| Budget Amount *help |
¥3,600,000 (Direct Cost: ¥3,600,000)
Fiscal Year 2004: ¥1,700,000 (Direct Cost: ¥1,700,000)
Fiscal Year 2003: ¥1,900,000 (Direct Cost: ¥1,900,000)
|
|---|
| Research Abstract |
Oxidation of unsaturated sugar nucleosides with an acetone solution of dimethyldioxirane allowed isolation of the corresponding 1',2'- and 4',5'-epoxides for the first time, This enabled us to carry out the reaction of these epoxides with organoaluminum and organosilicon regants. As a result, a new access to 1'-and 4'-branched nucleosides has been disclosed The branched nucleosides thus synthesized were evaluated their antiviral activity.
Among these nucleoside analogues, 4'-ethynylstavudine was found to show higher anti-HIV activity than the parent compound stavudine which is under clinical use. Additional appeals of 4'-ethynylstavudine are listed below:
1) This compound is much less cytotoxic than stavudine,
2) to contrast to stavudine, this compound does not inhibit mitochondrial DNA synthesis,
3) This compound acts synergistically with lamivudine, elvucitabine, didanosine, and zidovudine against HIV,
4) This compound is phosphorylated by purified human thymidine kinase 1(TK-1) from CEM
… More
cells with a faster relative V_<mm> and a lower K_m value than stavudine, and efficiency of TK-1 in the phosphorylation of this compound is fourfold better than stavudine.
5) While stave dine is broken down by the catabolic enzyme thymidine phosphorylase, the level of breakdown of this compound is below detection.
These characteristics of 4'-ethynylstavudine led us to carry out further investigation, especially its large scale preparation that is necessary when developing this compound as an HIV agent. The above synthetic method utilizing dimethyldioxirane is not suitable for this purpose, because a 4 concentrated acetone solution of dimethyldioxirane cannot be prepared. We, therefore, decided to apply nucleophilic substitution at the 4'-position. The substrate for this reaction was prepared again from 4',5'-unsaturated thymine derivative by reacting with lead tetrabenzoate. The resulting 4'-benzoyloxy derivative, upon reacting with an ethynylaluminum reagent, gave the 4'-ethynylated product with the desired stereochemistry in 62% yield. Precise examination of this reaction revealed that chlorination at the 4'-position is the initial step for the ethynylation. Although actual reaction mechanism remains to be investigated and also the yield has to be improve, it is to be mentioned that this ethnylation gave none of the product having opposite 4'-stereochemstry.
Other studies carried out in this project are 1) the synthesis of 5'-aldehyde derivative of 4'-ethynylstavudine : this compound is to be used for the preparation oftritium labeled compound, 2) structure-activity relationships of 4'-ethynylstavudine. For the latter purpose, analogues with CH_2 and sulfur instead of furanose oxygen were synthesized each as a racemate. As a result of antiviral evaluation of these analogues, the sulfur-replaced analogue was found to be as active as stavudine. Optical resolution of this sulfur analogue is now under way to find out which enantiomer is actual anti-HIV active compound. Less
|
