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(10E,12Z)-hexadeca-10,12-dien-1-ol Bombykol (10E,12Z)-hexadeca- The sex pheromone 10,12-dien-1-ol (10E,12Z)-hexadeca- 10,12-dien-1-ol765-17-3
Well, it was the first insect pheromone to be identified nearly50 years ago, in 1959, by Adolf Friedrich Johann Butenandt (1903-1995), photo,.He won a Nobel Prize for Chemistry in 1939 at the age of 36, for his work on sex hormones; after that, he turned hisattention to insect attractants, successively at theKaiser-Wilhelm Institute of Biochemistry atBerlin-Dahlem;the University of Tübingen(1945-56), and the University ofMunich (1956-71).
The saturated acid first undergoes oxidationcatalysed by a Z11 desaturase enzyme, togenerate the first double bond.The second step is more unusual, involving1,4-elimination of two hydrogens to afford aconjugated diene, catalysed by a 10,12-desaturase enzyme.Finally a reductase enzyme converts thecarboxylic acid group into a primary alcohol(fatty acyl reduction).
Bombykol, 10(E),12(Z)-hexadienol, has been identified as a sex pheromone of the silkworm Bombyx mori and can be used in pest control. It has been synthesized on a gram scale according to the route indicated in Fig. 1. Starting from vernolic acid (1), first the epoxy group was ring- opened, resulting in a diol product (2). This diol could be selectively cleaved to the aldehyde (3) without affecting the carbon-carbon double bond and leaving hexenal (4) as a side-product, that in itself may find useful applications in the flavor industry. Protecting the carboxylic acid group and isomerization of the double bond yielded a reactive intermediary product [12-oxo-10(E)-dodecenoic acid (5)] which contained a carboxylic ester and also an aldehyde functionality in conjugation with the carbon-carbon double bond. Subsequent Wittig olefination of (5) leads to the 10(E), 12(Z)-product (6), which is selectively reduced to bombykol (7).
He did this by bioassays. Unlike the wild silk moth (Bombyxmandarina), the domesticated silk moth cannot fly, but responds tothe females pheromone by getting excited and flapping his wingsin what is known as a "flutter dance".The scientists tested each fraction by diluting it and finding out theminimum concentration needed to make 50% of the males in asample respond.The purer the material, the less needed to produce the flutterdance. Eventually material was obtained that contained just onecomponent, and was pure bombykol.The team were lucky in that the pheromone only comprised onesubstance; multi-component pheromones are common (althoughthe female Bombyx mori emits a mixture comprising bombykolwith a small amount of the corresponding aldehyde, bombykal, themale receptor only bonds bombykol).
Male silk moth, right, gets excited bythe female. The female is bigger,because of the eggs she is carrying.She is extending her pheromone glandand releasing bombykol.Reproduced with the permission ofProfessor Walter S. Leal.
Overall structure of the B. mori PBP.Disulfide bridges are shown in yellow,and the loop covering the bindingpocket (see text) is in orange.Bombykol is shown in a ball-and-stickrepresentation with double bonds ingreen.Reproduced with permission ofProfessors Jon Clardy and Walter S.Leal from:B.H.Sandler, L.Nikonova, W.S.Leal andJ.Clardy, Chem. Biol., 7, (2000) 143.
Bombykol is at the centre of the figurein ball-and-stick representation. Thehydroxyl group is red,and the double bonds are green.Residues surrounding bombykol areshown in stick representation.The hydroxyl group of bombykol formsa hydrogen bond with the sidechain ofSer56 with an O-O distance of 2.8 Å.Reproduced with permission ofProfessors Jon Clardy and Walter S.Leal from:B.H.Sandler, L.Nikonova, W.S.Leal andJ.Clardy, Chem. Biol., 7 (2000) 143.
1.Bombykol, the sex pheromone of the silkworm moth,has been prepared in the following way:1-pentyne + n-C4H9MgBr CH3CH2CH2C CMgBrA + HCHO; then H+ CH3CH2CH2C CCH2OHB + PBr3 CH3CH2CH2C CCH2BrC + Ph3P, base CH3CH2CH2C CCH=PPh3D + OHCCH2(CH2)7CO2C2H5 CH3CH2CH2C CCH=CHCH2(CH2)7CO2C2H5E + H2/Pd CH3CH2CH2CH=CHCH=CHCH2(CH2)7CO2C2H5 (cis)F + LiAlH4 CH3CH2CH2CH=CHCH=CHCH2(CH2)7CH2OH (cis)
Extraction and purificationIt was the German chemist AdolfButenandt whoworked out what was really going on.He started by taking the pheromoneglands from the female silk mothand extracting the chemicals theyproduced.Since bombykol is only ever producedin tiny quantities bythe moths, he needed lots of glands toget even thetiniest amounts of material to work with
Spectroscopy and identificationAfter many cycles of purification,Butenandt started towork out the chemical structure of themolecule. Heused infrared spectroscopy to revealthat there is analcohol group and two carbon-carbondouble bondspresent. He used a variety of chemicaldegradationmethods to work out the length of thecarbon chain andthe position of the double bonds.Butenandt managed to confirm thestructure bysynthesising bombykol from scratch.He prepared allfour of the possible geometric isomersof the doublebonds, and found that one of themwas at least a billiontimes more effective at exciting themale moths!
Bibliography Dictionary of Organic Compounds, J. Buckingham and F. McDonald, eds., Chapman and Hall, London, 6th edition, 1995, Compound H-0-00578 http://en.wikipedia.org/wiki/Bombykol J.H. Fabre, The Life of the Caterpillar, trans. A. Texeira de Matos, Hodder and Stoughton, London, 1912, p.246 ff;http://www.ibiblio.org/eldritch/jhf/c11.html W. C. Agosta, Chemical Communication. The Language of Pheromones, Scientific American Library, 1992, esp. pp 63 ff. D. Schneider, Science, 1969, 163, 1031. (insect olfaction: deciphering system for chemical messages) P. Witzgall and A. El-Sayed (eds), Insect Semiochemicals - IOBC wprs Bulletin 22(9), 2000 (Proceedings of IOBC wprs Symposium, Dachau 1998) http://www.phero.net/iobc/dachau/bulletin99/schneider.pdf (Schneiders research on detecting pheromones) A. Butenandt, R. Beckmann, D. Stamm and E. Hecker, Z. Naturforsch, Teil B, 1959, 14, 283 (characterisation of bombykol) T. Ando, T. Hase, A. Funayoshi. R. Arima and M. Uchiyama, Agric. Biol. Chem., 1988, 52, 141 (biosynthesis of bombykol) B.H. Sandler, L. Nikonova, W.S. Leal and J. Clardy, Chem. Biol., 2000, 7, 143 (structure of the bombykol-PBP complex) V. Klusák, Z. Havlas, L. Rulíšek, J. Vondrášek and A. Svatoš, Chem. Biol., 2003, 10, 331 (ab initio study of the bombykol-PBP complex) W.S. Leal, A.M. Chen, Y. Ichida, V.P. Chiang, M.L. Erikson, T.I. Morgan and J.M. Tsuruda, Proc. Nat. Acad. Sci. USA, 2005, 102, 5386 (pheromone binding) R. Rybczynski, R.G. Vogt and M.R. Lerner, J. Biol. Chem., 1990, 265, 19712 (deactivating pheromones) Y. Ichida and W.S. Leal, Proc. Nat. Acad. Sci. USA, 2005, 102, 14075 (deactivating pheromones) F. Gräter, B.L. de Groot, H. Jiang and H. Grubmüller, Structure, 2006, 14, 1567 (pheromone release from the bombykol-pheromone binding protein complex) C. Lautenschlager, W.S. Leal and J. Clardy, Structure, 2007, 15, 1148. (flexibility of the PBP binding site)
Silkmoth Sex PheromonesWe have identified a fatty acid desaturase gene (bmpgdesat1) and apheromone gland-specific fatty-acyl reductase gene (pgFAR) involved inspecies-specific sex pheromone biosynthesis in the Bombyxmori silkmoth. A transformed yeast,Saccharomycescerevisiae, expressed the B. mori pgFAR evoked typical mating behaviorin male moths when cultured with the pheromone precursor. We hope toestablish a novel method for pest control using similar insect genes. Forexample, if we plant transgenic weeds that express these insect genesaround grains, the species-specific sex pheromone released from theweeds may interrupt the chemical communication among the harmfultarget insects, and thus may decrease our dependency on agriculturalchemicals in the future. t
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