A compound is represented by Structural Formula (I): or a pharmaceutically acceptable salt thereof A pharmaceutical composition comprises a compound represented by Structural Formula (I) or a pharmaceutically acceptable salt thereof. A method of treating a subject in need thereof comprises administering to the subject a therapeutically effective amount of a compound represented by Structural Formula (I) or a pharmaceutically acceptable salt thereof. The subject has type 2 diabetes； renal hypertrophy or hyperplasia associated with diabetic nephropathy； Tay-Sachs； Gaucher's or Fabry's disease. Methods of decreasing plasma TNF-α, lowering blood glucose levels, decreasing glycated hemoglobin levels, inhibiting glucosylceramide synthase, and lowering glycosphingolipid concentration in a subject in need thereof respectively comprise administering to the subject a therapeutically effective amount of a compound represented by Structural Formula (I) or a pharmaceutically acceptable salt thereof.
