Phase 1 dose-escalation is currently evaluating.
The platform read. The platform's anticancer corpus ↗ already engages the macrocyclic and bicyclic peptide design space that LUNA18 sits in, with bicyclic peptide-drug conjugates and other constrained-cycle architectures making up an expanding share of recent additions. What changes with the LUNA18 chemistry milestone is the gating constraint on the design space. Cheaper kilogram-scale synthesis at GMP grade means that a candidate that emerges from the in silico design and lab validation stages has a clearer path to preclinical scale and Phase 1 supply, which is the bottleneck the platform's oncology design space is most directly trying to compress. Two large-pharma macrocyclic-peptide chemistry advances in two weeks (Merck and Chugai) is enough evidence to say that the synthesis-cost problem has started to give way across multiple chemistry approaches, not just one.
What this is not. A near-term approved oral KRAS pan-inhibitor. Phase 1 monotherapy and combination dose escalation are still the developmental position, and the Chugai program faces the same long road from chemistry milestone to pivotal efficacy data that every preclinical-stage oncology peptide does. What this is is the first concrete process-chemistry evidence that the oral-cyclic-peptide-against-intracellular-targets thesis can produce commercial-scale material, and a leading indicator that the macrocyclic-peptide manufacturing bottleneck is no longer the load-bearing reason most programs in this class are stuck below Phase 3.