Non-stepwise methods in the preparation of building blocks for polynucleotide synthesis

Oligonucleotide fragments of the general sequence ABn, BnC and ABnC as building units for polynucleotide synthesis can be obtained by three types of reactions, namely the sequence-specific co-condensation of nucleic acid constituents, the sequence-specific degradation of copolymers and the limited addition of nucleotides to primers. Examples for these reactions are described and the scope and application of the approach discussed.