Résumé
In an effort to develop alternative methods that can be scaled-up for the synthesis of oligonucleotides, we have designed solution-phase phosphoramidite and H-phosphonate approaches using solid-supported reagents. Polyvinylpyridinium tosylate and polystyrene chlorocarbonyl were used as activators for internucleosidic bond formation by the phosphoramidite and the H-phosphonate methods, respectively. The resulting phosphate triesters or H-phosphonate diesters were either oxidized or sulfurized using polystyrene-bound trimethylammonium periodate and tetrathionate, respectively. The work-ups of the reactions are simplified as they avoid tedious and expensive chromatography purification steps. They involve filtration of the excess of solid-supported reagents, aqueous extraction and precipitation. Polymer-bound reagents resulting from ionic bridge interaction with the polymers are easily regenerated. As regards the supported acyl chloride resin could be recycled several times without loss of efficacy. Analysis of the reaction mixtures with conventional analytical techniques such as TLC, HPLC, NMR and mass spectrometry is another advantage over a solid-phase synthesis process. Short oligonucleotides (from dimers to hexamers) were prepared with good yields and high purities. The syntheses were scaled up to 10 mmol for dimers and 1 mmol for hexamers.