Preferential extraction of the (+)-TB isomer by
butanol from the water solution containing racemic TB
and DNA unambiguously proves that the (-) isomer selectively
binds to calf-thymus DNA. The 7R,17R configuration was assigned
to the (-)-TB enantiomer based on its circular dichroism
spectrum (exciton mechanism). This configuration is consistent
with enantioselective binding to right-handed B-DNA either
through intercalation or by interaction in the groove.
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DNA-B
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(-)-TB
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This study shows that Tröger's Bases
represent a new class of enantioselective DNA-binders that
can be compared to the extensively studied metallocomplexes.
The (-)-TB enantiomer binds to B-DNA. It would be now
interesting to study the binding of the two isomers with
Z-DNA and other DNA conformations and structures.
The potentiality of the series resides
in the numerous variations that can be introduced. Various
amino substituted aromatic subunits can be envisioned for the
building of the Tröger's Base and different substituents
can be introduced to give to the molecules the solubility,
luminescent, photochemical, or cleavage properties required
for the design of new DNA (or RNA) conformation probes.
