Synthesis of 2'-O,4'-C-Methyleneuridine and -cytidine. Novel Bicyclic Nucleosides Having a Fixed C a ,-endo Sugar Puckering
As a direct way to treat serious diseases such as cancer, viral infections and genetic disorders, antisense (targeting mRNA) and antigene (targeting DNA) strategies for selective regulation of gene expression are attracting the widespread attention of many scientists. 1 Recent studies have been focused on developing various types of backbone-, sugar-, and/or base-modified oligoribo- or oligodeoxyribonucleotides to find more effective antisense and antigene molecules. 2 In particular, many efforts are concentrated on acquisition of the derivatives possessing high binding affinity with complementary RNA and/or DNA strands. The sugar moiety of nucleosides (nucleotides) has two representative preferential conformations, C2,-endo and Cy-endo conformations (in other words, S- and N-conformations). Although each nucleoside (nucleotide) exists in an individual equilibrium mixture between these two conformations, it is well known that the B-form DNA duplex possesses C2,-endo sugar puckering and the A-form RNA duplex has the Cy-endo. 3 B.
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