Lithium bromide–DBU mediated synthesis of chlorophosphoramidate-activated morpholino nucleoside subunits

An efficient and rapid protocol for the synthesis of chlorophosphoramidate-activated morpholino subunits has been developed. A unique combination of lithium bromide–DBU has been found to activate the 7′-hydroxyl toward the reaction. All the four morpholino units of adenosine, guanosine, cytosine, and thymine responded smoothly to the developed protocol.