| Summary: | Two furoquinoline alkaloids, skimmianine and dictamnine, were purified from the
dried leaves of Skimmia japonica (Rutaceae) and dried root of Dictamnus albus
(Rutaceae), respectively. The furoquinolines were isolated through acid fractionation
and silica gel column chromatography, and their identity was confirmed through HPLC
and mass spectroscopic analysis.
Skimmianine and dictamnine, as well as the furanocoumarins 8-methoxypsoralen
(8-MOP) and 5-methoxypsoralen (5-MOP) were quantified in leaf tissue of S. japonica
and Ruta graveolens (Rutaceae). Of these compounds, S. japonica contained
skimmianine and 5-MOP, and quantities differed depending on the sex of the plant from
which the leaves were taken. The compounds were not present on the surface of the
leaves. R. graveolens was found to contain skimmianine, 5-MOP and 8-MOP, both on
the surface and interior of the leaves. Neither plant contained detectable levels of
dictamnine.
Growth assays using Spodoptera litura (Lepidoptera: Noctuidae) and
Trichoplusia ni (Lepidoptera: Noctuidae) demonstrated that both furoquinolines are
potent antifeedants at concentrations below those found naturally. Skimmianine is twice
as deterrent to S. litura as dictamnine on a weight to weight basis. 8-MOP was also
deterrent to S. litura, but not as potent as either furoquinoline. Skimmianine was
deterrent to T. ni, but 8-MOP had no effect on its growth. Simulated daylight conditions,
with appropriate UV wavelengths, were found to have no effect on the antifeedant
properties of either furoquinoline or 8-MOP in the S. litura trials. In addition, none of the
compounds were physiologically toxic to larvae.
It was found that a non-ratio-based method was more accurate than a ratiobased
method for the analysis and interpretation of experimental data.
In conclusion, the furoquinolines skimmianine and dictamnine, and the
furanocoumarin 8-MOP, are deterrent to S. litura larvae. Skimmianine is deterrent to T.
ni. The intensity of experimental light conditions may be essential for inducing toxicity in
potentially phototoxic compounds. === Science, Faculty of === Botany, Department of === Graduate
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