Identification of the Double Bond Position in Insect Sex Pheromones by Mass Spectrometry; Trial Comparison of Methyl Undecenoates with the Natural Pheromone of the Varied Carpet Beetle

Abstract

Since all positional isomers of methyl undecenoates were available and also an undecenoate sex pheromone of the varied carpet beetle, identification of the double bond position of the pheromone was attempted by comparing the mass spectra of the isomers with that of the pheromone,~sing a newly devised' fitness index. The index (%) was calculated by dividing the absolute difference between the intensity ratio of every fragment ion-pair of an isomer and the corresponding ratio of the pheromone by the latter for each isomer. All the index values were summed up for each isomer and averaged to determine the similarity to the pheromone. The smallest average among the isomers indicates the best fit to the pheromone. The results of a comparison based on all commonly observable ions (a total of 63 ions above m/z 41, with intensities more than 0.1%) and 17 selected ion groups (above m/z 55 or m/z 59 with intensities of more than 0.1 %, 1%, 3%, 5%, 10% or 20%, respectively, and above m/z 41 with intensities more than 1%,3%,5%, 10% or 20%, respectively) indicated that methyl 5-undecenoate was the most probable candidate for the pheromone, except two ion groups (above m/z 41 with intensities of more than 10% and 20%, respectively). Furthermore, statistically significant results were obtained for all groups above m/z 41 with intensities up to 5% and groups above m/z 55 and 59 with intensities more than 10%. Therefore the present study verified the feasibility of using mass' spectrometry for the identification of the double bond position of a pheromone.

Mass Spectra of Lepidopterous Sex Pheromones with a Conjugated Diene System

“…13 ) The former ion would be mostly produced by cleavage of the C 6 _C 7 bond, and the latter ion by cleavage of the C 7 _C 8 bond after hydrogen rearrangement (see the fragmentation pathways A and B in Fig. I, RI for CH 3 and R2 for (CH 2 )sOH). Both ions could be stabilized by the n-electrons of the C = C double bond(s) and appeared as significantly abundant peaks.…”

Lepidopteran Sex Pheromones

“…In this case, it is necessary to have a large number of females for the analysis. Since the molecular ions (M + ) of C 10 -C 18 monoenyl compounds in Type I are hardly detected by EI, their occurrence in the extract is examined by systematic analysis of the GC-MS data using mass chromatograms for the fragment ions at the highest m/z values; i.e., The positional isomers of monoenyl compounds show similar EI-mass spectra, but the spectra can differentiate the relative intensities of some fragment ions [160].While these subtle differences are not rationally explained, it is possible to estimate the double-bond position of a natural pheromone by calculating the similarity of the spectra published for a series of synthetic monoenyl compounds [146,161]. Recently, direct determination by the spectra has been attempted operating chemical ionizationion-trap mass spectrometry [162].…”