A potent and selective inhibitor of glucosylceramide synthase (IC50 = 40 nM for reduction of glucosylceramide synthesis in K562 cells); inhibits glucosylceramide synthase to reduce production of GM1 and GM3 on K562 and B16/F10 cells (IC50s = 24 and 29 nM, respectively); has minimal activity (IC50 = >10 μM) at α-glucosidase I and II, GBA1, GBA2, sucrase, and maltase; induces a dose-dependent decrease in glucosylceramide accumulation in the liver and lungs of D409V/null mice, a model of Gaucher disease; prevents further glucosylceramide accumulation if administered after liver and lung deposits have been established