Halides

Halogens are among the most strategically deployed substituents in small-molecule drug discovery, with approximately 25% of FDA-approved small molecules containing at least one halogen atom. Their capacity to modulate lipophilicity, metabolic stability, membrane permeability, and target binding affinity makes them indispensable to the medicinal chemist's toolkit. Fluorine is the most widely incorporated, owing to the strength and polarity of the C-F bond, which confers resistance to cytochrome P450-mediated oxidative metabolism at that position. Beyond metabolic protection, fluorine substituents modulate the pKa of adjacent ionisable groups, constrain molecular conformation through C-F dipole interactions, and can function as bioisosteres for hydroxyl, methyl, and carbonyl groups. The CF3 and CHF2 groups have become particularly prevalent motifs, appearing across a large proportion of recently approved drugs. Chlorine, the second most common halogen in approved drugs, contributes to hydrophobic binding pocket interactions and serves as a bioisostere for methyl, hydroxyl, and cyano groups. The so-called "magic chloro effect," described in the medicinal chemistry literature, refers to the observation that substituting a single hydrogen atom for chlorine can improve target potency by up to 100,000-fold, while simultaneously improving pharmacokinetic parameters such as clearance, half-life, and in vivo drug exposure. Heavier halogens, bromine and iodine, are used more selectively: bromine is exploited for halogen bonding interactions with protein carbonyl and heteroatom residues, and iodine finds application primarily in radiopharmaceuticals and PET tracers.

Two approved, first-in-class drugs illustrate the centrality of halogens to modern drug design. Suzetrigine (Journavx, Vertex Pharmaceuticals), approved by the FDA in January 2025, is the first selective NaV1.8 voltage-gated sodium channel inhibitor and the first non-opioid analgesic approved for moderate-to-severe acute pain in over two decades. Its structure incorporates a CF3 group and two adjacent fluorine atoms, which are critical to the hydrophobic interactions that confer its exceptional potency and selectivity for NaV1.8 over closely related channel subtypes. Vorasidenib (Voranigo, Servier Pharmaceuticals), approved in August 2024, is the first targeted therapy for grade 2 IDH-mutant glioma, acting as a brain-penetrant dual inhibitor of mutant IDH1 and IDH2 enzymes. The molecule incorporates both fluorine and chlorine atoms, contributing to its high brain penetrance and favourable pharmacokinetic profile.

In organic synthesis, aryl and alkyl halides are pivotal reaction partners across a broad range of named reactions. Palladium-catalysed cross-coupling reactions, including the Suzuki-Miyaura, Buchwald-Hartwig, and Negishi couplings, rely on aryl halides as the electrophilic coupling partner, and these transformations have become the most widely applied methods for C-C and C-N bond formation in pharmaceutical synthesis. The Ullmann condensation uses aryl halides under copper catalysis to form C-O, C-S, and C-N bonds. The Finkelstein reaction enables halide exchange via equilibrium-driven SN2 substitution, facilitating conversion between alkyl halide types. Halides also serve as the electrophilic component in nucleophilic substitution routes to amines, ethers, and thioethers, and as precursors to Grignard and organolithium reagents.

Emerging synthetic methods are significantly expanding the application of halides. In photochemistry, photoredox-catalysed late-stage C-H fluorination via aryl sulfonium intermediates enables site-selective introduction of fluorine into complex drug-like scaffolds without requiring prefunctionalisation. Electrochemical approaches have enabled direct C(sp3)-H fluorination using nucleophilic fluoride sources under anodic oxidation conditions, avoiding the stoichiometric electrophilic fluorinating reagents that present safety and handling challenges at scale. Electrophotochemical methods, combining highly reducing photoexcited radical anions with electrochemical generation, have extended the activation of electron-rich aryl chlorides, a substrate class previously inert to palladium catalysis under mild conditions, opening new retrosynthetic disconnections in complex molecule synthesis.

Our catalogue features a range of halides that includes a broad selection of aryl, heteroaryl, and alkyl fluorides, chlorides, bromides, and iodides. We offer halides with additional substitution patterns and functional group handles to support medicinal chemistry programmes and late-stage diversification strategies.