Abstract: Described herein are compounds having general formula (1), wherein groups R1, R2, R3, Ar1, Ar2, Ar3, X, Y, p and n are as defined in the specification, and a salt, solvate and hydrate thereof. Such compounds inhibit glycine transport (or reuptake) via the GlyT-1 transporter, or are precursors (for example, pro-drugs) of such compounds and, thus, are useful in the treatment of schizophrenia, as well as other CNS-related disorders such as dementia, Alzheimer's disease, attention deficit disorder and depression.