The easy accessible building units 3,4,6-tetra-O-benzoyl-alpha-D-manno
pyranosyl)penyl 2-cyanoethyl N,N-diisopropylphosphoramidite (9) and 2,
2-bis(4,4'-dimethoxytrityloxymethyl)propyl 2-cyanoethyl N,N-diisopropy
lphosphoramidite (12) were used for the sequential elongation of immob
ilized tetrametric thymidylic acid according to a DNA synthesis protoc
ol. Ammonolysis of the individual immobilized adducts led to the isola
tion of the target compounds 1 and 2.