Study on reactivity and protection of the alpha-hydroxyphosphonate moiety in 5'-nucleotide analogues: formation of the 3'-O-P-C(OH)-C4' internucleotide linkage

Synthesis and properties of ApA analogues with shortened phosphonate internucleotide linkage

A complete series of the 2 '-5 ' and 3 '-5 ' regioisomeric types of r(ApA) and 2 '-d(ApA) analogues with the α-hydroxy-phosphonate C3 '-O-P-CH(OH)-C4 ″ internucleotide linkage, isopolar but non-isosteric with the phosphodiester one, were synthesized and their hybridization properties with polyU studied. Due to the chirality on the 5 '-carbon atom of the modified internucleotide linkage bearing phosphorus and hydroxy moieties, each regioisomeric type of ApA dimer is split into epimeric pairs. To examine the role of the 5 '-hydroxyl of the α-hydroxy-phosphonate moiety during hybridization, the appropriate r(ApA) analogues with 3 '(2 ')-O-P-CH(2)-C4 ″ linkage lacking the 5 '-hydroxyl were synthesized. Nuclear magnetic resonance (NMR) spectroscopy study on the conformation of the modified sugar-phosphate backbone, along with the hybridization measurements, revealed remarkable differences in the stability of complexes with polyU, depending on the 5 '-carbon atom configuration. Potential usefulness of the α-hydroxy-phosphonate linkage in modified oligoribonucleotides is discussed.

Activation of human RNase L by 2'- and 5'-O-methylphosphonate-modified oligoadenylates

To determine the influence of internucleotide linkage and sugar ring conformation, and the role of 5'-terminal phosphate, on the activation of human RNase L, a series of 2'- and 5'-O-methylphosphonate-modified tetramers were synthesized from appropriate monomeric units and evaluated for their ability to activate human RNase L. Tetramers pAAAp(c)X modified by ribo, arabino or xylo 5'-phosphonate unit p(c)X activated RNase L with efficiency comparable to that of natural activator. Moreover, incorporation of phosphonate linkages ensured the stability against cleavage by nucleases. The substitution of 5'-terminal phosphate for 5'-terminal phosphonate in tetramer p(c)XAAA afforded tetramers with excellent activation efficiency and with complete stability against cleavage by phosphomonoesterases.

A-hydroxyphosphonate oligonucleotides: a promising DNA type?

The synthesis of monomers (S)-1, (R)-1 and 2 derived from (5'S)-, (5'R)-2'-deoxythymidine-5'-C-phosphonic acids and 2',5'-dideoxythymidine-5'-C-phosphonic acids was elaborated. The protection of the 5'-hydroxyl by the methoxycarbonyl group was a key step of the synthesis. Prepared monomers were used for the solid-phase assembly of several types oligothymidylate 15-mers (S)-3, (S)-4, (S)-5, (R)-4 and (R)-5 containing the chiral 3'-O-P-CH(OH)-5'' internucleotide linkage. Their hybridization properties with dA15 and rA15 were studied as well as their resistance against nuclease cleavage.