Pyrimidine alkynes can be transformed into the corresponding annulated pyridines efficiently in flow. The superheating of organic solvents far beyond their boiling point enables toxic and difficult to workup solvents such as nitrobenzene or chlorobenzene, which are usually employed for these reactions, to be replaced by less harmful ones like toluene. The relative rate of reactivity for a series of structurally close starting materials was investigated and a scalable flow process was developed, providing facile access to a series of novel annulated pyridine building blocks. The effect of thermal volume expansion of solvents under superheated conditions was found to be significant and influenced the residence times considerably. To obtain meaningful and accurate residence times, flow rates need to be corrected for volume expansion. To avoid confusion with residence times, tR, calculated from nominal flow rates, we would propose to use for such corrected residence times the term effective residence time, tR,eff.

Drug discovery is a multifaceted endeavor encompassing as its core element the generation of structure-activity relationship (SAR) data by repeated chemical synthesis and biological testing of tailored molecules. Herein, we report on the development of a flow-based biochemical assay and its seamless integration into a fully automated system comprising flow chemical synthesis, purification and in-line quantification of compound concentration. This novel synthesis-screening platform enables to obtain SAR data on b-secretase (BACE1) inhibitors at an unprecedented cycle time of only 1 h instead of several days. Full integration and automation of industrial processes have always led to productivity gains and cost reductions, and this work demonstrates how applying these concepts to SAR generation may lead to a more efficient drug discovery process.

Macrocyclic inhibitors of rhodesain (RD), a parasitic cysteine protease and drug target for the treatment of human African trypanosomiasis, have shown low metabolic stability at the macrocyclic ether bridge. A series of acyclic dipeptidyl nitriles was developed using structure-based design (PDB ID: 6EX8 ). The selectivity against the closely related cysteine protease human cathepsin L (hCatL) was substantially improved, up to 507-fold. In the S2 pocket, 3,4-dichlorophenylalanine residues provided high trypanocidal activities. In the S3 pocket, aromatic residues provided enhanced selectivity against hCatL. RD inhibition ( K values) and in vitro cell-growth of Trypanosoma brucei rhodesiense (IC values) were measured in the nanomolar range. Triazole-based ligands, obtained by a safe, gram-scale flow production of ethyl 1 H-1,2,3-triazole-4-carboxylate, showed excellent metabolic stability in human liver microsomes and in vivo half-lives of up to 1.53 h in mice. When orally administered to infected mice, parasitaemia was reduced but without complete removal of the parasites.

Potency with potential: 2-Phenoxy-nicotinamides were identified as potent agonists at the GPBAR1 receptor, a target in the treatment of obesity, type 2 diabetes and metabolic syndrome. Extensive structure-activity relationship studies supported by homology modeling and docking resulted in the identification of optimized GPBAR1 agonists, potent against both human and mouse receptors, endowed with favorable physicochemical properties and good metabolic stability.

A combination of flow and batch chemistries has been successfully applied to the assembly of a series of trisubstituted drug-like pyrrolidines. This study demonstrates the efficient preparation of a focused library of these pharmaceutically important structures using microreactor technologies, as well as classical parallel synthesis techniques, and thus exemplifies the impact of integrating innovative enabling tools within the drug discovery process.