California Lomatiums, Part IV(a): Composition of the Essential Oils of Lomatium rigidum (M.E. Jones) Jepson. Structures of Two New Funebrene Epimers and a Tridecatriene

Journal of Essential Oil Research: JEOR, Nov/Dec 2004 by Beauchamp, Philip S, Descalzo, Josette T, Dev, Barbara C, Dev, Vasu, Et al

Isolation of(Z,Z,Z)-3,6,9-tridecatriene IV: The 1.59 g of oil from the roots obtained from collections (ii) and (iii) was chromatographed with 30 g of silica gel packed as a slurry in hexane. The column was eluted with 50 mL each of 100:0, 99:1,98:2,96:4,92:8,84:16,68:32 hexane:ether. After collecting the first 20 mL of eluent in a flask, 60 fractions of ~6 mL each were collected. TLC and GC of selected earlier fractions indicated that fractions 2-5 could be used for the enrichment of I. Fractions 6-8 were enriched in IV to the extent of ~40%. They were combined, concentrated with a rotary evaporator and dried at ~10 torr. The oily material (0.493 g) was chromatographedwith 8 g of 15% AgNO^sub 3^ impregnated Si gel. Twenty-five fractions ~2 mL each were collected using 95:5 hexane:benzene as the mobile phase. The middle to latter fractions gave 32 mg IV of 88% purity, deemed appropriate for NMR data acquisition (Table IV). MS m/z (rel. intensity) 178 [M ] (1), 149(4), 135(4), 122(31), 108(36), 95(23), 93(44), 91(25), 79(100), 67(66), 55(21), 41(29).

Results and Discussion

Analysis of oils from collection (i): The identification of the components present in the hydrodistilled oils was carried out by a comparison of their retention indices (RI) and mass spectra, which matched exceedingly well with those reported for these compounds (Table I). Identification of several components was further supported by coinjection of the oils with authentic samples (Table I). β-Phellandrene/ limonene, δ-cadinene, epi-α-cadmol/muurolol and α-cadinol were the major components of the fruits, stems and leaves oils. It might be pointed out that limonene has been reported to elute faster than β-phellandrene on a 30 m × 25 mm (0.25 µm film thickness) J&W DBS column (10). However, we have determined from the MS scans of the mixture as well as from the NMR data of the isolated hydrocarbons that limonene elutes slower than β-phellandrene on a AGILENT HP-5MS column of identical dimensions used in the present study. In all, 91.2% and 92.4% of the components of the respective oils were identified. Compared to these two oils, the root oil was rather simple in the number of components present. Of the three major components, (Z)-falcarinoI (14.9%) was identified by coinjection with an authentic sample as well as correspondence with its reported mass spectrum. The RI and mass spectrum of the second component (5.0%) corresponded with the reported RI and mass spectrum of β-duprezianene (10). More interesting and challenging was the third component I, which accounted for 48.2% of the oil. Its RI and MS matched closely with β-cedrene (C^sub 15^H^sub 24^); however, its ^sub 1^H- and ^sub 13^CNMR spectral data did not agree with the reported NMR spectral data for β-cedrene ( 11 ). The compound slowly isomerizedto another hydrocarbon II during NMR data acquisition. This hydrocarbon (RI 1385) was also present (1.8%) in the root oil. Structures of both I and II were derived from their respective 2D NMR spectral data. The assigned structure and the stereochemistry of I as 2-epi-β-funebrene was further confirmed from the x-ray diffraction data of its crystalline 9BBN hydroboration product III.