Investigating the C2 modulation of the imidazo[1,2-a]pyrazine-based hit compound CTN1122: synthesis, in vitro antileishmanial activity, cytotoxicity and casein kinase 1 inhibition.

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Our research group previously discovered CTN1122, an imidazo[1,2-a]pyrazine compound with promising antileishmanial activity against intramacrophage amastigotes of Leishmania major and L. donovani strains. CTN1122 effectively targets Leishmania casein kinase 1 (L-CK1.2) and exhibits a favorable safety profile. To further explore its chemical space, we developed a convergent strategy to modify the C2 position of the imidazo[1,2-a]pyrazine core using Suzuki-Miyaura coupling of the corresponding triflate intermediate. Among 15 newly synthesized analogs, seven derivatives featuring variously substituted phenyl rings at C2 demonstrated L-CK1.2 inhibition within micromolar to submicromolar ranges and antileishmanial activity in vitro with low cytotoxicity in macrophages. Compounds 7d and 7l were particularly potent, with IC50 values of 1.25 µM and 0.92 µM against L. major, and 1.44 µM and 2.34 µM against L. donovani, respectively. They showed IC50 L-CK1.2 = 0.3 μM and 0.57 µM with enhanced selectivity indices (SI = 3.8 and 1.6) over the human CK1ε ortholog. Additionally, four C2 analogs and two C5 isomers exhibited notable antiparasitic effects without strongly inhibiting L-CK1.2, indicating a possible alternative mechanism of action. Compound 7k displayed the highest general activity, with IC50 values of 0.31 µM on L. major and 0.27 µM on L. donovani, coupled with favorable selectivity indexes.