PURPOSE: To efficiently obtain the subject compds. for an advantageous synthesis intermediate, etc., for DNA phosphonate useful for study of inter-DNA and DNA-protein interaction by reacting a specific bifunctional phosphonylation reagent with a nucleoside.

CONSTITUTION: The objective compds., which are the advantageous synthesis intermediate for the deoxypolynucleoside (DNA) phosphonate expressed by formula IV, are obtd. by reacting a bifunctional phosphonylation reagent (e.g. methyldichlorophosphane, etc.) of formula I [X is chlorine, Y; Y is a group of formula II (R1, R2 are each a 1-8C alkyl, cycloalkyl, phenyl, R1 and R2 are, together with nitrogen, a heterocycle which may contain heteroatoms in addition thereto); R is a 1-8C alkyl, cycloalkyl, benzyl] with a nucleoside expressed by formula III (T is a protecting group for a primary hydroxyl group; B is a nucleoside base, by which the existing exo-myno group is protected).