Bifeprunox, code name DU-127,090 is an atypical antipsychotic agent, which combines minimal D2 receptor agonism with 5-HT receptor agonism. Bifeprunox was in phase III of clinical trials for the treatment of schizophrenia, Bipolar Depression and in phase I for Parkinson's disease, but these studies were discontinued because efficacy data did not support pursuing the existing development strategy of stabilization of non-acute patients with schizophrenia.

Omigapil (CGP 3466 or TCH346) is a structurally related analog of R-(-)-deprenyl that exhibits virtually no monoamine oxidase type B inhibiting activity but is neuroprotective in the picomolar concentration range. It binds to glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and at subnanomolar concentrations prevent the S-nitrosylation of GAPDH, inhibit GAPDH-Siah binding and prevent the nuclear translocation of GAPDH. Omigapil demonstrated promising potential in the treatment of Parkinson's disease and motoneuron disease in animal models, however, it did not show efficacy in clinical trials. Omigapil is in development for the treatment of congenital muscular dystrophy.

Pardoprunox is a partial D2/3 dopamine receptor agonist and full 5-HT1A serotonin receptor agonist. Partial D(2/3) dopamine (DA) receptor agonists provide a novel approach to the treatment of the motor symptoms of Parkinson's disease that may avoid common dopaminergic side effects, including dyskinesia and psychosis. Pardoprunox passed phase III clinical trial for the treatment of Parkinson's disease.

Preladenant (SCH-420814) is an adenosine A(2A) receptor antagonist with a high affinity and very high selectivity for adenosine A(2A) receptors, which is being developed by Merck & Co Inc (following its acquisition of Schering-Plough Corp) for the potential treatment of Parkinson's disease. Preladenant is a potent competitive antagonist of the human A2Areceptor (Ki = 1.1 nM) and has >1000-fold selectivity over all other adenosine receptors, making this compound the most selective A2A receptor antagonist reported to date. Preladenant was being researched as a potential treatment for Parkinson's disease. Positive results were reported in Phase II clinical trials in humans, but it did not prove itself to be more effective than a placebo during Phase III trials, and so was discontinued in May 2013.

Vanoxerine, also known as GBR-12909, is a piperazine derivative exhibiting potent selective inhibition of sodium-dependent dopamine reuptake transporters. Vanoxerine has been in clinical trials for Parkinsonism, depression and cocaine addiction but lacked efficacy. Vanoxerine has also been observed as a potent blocker of the following channels: cardiac hERG/IKr potassium channel, Calcium channel, voltage-dependent, L type, alpha 1C subunit (also known as Cav1.2) and voltage-gated sodium channel Nav 1.5. Vanoxerine was studied as a potential treatment for atrial fibrillation. However, phase III clinical trials for this condition were terminated because of cardiac safety concerns. Research also indicates that vanoxerine may have additional mechanisms of action including antagonist action at nicotinic acetylcholine receptors (nAChRs).

Meclinertant (SR-48692) is the first non-peptide antagonist of neurotensin receptors. It is potent and selective vs the high-affinity binding sites and with a small activity on the levocabastine-sensitive binding sites. It is active on several species including man without partial agonist properties. In vivo, it is active by oral route with a long duration of action and it is able to cross the blood-brain barrier. Meclinertant may be considered a powerful tool for investigating the role of neurotensin in physiological and pathological processes. Meclinertant has been developing for the treatment of anorexia nervosa; colorectal cancer; irritable bowel syndrome; pain; pancreatic cancer; prostate cancer; schizophrenia; small cell lung cancer however its development was discontinued.

Quizapine is a piperazine-based nonselective serotonin (5-HT) receptor agonist with antidepressant and oxytocic activities. Quipazine targets and binds to serotonin receptors, particularly to the 5HT2A and 5HT3 receptors. Quipazine is a potential anti-parkinsonian agent. Serotonin receptor activation by quipazine may lead to smooth muscle contraction and antidepressant effects. quipazine, a central serotonergic agent, counteracted some of the drug-induced symptoms of pseudoparkinsonism in laboratory animals. Cholinergic, dopaminergic and histaminergic receptors play an important role in the manifestations of these symptoms.

Brocresine, an aromatic L-amino acid decarboxylase inhibitor with both a peripheral and central action was shown to potentiate the therapeutic effect of levodopa in Parkinson's disease.

RG2833 is a compound originally developed by the Scripps Insitute for the treatment of Friedrick's Ataxia. RG2833 is a potent and selective inhibitor of neuronal histone deacetylase. RG2833 has been granted orphan drug status has been investigated in phase one clinical trials. There has also been proof of concept studies conducted for the treatment of Parkinson's disease.

Schisantherin A is a dibenzocyclooctadiene originally found in Schisandra that exhibits anti-tussive, sedative, anti-inflammatory, anti-osteoporotic, neuroprotective, cognition enhancing, and cardioprotective activities. In macrophages, schisantherin A decreases LPS-induced expression and activity of iNOS, COX-2, NO, IL-6, and TNF-α. Schisantherin A also decreases RANKL-induced NF-κB signaling by inhibiting IκBα degradation and suppressing JNK and ERK1/2 activation in vitro; it also inhibits osteoclast function and bone erosion in vivo. In animal models of Alzheimer’s disease, schisantherin A inhibits amyloid-β (Aβ)-induced learning and memory impairments in Y maze, shuttle box, and Morris water maze assays. Additionally, this compound lowers left ventricular systolic and end diastolic pressures, decreases infarct size and maldionaldehyde release, and increases superoxide dismutase activity, preventing myocardial apoptosis in animal models of cardiac ischemia/reperfusion. Schisantherin A conferred significant protection against MPTP-induced loss of TH-positive dopaminergic neurons in a Parkinson's disease (PD) mice model. Western blotting analysis demonstrated that Schisantherin A exhibited neuroprotection against MPP(+) through the regulation of two distinct pathways including increasing CREB-mediated Bcl-2 expression and activating PI3K/Akt survival signaling suggesting that StA might be a promising neuroprotective agent for the prevention of PD.