Compounds of general formula (I) : (Formula I)) wherein R1, Q, R3, R4, R5, R6, R7 and Ar1 are as defined herein are inhibitors of class I histone deacetylases and are of use in the treatment of lysosomal storage disorders, especially Niemann-Pick type C disease, as well as other lysosomal storage disorders, defective autophagy, accumulation of free cholesterol and mycobacterial diseases.