Section 27.16 Laboratory Synthesis of DNA Strands 065
are 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 2
5 ¿-OH
O
O
O
O−
DMTr O base Pr
an H-phosphonate
activated monomer
solid support
solid support
H P
O
O
O
O
DMTr O
base Pr
O
O
base Pr
H P
solid support
O
O
O
O
base Pr
O
O
base Pr
H P
O
O
O
O
O
DMTr O base Pr
O
O
base Pr
H P
R CCl
O
CR
HO
HO
solid support
O
O
O
O
base Pr
O
O
base Pr
H P
O
O
O
O
base Pr
H P
HO
H+
chain extension
- activated monomer
- H+
5 ′-OH group
a phosphoanhydride