The potential of anti-sense oligonucleotides to modify viral activity has recently become apparent in a variety of areas of research. Now researchers are beginning to create oligonucleotides with internucleotide phosphate modifications designed to impart specific properties to synthetic DNA: phosphorothioate linkages (2) have similar properties to natural phosphodiesters (1) but offer the advantage of being resistant to cleavage by nucleases; alkyl phosphotriesters (3) and phosphoramidates (4) increase lipophilicity of synthetic DNA, thereby allowing sequences to pass through cell membranes more readily, while also being nuclease resistant.
Future research may focus on the attachment of marker molecules to the phosphate backbone with applications in sdiagnostic probes or DNA sequencing. These techniques would similarly allow the attachment of amino acids, peptides, poly-saccharides, or aromatic intercalating molecules.
It should be noted that the replacement of a pro-chiral oxygen from a natural phosphodiester linkage produces a chiral center at phosphorus. With every phosphate modification a pair of diastereoisomers is therefore formed. If a sequence is modified n times, there will be produced 2n diastereomers, all of which, in principle, may exhibit differing biological activity.
Modified anti-sense oligonucleotides show potential for the development of novel diagnostic tests and therapeutic agents against viral diseases. A method for point modification of DNA is presented overleaf.
