Insecticidal, repellent and fungicidal properties of novel trifluoromethylphenyl amides

Abstract

Twenty trifluoromethylphenyl amides were synthesized and evaluated as fungicides and as mosquito toxicants and repellents. Against Aedes aegypti larvae, N-(2,6-dichloro-4-(trifluoromethyl)phenyl)-3,5-dinitrobenzamide (1e) was the most toxic compound (24h LC50 1940nM), while against adults N-(2,6-dichloro-4-(trifluoromethyl)phenyl)-2,2,2-trifluoroacetamide (1c) was most active (24h LD50 19.182nM, 0.5μL/insect). However, the 24h LC50 and LD50 values of fipronil against Ae. aegypti larvae and adults were significantly lower: 13.55nM and 0.787×10-4nM, respectively. Compound 1c was also active against Drosophila melanogaster adults with 24h LC50 values of 5.6 and 4.9μg/cm2 for the Oregon-R and 1675 strains, respectively. Fipronil had LC50 values of 0.004 and 0.017μg/cm2 against the two strains of D. melanogaster, respectively. In repellency bioassays against female Ae. aegypti, 2,2,2-trifluoro-N-(2-(trifluoromethyl)phenyl)acetamide (4c) had the highest repellent potency with a minimum effective dosage (MED) of 0.039μmol/cm2 compared to DEET (MED of 0.091μmol/cm2). Compound N-(2-(trifluoromethyl)phenyl)hexanamide (4a) had an MED of 0.091μmol/cm2 which was comparable to DEET. Compound 4c was the most potent fungicide against Phomopsis obscurans. Several trends were discerned between the structural configuration of these molecules and the effect of structural changes on toxicity and repellency. Para- or meta- trifluoromethylphenyl amides with an aromatic ring attached to the carbonyl carbon showed higher toxicity against Ae. aegypti larvae, than ortho- trifluoromethylphenyl amides. Ortho- trifluoromethylphenyl amides with trifluoromethyl or alkyl group attached to the carbonyl carbon produced higher repellent activity against female Ae. aegypti and Anopheles albimanus than meta- or para- trifluoromethylphenyl amides. The presence of 2,6-dichloro- substitution on the phenyl ring of the amide had an influence on larvicidal and repellent activity of para- trifluoromethylphenyl amides. © 2013 The Authors.