An improved process for the preparation of 2'-modified nucleosides and 2'-deoxynucleosides, such as, β-L-2'-deoxy-thymidine (LdT), is provided. In particular, the improved process is directed to the synthesis of a 2'-deoxynucleoside that may utilize different starting materials but that proceeds via a chloro-sugar intermediate or via a 2,2' anhydro-1-furanosyl-nucleobase intermediate. Where an 2,2'-anhydro-1-furanosyl base intermediate is utilized, a reducing agent, such as Red-Al, and a sequestering agent, such as 15-crown-5 ether, that cause an intramolecular displacement reaction and formation of the desired nucleoside product in good yields are employed. An alternative process of the present invention utilizes a 2,2'-anhydro-1-furanosyl base intermediate without a sequestering agent to afford 2'-deoxynucleosides in good yields. The compounds made according to the present invention may be used as intermediates in the preparation of other nucleoside analogues, or may be used directly as antiviral and/or antineoplastic agents.
Addition of bromine to β′-(functional alkyl) α,β-unsaturated esters stereoselective synthesis of β-haloderivatives
作者:Taïcir Ben Ayed、Hassen Amri、Mohamed Moncef El Gaied
DOI:10.1016/s0040-4020(01)91028-2
日期:1991.11
A new convenient stereoselective synthesis of β-brominated β′-(functional alkyl) α,β-unsaturatedesters has been developed by the reaction of tetraalkylammonium fluoride in HMPA with ethyl 2,3-dibromo 2-(functional alkyl) propionates which can be easily prepared by addition of bromine to β′-(functional alkyl) acrylates. An interpretation of the observed stereoselectivity is proposed.