New Sesquiterpene Lactone from Inula britannica
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NEW SESQUITERPENE LACTONE FROM Inula britannica
D. E. Dusmatova, K. K. Turgunov, Kh. M. Bobakulov, R. F. Mukhamatkhanova,* I. D. Sham′yanov, B. Tashkhodzhaev, and N. D. Abdullaev
A new sesquiterpene lactone that was called inulonolide was isolated from Inula britannica. Its structure was established as 2-keto-1β,10β-epoxy-5,7,8,11α(H)-guai-3-en-8,12-olide based on spectral data and an X-ray crystal structure analysis. Keywords: Inula britannica L., sesquiterpene lactone, inulonolide, IR, NMR, X-ray crystal structure analysis. In continuation of research on Inula britannica (Asteraceae) growing in Uzbekistan [1], a sesquiterpene lactone that was previously unreported in the literature was isolated and called inulonolide by us. The IR spectrum of 1 had an absorption band at 1742 cm–1 that corresponded to a γ-lactone carbonyl and bands for ketone carbonyl at 1692 cm–1, C=C double bond at 1604 cm–1, and epoxy group at 1269 and 931 cm–1. 14
O O 1
10 B
A
3
O C
5
O
11
15
13
1
The structure of 1 was established based on an analysis of PMR and 13C NMR spectra and a DEPT experiment. The PMR spectrum of 1 showed resonances for tertiary methyl as a singlet at δ 1.72 ppm (H-14), methyl on a double bond as a triplet at δ 2.20 ppm (H-15) with a through-space spin–spin coupling constant (SSCC) (J = 1.3 Hz), and secondary methyl at δ 1.21 ppm (H-13) as a doublet with SSCC J = 7.2 Hz. Furthermore, the strong-field region showed resonances for protons of two methylenes at δ 1.44 (ddd, J = 13.6, 12.7, 10.9 Hz; H-6a), 1.75 (dd, J = 13.6, 5.9 Hz; H-6b), and 2.33 (m, H-9) and for two methines at δ 2.68 (br.d, J = 10.9 Hz, H-5) and 2.81 (quintet, J = 7.1, H-11). The SSCC (J = 10.9 Hz) for H-5 was indicative of its α-configuration [2]. Resonances of γ-lactone protons H-7 and H-8 in the PMR spectrum were located at δ 2.77 and 4.47 ppm as a multiplet and triplet of doublets with SSCC J = 4.6 and 2.6 Hz, respectively. A SSCC of 2σ (I) R1 (I > 2σ (I) and total) wR2 GOOF ° –3 Difference ED peaks, e A CCDC
C15H18 O4 262.29 P 21 2 8.4895(9) 5.7927(5) 13.960(2) 90 105.41(2) 90 661.9(2)
1.316 0.8 × 0.2 × 0.5 3.3 ≤ θ ≤ 76.2 0.779 2539 2237 0.041 (0.048) 0.110 (0.119) 0.791 0.14 and –0.20 1977382
C14 C10 C9
O1 C1
O4 O3
O2 C8
C2
C7
C5
C3
C12
C11 C6 C4
C13
C15
Fig. 1. Molecular structure of inulonolide (1). The structure 2-keto-1,10-epoxyguai-3-en-8,12-olide was proposed for lactone 1 based on the obtained data. An X-ray crystal structure analysis (XSA) of 1 was performed for unambiguous proof of its structure. Figure 1 shows the molecular structure of inulonolide. The molecular structure of 1 according to the XSA (Fig. 1) showed that the compound was a sesquiterpene ° . The lactone 7,8-guaiane lactone. The three rings were A/B/C-cis fused. Ring A of inulonolide was planar within ± 0.035 A ring had the 7α-envelope conformation. Seven-membered ring B adopted the chair conformation. The experimental Flack parameter [0.1(2)] defined the absolute configurations of the chiral centers as 1S,5S,7R,8R,10R,11S. The epoxide ring of i
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