Section 27.16 Laboratory Synthesis of DNA Strands 065are not needed. However, the yields are not as good. The H-phosphonate monomers
are activated by reacting with an acyl chloride, which converts them into phosphoan-
hydrides. The group of the nucleoside attached to the solid support reacts with
the phosphoanhydride, forming a dimer. The DMTr protecting group is removed
with acid under mild conditions, and a second activated monomer is added.
Monomers are added one at a time in this way until the strand is complete. Oxidation
with (or tert-butyl hydroperoxide) converts the H-phosphonate groups to phos-
phate groups. The base-protecting groups are removed by aqueous ammonia as in the
phosphoramidite method.
I 25 ¿-OHOOOO−DMTr O base Pran H-phosphonateactivated monomersolid supportsolid supportH POOOODMTr O
base PrOObase PrH Psolid supportOOOObase PrOObase PrH POOOOODMTr O base Pr
OObase PrH PR CClOCRHOHOsolid supportOOOObase PrOObase PrH POOOObase PrH PHOH+chain extension- activated monomer
- H+
5 ′-OH groupa phosphoanhydride