Troxacitabine is a synthetic nucleoside analogue. It is a poor substrate for nucleoside transporters and gains entry into cells by passive diffusion. Intracellular conversion to its active triphosphate form is via deoxycytidine kinase. Incorporation of this metabolite into DNA results in immediate chain termination and apoptosis induction. It is the first nucleoside analog with anticancer activity that has an unnatural stereochemical configuration. The dose-limiting adverse reactions were stomatitis and hand–foot syndrome.

Lometrexol, formerly known as DDATHF; LY 264618; T-64 was the first glycinamide ribonucleotide formyl transferase (GARFT) inhibitor to be investigated clinically. Lometrexol had been in phase II clinical trial for the treatment non-small cell lung cancer (NSCLC). However, the studies have been discontinued by Tularik Inc, because Company had suggested, that drug would face competition from other companies in the indication

CNDAC (TAK-109) is an analog of the nucleoside deoxycytidine with potential antineoplastic activity. CNDAC is incorporated into DNA and induces single-strand breaks, which are converted into double-strand breaks (DSBs) when cells go through a second S phase. This results in the cell cycle arrest in the S and G2/M phases, DNA fragmentation, and tumor cell apoptosis. Sapacitabine, a prodrug of CNDAC, is being developed by the US biotechnology company Cyclacel for the treatment of hemalogical cancers and solid tumors.

Valopicitabine is a nucleoside analog and the orally bioavailable prodrug of NM107 that competitively inhibits HCV NS5B polymerase, causing chain termination. Valopicitabine had been in phase II clinical trial for once-daily oral treatment of Hepatitis C virus infection. However, because of the overall risk/benefit profile of subjects undergoing clinical trials, further development of the drug has been temporarily placed on hold by the Swiss drug major Novartis and USA-based Idenix Pharmaceuticals company and the FDA.

Tezacitabine is a cytidine derivative patented by Merrell Dow Pharmaceuticals, Inc. as an antineoplastic and antiviral agent. Tezacitabine acts as irreversible ribonucleotide reductase inhibitor and DNA chain terminator. Tezacitabine shows as potent activity in a broad spectrum of tumor cell lines and in vivo tumor models, including human colon, prostate, and breast tumor xenografts, In clinical trials combination of Tezacitabine and 5-Fluorouracil exerts favor influences in patients with advanced solid tumors particularly in patients with esophageal and other gastrointestinal carcinomas.

Triciribine is a purine analogue which inhibits DNA and protein synthesis, it is a synthetic tricyclic nucleoside which acts as a specific inhibitor of the Akt signaling pathway. It selectively inhibits the phosphorylation and activation of Akt1, -2 and -3 but does not inhibit Akt kinase activity nor known upstream Akt activators such as PI 3-Kinase and PDK1. It inhibits cell growth and induces apoptosis preferentially in cells that express aberrant Akt1. In whole cells triciribine is phosphorylated by adenosine kinase which may be necessary for its activity. Triciribine is a cancer drug which was first synthesised in the 1970s and trialled clinically in the 1980s and 1990s without success. Following the discovery in the early 2000s that the drug would be effective against tumours with hyperactivated Akt, it is now again under consideration in a variety of cancers. As PTX-200, the drug is currently in two early stage clinical trials in breast cancer and ovarian cancer being conducted by the small molecule drug development company Prescient Therapeutics.

Brequinar is a synthetic quinolinecarboxylic acid analogue with antineoplastic properties. Brequinar inhibits the enzyme dihydroorotate dehydrogenase, thereby blocking de novo pyrimidine biosynthesis. This agent may also enhance the in vivo antitumor effect of antineoplastic agents such as 5-FU. Brequinar had been in phase II clinical trials by Bristol-Myers Squibb for the treatment of cancer and transplant rejection. However, this research has been discontinued. Brequinar had been also in preclinical studys for the treatment of cytomegalovirus infections. However, this research has been discontinued.

Omaciclovir (previously known as H2G), a cyclic guanosine analog that is structurally similar to acyclovir and was in clinical development for the treatment of herpesvirus infections. This drug acted against varicella-zoster virus (VZV), by the formation of high concentrations of relatively stable H2G-triphosphate, which is a potent inhibitor of the viral DNA polymerases. However, further development of this drug was discontinued.

Valopicitabine is a nucleoside analog and the orally bioavailable prodrug of NM107 that competitively inhibits HCV NS5B polymerase, causing chain termination. Valopicitabine had been in phase II clinical trial for once-daily oral treatment of Hepatitis C virus infection. However, because of the overall risk/benefit profile of subjects undergoing clinical trials, further development of the drug has been temporarily placed on hold by the Swiss drug major Novartis and USA-based Idenix Pharmaceuticals company and the FDA.

Sparfosate (PALA) is a stable transition state analogue for an aspartate transcarbamylase- cartalyzed reaction with antineoplastic activity. PALA is a potent inhibitor of aspartate transcarbamylase (Ki about 10(-8) M for ACTases of various origins), which in whole cells blocks the de novo synthesis of pyrimidines. Thus PALA inhibits de novo pyrimidine biosynthesis and increases the extent to which fluorouracil metabolites are incorporated into RNA. In vivo, low doses of PALA inhibit whole body pyrimidine synthesis. While this action is cytotoxic in vitro, extensive human testing demonstrates that PALA alone is devoid of selective antitumor activity. Interest in the therapeutic action of PALA derives from the demonstration that its action potentiates the cytotoxicity of several cytotoxic drugs, notably 5-fluorouracil (5-FU). Development of Sparfosate for cancer and Hepatitis B treatment is assumed to have been discontinued.