and pharmaceutically acceptable salts thereof； wherein R1, R2, R3, and R4 are as defined herein, and A is a heteroaryl ring system comprising 3 or 4 nitrogens as defined herein. Such compounds are contemplated useful for the prevention and treatment of a variety of CNS-related conditions, for example, treatment of sleep disorders, mood disorders, schizophrenia spectrum disorders, convulsive disorders, disorders of memory and/or cognition, movement disorders, personality disorders, autism spectrum disorders, pain, traumatic brain injury, vascular diseases, substance abuse disorders and/or withdrawal syndromes, and tinnitus.
