By the condensation of 2-amino-6-chloropurine (I) (which has been silylated with 1,1,1,3,3,3-hexamethyldisilazane) with (1,3-dibenzyloxy-2-propoxy)methyl chloride (II) by means of mercuric cyanide in benzene at reflux. BIOLF-7O is purified by chromatography over silica gel.