Pheromone synthesis. Part 247: New synthesis of the enantiomers of 13-methylheptacosane, the female sex pheromone of pear psylla, Cacopsylla pyricola☆
Introduction
Pear psylla, Cacopsylla pyricola (Förster) (Hemiptera: Psyllidae), is a major pest of commercial pears in North America and Europe. In 2009 Guédot et al. identified 13-methylheptacosane 1 (Scheme 1) as its female-produced sex pheromone, which might be useful as a monitoring tool for C. pyricola.2 They also showed that synthetic (±)-1 attracted male pear psylla both in the laboratory and the field. The absolute configuration of the naturally occurring 1, however, remains unknown. It is of interest to know whether the slight dissymmetry due to the small two-carbon-difference in the length of two alkyl groups attached to the C-13 atom can be recognized by pear psylla.
Previously, in 2001, we synthesized both (R)- and (S)-1 as the reference samples to identify a methyl-branched cuticular hydrocarbon of the ant, Diacamma sp.3 The synthesis provided 97 mg of (R)-1 and 50 mg of (S)-1, which might be insufficient for thorough biological studies of 1 as the pheromone of C. pyricola. A new synthesis of (R)- and (S)-1 was, therefore, planned in order to provide them in gram quantities. Herein we report the synthesis of the enantiomers of 1 in 23–28% overall yield (eight steps) from the enantiomers of citronellal 2, which are widely employed in natural products synthesis.4
Section snippets
Synthesis of (R)- and (S)-13-methylheptacosane
Scheme 1 summarizes the synthesis of (R)- and (S)-1. The same strategy was employed twice to extend the carbon chain of the intermediates. The strategy consisted of the Grignard reaction (2 plus decylmagnesium bromide and 7 plus undecylmagnesium bromide) followed by mesylation of the resulting alcohols 3 and 8, and subsequent reductive removal of the mesyloxy group of the mesylates 4 and 9 to give 5 and 1, respectively. Similar strategies were also employed in the cases of the synthesis of the
Conclusion
Both the crystalline enantiomers of 13-methylheptacosane 1 were synthesized in gram quantities to enable their detailed biological studies in the future. The enantiomers of citronellal (2) were again shown to be versatile starting materials in pheromone synthesis.
General
Refractive indices (nD) were measured with an Atago DMT-1 refractometer, and IR spectra with a Jasco FT/IR-410 spectrometer. 1H NMR spectra (400 MHz, TMS at δ = 0.00 as an internal standard) and 13C NMR spectra (100 MHz, CDCl3 at δ = 77.0 as an internal standard) were recorded by a Jeol JNM-AL 400 spectrometer. GC–MS data were measured with an Agilent Technologies 5975 inert XL instrument. HRMS data were recorded by a Jeol JMS-SX 102A instrument. Column chromatography was carried out on Merck
Acknowledgments
My thanks are due to Mr. M. Kimura (President, Toyo Gosei Co., Ltd.) for his support. I thank Mr Y. Shikichi (Toyo Gosei Co., Ltd.) for NMR and GC–MS measurements. I am grateful to the following people for their help: Drs. T. Nakamura and Y. Hongo (RIKEN) for HRMS analyses; Dr. T. Tashiro (RIKEN) for preparing both Figure 1 and Scheme 1; Dr. M. Fujiwhara (Takasago International Corporation) for the generous gift of (R)- and (S)-citronellal.
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Pheromone synthesis. Part 256: Synthesis of the four stereoisomers of 5,11-dimethylpentacosane, a new sex pheromone component of the male Galleria mellonella (L.), with high stereochemical purities as determined by the derivatization-HPLC analysis of the eight stereoisomers of 5,11-dimethyl-8-pentacosanol
2015, TetrahedronCitation Excerpt :When fresh LiAlH4 was employed for the reduction, no formation of alkenes was observed, and pure 1 could be secured. In a previous work, a small amount (1.4%) of alkenes was generated in the course of the reduction of 12-methanesulfonyloxy-15-methylheptacosane, when it was reduced with aged LiAlH4.26 It might have been due to the presence of a small amount of LiOH and Al(OH)3 on the surface of aged LiAlH4.
Efficient asymmetric synthesis of long chain methyl-branched hydrocarbons, components of the contact sex pheromone of females of the cerambycid beetle, Neoclytus acuminatus acuminatus
2013, Tetrahedron AsymmetryCitation Excerpt :As a result, few studies have been performed to determine the effect of the stereochemistry on the bioactivity of these compounds,10 despite the fact that for many other types of insect pheromones, bioactivity is often directly correlated with chirality, with one enantiomer being active and the other being benign or frequently antagonistic.11 Previous syntheses of monomethyl-branched hydrocarbons have been primarily based on the use of commercially available chiral synthons such as propylene oxide,6 methyl 3-hydroxy-2-methylpropanoate,8 citronellol or citronellal,11,12 2-methylbutanol,13 aromadendrene,14 or pulegone.15 These starting materials are commercially available but are often relatively expensive, the overall yields have generally been low, and in at least some cases, the syntheses are lengthy.
Research Progress on the Syntheses of Chiral Methyl-Branched Aliphatic Hydrocarbons Insect Pheromones
2021, Chinese Journal of Organic ChemistryIsolation and determination of absolute configurations of insect-produced methyl-branched hydrocarbons
2015, Proceedings of the National Academy of Sciences of the United States of AmericaDeciphering the signature of cuticular lipids with contact sex pheromone function in a parasitic wasp
2012, Journal of Experimental Biology