Nucleoside phosphinoamidite carboxylates and analogs are provided that have the structure of formula (III) ##STR00001## wherein A is hydrogen, hydroxyl, lower alkoxy, lower alkoxy-substituted lower alkoxy, halogen, SH, NH.sub.2, azide or DL wherein D is O, S or NH and L is a heteroatom-protecting group, unsubstituted hydrocarbyl, substituted hydrocarbyl, heteroatom-containing hydrocarbyl, or substituted heteroatom-containing hydrocarbyl; B is a nucleobase; and one of R.sup.11 and R.sup.12 is a blocking group and the other is (IV) or (VI) ##STR00002## in which W, X, Y, Z, R.sup.1 and n are as defined herein.