Synthesis and biochemical evaluation of phosphonoformate oligodeoxyribonucleotides

Phosphonoformate oligodeoxyribonucleotides were prepared via a solid phase synthesis strategy. The first step in the preparation of appropriate synthons was condensation of bis(N,N-diisopropylamino)phosphine and diphenylmethylsilylethyl chloroformate in the presence of sodium metal to yield formic acid, [bis(N,N-diisopropylamino)phosphino]-beta-(diphenylmethylsilylethyl) ester. The product of this reaction was then condensed with appropriately protected 2'-deoxynucleosides using 4,5-dicyanoimidazole to yield the 3'-O-phosphinoamidite reactive monomers. The exocyclic amines of cytosine, adenine, and guanine were protected with 9-fluorenylmethyloxycarbonyl, and oligodeoxyribonucleotides were synthesized on controlled pore glass using the hydroquinone-O,O'-diacetic acid linker. Synthons were sequentially added to this support using tetrazole as an activator, oxidized to phosphonoformate, and the transient 5'-protecting group was removed with acid. Following total synthesis of an oligomer, protecting groups were removed with TEMED.HF and products purified by HPLC. These analogues were resistant to nucleases, formed duplexes with complementary RNA (A-form), and, as chimeric oligomers containing phosphate at selected sites, stimulated RNase H1 activity.