A 2-N-amidoethyl protected nucleoside analog phosphoramidite of formula (1): ##STR1## is useful in the synthesis of a wide variety of oligonucleotide analogs. Coupling yields with phosphoramidite (1) in solution or solid phase oligonucleotide analog synthesis are high and the 2-N-amidoethyl protecting group can be removed easily under standard conditions.