Cyclic Glycerol Acetals from the Abdominal Hair Pencil Secretion of the Male African Sugarcane Borer Eldana Saccharina (Lepidoptera: Pyralidae) B
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Cyclic Glycerol Acetals from the Abdominal Hair Pencil Secretion of the Male African Sugarcane Borer Eldana saccharina (Lepidoptera: Pyralidae) B. V. Burger, A. E. Nell, D. Smit, and H. S. C. Spies Laboratory for Ecological Chemistry, Department of Chemistry, University of Stellenbosch, Stellenbosch 7600, South Africa Z. Naturforsch. 46c, 678-686 (1991); received January 8, 1991 Cyclic Acetals, Darmstoff, Eldana saccharina, Mass Spectrometry, NMR Four constituents of the hair pencil secretion of the male African sugarcane stalk borer, Eldana saccharina, having a molecular mass of 312 and peculiar El mass spectra with an excep tionally abundant base peak at m/z 103, were isolated preparatively from an extract of the se cretion. Using 'H and l3C NMR spectral analysis, these constituents were identified as five- and six-membered cyclic glycerol acetals of Z-9-hexadecenal, viz. cis- and trans-2-(Z- 8-pentadecenyl)-4-hydroxymethyl-l,3-dioxolane, and cis- and fra«s-2-(Z-8-pentadecenyl)- 5-hydroxy-l,3-dioxane. These compounds are related to the 2-alkenyl-4-hydroxymethyl-l,3- dioxolane dihydrogen phosphate esters, known to be the active constituents of the smooth muscle contracting acidic phospholipid (Darmstoff) which was isolated from the intestine of mammals. The presence of these acetals in the tail brush secretion of E. saccharina could possi bly be the first evidence that compounds related to the active principle of Darmstoff, may also be present in the insect kingdom. The possibility that these four compounds or their dihydro gen phosphate esters might play a part in the eversion or retraction of the tail brushes of the male insect, is briefly discussed. Introduction trusion of the hair pencils, the emerged moths were exposed to constant light regime. About 24 h after In a recently completed investigation of the con the moths had emerged, they were anaesthesized stituents of the wing gland and abdominal hair with chloroform vapour for the collection of the pencil secretions of the male African sugarcane hair pencil secretion. Applying slight pressure to borer, Eldana saccharina Walker, the results of the abdomen of a male resulted in a gradual extru which were reported in a preliminary note [1], a sion of its abdominal hair pencils which were re group of five compounds having the same molecu moved with a pair of ophthalmic scissors before lar mass and similar mass spectra, remained un they were fully everted and allowed to fall into a identified, since their mass spectra afforded insuf Reacti-Vial with dichloromethane (Merck, Resi ficient structural information. Although these due Analysis Grade). The hair pencils of a thou components did not elicit any electroantenno- sand males were collected in a total volume of graphic (EAG) response in gas chromatographic 10 ml of dichloromethane. The extract was filtered analyses with FID/EAG detection (GC-EAD), and through a small sintered glass filter at 3000 r.p.m. therefore probably have no direct semiochemical in a centrifuge and the filtrate concentrated in a function, their peculiar mass spectral properties purified (activated charcoal) nitrogen atmosphere. prompted us to determine their structures. To eliminate heavy waxes which were expected to hamper the isolation of individual components, Experimental this extract was subjected to a preliminary prepar General ative gas chromatographic separation on a Perkin- Pupae of the insect under investigation were Elmer 900 gas chromatograph fitted with a short sexed and the male pupae maintained in environ packed column [1.7 m x 8 mm glass, 2.5% SE-30 mental chambers using a 12 h at 26 °C and 12 h at on 60-80 mesh Chromosorb WAW DMCS, 15 ml 18 °C temperature cycle. To prevent premature ex- H2/min, effluent splitter 9:1, temperature pro grammed at 2 °C/min from 40-250 °C and held isothermally at 200 °C (5 min), 220 °C (5 min), Reprint requests to Prof. B. V. Burger. 230 °C (5 min), 240 °C (10 min) and 250 °C Verlag der Zeitschrift für Naturforschung, D-7400 Tübingen (5 min)]. The effluent fractions were collected in 0939-5075/91/0700-0678 $01.30/0 1 ml quantities of dichloromethane. Capillary gas Dieses Werk wurde im Jahr 2013 vom Verlag Zeitschrift für Naturforschung This work has been digitalized and published in 2013 by Verlag Zeitschrift in Zusammenarbeit mit der Max-Planck-Gesellschaft zur Förderung der für Naturforschung in cooperation with the Max Planck Society for the Wissenschaften e.V. digitalisiert und unter folgender Lizenz veröffentlicht: Advancement of Science under a Creative Commons Attribution Creative Commons Namensnennung 4.0 Lizenz. 4.0 International License. B. V. Burger et al. • Cyclic Glycerol Acetals from the Abdominal Hair Pencil Secretion of Eldana saccharina 679 chromatographic analysis of each fraction showed drying agent and evaporation of the solvent at re the compounds under investigation to be present duced pressure, gave a viscous residue which was in the fraction collected at 230-240 °C (10 min). saponified to remove the protective ester group. Preparative isolation of the individual components The product of the condensation reaction was in this fraction was carried out with the above gas dissolved in methanol (2 ml), treated with a solu chromatograph fitted with a wide-bore capillary tion of KOH (40 mg) in water (0.1 ml) and the column [35 m x 0.6 mm glass, coated with PS-255 reaction mixture stirred magnetically at room tem at a film thickness o f 2.0 |xm, 15 ml H 2/min, perature for 24 h. The resulting deprotected ace- temperature programmed at 12 °C/min from tals were extracted with ether, the extract washed 40-200 °C and at 1 °C/min from 200-250 °C free from alkali with water and dried on Na2S04. (hold)]. Four components were collected in stain- The normal work-up procedure gave an oily resi less-steel needles, rinsed into Reacti-Vials with due (56 mg) which, according to GC-MS analysis, benzene-d6 and transferred first to precision consisted of a practically pure mixture of four 1.7 mm sample tubes for preliminary recording of cyclic acetals, all of which showed a base peak at 'H NMR spectra at 80 MHz on a Varian FT-80 m /z 103. NMR spectrometer and subsequently to 5 mm sample tubes for detailed ’H and 13C NMR ana 2- ( Z-8-pentadecenyl) -5-hydroxy-1,3-dioxanes lyses at respectively 300 MHz and 75 MHz on a Condensation of 2-monohexadecanoylglycerol Varian VXR-300 NMR spectrometer. (50 mg) and Z-9-hexadecenal (45 mg) as described Analytical gas chromatographic analyses were for the preparation of the dioxolanes above, gave a carried out with a Carlo Erba 4160 gas chromato product which, according to 13C NMR analysis, graph equipped with a flame ionization detector contained substituted dioxolanes as well as the ex and fitted with a glass capillary column pected substituted dioxanes. Removal of the pro (40 m x 0.3 mm) coated with PS-255 at a film tective ester group as described before, gave a mix thickness of 1.0 [im. Helium was used as carrier ture of cyclic acetals, containing the acetals present gas at a linear velocity of 28.6 cm/s and the column in the tail brush secretion with the dioxolanes as was temperature programmed at 2 °C/min from the major products. 40-240 °C. El and Cl mass spectra were obtained As the substituted dioxolanes, unexpectedly, by GC-MS analyses of the extract on Varian MAT were the major constituents of this condensation, 311 A, Finnigan 4510, and Carlo Erba Q M D 1000 it was repeated in a NMR sample tube and the mass spectrometers, using the column and gas progress of the reaction followed by monitoring chromatographic parameters specified above. the resonance of the aldehyde proton. 2-Mono- The location of the double bond in the side hexadecanoylglycerol (100 mg) was suspended in a chain of each of the isolated constituents was solution of Z-9-hexadecenal (44.8 g) in benzene-fi?6 established by microozonolysis according to the (600 }il) containing a catalytic quantity of method of Beroza and Bierl [2] and gas chromato /?-toluenesulfonic acid and heated at 80 °C in a graphic identification of the alkanal derived from 5 mm NMR sample tube. After 5 min at 80 °C the the terminal portion of the side chain. reaction mixture which, due to the low solubility of the glyceride in the solvent, had been a suspen 2-( Z-8-Pentadecenyl) -4-hydroxymethyl-1,3- sion at the beginning of the experiment, became dioxolanes homogeneous. The 'H NMR spectrum of the mix A solution of 1-monooctanoyl-rac-glycerol ture showed that about 50% of the aldehyde had (41 mg), Z-9-hexadecenal (45 mg) and toluene- already been consumed at this stage. After a fur 4-sulfonic acid (1 mg) in benzene (2 ml) was re ther 5 min at 80 °C the resonance of the aldehyde fluxed for 2 h, traces of moisture in the reagents proton was barely visible and the reaction mixture and the water formed in the condensation reaction was cooled to room temperature. NMR analysis being removed azeotropically. After cooling the showed that the cis- and /rarcs-substituted dioxo reaction mixture, it was diluted with ether, washed lanes were the major products of the condensation. successively with saturated aqueous N aH C03 and Removal of the protective ester group by sapon water, and dried on Na2S04. Removal of the ification with KOH (100 mg) in M e0H/H20 gave 680 B. V. Burger et al. ■ Cyclic Glycerol Acetals from the Abdominal Hair Pencil Secretion of Eldana saccharina an oily product (51 mg) consisting of a mixture of the four cyclic acetals.