A compound having the formula: ##STR1## wherein, R1 represents 2'-O-R.sub.3 -thio-R.sub.3 and/or 2'-C-R.sub.3 -thio-R.sub.3, wherein R.sub.3 is a compound independently selected from a group consisting of alkyl, alkenyl, alkynyl, aryl, alkylaryl, carbocyclic aryl, heterocyclic aryl, amide and ester, X represents a base or H; Y represents a phosphorus-containing group; and R2 represents H, DMT or a phosphorus-containing group.

Um composto que tem a fórmula: ## do ## STR1 wherein, R1 representa 2'-O-R.sub.3 - thio-R.sub.3 e/ou 2'-C-R.sub.3 - thio-R.sub.3, wherein R.sub.3 é um composto selecionado independentemente de consistir do grupo alkyl, alkenyl, do alkynyl, do arilo, do alkylaryl, do arilo carbocyclic, do arilo heterocyclic, do amido e do ester, X representa uma base ou um H; Y representa um grupo phosphorus-containing; e R2 representa H, DMT ou um grupo phosphorus-containing.