As part of Drugs for Neglected Diseases initiative's lead optimization program for the development of new chemical entities to treat visceral leishmaniasis (VL), a series of aminothiazoles were synthesized and screened for in vitro efficacy, solubility and microsomal stability. The primary aim of identifying a lead structure with sub-micromolar activity was achieved. Out of 43 compounds synthesized, 16 compounds showed in vitro activity at less than 1 μM against VL. Compound 32 showed excellent antileishmanial potency (IC50 = 3 nM) and had all the acceptable properties except for metabolic instability. Blocking the metabolic soft spots in compound 32, where the 4-methoxy pyridine substituent was replaced by 5-ethoxy group, led to compound 36 (IC50 = 280 nM) with improved stability. To understand the disposition of 36, in vivo pharmacokinetic study was conducted in a mouse model. Compound 36 showed high clearance (91 mL/min/kg); short half-life (0.48 h) after intravenous administration (1 mg/kg) and exposure (AUC0-24) following oral administration was 362 ng h/mL with absolute bioavailability of 8%. To summarize, 43 analogs were synthesized out of which 15 compounds showed very potent sub-nanomolar efficacy in in vitro systems but the liability of metabolic instability seemed to be the major challenge for this chemical class and remains to be addressed.
Bhuniya, D.; Mukkavilli, R.; Shivahare, R.; Launay, D.; Ravindra, T.; Dere, Deshpande A.; Verma, A.; Vishwakarma, P.; Moger, M.; Pradhan, A.; Pati, H.; Gopinath, V.S.; Puri, S.K.; Martin, D. Aminothiazoles: Hit to lead development to identify antileishmanial agents. European Journal of Medicinal Chemistry (2015) 102: 582-593. [DOI: 10.1016/j.ejmech.2015.08.013]