Nucleoside 3 -6>-oxazaphospholidine

Scheme 38 Synthesis of the nucleoside 3 -0-oxazaphospholidine derivatives 132a-f...

Oxazaphospholidines of type 140 have been advocated as alternatives to the more normal phosphoramidite units used in solid-phase synthesis. The unit 141, as an isomeric mixture, has been developed as an all-purpose adaptor for synthesis of oligonucleotides on any of the commercial supports. The unit 141 is attached to the support through 0-5. After removal of the Dmtr group, the first nucleoside is attached via a 2 (3 )-3 link using a phosphoramidite. The desired oligonucleotide is then conventionally assembled, and disconnected by removal of the 0-benzoyl group from the adaptor, which is followed by cyclic phospho-diester formation. ... 

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