Alkyl Linkers

Alkyl linkers are flexible, saturated carbon chain segments used in medicinal chemistry to connect pharmacophoric groups, modulate physicochemical properties, and optimize the spatial orientation of functional elements within a drug molecule. Their primary utility lies in fine-tuning potency, selectivity, and ADMET profiles by adjusting chain length, branching, and substitution patterns. In small-molecule drug discovery, alkyl linkers are employed to bridge binding fragments, tether warheads to targeting moieties in covalent inhibitors, and connect ligands to degrader scaffolds in PROTACs and molecular glues. Their metabolic lability can be exploited or mitigated by strategic incorporation of branching or bioisosteric replacements, making them versatile tools in lead optimisation.

Brexpiprazole (Rexulti, Otsuka/Lundbeck), FDA-approved in July 2015 for schizophrenia and as an adjunctive treatment for major depressive disorder, and subsequently approved in May 2023 as the first pharmacological treatment for agitation associated with Alzheimer's disease, exemplifies how a four-carbon butyl alkyl linker can be used to span and optimally orient two distinct pharmacophoric domains within a CNS drug. The molecule consists of a hydroxyquinolinone partial agonist moiety connected via a tetramethylene (C4) alkyl chain through an ether oxygen to a piperazine nitrogen bearing a benzothiophene group, with the butoxy linker providing the precise geometric relationship between the quinolinone and benzothiophene pharmacophores required for the compound's characteristic serotonin-dopamine activity modulator (SDAM) profile — partial agonism at dopamine D2 and serotonin 5-HT1A receptors combined with antagonism at 5-HT2A receptors. In synthesis, the linker is installed by alkylation of the quinolinone with 1,4-bromochlorobutane, demonstrating the straightforward and scalable utility of simple alkyl chain building blocks in constructing CNS drug candidates where linker length directly determines receptor binding geometry and functional selectivity.

Our range of alkyl linkers feature a range of linker lengths and incorporates a variety of synthetically tractable functional groups such as amines, carboxylic acids, ketones, hydroxyls and halogens to enable expedient synthetic strategies. In addition, functional groups to enable use in chemical biology applications can be found, such as NHS Esters for amine conjugation, azides for CuAAC or Staudinger ligation, and strained alkynes for SPAAC. Please examine a selection of alkyl linkers in our catalogue. The full range can be found using our Search tools.