engleski

Efficient Synthetic Routes for the Preparation of the Oxazolo[3, 2-c]Pyrimidines

Cyclonucleosides, the compounds that have an extra linkage between the nucleobase and sugar, are an interesting class of compounds since they can be used as intermediates in the synthesis of 2-, 4-, and 6-substituted pyrimidine nucleosides or the sugar-substituted derivatives. The O6, 2¢-cyclonucleosides can be readily prepared by treatment of arabinosyl-5-bromopyrimidines with sodium methoxide in methanol by an intramolecular anti-cyclisation. However, the attempted cyclisation reactions of dihydroxypropyl 5-bromo-3-methyl-derivative 1 and 5-bromo derivative 3 under the same conditions failed. We found that treatment of 5-bromo-3-methyl derivative 1 with DBU/DMF affected its anti-cyclisation into 2 in 95% yield. On the contrary, the unprotected derivative 3 was unaffected under the same conditions. Using KCN/DMF the anti-cyclisation of 3 into 4 was observed in 70% yield. The mechanism of these anti-cyclisation reactions will be discussed on the basis of different intermediates isolated in these reactions.

Cyclonucleosides ; Intramolecular Anticyclisation

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