Didanosine is a reverse transcriptase inhibitor, effective against HIV and used in combination with other antiretroviral drug therapy as part of highly active antiretroviral therapy (HAART). When HIV infects a cell, reverse transcriptase copies the viral single stranded RNA genome into a double-stranded viral DNA. The viral DNA is then integrated into the host chromosomal DNA which then allows host cellular processes, such as transcription and translation to reproduce the virus. RTIs block reverse transcriptase's enzymatic function and prevent completion of synthesis of the double-stranded viral DNA thus preventing HIV from multiplying.

Didanosine was developed by Samuel Broder, Hiroaki Mitsuya, and Robert Yarchoan in the National Cancer Institute (NCI). Since the NCI cannot market a product, the National Institutes of Health (NIH) awarded a ten-year exclusive licensed to Bristol-Myers Squibb Co. (BMS) to market and sell ddI as Videx® tablets. Didanosine became the second drug approved for the treatment of HIV infection in many other countries, including in the United States by the Food and Drug Administration (FDA) on Oct 9, 1991. Its FDA approval helped bring down the price of zidovudine (AZT), the initial anti-HIV drug.

Didanosine (ddI) is a nucleoside analogue of adenosine. It differs from other nucleoside analogues, because it does not have any of the regular bases, instead it has hypoxanthine attached to the sugar ring. Within the cell, ddI is phosphorylated to the active metabolite of dideoxyadenosine triphosphate, ddATP, by cellular enzymes. Like other anti-HIV nucleoside analogs, it acts as a chain terminator by incorporation and inhibits viral reverse transcriptase by competing with natural dATP.

Formal Chemical Name (IUPAC)
9-((2R,5S)-5-(hydroxymethyl)tetrahydrofuran-2-yl)-9H-purin-6-ol

References

http://en.wikipedia.org/wiki/Didanosine