Artificial DNA Directed toward Synthetic Metallofoldamers - Metallofoldamers: Supramolecular Architectures from Helicates to Biomimetics - page 316

Figure 9.9 X-ray crystal structures of the Dipic-Cu(II)-Pyridine base pair in a palindromic
dodecamer sequence: (a) side view (the contacts to the upper base oxygen and lower sugar
oxygen are represented by dashed lines, Reproduced with permission from [37c]. Copyright
2001 American Chemical Society); (b) top view. Reproduced with permission from [37c].
Copyright 2001 American Chemical Society. (c) X-ray structure of a backbone-modified GNA
duplex containing two hydroxypyridone-Cu(II) base pairs. Reproduced with permission from
[38a]. Copyright 2001 American Chemical Society.
to elevate the melting temperature of this short double strand significantly above room
temperature. Therefore, the incorporation of metal base pairs into this duplex can be seen
as an early application of the concept of metal base pairing.
The X-ray structure of a salen-Cu(II)-containing DNA strand in complex with a frag-
ment of DNA polymerase I from Bacillus stearothermophilus was recently reported [39].
The structure shows that the metal base pair fits perfectly inside the B-DNA-like helical
structure. Furthermore, it was shown that the salen metal base pair can be enzymatically
incorporated into oligonucleotides using the triphosphate of a salicylic aldehyde nucleo-
side in the presence of ethylenediamine as a reversible cross-linker.
9.5 Artificial DNA for Synthetic Metallofoldamers
9.5.1 Overview
Since the pioneering work by Shionoya, Tanaka [40] and Schultz [37], a number of fur-
ther metal base pairing systems have been developed, a selection of which are depicted
in Figure 9.10 [20,41]. Simple monodentate nitrogen ligands such as imidazole
(Figure 9.10a) [33,42] and pyridine (Figure 9.10b) [43] were found suitable to coordinate