The invention provides a chemical entity of Formula (I) wherein R1, R2, R3, R4, X, and Y have any of the values described herein, and compositions comprising such chemical entities; methods of making them; and their use in a wide range of methods, including metabolic and reaction kinetic studies; detection and imaging techniques; radioactive treatments; modulating and treating disorders mediated by GlyT1 activity; treating neurological disorders, CNS disorders, dementia, neurodegenerative diseases, and trauma-dependent losses of function; treating stroke, including cognitive and motor deficits during stroke rehabilitation; facilitating neuroprotection and neurorecovery; enhancing the efficiency of cognitive and motor training, including animal skill training; and treating other disorders, including pain and alcohol-dependence.