Velusetrag (TD-5108) is a potent, selective high intrinsic activity serotonin 5-HT(4) receptor agonist. Velusetrag has achieved proof-of-concept in patients with chronic idiopathic constipation and was on phase II of clinical trial for the treatment of Alzheimer's disease and constipation, when studies were discontinued. In addition, velusetrag is on the phase II of clinical trial for the treatment of gastroparesis.

Clibucaine is a piperidine derivative possessing local anesthetic properties and used in the clinic as a local anesthetic in the 1980s.

Clantifen is an aminothiophene derivative invented by Hoersht AG. The compound is claimed to have antiphlogistic and antipyretic properties.

Clinpirin is an investigational compound developed by CIBA and Schering as an acaricide, used for controlling spider mites. The compound possesses ovicidal and adulticidal efficacy and is active in the cattle tick resistant to organophosphorus pesticides.

Clanfenur is a benzoylphenyl urea derivative, developed as an anticancer drug, developed by Solvay. In preclinical studies, clanfenur exhibited anti-tumor activity in mice. A phase I study was initiated to establish the maximum tolerable dose (MTD) and safety of clanfenur. The study had to be discontinued because of intolerance to the vehicle and because the target plasma concentration of 1 ug/mL could not be reached due to very poor solubility of clanfenur.

Citenazone (Hoe 105) is an antiviral compound, developed in the 1970s by Hoechst. It is claimed to have activity for vaccinia infection in mice, baby rats, and rabbits, and for variola infection in baby mice.

Cinoxopazide is a compound disclosed in the patent application by Delalande S.A. The compounds of the series are claimed to have applications for stimulating intellectual efficiency in normal subjects, for preserving the cerebral function in aged subjects and for treating trouble of vigilance and/or memorization consequent on different pathologies.

Sitalidone (HOE-708) is a potent thiazide-like diuretic and antihypertensive drug.

Sinefungin, a natural nucleoside isolated from cultures of Streptomyces incarnatus and S. griseolus, is structurally related to S-adenosylhomocysteine and S-adenosylmethionine. Sinefungin is a DNA methyltransferase (DNMT) inhibitor (IC₅₀ = 0.1 - 20 uM). Sinefungin has been shown to inhibit the development of various fungi and viruses, but its major attraction to date resides in its potent antiparasitic activity. This compound has been reported to display antiparasitic activity against malarial, trypanosomal, and leishmanial species. Sinefungin inhibits pneumococcal biofilm growth in vitro and colonization in vivo, decreases AI-2 production, and downregulates luxS, pfs, and speE gene expressions. Sinefungin was significantly suppressive against both L. donovani and L. braziliensis panamensis infections in hamsters when compared with meglumine antimonate. An immunosuppressed rat model was used to investigate the anti-Cryptosporidium parvum activity of sinefungin. In infected animals, oral sinefungin therapy resulted in a dose-related suppression of oocyst shedding, which correlated with oocyst disappearance from ileal sections. When administered prior to or on the day of oocyst challenge, sinefungin successfully prevented infection. These data suggest that sinefungin could be considered as a candidate molecule in the treatment of human cryptosporidiosis, considered to be the most significant enteric opportunistic infection in AIDS.