Nucleoside phosphoramidites containing cleavable linkers

Phosphoramidite reagents (linker phosphoramidites) containing a cleavable 3'-ester linkage between the nucleoside and the phosphoramidite group can be used to attach the first nucleoside to a solid-phase support. Inexpensive underivatized supports such as LCAA-CPG can then be used as universal supports for oligonucleotide synthesis. No modifications to synthesis coupling conditions and no 3'-dephosphorylation are required. Only oligonucleotides with terminal 3'-OH ends are produced. Phosphoramidites containing both a succinate and a sulfonyldiethanol linkage are particularly useful and create oligonucleotides with both a 3'-OH and 5'-phosphate. In addition, by using these reagents, one oligonucleotide sequence can be added onto the 5'-end of another (tandem synthesis) to produce a string of multiple oligonucleotides linked end-to-end. Deprotection releases the oligonucleotides from each other to yield a mixture of oligonucleotides. This approach is particularly useful for making pairs of PCR primers or both strands of a double-stranded sequence in a single operation.