Leucettine L is an inhibitor of dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A), DYRK2, CDC-like kinase 1 (CLK1), and CLK3 (ICs = 0.04, 0.035, 0.015, and 4.5 µM, respectively). It also inhibits GSK3α/β and Pim1 with IC values of 0.41 and 4.1 µM, respectively. It inhibits phosphorylation of the serine/arginine (SR) protein 9G8 by DYRK2, DYRK3, CLK1, CLK2, and CLK4 and inhibits TNF-α-induced SRp75 and SRp55 phosphorylation in human microvascular endothelial cells when used at concentrations ranging from 0.1 to 10 µM. Leucettine L modulates alternative pre-RNA splicing of a synthetic CLK1 minigene in a reporter model. It prevents lipid peroxidation and the accumulation of reactive oxygen species (ROS) induced by amyloid-β 25-35 in the hippocampus in a mouse model of Alzheimer’s disease-like toxicity. Leucettine L (0.4, 1.2, and 4 µg, i.c.v.) also prevents memory deficits induced by amyloid-β 25-35 in the same model.