Two new ent-kaurane diterpenoids from Albizia mollis (Wall.) Boiv

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Mollisside A (1) was isolated as white powder. Its molecular formula was determined to be C₂₆H₄₄O₈ with five unsaturation degrees by HRFABMS (m/z 483.2959 [M-1]^-) and ¹³C NMR spectra. The ¹H NMR spectrum of compound 1 clearly showed signals to three methyls at δ 0.83 (3H, s), 1.03 (3H, s), 1.07 (3H, s), and one anomeric hydrogen of β-type sugar at δ 4.30 (1H, d, J 7.8 Hz). The ¹³C NMR ({¹H} and DEPT) spectroscopic data (Table 1) revealed the presence of 3 methyls, 10 methylenes, 9 methines and 4 quaternary carbons. Carbon signals at δ 106.8 (d), 75.6 (d), 77.7 (d), 71.6 (d), 78.2 (d), 62.8 (t) suggested the presence of one glucose, which were further confirmed by its MS fragmentation peaks at m/z 323 [M-1-160 = C₆H₈O₅ formed by fragmentation involving glc moiety C₆H₁₀O₅]^- and the acid hydrolysis of 1. Comparison of these NMR data with those similar data reported in the literature¹³ showed that compound 1 had the same ent-kaurane skeleton. The linkage of glucose moiety to C-3 was determined by the HMBC correlations from H-1' (δ 4.30), H-18 (δ 1.03) and H-19 (δ 0.83) to C-3 (δ 90.9) (Figure 2). The attachment of one hydroxyl at C-17 in 1 was established by HMQC and HMBC spectra revealing correlations of H-17 (δ 3.27) with C-16 (δ 80.7), C-13 (δ 42.3) and C-15 (δ 53.1). Besides, the relative configuration of 1 was elucidated by a ROESY experiment and by comparison of the NMR data with those reported in the literature.¹⁴ The key ROESY correlations of H-3/H-18, H-3/H-5 and H-9/H-5 (Figure 3), indicated α-orientation of C-3 glycoside and β-orientations of H-5 and H-9. The α-orientation of CH₂OH-17 (δc 70.6) in 1 was elucidated by comparison of the ¹³C NMR data with those reported δc 69.8 for α-orientation and δc 66.2 for β-orientation at C-17.¹⁴ Based on the above evidences, compound 1 was identified as 3α, 16β, 17-trihydroxy-ent-kaurane 3-O-β-D- glucopyranoside, named Mollisside A.
 

Mollisside B (2) was determined to have a molecular formula C₂₆H₄₀O₉ on the basis of the positive HRFABMS (m/z 519.2565 [M+Na]⁺) and ¹³C NMR (DEPT) spectra, which possessed seven unsaturation degrees. Its IR spectrum showed a broad band (3518-2930 cm^-1) and absorption 1691 cm^-1 for a carboxyl and 1607 cm^-1 for a double bond. The ¹H NMR spectrum of compound 2 exhibited three methyls at δ 0.88 (3H, s), 1.12 (3H, s), 1.16 (3H, s), one anomeric proton of β-type sugar at δ 4.32 (1H, d, J 7.8 Hz) and one olefinic proton at δ 6.48 (1H, s). The ¹³C NMR spectroscopic data (Table 1) revealed 26 carbon atoms, including one carboxyl (C-17 at δ 164.1) and two olefinic carbons (C-16 at δ 139.9, C-15 at δ 154.7). Comparison of these NMR data with mollisside A showed that compound 2 had the similar skeleton of compound 1 except for the distinct differences of chemical shift of C-2 (δ 68.1) adjacent one oxygenated group and C-17, C-15 and C-16 conforming the α,β-unsaturation ketone system. The linkage of the glucose moietiy to C-3 (δ 96.1) was determined by the HMBC correlations from H-1' (δ 4.32), H-18 (δ 1.12) and H-19 (δ 0.88) to C-3 (Figure 2). Besides, the relative configuration of 2 was elucidated by a ROESY experiment and by comparison of the NMR data with 1. The α-orientation of H-2 was established by key ROESY correlations of H-2/H-1α, H-2/H-19 and H-2/H-20 (Figure 3) and the coupling constant J 9.3 Hz observed in the signal corresponding to H-3 (interaction axial- axial with H-2). Moreover, the β-orientations of H-3, H-5 and H-9 were confirmed by ROESY between H-3/H-5, H-3/H-18 and H-5/H-9. Based on the above evidences, the structure of 2 was elucidated as 2β,3α-dihydroxy-ent-kaur-15-en-17-oic acid 3-O-β-D-glucopyranoside, named Mollisside B.


Mollisside A
White powder, mp 292-294 ºC; [α]_D²¹ +6.3116 (c 0.101, CH₃OH); UV (CH₃OH) λ_max/nm (log ε): 193(3.587), 205 (3.829), 277 (3.250); IR (KBr) ν_max/cm^-1: 3420, 2937, 1166, 1074, 1020; ¹H NMR (400 MHz, CD₃OD) and ¹³C NMR (100 MHz, CD₃OD) see Table 1; HRESIMS (negative ion) m/z 483.2959 [M-1]^- (Calc. for C₂₆H₄₄O₈, 483.2957); FABMS (negative ion) m/z(%) 483[M-1]^- (100), 391 (5), 323 (15), 282 (5), 159 (6), 113 (5).
Mollisside B
White powder, mp 270-271 ºC; [α]_D²¹ -1.5989 (c 0.246, CH₃OH); UV (CH₃OH) λ_max/nm (log ε): 196 (3.393), 203 (4.108), 276 (2.890); IR (KBr) ν_max/cm^-1: 3518, 3380, 3190, 2980, 2930, 1691, 1607, 1073, 1037; ¹H NMR (500 MHz, CD₃OD) and ¹³C NMR (125 MHz, CD₃OD) see Table 1; HRESIMS (positive ion) m/z 519.2565 [M+Na]⁺ (Calc. for C₂₆H₄₀O₉Na, 519.2570); FABMS (negative ion) m/z(%): 495[M-1]^- (100), 400 (5), 335 (5), 281(6), 123 (4).

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ABSTRACT
Two new kaurane diterpenoids, 3α, 16β, 17-trihydroxy-ent-kaurane 3-O-β-D-glucopyranoside and 2β,3α-dihydroxy-ent-kaur-15-en-17-oic acid 3-O-β-D-glucopyranoside, were isolated from the bark of Albizia mollis (Wall.) Boiv. The structures of two new compounds were elucidated by extensive 1D- and 2D-NMR spectroscopic methods in combination with MS experiments.

Journal of the Brazilian Chemical Society

Print version ISSN 0103-5053

J. Braz. Chem. Soc. vol.21 no.9 São Paulo  2010

http://dx.doi.org/10.1590/S0103-50532010000900025 

Two new ent-kaurane diterpenoids from Albizia mollis (Wall.) Boiv


Zhong-Quan Cheng^I,II; Dan Yang^I; Yu-Qing Liu^I; Jiang-Miao Hu^I; He-Zhong Jiang^I; Peng-Cheng Wang^I; Ning Li^III; Jun Zhou^I; You-Xing Zhao^I,*
IState Key Laboratory of Phytochemistry and Plant Resources in West China, Kunming Institute of Botany, the Chinese Academy of Sciences, Kunming 650204, P. R. China
^IIGraduate School of the Chinese Academy of Sciences, Beijing 100049, P. R. China
^IIISchool of Life Sciences, Anhui University, Hefei 230039, P. R. China



Keywords: Albizia mollis, kaurane diterpenoids, mollisside A, mollisside B

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