Fig. 4.
1H NMR spectra (300 MHz) and structure of (R)-maconelliyl (S)-2-methylbutanoate.
Sex pheromone of the pink hibiscus mealybug,Maconellicoccus hirsutus, contains an unusual cyclobutanoid monoterpene
Two compounds that together constitute the female sex pheromone of the pink hibiscus mealybug (PHM),Maconellicoccus hirsutus, were isolated, identified, and synthesized. They are (R)-2-isopropenyl-5-methyl-4-hexenyl (S)-2-methylbutanoate [common name is (R)-lavandulyl (S)-2-methylbutanoate] and [(R)-2,2-dimethyl-3-(1-methylethylidene)cyclobutyl]methyl (S)-2-methylbutanoate [which we refer to as (R)-maconelliyl (S)-2-methylbutanoate]. Maconelliol is an unusual cyclobutanoid monoterpene, and its structure has been established by enantioselective synthesis from precursors of known structure and configuration. A 1:5 synthetic mixture of the two RS esters (1 μg per rubber septum) proved to be a potent attractant of males in field bioassays. The pheromone component, maconelliyl 2-methylbutanoate, represents a heretofore undescribed natural product.
The 1H NMR spectrum (Fig. 4) of purified compound 2 (≈30 μg obtained by preparative GC) contained resonance for 26 protons, including six methyl groups, consistent with the assumed molecular formula C15H26O2. A doublet at 4.15 ppm (d, 2 H, J = 7.57 Hz) corresponded to a methylene in an ester (—O—CH2—CH—). Four distinct methyl signals were clearly displayed; two signals at 1.51 (s, 3 H) and 1.40 (s, 3 H) ppm from two methyl groups on the double bond (CH3—C
C), and another two signals at 1.24 (s, 3 H) and 1.12 (s, 3 H) ppm corresponding to a geminal dimethyl [(CH3)2C—] or two methyl groups on quaternary carbons. The remaining two methyl groups supported the presence of a 2-methyl butyrate moiety CH3CH2CH(CH3)CO (δ 0.83, t, 3 H, J = 7.19 Hz; 1.077, d, 3 H, J = 6.82 Hz). Accordingly, in the absence of any olefinic protons, the tetra-substituted cyclobutane 2-methylbutanoate (compound 3 or 4, Fig. 3) were considered as reasonable pheromone candidates. The structure 3 was more consistent with the long-range homoallylic coupling (H—C—C
C—CH) observed for the methylene group in the four-member ring. The two protons at the 4 position were not equivalent. Broad signals at δ 2.47 and 2.05 could be interpreted as the homoallylic long-range coupling with the terminal methyl groups on the double bond. Correspondingly, these two methyl groups (δ 1.51 and 1.40) also exhibited the same coupling pattern (coupling constant < 1 Hz). This homoallylic long-range coupling was confirmed by a 1H-1H COSY spectrum and decoupling experiments.
C), and another two signals at 1.24 (s, 3 H) and 1.12 (s, 3 H) ppm corresponding to a geminal dimethyl [(CH3)2C—] or two methyl groups on quaternary carbons. The remaining two methyl groups supported the presence of a 2-methyl butyrate moiety CH3CH2CH(CH3)CO (δ 0.83, t, 3 H, J = 7.19 Hz; 1.077, d, 3 H, J = 6.82 Hz). Accordingly, in the absence of any olefinic protons, the tetra-substituted cyclobutane 2-methylbutanoate (compound 3 or 4, Fig. 3) were considered as reasonable pheromone candidates. The structure 3 was more consistent with the long-range homoallylic coupling (H—C—CC—CH) observed for the methylene group in the four-member ring. The two protons at the 4 position were not equivalent. Broad signals at δ 2.47 and 2.05 could be interpreted as the homoallylic long-range coupling with the terminal methyl groups on the double bond. Correspondingly, these two methyl groups (δ 1.51 and 1.40) also exhibited the same coupling pattern (coupling constant < 1 Hz). This homoallylic long-range coupling was confirmed by a 1H-1H COSY spectrum and decoupling experiments.
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| [(R)-2,2-Dimethyl-3-(1-methylethylidene)-cyclobutyl]methyl (S)-2-methylbutanoate |
| Formula: | C15H26O2 |
| CAS#: | |
| MW: | 238.37 |
| Zhang, A.J., and Nie, J.Y. 2005. Enantioselective synthesis of the female sex pheromone of the pink hibiscus mealybug, Maconellicoccus hirsutus. J. Agric. Food Chem. 53:2451-2455. |
| Zhang, A.J., Nie, J.Y., and Khrimian, A. 2004. Chiral synthesis of maconelliol: a novel cyclobutanoid terpene alcohol from pink hibiscus mealybug, Maconellicoccus hirsutus. Tetrahedron Lett. 45:9401-9403. |
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| Reference(s) |
| Zhang, A.J., and Nie, J.Y. 2005. J. Agric. Food Chem. 53:2451-245 |
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[(R)-2,2-Dimethyl-3-(1-methylethylidene)cyclobutyl]methyl (S)-2-methylbutanoate [(R)-maconelliyl (S)-2-methylbutanoate] (2a). To a solution of 2.2 mL (20.1 mmol) of (S)-(+)-2-methylbutanoic acid {Aldrich, 99% ee, [α]24 D+24.0 (c 0.1, MeOH)} in 15 mL of benzene was treated with 2.2 mL (25.2 mmol) of oxalyl chloride and 10 μl of DMF. After 1.5 h at room temperature, the benzene and excess oxalyl chloride were removed followed by the addition of another 15 mL portion of benzene. The acid chloride residue was dissolved in 15 mL of benzene, and then a solution of 1.65 g (10.7 mmol) of 6a and 18 ml (22.2 mmol) of pyridine in 15 mL of benzene were added dropwise. After stirring at room temperature for 1 h, the solvent was removed. The residue was treated with 20 mL of water, and extracted with ether. The organic solution was washed with water, 1N hydrochloric acid, 1N aqueous sodium bicarbonate, and brine, dried over sodium sulfate, and concentrated to afford yellow oil. Pure 2a (2.0 g, 79% yield) was obtained by chromatography (silica gel, 2% of ethyl acetate in hexanes). Optical purity: 99% ee; [α]24 D−0.79 (c 2.03, MeOH); 1H NMR (C6D6): δ 0.84 (3H, t, J=7.19 Hz), 1.08 (3H, d, J=6.82 Hz), 1.12 (3H, s), 1.24 (3H, s), 1.36 (1H, m), 1.40 (3H, bs), 1.51 (3H, t, J=1.89 Hz), 1.67 (2H, m), 2.05 (1H, m), 2.17 (1H, m), 2.27 (1H, m), 2.48 (1H, ddt, J=14.75, 8.79, 1.52 Hz), 4.15 (2H, d, J=7.57 Hz); 13C NMR (C6D6): δ 175.76, 137.48, 122.55, 65.30, 44.43, 41.39, 39.71, 28.62, 27.79, 27.13, 21.17, 19.60, 18.64, 16.85, 11.80; EI-MS m/z (%): 238 [M]+ (2), 136 (29), 121 (100), 107 (12), 93 (20), 81 (26), 67 (5), 57 (16), 41 (10); HREIMS: obsd. 238.1929, calcd. for C15H26O2 (M+): 238.1933.......http://www.google.com/patents/US8062651...
Beltsville
Beltsville Agricultural Research Center
Henry A. Wallace Beltsville Agricultural Research Center – Beltsville MD
Beltsville MD 20705-2935 & Touch Point Church Ministries Touch Point Church Ministries 11310 Montgomery Road Beltsville, Maryland 20705
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