Germacrone Derivatives as new Insecticidal and Acaricidal Compounds: A Structure-Activity Relationship.

Alberto Galisteo Pretel,Helena Pérez Del Pulgar,José Luis López-Pérez,Estela Guerrero De León,Azucena Gonzalez-Coloma,Alejandro F Barrero,José Francisco Quílez Del Moral,A Sonia Olmeda

doi:10.3390/molecules24162898

Abstract

Currently, the use of synthetic pesticides is the main method of plant protection applied in agri- and horticulture. However, its excessive use leads to the development of pesticide resistance, a contamination of the environment, toxicity to non-target organisms, and risks for human health. With the ultimate aim of contributing to the develop of a more sustainable pest management, we used the natural product germacrone (compound 1), reported to possess significant insecticidal activity, as starting material for the generation of molecular diversity (2–24). Some of the generated derivatives are natural compounds, such as 1,10-epoxygermacrone (2), 4,5-epoxygermacrone (3), gajutsulactone A (7), germacrol (11), isogermacrone (14), 9-hydroxyeudesma-3,7(11)dien-6-one (19), eudesma-4,7(11),dien-8-one (20), eudesma-3,7(11)-dien-8-one (21) and eudesma-4(15),7(11)-dien-8-one (22). Compounds, 7,11-9,10-diepoxigermacr-4,5-en-8-ol (17), 7,11-epoxieudesma-4,7(11)-dien-8-one (23) and 7,11-epoxieudesma-3,7(11)-dien-8-one (24) are described for the first time. The biocidal activity of most of these compounds was assayed against the tick Hyalomma lusitanicum. The acaricidal effects of compound 24 were four times higher than that of germacrone (1). Compound 2 is an insect antifeedant a thousand times more potent than germacrone against Rhopalosiphum padi, which makes this substance a promising selective antifeedant against this cereal pest.

Highlights

Germacrone (1) is a sesquiterpene isolated in significant amounts from the essential oil of Geranium macrorhyzum (Hungary chemotype) [1]
The synthesis of compounds 2–10 are summarized in Scheme 1
Epoxides 2 and 3 are natural products obtained from the rhizomes of several Curcuma species [9,10,11]

Summary

Introduction

Germacrone (1) is a sesquiterpene isolated in significant amounts from the essential oil of Geranium macrorhyzum (Hungary chemotype) [1]. This essential oil shows antifeedant effects against aphids and ixodicidal activity against the tick Hyalomma lusitanicum along with antifeedant effects against the insect pests Spodoptera littoralis Boisd, Myzus persicae Sulz, and Rhopalosiphum padi, with compound 1 being, to a large extent, responsible for these activities [1]. Benelli et al report both the insecticidal activity of germacrone (1) against mosquito larvae (Culex quinquefasciatus) [2], and its acaricidal effects against Tetranychus urticae [3]. Regarding the contact toxicity of germacrone against Tribolium castaneum, García et al report that germacrone results in not being toxic [4], whereas Liang et al confirm its contact toxicity [5].

Methods

Results

Conclusion