Abstract: The present invention provides compounds of Formula (II), and pharmaceutically acceptable salts, solvates, hydrates, polymorphs, co-crystals, tautomers, stereoisomers, isotopically labeled derivatives, pro-drugs, and compositions thereof. Also provided are methods and kits involving the compounds of Formula (I), (II) or (III) for treating diseases associated with the over-expression of phosphoglycerate dehydrogenase (PHGDH) in a subject, such as proliferative diseases (e.g., cancers (e.g., breast cancer, ER negative breast cancer, melanoma, cervical cancer), benign neoplasms, diseases associated with angiogenesis, inflammatory diseases, autoinflammatory diseases, and autoimmune diseases). Treatment of a subject with a proliferative disease using a compound or composition of the invention may inhibit the activity of PHGDH or inhibit the serine biosynthetic pathway, or both.