Taranabant is a highly selective cannabinoid-1 (CB1) receptor inverse agonist developed by Merck & Co for the treatment of obesity. The Phase III taranabant study involved about 2,400 patients and was to be conducted for two years. In March 2008, after completion of 52 weeks of the study, Merck reported positive results of the drug in conjunction with diet and exercise in obese patients. The patients experienced double the amount of weight loss by taking 2mg of taranabant when compared to the patients treated with placebo. However, in October 2008, the company discontinued the Phase III programme and clinical development of taranabant because of its side effects. The drug showed gastrointestinal and psychiatric side effects such as increased anxiety, depression and irritability. Merck had previously planned to file for regulatory approval with the US Food and Drug Administration in 2008, but subsequently withdrew it.

Enpiprazole is a heterocyclic three-ringed pyrazolylalkyl piperazine derivative. Enpiprazole has a cataleptic action very similar to that of neuroleptics, and its effect on muscle relaxation is comparable with that of diazepam. Enpiprazole exerts anxiolytic properties in animals.

PF-06840003 is a highly selective orally bioavailable Indoleamine 2,3-dioxygenase-1 (IDO-1) inhibitor with a potent antineoplastic activity. PF-06840003 reversed IDO-1-induced T-cell anergy in vitro. In vivo, PF-06840003 reduced intratumoral kynurenine levels in mice by >80% and inhibited tumor growth in multiple preclinical syngeneic models in mice, in combination with immune checkpoint inhibitors. A Phase 1 study of PF-06840003 in patients with Malignant Gliomas is ongoing.

Adonitol, also known as ribitol, is the reduced alcohol form of ribose. This compound was first described in 1892 Merck annual report as a crystalline pentahydric alcohol obtained from Adonis vernalis. It is a component of teichoic acids found in the cell walls of Gram positive bacteria. Adonitol is a substrate of the enzyme, called ribitol dehydrogenase, which can be used for direct production of allitol from d-fructose without any by-product formation and this may have potential use as an industrial enzyme. Adonitol is also a moiety present in riboflavin (vitamin B2).

L-778123 is a dual inhibitor of Farnesyl Protein Transferase (FPTase) and Geranylgeranyl Protein Transferase type-I (GGPTase-I), which can completely inhibit Ki-Ras prenylation. L-778123 has been used in phase I clinical trials to determine its effectiveness in treating patients with recurrent or refractory solid tumors. L-778123 was also studied in combination with paclitaxel to determine efficacy as a treatment for both recurrent or refractory solid tumors, and lymphomas.

MK-8033 is a dual c-Met/Ron inhibitor, which is under investigation by Merck for the treatment of cancer.

The receptor tyrosine kinase c-Met is an attractive target for therapeutic blockade in cancer. MK-2461 is a novel ATP-competitive multitargeted inhibitor of activated c-Met, was synthesized by Merck and was investigated in phase I of clinical trial for the potential treatment of patients with advanced solid tumors.

Merck was developing MK 8245, an orally active inhibitor of stearoyl CoA desaturase for the treatment of type-2 diabetes mellitus. MK-8245 is a liver-targeting inhibitor of stearoyl-CoA desaturase (SCD) with IC50 of 1 nM for human SCD1 and 3 nM for both rat SCD1 and mouse SCD1, with anti-diabetic and anti-dyslipidemic efficacy. It is in Phase 2 clinical studies for type 2 diabetes mellitus.

MK-0812 is a potent and selective CCR2 antagonist, which was developed by Merck. This drug has entered clinical trials for both rheumatoid arthritis and multiple sclerosis. However, the rheumatoid arthritis trial was terminated because of lack of favorable outcomes when MK-0812 failed to show any early clinical improvement. The outcome of the multiple sclerosis trial of MK-0812 also had negative outcomes.