Chemistry Reference
In-Depth Information
number of techniques, including CD spectroscopy,
109,130
1
H NMR spectroscopy
108,130
and molecular modeling.
110
On the basis of the observation that both nucleotides of
each complex were
anti
(Figure 5.12 ),
130
the crosslinks were initially assigned struc-
tures in the HH1 conformer class. Studies of retro models have shown that there
are three other classes, namely, HH2, DHT1, and LHT2 (Figure 5.13). Members of
adjacent classes are separated by ca. 180 ° rotation of one G about its Pt-N7 bond.
Variants in nonHH1 conformer classes have been found for bip-Pt(d(GpG))
and bip - Pt(GpG) adducts.
101,103,106
Moreover, the bases can have right-handed (R)
or left-handed (L) canting (handedness of canting is defi ned by the following
two straight lines: one connecting the platinum-coordinated N7 atoms of the two
guanines and the second connecting the N1 and C8 atoms of a given guanine).
The base canting is determined by the chirality of the amine: (
S,R,R,S
) - bip induces
left-handed canting (L, upper row of Figure 5.7) while (
R,S,S,R
) - bip induces
right-handed canting (R, lower row of Figure 7) of the guanine bases. (
S,R,R,S
) - bip -
O
N7
H
N
H8
H5'
OH
H5''
N
NH
2
O
N
H3'
H2'
H4'
H1'
O
O
H2''
O
(a)
N7
H
P
N
O
H8
O
H5'
N
NH
2
O
N
H5''
H3'
H2'
H4'
H1'
HO
H2''
H
H
2
N
N
O
O
H
N
N
OH
N
OH
H
H
H
N
N
NH
2
O
N
N
O
H
H
H
H
H
H
H
H
HO
H
H
H
HO
H
H
(b)
(c)
Figure 5.12
Structure of d(GpG) (a) and schematic
anti
(b) and
syn
(c) guanine glycosidic
torsion angle alignments. The H8 and sugar H1
protons are closer to each other (2.5 Å) in
the syn alignment compared to a longer distance (3.7 Å) in the
anti
alignment, a feature that
can be readily monitored by NMR
′
