PfCLK3-IN-1 (Compound 4) is a covalent inhibitor for Plasmodium falciparum CLK3 ( Pf CLK3 ) under alkaline conditions with an pEC 50 of 7.1. PfCLK3-IN-1 reduces mature gametocytes in sexual stage parasites, and prevents transmission. PfCLK3-IN-1 inhibits P. falciparum Dd2-B2 clone with an IC 50 of 239.5 nM.