Sumanirole (PNU-95,666) is a highly selectiveD2 receptorfull agonist, the first of its kind to be discovered. It was developed for the treatment of Parkinson's disease and restless leg syndrome. While it has never been approved for medical use  it is a highly valuable tool compound for basic research to identify neurobiological mechanisms that are based on a dopamine D2-linked (vs. D1, D3, D4, and D5-linked) mechanism of action.
In 2004, Pfizer announced the end of their clinical development program for sumanirole, citing “recent studies that failed to sufficiently distinguish sumanirole from currently available therapies”.
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^Barone P, Lamb J, Ellis A, Clarke Z (March 2007). "Sumanirole versus placebo or ropinirole for the adjunctive treatment of patients with advanced Parkinson's disease". Movement Disorders. 22 (4): 483–9. doi:10.1002/mds.21191. PMID17115380.
^Garcia-Borreguero D, Winkelman J, Adams A, Ellis A, Morris M, Lamb J, Layton G, Versavel M (March 2007). "Efficacy and tolerability of sumanirole in restless legs syndrome: a phase II, randomized, double-blind, placebo-controlled, dose-response study". Sleep Medicine. 8 (2): 119–27. doi:10.1016/j.sleep.2006.05.018. PMID17239657.