 In this phase II study, the investigational new drug not approved by the FDA GPI 1485 is being assessed for its ability to delay or stop disease progression and improve symptoms in patients with mild to moderate Parkinsons disease PD. These potential effects of GPI 1485 are based on animal studies in which the drug was shown to both protect nerves from damage and to regrow damaged nerves. Participants in this study will be randomly assigned to receive either GPI 1485 or placebo inactive pill. GPI 1485 will be supplied as an oral tablet formulation to participants enrolled in the study. Participants randomly assigned to receive GPI 1485 will be required to take four tablets four times a day by mouth. GPI 1485 matching placebo will also be supplied as an oral tablet formulation. Participants randomly assigned to placebo will be required to take four placebo tablets four times a day by mouth. The duration of this study is 24 months which includes 12 clinical visits at one of 21 participating sites and three imaging visits to Molecular NeuroImaging MNI in New Haven Connecticut. At MNI, participants will be injected with a radioactive investigational drug b-CIT to obtain images of the activity in the brain with Single Photon Emission Computed Tomography SPECT. This will evaluate whether GPI 1485 slows or delays the loss of brain activity in patients with mild to moderate PD. During this study you will also have other clinical evaluations including a physical exam, blood work, ECG tracing of your heart rhythm, and urinalysis. Tests specific to Parkinsons disease will also be performed including: Unified Parkinsons Disease Rating Scale UPDRS, Dyskinesia Rating Scale, Bilateral finger-tapping test, and Parkinsons Disease Sleep Scale PDSS. In addition assessments of your health and mood will be done. 