The present invention relates to Compounds of Formula I: and pharmaceutically acceptable salts or
prodrug thereof. The present invention also relates to compositions comprising at least one compound of Formula I, and methods of using the compounds of Formula I for treatment or prophylaxis of lysosomal storage diseases, neurodegenerative
disease, cystic
disease,
cancer, or a diseases or disorders associated with elevated levels of glucosylceramide (GlcCer), glucosylsphingosine (GlcSph) and / or other glucosylceramide-based glycosphingolipids (GSLs).