Pfizer’s ritlecitinib, a first-in-class, selective, oral covalent inhibitor of JAK3 and the TEC family of kinases, was FDA-approved in June 2023 for the treatment of severe alopecia areata. Ritlecitinib derives its JAK-family kinase selectivity from the covalent modification of a unique cysteine on JAK3. This annotation reviews the discovery of ritlecitinib, highlighting the interpretation of selectivity assays, the PK optimization, the evolution of the JAK3 therapeutic hypothesis, and how this 2023 Molecule of the Year nominee has become a classic case study for covalent drug discovery.

AZD4747 is a CNS-penetrant, oral KRAS G12C covalent inhibitor for the treatment of CNS-metastatic KRAS-mutant cancers. KRAS inhibitors have tended to be quite large and fall outside the range of physicochemical properties generally required for CNS permeability. (MW < 360 Da, cLogD < 2, TPSA < 90 Å2. AZD4747 is much smaller than marketed KRAS G12C inhibitors but maintains exceptional cellular potency. The team also encountered an unexpected toxicity that scientists working on covalents should pay attention to.

Last year, Biogen announced that it would acquire Texas biotech Reata Pharmaceuticals for $7.3B. Reata’s lead molecule, omaveloxolone (SKYCLARYS®), an oral, reversible covalent inhibitor of the E3 ligase KEAP1, became the first drug approved for Friedrich’s Ataxia. Omaveloxolone was previously highlighted as a Molecule of the Month in July 2023. Now, this 2023 Molecule of the Year nominee reflects a historic milestone for neurological drug discovery. This comprehensive explainer dives into Nrf2 target rationale, how it works, how the drug was discovered, its synthesis, and why it’s a big deal.

CDI (Clostridioides difficile) infection is a leading cause of healthcare-associated diarrhea with significant morbidity and mortality, and with the rise of hypervirulent and resistant strains, novel and selective antibiotics to treat these infections are needed. Cadazolid, a hybrid antibiotic that combines pharmacophores of two classes of antibacterials, demonstrated potent activity in vitro against relevant C. difficile strains, while avoiding native gut flora. Additionally, the compound was designed to be gut-restricted, with minimal systemic circulation following PO dosing.

AM-2-19 (SF001) is an analog of the notoriously toxic IV antifungal drug, amphotericin B (AmB). Compared with AmB, AM-2-19 is significantly less toxic against primary human cells and in mice, while more broadly active against fungal pathogens including antifungal drug-resistant strains. SF001 received Fast-Track Designation from the FDA in 2023 and has progressed to Ph. I clinical development. This article highlights the history of antifungal polyene natural products, a new mechanistic hypothesis for polyene antibiotic activity, and the design of 3rd generation Erg-specific polyenes.