Structure-based linker exploration: Discovery of 1-ethyl-1H-indole analogs as novel ATX inhibitors

Aiming to develop novel ATX inhibitors, an indole-3-carboxylic acid lead Indole-1 was identified through high-throughput screening (HTS) efforts. The Indole-1 analogs 1-7 was firstly prepared which exerted mild activity comparable to Indole-1 (740 nM) in ATX enzyme assay. Further structural modification to identify type IV ATX inhibitors was proceeded through derivatization of the indole-3-carboxylic acid group. Resultantly, compounds 8-17 containing acyl hydrazone linker displayed poor activity (over 3.49 μM). Alternatively, replacing the acylhydrazone linker with urea counterpart by the amide bond reversal principle, the acquired compounds 18-22 achieved obvious improvements with submicromolar activities. Furthermore, with the aim to reducing cLogP, the thiazole ring of 18-22 was altered to the benzamide (23-32) with the urea linker unchanged. Remarkably, the benzamide derivative 24 with 4-hydroxy piperidine fragment was identified which exhibited prominent activity with IC₅₀ value of 2.3 nM. Especially, dedicated molecular docking study was throughout the modification process which qualified 24 as optimal entity in accordance with the ATX inhibitory results.