4'-Alkoxy oligodeoxynucleotides: a novel class of RNA mimics.

4'-Alkoxy-oligothymidylates were prepared as model compounds to study the influence of a C4'-alkoxy group on hybridisation. The phosphodiester homooligomers (15 units long) containing either a 4'-methoxy or 4'-(2-methoxyethoxy) group were found to display increased hybridisation with both dA(15) and rA(15) complementary counterparts compared to the natural oligothymidylate. In addition, we found their hybridisation behaviour to be similar to that of the regioisomeric 2'-O-methyl-oligothymidylate. The formed complexes (duplexes and triplexes) were studied using UV spectroscopy and polyacrylamide gel electrophoresis (PAGE). Structural background of the hybridization behaviour was examined using NMR and MDS. The favourable hybridisation properties of the 4'-alkoxyoligothymidylates indicated that 4'-alkoxy modified nucleotides are promising compounds for the assembly of chimeric oligonucleotides with tunable properties.

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.

Structural diversity of nucleoside phosphonic acids as a key factor in the discovery of potent inhibitors of rat T-cell lymphoma thymidine phosphorylase.

Structurally diverse, sugar-modified, thymine-containing nucleoside phosphonic acids were evaluated for their ability to inhibit thymidine phosphorylase (TP, EC 2.4.2.4) purified from spontaneous T-cell lymphomas of an inbred Sprague-Dawley rat strain. From a large set of tested compounds, among them a number of pyrrolidine-based derivatives, 10 nucleotide analogues with IC(50) values below 1 microM were selected. Out of them, four compounds strongly inhibited the enzyme with IC(50) values lying in a range of 11-45 nM. These most potent compounds might be bi-substrate analogues.

Oligomerization of adenosin-5'-O-ylmethylphosphonate, an isopolar AMP analogue: evaluation of the route to short oligoadenylates.

In an attempt to prepare a library of short oligoadenylate analogues featuring both the enzyme-stable internucleotide linkage and the 5'-O-methylphosphonate moiety and thus obtain a pool of potential RNase L agonists/antagonists, we studied the spontaneous polycondensation of the adenosin-5'-O-ylmethylphosphonic acid (p(c)A), an isopolar AMP analogue, and its imidazolide derivatives employing N,N'-dicyclohexylcarbodiimide under nonaqueous conditions and uranyl ions under aqueous conditions, respectively. The RP LC-MS analyses of the reaction mixtures per se, and those obtained after the periodate treatment, along with analyses and separations by capillary zone electrophoresis, allowed us to characterize major linear and cyclic oligoadenylates obtained. The structure of selected compounds was supported, after their isolation, by NMR spectroscopy. Ab initio calculation of the model structures simulating the AMP-imidazolide and p(c)A-imidazolide offered the explanation why the latter compound exerted, in contrast to AMP-imidazolide, a very low stability in aqueous solutions.

Conformational evaluation of labeled C3'-O-P-(13)CH(2)-O-C4'' phosphonate internucleotide linkage, a phosphodiester isostere.

Modified internucleotide linkage featuring the C3'-O-P-CH(2)-O-C4'' phosphonate grouping as an isosteric alternative to the phosphodiester C3'-O-P-O-CH(2)-C4'' bond was studied in order to learn more on its stereochemical arrangement, which we showed earlier to be of prime importance for the properties of the respective oligonucleotide analogues. Two approaches were pursued: First, the attempt to prepare the model dinucleoside phosphonate with (13)C-labeled CH(2) group present in the modified internucleotide linkage that would allow for a more detailed evaluation of the linkage conformation by NMR spectroscopy. Second, the use of ab initio calculations along with molecular dynamics (MD) simulations in order to observe the most populated conformations and specify main structural elements governing the conformational preferences. To deal with the former aim, a novel synthesis of key labeled reagent (CH(3)O)(2)P(O)(13)CH(2)OH for dimer preparation had to be elaborated using aqueous (13)C-formaldehyde. The results from both approaches were compared and found consistent.

On the stereochemistry of C3'-O-P-CH2-O-C4'' phosphonate internucleotide bond, a phosphate isostere.

The work deals with structural evaluation of the internucleotide phosphonate C3'-O-P-CH2-O-C4'' linkage which is an isosteric alternative to natural phosphodiester bond. A thorough description of its stereochemical features was made possible now by matching the results from additional NMR data obtained from the synthesised (13)C-labeled dimeric model compounds and the new findings provided by the extended MDS and ab initio studies. It completed the earlier assumptions. The obtained overall picture in terms of specifying the linkage conformational preferences shows explicitly why the respective phosphonate oligonucleotides differ in properties from those with related phospodiester chain.

Nucleoside phosphonic acids in thymidine phosphorylase inhibition: structure-activity relationship.

A number of structurally diverse nucleoside phosphonic acids have been tested against human recombinant thymidine phosphorylase and human platelets supernatant using 2'-deoxy-5-nitrouridine as the substrate. We have selected several inhibitors working at micromolar level as lead structures for further evaluation.

Novel isosteric, isopolar phosphonate analogs of oligonucleotides: preparation and properties.

A synthetic approach leading to novel-type modified oligothymidylates containing an isosteric, isopolar, enzyme-stable C3'-O-P-CH(2)-O-C4'' phosphonate alternative to phosphodiester internucleotide bond was elaborated. The suitable monomers were prepared from 4'-phosphonomethoxy derivatives of alpha-L-threo and beta-D-erythro-2',5'-dideoxythymidine, which were considered interesting as structurally related to nucleoside 5'-monophosphates. The phosphotriester method was applied to the automated synthesis of both homooligomeric phosphonate 15-mer chains and alternating phosphonate-phosphate constructs. The fully modified homooligomers did not hybridize while homooligomers with alternating sequences containing alpha-L-threo-configured units (but not beta-D-erythro-) showed a significant decrease in T(m) values in comparison with natural dT(15). For a comparative study, phosphodiester 4'-CH(3)-substituted oligothymidylate was synthesized and physical studies (NMR, CD, MDS modeling) were undertaken to shed more light on the changes in conformational behavior arising from the chosen structural alterations.