Proline method helps chemists add key building blocks to complex molecules

Proline-catalysed method enables selective installation of dichloromethyl ‘molecular handles’ in complex drug-like compounds, overcoming long-standing limitations

A team of chemists from the Hebrew University, Israel, Jerusalem, has reported a streamlined method to install a dichloromethyl functional group into complex molecular frameworks which has been a long-standing challenge in synthetic and medicinal chemistry. The approach has replaced harsh, metal-intensive or radiation-dependent strategies with a catalytic system based on the naturally occurring amino acid proline, enabling selective modification under comparatively mild conditions.

“Rather than forcing these molecules into conventional reactivity modes or circumventing their electronic ambivalence, we harnessed their electronic ambivalence as a design principle,” said Professor Dmitry Tsvelikhovsky – who led the research at the Institute for Drug Research at the Hebrew University – alongside students in the department Elihay Kuniavsky and Dvora R. Levy.

The dichloromethyl group has served as a valuable synthetic handle in pharmaceutical chemistry, as it permits subsequent functionalisation to optimise biological activity, pharmacokinetics and safety profiles. However, to introduce this group into structurally complex or electronically ambiguous molecules has typically required forcing conditions that risk degradation or uncontrolled side reactions. This limitation has constrained its broader application in late-stage functionalisation, where delicate scaffolds must remain intact.

The reported method has addressed this constraint by exploiting the catalytic properties of proline as a transient, structure-directing agent. Proline has temporarily bound to the target substrate and induced a defined three-dimensional conformation, which in turn has modulated the electronic distribution within the molecule. This conformational control has enabled the otherwise reluctant incorporation of the dichloromethyl group without recourse to aggressive reagents or extreme conditions.

A central feature of the reaction is what the authors have described as a stereochemically gated resolution mechanism. Upon interaction with the substrate, proline has generated two distinct stereochemical intermediates. Only one of these configurations has aligned correctly to proceed along the productive reaction pathway, leading to formation of the desired product with high stereochemical purity. The alternative configuration has remained unreactive and has reverted to the starting material during work-up, thereby avoiding the accumulation of undesired byproducts. This intrinsic selectivity has simplified purification and improved overall efficiency.

This level of stereochemical control is particularly relevant in drug discovery, where the spatial arrangement of atoms can determine biological activity, target selectivity and toxicity. To access a single, well-defined stereoisomer without extensive downstream separation has therefore represented a substantial operational advantage.

The researchers have demonstrated that the method is compatible with a range of chemically complex substrates, including scaffolds relevant to antibiotic development, natural product synthesis and neuroactive compounds that interact with serotonin receptors. These results suggest that the platform may support late-stage diversification strategies, where small structural changes can yield significant improvements in therapeutic performance.

By converting a persistent synthetic limitation into a predictable and programmable transformation, the work has provided medicinal chemists with a versatile tool to expand chemical space. The ability to introduce a dichloromethyl handle under mild, selective conditions may accelerate the design and optimisation of candidate drugs, particularly in areas where structural complexity has previously restricted exploration.

For further reading please visit: 10.1038/s41467-026-71815-z