Structural significance of the alkyl substituent at the C-4 of (+)-trans-verbenyl acetate in sex pheromonal activity of the American cockroach

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Abstract
The significance of the alkyl group at the C-4 of (+)-trans-verbenyl acetate, which is the sex pheromone mimic of the American cockroach, was investigated. Seven alcohols possessing an ethyl, propyl, or dimethyl group at this position of the 6,6-dimethylbicyclo[3.1.1]heptane skeleton were synthesized and evaluated by behavioral assay. All of the alcohols were inactive, while three of four acetates of the 2α-alcohols induced sexual behavior in male cockroaches at the 0.02 or 0.5 mg dosage level, either of which is many orders of magnitude higher than the threshold level of the natural sex pheromones (10−8 mg). Among the acetates, the compounds with a methyl group or an α-oriented ethyl group at C-4 showed the highest activity. The results are discussed in terms of spatial requirements of the molecules for interactions with the receptor.