2,5-DialkyItetrahydrofurans, Common Components of the Cuticular Lipids of Lepidoptera Stefan Schulz2, George Beccalonib, Ritsuo Nishidac, Yves Roisind, R. I. Vane-Wrightb, Jeremy N. McNeil6 a Institut für Organische Chemie, Universität Hamburg, Martin-Luther-King-Platz 6, D-20146 Hamburg, Germany b Department of Entomology British Museum (Natural History), Cromwell Road, London SW7 5BD, United Kingdom c Pesticide Research Institute, Kyoto University, Kyoto, 606-01, Japan d Faculte des Sciences C. P. 160, Universite Libre de Bruxelles, Avenue F. D. Roosevelt 50, B-1050 Bruxelles, Belgium e Departement de biologie, Universite Laval, Quebec, P. Q., G1K 7P4, Canada Z. Naturforsch. 53c, 107-116 (1998); received October 22/November 17, 1997 Lipids, Tetrahydrofurans, Cyclic Ethers, Lepidoptera, Cuticula In more than 50 lepidopteran species 2,5-dialkyltetrahydrofurans were identified as com­ ponents of the cuticular lipids. The chain length of these compounds varies between C25 and C37 and both cis- and rram-compounds are present. In addition, previously unknown 2-alkyl- 5-(l-hydroxyalkyl)tetrahydrofurans were found in some species. The identification procedure and synthesis of representative compounds are reported. Introduction Lepidoptera and discuss their identification and the synthesis of new derivatives. The cuticle of insects is covered with a lipid layer the primary function of which is to prevent Material and Methods desiccation. Cuticular lipids can consist of hy­ drocarbons (the major group of compounds in Samples, analysis and sample preparation most species), alcohols, aldehydes, ketones, wax We studied the cuticular lipids of adult male esters, and fatty acids. In addition, dialkyl ethers, butterflies of over 50 species, collected from dif­ glyceride ethers or triglycerides have been found ferent sources worldwide (Table I). For compari­ (Nelson and Blomquist, 1995). son we also examined males from a limited Recently it has been shown that the parasitoid number of moth species (Table II). Finally, as Apanteles kariyai locates its host, the common ar- tetrahydrofurans (THFs) present in cuticle of myworm Pseudaletia separata, by detection of 2,5- young Pseudaletia separata larvae serve as a kairo- dialkyltetrahydrofurans present on the surface of mone for parasitic Hymenoptera (Takabayashi the larvae (Takabayashi and Takahashi, 1986a, b). and Takahashi, 1986a, b), we compared the cuticu­ During our studies on pheromones of danaine but­ lar profiles of early and late instar larvae, as well terflies we identified similar compounds associ­ as adult males of the true armyworm,P. unipuncta. ated with the male hairpencils (Schulzet al., 1993; Whole insects or body parts (see Tables I and II) Schulz and Nishida, 1996). In this study we show were extracted with pentane or dichloromethane that 2,5-dialkyltetrahydrofurans occur as constitu­ and stored at -4 0 °C until analysed by gas chro­ ents of cuticular lipids of various genera of adult matography - mass spectrometry (G C -M S). Mass spectra (70 eV) were obtained with a VG 70/250 S mass spectrometer coupled to a Hewlett- Packard HP 5890 A gas chromatograph and a Fi- Reprint requests to S. Schulz. sons MD-800 mass spectrometer coupled to a Fi- Institut für Organische Chemie, Technische Universität sons GC 8000. Gas chromatographic analyses Braunschweig, Hagenring 30, 38106 Braunschweig, Germany. were carried out with a Carlo-Erba Fractovap Fax: +495313915272. 2 1 0 1 gas chromatograph equipped with a flame 0939-5075/98/0100-0107 $ 06.00 © 1998 Verlag der Zeitschrift für Naturforschung. All rights reserved. N Bereitgestellt von | Technische Universität Braunschweig Angemeldet Heruntergeladen am | 20.03.19 13:28 108 St. Schulz et al. ■ 2,5-Dialkyltetrahydrofurans, Cuticular Lipids of Lepidoptera ionization detector and on-column or split/splitless- separate the enantiomers on different chiral cyclo- injection. Separations were performed on capillary dextrine phases were unsuccessful. The synthetic columns with apolar phases like Rtx-5, DB-5, CP- compounds exhibited identical mass spectra and Sil-8 , or BPX-5. The last mentioned phase was retention times to the natural compounds. used for the determination of retention indices. ]H NMR and 13C NMR spectra were obtained with 2-Heptyl-5-octadecylfuran Bruker WM 400 or AC250P instruments. Silyl- ations were performed by adding 50 jil MSTFA 2-Heptylfuran was prepared according to the (A^-methyl-A^^trimethylsilyO-trifluoroacetamide) method of Brandsma and Verkruijsse (1986), by to 50 ^1 of a lipidic extract. After 30 minutes at alkylation of furan with heptyl bromide. A second 60 °C, the silylated samples were concentrated un­ alkylation with octadedyl bromide yielded 2 -hep- der a stream of nitrogen and then analyzed. tyl-5-octadecylfuran. JH NMR (250 MHz, CDC13): 6 = 0.95 (t, 6 H, Synthesis o f representative compounds CH3), 1.24-1.40 (m, 38H, CH2), 1.63 (quin, 4H, H-2'), 2.60 (t, 4H, H-l\ J = 7.8 Hz), 5.92 (s, 2H, For confirmation of our identifications, several H-3, H-4). THFs were synthesized (see Fig. 1). Furan was EI-MS (70 eV): m/z (% ) = 43 (72), 57 (39), 81 consecutively alkylated twice according to the (24), 95 (85), 107 (32), 127 ( 8 ), 179 (100), 193 (22), method of Brandsma and Verkruijsse (1986). The 291 (3), 323 (35), 337 (12), 418 (83, M+). 2,5-dialkylfuran obtained was then hydrogenated over palladium/charcoal, to yield a 99:1 mixture 2-Heptyl-5-octadecyltetrahydrofuran of cis- and rrfl«5'-2 ,5 -dialkyltetrahydrofurans. The alcohol 2-heptyl-5-(l-hydroxyoctadecyl)-tetrahy- A solution of 2-heptyl-5-octadecylfuran (50 mg) drofuran (C7/1HOC18-THF) was synthesized in 5 ml hexane was hydrogenated at 0.5 bar with starting from 2-heptylfuran. After lithiation of the 10% Pd/C as catalyst. After filtration, a 99:1 cis/ furan, octadecanal was added. The resulting 2- trans mixture of pure 2-heptyl-5-octadecyltetrahy- heptyl-5-(l-hydroxyoctadecyl)-furan can be hy­ drofuran was obtained. drogenated with rhodium on charcoal to yield a !H NMR (250 MHz, CDC13): 6 = 0.88 (t, 6 H, 1 : 1 mixture of the two diastereomers of cis-Cl I CH3), 1.20-1.45 (m, 42H, CH2), 1.60 (quin, 4H, lHOC18-THFs, which elute as one peak on an H -l'), 1.90 (m, 2H, H-3, H-4), 3.65-3.90 (m, 2H, apolar gas chromatographic phase. Attempts to H-2, H-5). 1) n-BuLi O 2) C7H15Br 1) n-BuLi 2) C18H37Br C 1 7 H 3 5 XL C17H35 ^ 1 5 ^ 7 O C 18H 3 OH H2, Pd/C H2, Rh/Al20 3 C17H35 + / v 3 \ ^ C 17H3 misW O T OH Fig. 1. Synthesis of 7/18-THF and 7/ erythro threo 1H018-THF. Bereitgestellt von | Technische Universität Braunschweig Angemeldet Heruntergeladen am | 20.03.19 13:28 St. Schulz et al. ■ 2,5-Dialkyltetrahydrofurans, Cuticular Lipids of Lepidoptera 109 13C NMR (62.9 MHz, C6D6): 6 = 14.4 (C-7\ 2'), 27.8 (threo-C-4), 29.2-29.7 (CH2), 31.4 (C-3), C l 8 "), 23.1 (C-6 ', C-l7"), 26.9 (C-2'), 29.8-30.3, 31.8 (C-5'), 31.9 (C-16"), 32.6 {erythro-C-2"), 34.0 31.6 (C-3), 32.3 (C-5'), 32.4 (C-16'), 36.8 (C-l), (threo-C-2"), 35.9 ( erythro-C-Y), 36.0 (threo-C-Y), 79.4 (C-2, C-5). 71.6 (erythro-C-1"), 74.5 (threo-C-l"), 79.6 (erythro-C-2), 79.9 (threo-C-2), 82.0 (erythro-C-5), 2-Heptyl-5-(l-hydroxy octadecyl)-furan 82.2 (threo-C5). A 1.6 m solution of n-butyllithium in hexane (1.5 Results ml) was added to a stirred solution of 2 -heptyl- furan (390 mg, 2 mmol) in 4 ml THF at 0 °C. After In the current study, cuticular lipids of adult but­ 2 h, a solution of octadecanal (500 mg, 1.87 mmol) terflies belonging to the Danainae, Heliconiinae, in 4 ml THF was added dropwise and the resulting Ithomiinae (all Nymphalidae) and Pieridae, as mixture stirred for 3 h at room temperature. A sat­ well as noctuid, arctiid, pyralid, tortricid, and plu- urated NH4 C1 solution was added, and the mixture tellid moth species were investigated. Because our extracted three times with diethyl ether. The com­ primary interest is the chemical communication bined organic extracts were dried with M gS04 and systems of male Lepidoptera, we analyzed body the solvent removed. The crude extract was puri­ parts associated with suspected pheromone emit­ fied by chromatography on 100 g neutral A12 0 3 ting structures. In some cases other body parts or (Woelm, activity 3 -4 ), giving 430 mg of pure 2- live stages as well as females of the ithomiine heptyl-5-(l-hydroxyoctadecyl)-furan (62% yield). Methona confusa were investigated, additionally lH NMR (CDCI 3 , 400 MHz): 6 = 0.88 (t, 6 H, (see Tables I and II). / = 6 . 8 Hz, CH3), 1.21-1.46 (m, 38H, CH2), 1.62 The lipids were extracted as described and the (quin, 2H, J = 7.4 Hz, C//2-CH2-furyl), 1.83 (m, extracts submitted to GC-MS. Long chain un­ 2H, C//2 -CHOH), 2.59 (t, 2H, J = 7.2 Hz, CH2- branched 2,5-dialkyltetrahydrofurans and related furyl), 4.60 (t, 1H, J = 6 . 6 Hz, CH-OH), 5.89 (d, alcohols were identified in addition to the usual 1H, J = 3.0 Hz, CH), 6.10 (d, 1H, J = 3.0 Hz, CH). alkanes and other compounds. They exhibited dis­ tinct mass spectra, permitting easy location of the 2-Heptyl-5-(l-hydroxy octadecyl)-tetrahydrofuran ring in the chain (Brandt and Djerassi, 1968; Zinbo and Jensen, 1985; Takabayashi and Taka- A solution of 50 mg 2-heptyl-5-(l-hydroxyocta- hashi, 1986a).