2',3'-Dideoxythymidine triphosphate
[CAS# 611-60-9]

Identification

• Classification: Biochemical >> Nucleoside drugs >> Deoxynucleotides and their analogues
• Name: 2',3'-Dideoxythymidine triphosphate
• Synonyms: ddTTP; [hydroxy-[[(2S,5R)-5-(5-methyl-2,4-dioxopyrimidin-1-yl)oxolan-2-yl]methoxy]phosphoryl] phosphono hydrogen phosphate
• Protein Sequence: N
• Molecular Formula: C₁₀H₁₇N₂O₁₃P₃
• Molecular Weight: 466.17
• CAS Registry Number: 611-60-9
• SMILES: CC1=CN(C(=O)NC1=O)[C@H]2CC[C@H](O2)COP(=O)(O)OP(=O)(O)OP(=O)(O)O

Properties

• Density: 1.8±0.1 g/cm³ Calc.^*
• Index of refraction: 1.582 (Calc.)^*

^* Calculated using Advanced Chemistry Development (ACD/Labs) Software.

Discovory and Applicatios

2',3'-Dideoxythymidine triphosphate (commonly abbreviated as ddTTP) is a synthetic nucleotide analog structurally related to the naturally occurring thymidine triphosphate (TTP), one of the four deoxyribonucleoside triphosphates required for DNA synthesis. The compound differs from its natural counterpart by the absence of hydroxyl groups at both the 2' and 3' positions of the deoxyribose sugar, which significantly alters its function during nucleic acid polymerization. This modification prevents the formation of phosphodiester bonds with incoming nucleotides, making ddTTP a potent chain terminator in enzymatic DNA synthesis.

The discovery and development of ddTTP are closely tied to the broader efforts in antiviral drug research during the late 20th century, particularly in the context of retroviral infections such as human immunodeficiency virus (HIV). It was synthesized as part of a class of 2',3'-dideoxynucleoside analogs originally studied for their ability to inhibit reverse transcriptase, the enzyme responsible for converting viral RNA into DNA in retroviruses. The compound is the triphosphate form of 2',3'-dideoxythymidine (ddT), a nucleoside analog also known as alovudine. While ddT itself has limited clinical use, its phosphorylated derivatives have served as critical tools in both therapeutic and experimental contexts.

In molecular biology, ddTTP is primarily used in DNA sequencing and related applications. It became especially important in the development of the Sanger dideoxy sequencing method, where dideoxynucleotides like ddTTP are incorporated into a growing DNA strand by DNA polymerase. Once a ddTTP is inserted, the lack of a 3'-hydroxyl group prevents further extension, resulting in termination of the DNA chain at a specific thymidine position. When combined with labeled primers or nucleotides and gel or capillary electrophoresis, this allows the precise determination of DNA sequences. The high fidelity and simplicity of this approach led to its widespread adoption in genomics research and played a central role in early genome sequencing projects.

Outside of sequencing, ddTTP is utilized in studies of DNA polymerase activity and substrate specificity. By comparing how different polymerases incorporate or discriminate against ddTTP, researchers can gain insights into enzyme mechanisms and fidelity. The compound is also useful for mapping enzyme active sites and for screening potential inhibitors in the context of both basic enzymology and drug discovery.

The triphosphate form of ddT is not stable under all storage or experimental conditions, and its synthesis requires careful chemical or enzymatic phosphorylation of the corresponding nucleoside. Typically, ddTTP is produced via multi-step synthesis involving activation of the nucleoside, protection and deprotection of functional groups, and controlled addition of the triphosphate chain. Commercially prepared ddTTP is available for research purposes, and its quality is critical for successful application in sequencing and enzymatic reactions.

Although ddTTP has no current therapeutic use as a drug itself, its structural analogs and related compounds have contributed to the design of clinically approved antiretroviral agents. The concept of chain termination through selective incorporation of dideoxynucleotides remains fundamental in antiviral therapy. Moreover, ddTTP continues to be used in structural studies of reverse transcriptase and DNA polymerases, helping elucidate how drugs and natural substrates interact with these enzymes at the molecular level.

In summary, 2',3'-dideoxythymidine triphosphate is a chemically engineered nucleotide analog that serves as a powerful tool in molecular biology and biochemistry. Its ability to terminate DNA chains upon incorporation has made it indispensable for DNA sequencing, polymerase studies, and enzymology. Though not a therapeutic agent in its own right, ddTTP exemplifies the utility of nucleotide analogs in both research and medicine.

References

1980. Inhibition of DNA synthesis in the adenovirus DNA replication complex by aphidicolin and 2',3'-dideoxythymidine triphosphate. Biochemical and Biophysical Research Communications, 92(2).
DOI: 10.1016/0006-291x(80)91511-9

1980. Effects of 2',3'-dideoxythymidine triphosphate on replicative DNA synthesis and unscheduled DNA synthesis in permeable mouse sarcoma cells. Biochimica et Biophysica Acta (BBA) - Nucleic Acids and Protein Synthesis, 607(1).
DOI: 10.1016/0005-2787(80)90034-9

1980. Inhibition of deoxyribonucleic acid polymerases of human leukemic leukocytes by 2',3'-dideoxythymidine triphosphate. Biochemical Pharmacology, 29(8).
DOI: 10.1016/0006-2952(80)90410-4