Antifeedant and Termiticidal Activities of 6-Alkoxycoumarins and Related Analogs Against Coptotermes formosanus Shiraki

Abstract

We synthesized 23 6-alkoxycoumarin derivatives, 20 of which are novel compounds. The structures of all compounds were confirmed by NMR, MS, and elemental analysis, and their antifeedant and termiticidal activities against Coptotermes formosanus Shiraki were examined. In a no-choice test, 6-(2-pentynyloxy)coumarin (2v), 6-(2-butynyloxy)coumarin (2u), 6-(2-octynyloxy)coumarin (2w), and 6-methoxycoumarin (2a), demonstrated high termiticidal activity at a concentration of 10 μmol. At a concentration of 5 μmol, 6-(2-butynyloxy)coumarin (2u) produced the highest mortality among the compounds tested. On the other hand, all of the 6-alkoxycoumarins showed antifeedant activity at both concentrations, except 6-octadecyloxycoumarin (2j) that was inactive at 5 μmol. Among the 23 compounds and the control, 6-ethoxycoumarin (2b), 6-isopropoxycoumarin (2d), and 6-isobutoxycoumarin (2f) exhibited the highest antifeedant activity with no mass loss (0.00%) at a concentration of 10 μmol. Our findings indicate that the presence of alkenyloxy and alkynyloxy groups was important for the termiticidal activity, while the incorporation of alkoxy groups with longer alkyl chains tended to reduce both the termiticidal and antifeedant activities. Furthermore, short chain alkoxy and arylalkoxy-substituted analogs showed good antifeedant activity, but methoxy groups on the benzene ring had a negative effect.