Different methods for the coupling of sugars with heterocyclic bases

Abstract

leading to the synthesis of nucleoside analogues. The following two methods have been used for the coupling of sugars with aza-heterocycles: 1. Triflte mediated glycosidation of aza-heterocycles. 2. Phase transfer glycosidation of aza-heterocycles. Triflate mediated coupling of sugars proceeds via substitution of trifluoromethanesulphonyloxy with benzimidazole. Hence Jnstead of getting the desired coupling product, substitution of hydride ion by flouride ion seems to take place leading to an unexpected product,. the evidence for the structure proposed comes from the spectroscopic data. Phase transfer catalysis requires the use of phase transfer catalysts. The use of tetraalkylammonium salts and crown ethers have been exploited to affect a CoN coupling. T etraalkylammonium salts were found to be effective catalyst for the coupling of aza-heterocycles with sugars. Coupling of benzimidazole ~ commercial sample of unsubstituted benzimidazole and benzodiazipinone 11 with sugar chloride J2 has been accomplished which led to a mixture of compounqs. However, only one component of the mixture could be isolated pure as a single coupling product. Mass 1 Hand 13C NMR of one of the coupling product 24 cOljlld be obtained. On the basis of these data, structure of the coupling product has been proposed. The spectral data of the coupling products 23 and 25 are still awaited. The use of crown ether as phase transfer catalyst did not lead to desire reaction.