Stereo-enriched phosphorothioate oligodeoxgnucleotides: Synthesis, biophysical and biological properties

Stereo-enriched [Rp] and [Sp]-phosphorothioate oligodeoxynucleotides are sy nthesized using oxazaphospholidine derivatized monomers. Three different de signs of phosphorothioate oligodeoxynucleotides (PS-oligos), (i) stereo-enr iched all-[Rp] or all-[Sp] PS-linkages, (ii) stereo-random mixture of PS-li nkages, and (iii) segments containing certain number of stereo-enriched [Rp ] and [Sp] PS-linkages ([Sp-Rp-Sp] or [Rp-Sp-Rp]), have been studied. Therm al melting studies of these PS-oligos with RNA complementary strands showed that the binding affinities are in the order [Rp] > [Sp-Rp-Sp] = [Rp-Sp-Rp ] > stereo-random > [Sp]. Circular dichroism (CD) studies suggest that the stereochemistry of the PS-oligo does not affect the global conformation of the duplex. The in vitro nuclease stability of these PS-oligos is in the or der [Sp] > [Sp-Rp-Sp], stereo-random > [Rp]. The RNase H activation is in t he order [Rp] > stereo-random > [Rp-Sp-Rp] > [Sp] > [Sp-Rp-Sp]. Studies in a cancer cell Line of PS-oligos targeted to MDM2 mRNA showed that all oligo s had similar biological activity under the experimental conditions employe d. Protein- and enzyme-binding studies showed insignificant stereo-dependen t binding to proteins. The [Sp] and [Sp-Rp-Sp] chimeric and stereo-random P S-oligos that contained a CpG motif showed higher cell proliferation than [ Rp] PS-oligo of the same sequence. (C) 2000 Elsevier Science Ltd. All right s reserved.