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J Org Chem. 2016 Apr 1;81(7):2753-62. doi: 10.1021/acs.joc.5b02793. Epub 2016 Mar 14.

Stereocontrolled Solid-Phase Synthesis of Phosphate/Phosphorothioate (PO/PS) Chimeric Oligodeoxyribonucleotides on an Automated Synthesizer Using an Oxazaphospholidine-Phosphoramidite Method.

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Department of Medicinal and Life Sciences, Faculty of Pharmaceutical Sciences, Tokyo University of Science , 2641 Yamazaki, Noda, Chiba 278-8510, Japan.
Department of Chemistry and Biomolecular Science, Faculty of Engineering, Gifu University , 1-1 Yanagido, Gifu 501-1193, Japan.


Stereocontrolled solid-phase synthesis of phosphate/phosphorothioate chimeric oligodeoxyribonucleotides (PO/PS-ODNs) was achieved by integrating the conventional phosphoramidite method into a previously developed oxazaphospholidine method for the stereocontrolled synthesis of P-chiral oligonucleotides. P-Stereodefined PO/PS-ODNs with mixed sequences (up to 12-mers) were obtained in good yields and high stereoselectivities by reacting different combinations of monomers (conventional phosphoramidites/diastereopure nucleoside 3'-O-oxazaphospholidines), activators (ETT/CMPT), capping reagents (Pac2O/CF3COIm), and oxidizing/sulfurizing reagents (TBHP/POS) on an automated synthesizer. A thermal denaturation study examined the resultant diastereopure PO/PS-ODN 12-mers with three consecutive (Rp)- or (Sp)-PS-linkages at the internal or terminal regions of the molecules. We found that (Rp)-PO/PS-ODNs can only moderately destabilize duplexes with complementary oligoribonucleotides (ORNs) compared with their unmodified ODN counterparts (ΔTm = -0.4 °C per modification). In contrast, (Sp)-PO/PS-ODNs have larger destabilizing effects (ΔTm = -1.2 to -0.8 °C per modification). Although smaller destabilizing effects were observed when the (Sp)-PS-linkages were incorporated into the terminal regions of the molecule, there was a weaker correlation between the location of an incorporated (Rp)-PS-linkage and its destabilizing effect.


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