Process for oligonucleo tide synthesis using phosphormidite intermediates

Claim 1

In a process for producing oligonucleotides which comprises the step of condensing the 3'-OH or 5'-OH group of a nucleoside or oligonucleotide with a nucleoside phosphite, the improvement being that the nucleoside phosphite is a compound of one of the formulae: ##STR24## wherein B is a nucleoside or deoxynucleoside base; A is H OH or OR 4 in which R 4 is a blocking group; R is a blocking group; R 1 ' is a hydrocarbyl radical containing up to about carbon atoms; and X is NR 2 'R 3 ', wherein R 2 ' and R 3 ' taken separately each represent alkyl, aryl, aralkyl, cycloalkyl and cycloalkylalkyl containing up to 10 carbon atoms; R 2 ' and R 3 ' when taken together form an alkylene chain containing up to 5 carbon atoms in the principal chain and a total of up to 10 carbon atoms with both terminal valence bonds of said chain being attached to the nitrogen atom to which R 2 ' and R 3 ' are attached; and R 2 ' and R 3 ' when taken together with the nitrogen atom to which they are attached form a saturated nitrogen heterocycle including at least one additional heteroatom from the group consisting of nitrogen, oxygen and sulfur.