Dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A) is a potential drug target because of its role in the development of Down syndrome and Alzheimer’s disease. The selective DYRK1A inhibitor 10-iodo-11H-indolo[3,2-c]quinoline-6-carboxylic acid (KuFal194), a large, flat and lipophilic molecule, suffers from poor water solubility, limiting its use as chemical probe in cellular assays and animal models. Based on the structure of KuFal194, 7-chloro-1H-indole-3-carbonitrile was selected as fragment template for the development of smaller and less lipophilic DYRK1A inhibitors. By modification of this fragment, a series of indole-3-carbonitriles was designed and evaluated as potential DYRK1A ligands by molecular docking studies. Synthesis and in vitro assays on DYRK1A and related protein kinases identified novel double-digit nanomolar inhibitors with submicromolar activity in cell culture assays.

The title compound was prepared by a Friedel–Crafts acylation-oxime synthesis-decarboxylation/dehydration sequence starting from commercially available 7-iodoindole with 2-(7-iodo-1H-indol-3-yl)-2-oxoacetic acid as isolated intermediate. The structural identity of the title compound was proven by elemental analysis and spectroscopic methods (IR, NMR, EI-MS), and purity was assessed by two independent HPLC methods.