Provided herein are compounds of formula (I): A-L-B  (I) and pharmaceutically acceptable salts and stereoisomers thereof, wherein A is wherein X is (i) CR1 or N, or (ii) O or NR2, each Y is independently N or CR3, and each Z is independently N or C, wherein R1, R2 and R3 are defined in the specification; L is a linker, and B is a multicyclic ring; methods of their synthesis, pharmaceutical compositions comprising the compounds, and methods of their use. The compounds provided herein are inhibitors of phosphodiesterases and useful for the treatment, prevention, and/or management of various disorders, such as CNS disorders and metabolic disorders, e.g., neurological disorders, psychosis, schizophrenia, obesity and diabetes.