568
NUCLEOSIDES, NUCLEOTIDES AND NUCLEIC ACIDS
O
base
p
HO
O
DMTr
N
HN
N
N
tetrazole
base
p = protected base
O
O
base
p
OCH 2 CH 2 CN
P
O
DMTr
i Pr 2 N
OCH 2 CH 2 CN
P
i Pr 2 N
N
i Pr 2
2-cyanoethyl N,N,N´,N´-tetraisopropylphosphorodiamidite
In what is essentially a repeat of this reaction, the
5
-hydroxyl of a second nucleoside can couple to this
intermediate; this is the crucial coupling reaction in
the sequence shown below.
O
base p1
O
CPG
HO
O
base p3
O
O
DMTr
P
NCH 2 CH 2 CO
N i Pr 2
N
HN
N
N
tetrazole
I 2 / H 2 O / pyridine
CCl 3 CO 2 H
repeat cycle
5´-hydroxyl (dimethoxytrityl) − CCl 3 CO 2 H
phosphate (cyanoethyl) − aq ammonia
base (benzoyl or isobutyryl) − conc aq ammonia
support (succinate) − aq base
CCl 3 CO 2 H
DMTr = dimethoxytrityl
O
base p1
O
CPG
O
DMTr
base p1 , base p2 , base p3 = protected bases
O
P
O
OH
O
base 3
O
HO
O
base 2
O
P
O
O
OH
O
base 1
HO
O
P
O
OCH 2 CH 2 CN
O
base p3
O
O
O
base p2
O
P
O
O
OCH 2 CH 2 CN
O
base p1
DMTr
O
CPG
HO
O
base p2
O
P
O
O
OCH 2 CH 2 CN
O
base p1
O
CPG
O
O
base p2
O
P
O
O
OCH 2 CH 2 CN
O
base p1
O
CPG
DMTr
O
O
base p2
OCH 2 CH 2 CN
P
O
DMTr
i Pr 2 N
O
O
base p2
O
P
O
OCH 2 CH 2 CN
O
base p1
O
CPG
DMTr
removal of 5´
protecting group
phosphoramidite
coupling reaction
oxidation of
P III to P V
removal of 5´
protecting group
Deprotection: