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Article Cite This: J. Nat. Prod. 2018, 81, 1777−1785

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Structurally Diverse Highly Oxygenated Triterpenoids from the Roots of Ailanthus altissima and Their Cytotoxicity Wei Bai,† Hong-Ying Yang,† Xing-Zhi Jiao,† Ke-Na Feng,‡ Jian-Jun Chen,*,† and Kun Gao*,† †

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State Key Laboratory of Applied Organic Chemistry, College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, People’s Republic of China ‡ State Key Laboratory of Phytochemistry and Plant Resources in West China, and Yunnan Key Laboratory of Natural Medicinal Chemistry, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650201, People’s Republic of China S Supporting Information *

ABSTRACT: Ten new triterpenoids, ailanaltiolides A−J (1−10), and three known analogues (11−13) were isolated from the roots of Ailanthus altissima. Compounds 1−7 are apotirucallane-type, compounds 8 and 9 are tirucallane-type, and compound 10 is a trinordammarane-type triterpenoid. This is the first study indicating the genus Ailanthus as a potential source for apotirucallane derivatives, which contain an α,β-unsaturated-ε-lactone A-ring and diversely modified C-17 side chains. Spectroscopic data interpretation, electronic circular dichroism analysis, and X-ray crystallographic data defined the structures and absolute configurations of these triterpenoids. Compounds 2, 7, and 8 showed cytotoxicity against four tumor cell lines (HeLa, 786-O, HepG2, and A549). In particular, compound 2 exhibited the highest activity against 786-O cells with an IC50 value of 8.2 μM in vitro.

I

three skeletal types (apotirucallane-, tirucallane-, and trinordammarane-type), along with three known compounds, 3-oxothreo-23,24,25-trihydroxytirucall-7-ene (11),7 bourjutinolone A (12),8 and cabralealactone (13),9 were identified. Compounds 1−7 are rare examples of apotirucallane-type triterpenoids, with compounds 1−6 featuring both an α,β-unsaturated-εlactone moiety in their A-ring and a five-membered acetal moiety or an α,β-unsaturated-γ-lactone moiety in their side chains, particularly compound 7, carrying a dihydrofuran ring in its side chain. Compounds 8−10 are tirucallane-type and trinordammarane-type triterpenoids. The structures of compounds 1−10 were characterized by combinations of spectroscopic data interpretation, electronic circular dichroism (ECD) data, and X-ray crystallographic data analysis. The cytotoxic effects of these compounds were evaluated against four human tumor cell lines (A549, 786-O, HeLa, and HepG2). Compounds 2, 7, and 8 were active against all the cell lines, whereas other compounds were inactive (IC50 > 40

n recent years, herbal medicines have become more significant due to their cost effectiveness and medicinal value. Therefore, precise scientific investigations of medicinal plants are required in order to label a plant as “an herbal medicine”. The Ailanthus genus, belonging to the family Simaroubaceae, currently contains 10 species, six of which are native to China.1 Ailanthus is an Ambonese word, with “ailanto” meaning “heaven’s tree”. In traditional Chinese medicine, different parts of Ailanthus altissima have been extensively used for the treatment of ascariasis, diarrhea, spermatorrhea, bleeding, and gastrointestinal diseases.2 Pharmacological studies indicated that the extracts of this plant have a broad range of bioactivities such as antitumor, antiviral, antimalarial, and antimicrobial actions.3 Previous phytochemical investigations reported that the main secondary metabolites of A. altissima were quassinoids, βcarboline alkaloids, sterols, and lipids.4 However, investigation of the triterpenoids, the precursors of quassinoids, drew less attention. 5 Therefore, during our ongoing studies of triterpenoids from medicinal plants,6 an array of new triterpenoids, ailanaltiolides A−J (1−10), which featured © 2018 American Chemical Society and American Society of Pharmacognosy

Received: March 13, 2018 Published: August 14, 2018 1777

DOI: 10.1021/acs.jnatprod.8b00208 J. Nat. Prod. 2018, 81, 1777−1785

Journal of Natural Products

Article

Chart 1

characteristic Δ14(15) double bond and an α,β-unsaturated-εlactone A-ring.12 This scaffold was confirmed by analysis of its 2D NMR data (Figure 1). The 1H−1H COSY couplings as well as the HMBC cross-peaks of H-1/C-3 and C-5; H3-19/C-1, C-5, and C-10; H3-29/C-3 and C-5 (A-ring); H-5/C-9 and C-10; H-7/C-9; H-9/C-8 (B-ring); H3-30/C-7, C-8, C-9, and C-14; H3-18/C12, C-13, C-14, and C-17; H-15/C-13 and C-14 (C-ring and D-ring); H-22, H3-26, and H3-27/C-24; and H-24, H3-26, and H3-27/C-25 indicated the apotirucallane-type triterpenoid skeleton. The oxygen-bearing carbon signals at δC 84.4, 71.1, 69.7, 109.6, 75.3, 76.3, and 77.2 were assigned as C-4, C-7, C11, C-21, C-23, C-24, and C-25, and a lactone carbonyl carbon at δC 167.2 was assigned as C-3. The tigloyloxy moiety was connected to C-11 based on the HMBC cross-peak from H-11 (δH 5.47) to the ester carbonyl carbon at δC 167.4. Similarly, the HMBC correlations from OCH3 (δH 3.23) to C-21 (δC 109.6) and from OCH3 (δH 3.22) to C-25 (δC 77.2) suggested the locations of methoxy groups at C-21 and C-25, respectively. According to the 10 IOHDs of 1, apart from the tigloyloxy group, a double bond, an α,β-unsaturated-εlactone moiety, and four rings, the remaining index required the presence of one more ring. The HMBC correlation of H21/C-23 as well as the chemical shift of C-21 (δC 109.6) suggested the linkage of a five-membered acetal moiety spanning C-21 and C-23. Considering the chemical shift of C-7 (δC 71.1) and the molecular formula of compound 1, a hydroxy group should be attached to C-7, even though no direct HMBC correlation was found. Hence, the 2D structure of 1 was deduced. The relative configuration of 1 was determined from the Jvalues and the NOESY correlations (Figure 1). H-7 was assigned a β-orientation based on the broad singlet at δH 3.95.13 The NOESY correlations of H-5/H-9 and H3-28, H-9/ H3-18, and H3-18/H-20 suggested that these protons were αoriented. The cross-peaks of H3-19/H-11 and H3-30 as well as H3-30/H-17 indicated that H-11, H-17, H3-19, and H3-30 were cofacial and were arbitrarily assigned β-orientations. The ECD

μM). Among these compounds, the IC50 value of 8.2 μM against 786-O cells in vitro showed that compound 2 is the most cytotoxic.

■

RESULTS AND DISCUSSION

The methanolic extract of the roots of A. altissima was dissolved in water and extracted with EtOAc. The EtOAc portion was fractionated using microporous resin and repeatedly subjected to silica gel, Sephadex LH-20, reversephase RP-C18 column chromatography (CC), and semipreparative HPLC to afford the new triterpenoids (1−10, ailanaltiolides A−J) and three known compounds (11−13), including 3-oxo-threo-23,24,25-trihydroxytirucall-7-ene (11), bourjutinolone A (12), and cabralealactone (13) (Chart 1). Ailanaltiolide A (1) was obtained as a white, amorphous powder, having a molecular formula of C37H56O9 based on the (+)-HRESIMS ion at m/z 667.3801 ([M + Na]+, calcd for C37H56O9, 667.3817), which required 10 indices of hydrogen deficiency (IOHD). Absorption bands for hydroxy (3368 cm−1) and α,β-unsaturated lactone (1685 cm−1) moieties were present in the IR spectrum.10 A typical tigloyloxy group was evidenced by the 1H NMR [δH 6.84 (q, J = 7.2 Hz), 1.80 (d, J = 7.2 Hz), and 1.81 (br s)] and 13C NMR signals (δC 167.4, 128.6, 138.4, 12.0, and 14.5) (Tables 1 and 2).11 In addition, signals at δC 49.1 and 55.5 as well as δH 3.22 (s) and 3.23 (s) accounted for two methoxy groups. The 13C NMR and HSQC spectra revealed the remaining 30 skeletal carbon resonances that could be assigned as seven methyls, four methylenes, 12 methines (four olefinic and an oxygen-bearing carbon), four quaternary carbons (one olefinic), two oxygen-bearing tertiary carbons, and an ester carbonyl carbon. The 1H NMR data exhibited resonances indicative of seven methyls at δH 1.10, 1.13, 1.15, 1.23, 1.29, 1.43, and 1.44, two conjugated olefinic protons supported by a pair of doublets at δH 6.03 (d, J = 12.8 Hz) and 5.64 (d, J = 12.8 Hz), and an isolated olefinic proton at δH 5.49. The aforementioned spectroscopic data showed that compound 1 is an apotirucallane-type triterpenoid with a 1778



Article

Table 1. 1H NMR Spectroscopic Data of Compounds 1−7 (δ in ppm, in CDCl3) 1a

2a

3a

4a

5a

6a

7b

δH (J in Hz)

δH (J in Hz)

δH (J in Hz)

δH (J in Hz)

δH (J in Hz)

δH (J in Hz)

δH (J in Hz)

d (12.8) d (12.8) dd (13.6, 2.4) m m br s d (8.8) overlap

6.00, d (12.8) 5.63, d (12.8) 2.86, dd (13.6, 2.4) 2.11, dt (13.6, 3.2) 1.88, m 3.96, br s 2.54, d (8.8) 5.47, dd (8.8, 5.6)

5.98, 5.60, 2.85, 2.09, 1.89, 3.99, 2.51, 5.47,

5.98, 5.60, 2.85, 2.11, 1.89, 3.99, 2.51, 5.56,

5.98, 5.60, 2.85, 2.10, 1.90, 3.99, 2.51, 5.55,

1.88, m (2H)

1.93, m 1.67, d (15.2)

2.08, m 2.01, m

2.08, m 2.01, d (16.0)

2.08, m 1.98, d (15.2)

5.49, br s 2.20, m (2H)

5.52, br s 2.20, m (2H)

1.74, m 1.10, s 1.29, s 2.29, m 4.67, d (4.0) 1.94, ddd (12.0, 7.2, 4.8) 1.62, overlap 4.22, ddd (12.0, 4.8, 2.4) 3.33, br s 1.13, s

2.01, 1.05, 1.29, 2.14, 4.66, 1.92,

5.57, 2.72, 2.41, 2.88, 0.93, 1.29,

5.60, 2.72, 2.43, 2.88, 0.94, 1.29,

5.60, 2.74, 2.38, 2.86, 0.93, 1.29,

1.23, 1.44, 1.43, 1.15, 6.84, 1.80, 1.81, 3.22, 3.23,

pos. 1 2 5 6a 6b 7 9 11a 11b 12a 12b 14 15 16a 16b 17 18 19 20 21 22a 22b 23 24 26a 26b 27 28 29 30 3′ 4′ 5′ 25-OMe 21-OMe 7-OCOCH3

6.03, 5.64, 2.86, 2.10, 1.89, 3.95, 2.57, 5.47,

s s s s q (7.2) d (7.2) br s s s

m s s m d (4.0) m

d (12.8) d (12.8) d (11.2) m m br s d (9.6) m

overlap m m m s s

d (12.8) d (12.8) d (11.2) m m br s d (8.8) m

overlap m m m s s

d (12.8) d (12.8) d (11.2) m m br s d (8.8) m

overlap m m m s s

6.54, 5.91, 2.32, 1.92, 1.82, 4.93, 1.39, 1.90, 1.66, 2.07, 1.30, 2.34,

d (12.0) d (12.0) m m m br s m m m m m s

6.13, 5.63, 2.84, 2.06, 1.96, 3.96, 2.58, 5.51,

d (12.8) d (12.8) dd (13.2, 2.4) dt (14.0, 3.2) d (14.0) br s d (9.6) dd (8.4, 6.8)

1.97, m 1.83, m

2.74, dd (19.2, 8.0) 2.43, dd (19.2, 11.2) 3.57, dd (11.2, 8.0) 0.86, s 1.30, s

5.57, 2.42, 2.26, 2.41, 1.00, 1.29,

d (3.2) m m m s s

7.20, br s

7.16, br s

7.03, br s

7.18, br s

1.81, overlap 4.46, m

5.18, d (3.2)

5.21, br s

5.03, d (6.4)

5.19, d (2.4)

6.09, s 2.76, ddd (14.4, 9.6, 1.2) 2.46, m 4.80, td (9.6, 2.0)

3.25, d (2.4) 1.16, s

3.50, d (3.2) 1.24, s

3.53, br s 1.31, s

3.50, d (2.4) 1.28, s

3.24, dd (9.2, 2.0) 1.29, s

1.23, 1.44, 1.43, 1.15, 6.83, 1.81, 1.81, 3.24, 3.33,

1.27, 1.43, 1.42, 1.20, 6.79, 1.78, 1.78, 3.22,

1.41, 1.44, 1.43, 1.21, 6.79, 1.78, 1.78,

4.08, 5.04, 5.02, 1.82, 1.44, 1.42, 1.20, 6.80, 1.78, 1.78,

1.26, 1.36, 1.42, 1.17,

1.26, 1.44, 1.44, 1.17, 6.84, 1.81, 1.81,

s s s s m d (7.2) br s s s

s s s s m d (7.2) br s s

s s s s m d (7.2) br s

d (6.4) br s br s s s s s m d (7.2) br s

s s s s

s s s s m d (7.2) br s

2.11, s

a

Data were recorded at 800 MHz. bData were recorded at 400 MHz.

the absolute configuration of 1 was defined as (5R, 7R, 8R, 9R, 10R, 11R, 13S, 17S, 20S, 21R, 23R, 24S). Compound 2 had the same molecular formula of C37H56O9 as 1, as determined by its (+)-HRESIMS analysis. IR spectra revealed these two compounds had the same functional groups. The 13C NMR data of 2 (Table 2) highly resembled those of 1 with slight variations at C-21 (δC 104.3 for 2 and 109.6 for 1) and C-17 (δC 52.2 for 2 and 56.9 for 1). This observation revealed that 2 was probably the C-21 epimer of 1. The signals for C-17 (δC 52.2) and C-21 (δC 104.3) in 2 were highly similar to those in xylogranatumine G (C-17, δC 52.2 and C21, δC 104.6),17a which had a 21β-OMe, implying the βorientation of 21-OMe in 2. This was verified by the shielding of C-17 (ΔδC −4.7 ppm) in 2 compared with that of 1, which was caused by the γ-gauche effect of 21β-OMe.16,18 Thus, the structure of 2, ailanaltiolide B, was defined as the C-21 epimer of 1. The absolute configuration of 2 was defined as (5R, 7R, 8R, 9R, 10R, 11R, 13S, 17S, 20S, 21S, 23R, 24S) by the

spectrum of 1 (Figure 2) showed sequential positive and negative Cotton effects at 218 and 200 nm, respectively. The UV absorption maximum at 211 nm indicated that this split Cotton effect was due to exciton coupling between the α,βunsaturated-ε-lactone and the tigloyloxy chromophores.14 The positive chirality and clockwise arrangement of the electronic transition dipoles of these two moieties defined the absolute configuration of the tetracyclic core of 1. For the C-17 side chain, the NOESY correlation of H-21/H-17 indicated the (20S) configuration, according to an earlier molecular model.15 Thus, the assignments of (21R) and (23R) absolute configurations were established by the correlations of H-20/ H-23 and H-21/H-17. The rotation of the C-23/C-24 bond seems to be limited by a hydrogen bond formed between the ring oxygen atom and 24-OH or steric hindrance.16 The broad H-24 singlet, along with the NOESY correlations of H-24/H222 and H-23, which is attributable to the gauche relationship of H-23/H-24, signifies a (24S) absolute configuration.17 Thus, 1779


Journal of Natural Products Table 2.

13

Article

C NMR Spectroscopic Data of Compounds 1−10 (δ in ppm, in CDCl3)

pos.

1,a type

2,a type

3,a type

4,a type

5,a type

6,a type

7,b type

8,a type

9,a type

10,b type

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 1′ 2′ 3′ 4′ 5′ 25-OMe 21-OMe 7-OCOCH3 7-OCOCH3

152.6, CH 116.2, CH 167.2, C 84.4, C 47.0, CH 27.3, CH2 71.1, CH 44.1, C 46.4, CH 45.1, C 69.7, CH 41.1, CH2 45.8, C 160.6, C 119.8, CH 34.6, CH2 56.9, CH 19.2, CH3 18.5, CH3 45.8, CH 109.6, CH 35.4, CH2 75.3, CH 76.3, CH 77.2, C 19.9, CH3 21.6,CH3 25.1, CH3 31.8, CH3 29.5, CH3 167.4, C 128.6, C 138.4, CH 12.0, CH3 14.5, CH3 49.1, CH3 55.5, CH3

152.6, CH 116.1, CH 167.2, C 84.4, C 47.0, CH 27.3, CH2 71.1, CH 44.1, C 46.4, CH 45.1, C 69.8, CH 41.8, CH2 45.4, C 160.2, C 120.5, CH 34.8, CH2 52.2, CH 19.9, CH3 18.5, CH3 44.4, CH 104.3, CH 32.1, CH2 77.8, CH 76.6, CH 77.2, C 19.9, CH3 22.4, CH3 25.1, CH3 31.8, CH3 29.6, CH3 167.4, C 128.6, C 138.5, CH 12.0, CH3 14.5, CH3 49.3, CH3 55.0, CH3

152.7, CH 116.2, CH 166.9, C 84.5, C 47.2, CH 27.5, CH2 71.4, CH 44.4, C 46.8, CH 45.2, C 69.2, CH 41.6, CH2 46.6, C 160.0, C 120.3, CH 33.9, CH2 50.2, CH 20.7, CH3 18.7, CH3 133.1, C 173.7, C 150.0, CH 80.8, CH 76.8, CH 77.4, C 19.9, CH3 22.1, CH3 25.2, CH3 31.9, CH3 29.4, CH3 167.5, C 128.6, C 138.6, CH 12.2, CH3 14.7, CH3 49.3, CH3

152.5, CH 116.1, CH 166.8, C 84.3, C 47.0, CH 27.4, CH2 71.3, CH 44.3, C 46.6, CH 45.1, C 69.0, CH 41.4, CH2 46.5, C 159.9, C 120.1, CH 33.7, CH2 50.1, CH 20.5, CH3 18.5, CH3 133.5, C 173.0, C 149.2, CH 81.1, CH 75.9, CH 72.5, C 26.1, CH3 27.1, CH3 25.0, CH3 31.8, CH3 29.6, CH3 167.4, C 128.5, C 138.5, CH 12.0, CH3 14.5, CH3

152.4, CH 116.1, CH 166.8, C 84.3, C 47.0, CH 27.4, CH2 71.3, CH 44.3, C 46.6, CH 45.1, C 69.0, CH 41.4, CH2 46.6, C 159.9, C 120.0, CH 33.6, CH2 50.2, CH 20.5, CH3 18.6, CH3 134.5, C 172.8, C 147.5, CH 82.8, CH 76.7, CH 142.4, C 114.8, CH2 18.5, CH3 25.0, CH3 31.8, CH3 29.6, CH3 167.4, C 128.3, C 138.6, CH 12.0, CH3 14.5, CH3

158.3, CH 121.7, CH 167.7, C 85.1, C 48.6, CH 27.9, CH2 72.7, CH 40.4, C 48.7, CH 43.4, C 19.3, CH2 35.0, CH2 42.5, C 61.0, CH 217.8, C 41.9, CH2 37.5, CH 27.9, CH3 15.6, CH3 132.0, C 173.8, C 150.3, CH 80.9, CH 76.6, CH 77.2, C 19.8, CH3 21.9, CH3 26.7, CH3 32.2, CH3 17.7, CH3

154.0, CH 116.5, CH 167.5, C 84.4, C 47.1, CH 27.5, CH2 71.4, CH 44.6, C 46.2, CH 44.0, C 69.5, CH 42.1, CH2 46.5, C 159.8, C 120.7, CH 33.3, CH2 52.6, CH 20.1, CH3 18.1, CH3 114.8, C 140.7, CH 35.7, CH2 81.3, CH 77.1, CH 72.7, C 26.5, CH3 26.6, CH3 25.5, CH3 31.9, CH3 29.1, CH3 167.4, C 128.4, C 138.9, CH 12.1, CH3 14.6, CH3

32.5, CH2 28.6, CH2 175.5, C 75.4, C 49.5, CH 28.1, CH2 117.9, CH 146.0, C 41.9, CH 38.1, C 17.6, CH2 33.7, CH2 43.4, C 51.2, C 34.1, CH2 28.5, CH2 53.6, CH 22.0, CH3 17.1, CH3 33.7, CH 18.9, CH3 40.5, CH2 69.7, CH 74.9, CH 74.3, C 26.2, CH3 27.5, CH3 26.0, CH3 33.6, CH3 27.2, CH3

37.6, CH2 34.0, CH2 214.8, C 47.1, C 65.3, CH 198.4, C 125.0, CH 170.4, C 49.6, CH 43.2, C 17.6, CH2 31.9, CH2 42.8, C 52.4, C 26.9, CH2 32.8, CH2 44.3, CH 22.2, CH3 13.9, CH3 37.2, CH 69.9, CH2 36.2, CH2 64.4, CH 86.5, CH 74.3, C 23.9, CH3 28.7, CH3 21.7, CH3 25.2, CH3 25.0, CH3

39.7, CH2 34.0, CH2 217.6, C 47.4, C 55.3, CH 19.6, CH2 34.0, CH2 39.6, C 49.3, CH 36.8, C 32.0, CH2 70.7, CH 49.6, CH 52.1, C 31.4, CH2 26.4, CH2 48.8, CH 15.2, CH3 15.9, CH3 89.0, C 26.4, CH3 29.2, CH2 28.5, CH2 176.0, C

26.6, CH3 21.0, CH3 17.5, CH3

49.2, CH3 169.5, C 21.2, CH3

a


IOHDs. Interpretation of the NMR (Tables 1 and 2) and IR data of 3 suggested that it was structurally related to 1. The A− D ring system and the substitutions of C-7 and C-11 in 1 and 3 were the same based on the similarities in the signals of their Δ14(15) double bonds, α,β-unsaturated-ε-lactone fragments, hydroxy moieties at C-7, and tigloyloxy moieties at C-11. Thus, compounds 3 and 1 featured the same carbon framework, which was confirmed by the 1H−1H COSY and key HMBC data (Figure S1, Supporting Information). However, the main difference between 3 and 1 was that the acetal ring in 1 was replaced by an α,β-unsaturated-γ-lactone moiety in 3 based on the observed resonances [δH 5.18 (d, J = 3.2 Hz) and 7.20 (br s); δC 80.8, 133.1, 150.0, and 173.7].15a This was verified by the coupling of H-22/H-23 in the 1H−1H COSY spectrum and the HMBC correlations of H-22/C-17, C-20, and C-21 as well as H3-26/C-24 and C-25. The similar NOESY spectra observed for 3 and 1 revealed the identity of their relative configurations. The absolute configuration of compound 3, ailanaltiolide C, was proposed to be (5R, 7R, 8R, 9R, 10R, 11R,

Figure 1. 1H−1H COSY, selected HMBC, and key NOESY correlations of 1.

similarity of its ECD spectrum to that of 1 (Figure S2, Supporting Information). The molecular formula of 3 was established as C36H50O9 by the (+)-HRESIMS ion at m/z 649.3354 [M + Na]+ (calcd for C36H50O9, 649.3347) and 13C NMR data, which required 12 1780



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C-24 configuration. The coupling constant (3J23,24 = 6.4 Hz) of H-23/H-24 suggested a pseudoaxial−axial assignment of the involved protons, which defined the (24R) absolute configuration.17,19 The configurations of other stereocenters of 5 were the same as those of 4 based on their similar ECD spectra (Figure S4, Supporting Information). Compound 6 had a molecular formula of C33H46O9 by its (+)-HRESIMS and 13C NMR data. The 1D NMR data of 6 (Tables 1 and 2) suggested that it was structurally related to compound 3, and the differences between these two structures were the substitution patterns at C-7 and C-11 as well as the Δ14(15) double bond being oxidized to a carbonyl group. These were confirmed by comparison of their chemical shifts: (i) the downfield-shifted H-7 (δH 4.93) in 6 and the HMBC crosspeak between H-7 and −OOCCH3 (δC 169.5) suggested that an acetoxy moiety was located at C-7 in 6 rather than the hydroxy group in 3; (ii) the C-11 oxymethine (δH 5.47, δC 69.2) in 3 was replaced by an sp3 methylene in 6, which was corroborated by the related spin-coupling segments of H-9/H11/H-12 in its 1H−1H COSY spectrum; and (iii) the Δ14(15) double bond (δC 160.0 and 120.3, δH 5.57) in 3 was oxidized to a C-15 carbonyl group (δC 217.8) in 6, which was confirmed by the HMBC correlations from H-14 and H2-16 to C-15. In the NOESY spectrum (Figure S3, Supporting Information), H14 correlated to H3-18, revealing that they were both αoriented. The other stereocenters had the same relative configurations as those of compound 3 by their similar Jvalues and NOESY spectra. Hence, compound 6 was named ailanaltiolide F and tentatively determined to have the same absolute configuration as that of 3, considering their biosynthetic relationship. Compound 7 possessed a molecular formula of C35H50O8, as revealed by its sodium-adduct ion at m/z 621.3417 [M + Na]+ (calcd for C35H50O8, 621.3398) in the (+)-HRESIMS and 13C NMR data. Comparison of the 1D NMR data of 7 (Tables 1 and 2) with those of 4 suggested that they were structural analogues, differing in that the signals for the α,β-unsaturatedγ-lactone moiety in 4 were replaced by resonances at δH 6.09 (H-21, s) as well as δC 114.8 and 140.7 in the spectra of 7. This suggested the presence of a dihydrofuran ring, which is unusual in natural apotirucallane-type triterpenoids.20 The HMBC correlations of H-21/C-22 and C-23 as well as the H-22/H23/H-24 spin systems in the 1H−1H COSY spectrum corresponded with this hypothesis (Figure S4, Supporting Information). In view of the J-value of H-23/H-24 (3J23,24 = 2.0 Hz) and the positive chirality indicated by the ECD spectrum, similar to that of 4 (Figure S5, Supporting Information), the (5R, 7R, 8R, 9R, 10R, 11R, 13S, 17R, 23R, 24S) absolute configuration of 7, ailanaltiolide G, was thus assigned. Compound 8, obtained as colorless gum, was found to have the formula C31H54O6 based on the (+)-HRESIMS (m/z: [M + Na]+, calcd for C31H54O6, 545.3813; found 545.3818) and 13 C NMR data, which indicated five IOHDs. Absorptions at 3398 and 1720 cm−1 in its IR spectrum indicated the presence of hydroxy and ester moieties.10 Comparison of the 1D NMR data of 8 (Tables 2 and 3) with those of the known compound 3-oxo-threo-23,24,25-trihydroxytirucall-7-ene (11) revealed a considerable degree of similarity in these two compounds except for their A-rings.7 The B−D-rings, the Δ7(8) double bond (δC 117.9 and 146.0), and the ester carbonyl moiety (δC 175.5) accounted for five IOHDs, implying that compound 8 possessed a 3,4-seco-tirucallane-type triterpenoid skeleton, which was verified by the HMBC correlations of H-2/C-3;

Figure 2. ECD and UV spectra of 1; arrow denotes the electric transition dipole of two chromophores.

13S, 17R, 23R, 24S) according to the similarity of its ECD curve in the 196−225 nm range (Figure S2, Supporting Information) to that of 1 and their biosynthetic correlations. Compound 3 carried both an α,β-unsaturated-ε-lactone A-ring and an α,β-unsaturated-γ-lactone moiety. This is the first report of the simultaneous presence of these moieties in an apotirucallane-type triterpenoid. Ailanaltiolide D (4) gave the molecular formula C35H48O9 via its (+)-HRESIMS and 13C NMR data. The 1D NMR data (Tables 1 and 2) indicated that 4 was highly similar to 3, with the only distinction being the presence of a hydroxy group at C-25 in 4 rather than the methoxy group in 3. This was confirmed by the chemical shift of C-25 in 4 being upfieldshifted to δC 72.5 (ΔδC −4.9 ppm), in conjunction with the HMBC cross-peaks from H-24, H3-26, and H3-27 to C-25. The relative configuration of 4 was assessed by the NOESY data and comparison of the NMR data of 3 and 4. The (5R, 7R, 8R, 9R, 10R, 11R, 13S, 17R, 23R, 24S) absolute configuration of 4 was defined by the similarity of the ECD spectrum to that of 3 (Figure S2, Supporting Information). The sodium-adduct HRESIMS ion at m/z 617.3068 [M + Na]+ (calcd for C35H46O8, 617.3085) established the molecular formula of ailanaltiolide E (5) as C35H46O8. Based on a comparison of the NMR data of 5 (Tables 1 and 2) with those of 4, the signals corresponding to one of the methyl groups in 4 had been replaced in 5 by those of an olefinic methylene [δH 5.02 and 5.04 (each 1H, br s); δC 142.4 (C) and 114.8 (CH2)]. The HMBCs of H-24/C-25 and C-26 as well as H226/C-27 indicated the Δ25(26) location of the double bond in 5. The relative configuration of 5 was highly similar to that of 4 via NMR comparison and the NOESY data, but differed in the 1781



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Table 3. 1H NMR Spectroscopic Data of Compounds 8−10 (δ in ppm, in CDCl3) 8a pos. 1a 1b 2a 2b 5 6a 6b 7a 7b 9 11a 11b 12a 12b 13 15a 15b 16a 16b 17 18 19 20 21a 21b 22a 22b 23 24 26 27 28 29 30

δH (J in Hz) 2.28, 1.61, 2.80, 2.18, 1.83, 2.20, 1.78, 5.20,

m overlap m overlap overlap m m d (2.4)

2.41, 1.50, 1.31, 1.63, 1.47,

m m overlap overlap m

9a δH (J in Hz) 1.98, m (2H) 2.76, overlap 2.31, dt (15.2, 3.2) 2.45, s

5.78, d (2.4) 2.74, overlap 1.68, m (2H) 2.00, m 1.71, m

2.32, m (2H)

2.09, m (2H)

2.00, 1.30, 1.50, 0.82, 0.86, 1.41, 0.92,

m overlap overlap s s overlap d (6.4)

1.86, 1.17, 4.12, 3.17, 1.31, 1.33, 1.30, 1.20, 0.99,

m overlap dd (8.8, 5.6) br s s s s s s

1.41, 1.20, 2.21, 0.80, 1.11, 1.75, 3.93, 3.42, 2.06, 1.53, 3.94, 2.93, 1.29, 1.33, 1.36, 1.38, 1.12,

m m m s s overlap overlap dd (12.0, 2.4) overlap m m d (8.8) s s s s s

the NOESY spectrum. However, the coupling constant of H23/H-24 was approximately zero, which corresponded to the syn-gauche conformation of C-23/C-24.21 The chemical shifts of C-20−C-27 in 8 showed similarities to those in 11,7 signifying a (23R,24S)-configuration. Accordingly, the structure of 8, ailanaltiolide H, was defined as methyl (23R,24S)4,23,24,25-tetrahydroxy-3,4-seco-tirucall-7-en-3-oate. Compound 9 possessed a molecular formula of C30H46O5, as indicated by the 13C NMR data and [M + Na]+ ion at m/z 487.3409 (calcd for C30H46O5, 487.3418) in its (+)-HRESIMS. Its NMR data (Tables 2 and 3) resembled those of the known compound bourjutinolone A (12),8 indicating that they were structurally related. The only difference was that an sp3 methylene was oxidized and, hence, a C-6 carbonyl group (δC 198.4) in 9. This moiety formed part of an α,β-unsaturated carbonyl group in the B-ring, which was in accordance with its IR absorption at 1655 cm−1. The HMBC correlations of H-5/ C-6; H-7/C-5, C-9, and C-14; and H-9/C-8 confirmed the presence of the carbonyl at C-6. The configurations of the stereocenters in the fused rings of tirucallane-type triterpenoids have been thoroughly studied, as pictured in Figure 4. The

10b δH (J in Hz) 1.46, 1.95, 2.50, 2.32, 1.35, 1.57, 1.50, 1.54, 1.33, 1.52, 1.85, 1.27, 3.64,

m overlap m m m m m m m overlap m m td (10.0, 4.8)

1.65, 1.54, 1.14, 1.96, 1.43, 2.37, 1.02, 0.97,

overlap m m m overlap m s s

1.43, s 2.28, m 2.04, m 2.62, m

Figure 4. 1H−1H COSY, selected HMBC, and key NOESY correlations of 9. 1.08, s 1.04, s 0.92, s

relative configurations of the stereogenic centers of the tetrahydro-2H-pyran ring were the same as those of 12 according to their similar NOESY data and 1D NMR spectra, in which the chemical shifts for C-20−C-27 of 9 were highly similar to those of 12. 8 To determine the absolute configuration, a single-crystal diffraction analysis of 9 was performed. The final refinement of Cu Kα data resulted in a Flack parameter of 0.06(11), allowing unambiguous assignment of the absolute configuration of 9 (Figure 5).22 Compound 10 was determined to have the molecular formula C27H42O4 based on its (+)-HRESIMS ion at m/z 453.2962 [M + Na]+ (calcd for C27H42O4, 453.2975) and 13C NMR data. The 1D NMR data of 10 (Tables 2 and 3) showed that it was structurally related to the known trinortriterpenoid cabralealactone (13), differing in that an sp3 methylene in 13 was replaced by an oxymethine (δC 70.7) in 10.9 The deshielded oxymethine moiety was assigned at C-12, based on the key HMBCs of H-13/C-12, C-14, C-17, C-11, and C-30 as well as H-17/C-12 and C-14. The relative configuration of 10 was similar to that of 13 based on their similar NOESY spectra. The NOESY correlations of H-12/H-17 and H3-30 suggested OH-12 was β-oriented. The ECD spectrum of 10 showed a positive Cotton effect at 288 nm due to the n → π* electronic transition of the C-3 carbonyl, corresponding to a UV absorption maximum at 288 nm (Figure 6). On the basis of the cyclohexanone octant rule, the (5R, 8R, 9R, 10R, 12R, 3R,

a


H3-29/C-4 and C-5; and H3-19/C-1, C-5, C-9, and C-10. The 2D structure of 8 was thus unequivocally elucidated (Figure 3).

Figure 3. 1H−1H COSY, selected HMBC, and key NOESY correlations of 8.

In its NOESY spectrum (Figure 3), the cross-peaks of H3-28/ H-5, H-5/H-9, and H-9/H3-18 suggested that these protons were cofacial and α-oriented. The correlation of H-17/H3-30 indicated that H-17 and H3-30 were β-oriented. Additionally, due to the free rotation of the triol side chain, the relative configurations of C-23 and C-24 could not be determined from 1782



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14R, 17S, 20S) absolute configuration of 10 was thus assigned.23 Ailanaltiolides A−G represent seven highly oxygenated examples of apotirucallane-type triterpenoids, each carrying an α,β-unsaturated-ε-lactone A-ring and a diversely modified eight-carbon side chain. Ailanaltiolides A−F are decorated with a five-membered acetal moiety or an α,β-unsaturated-γ-lactone moiety in their side chains. Notably, ailanaltiolide G possesses a dihydrofuran ring, which is rare in apotirucallane-type triterpenoids. Considering the cytotoxic activity of triterpenoids previously obtained from this plant,5a the isolated compounds were tested against A549, 786-O, HepG2, and HeLa cell lines using the MTT method. Colchicine was used as the positive control. Compounds 2, 7, and 8 displayed inhibitory activity against all the tested cell lines. Compound 2 exhibited considerable cytotoxic potency against 786-O cells with an IC50 value of 8.2 μM in vitro. Compounds 1, 3−6, and 9−13 were not active against the cells tested (IC50 > 40 μM) (Table 4). A structural comparison between compound 2 and the other compounds indicated that the five-membered acetal moiety in the C-17 side chain was presumably the cytotoxic pharmacophore. Interestingly, compound 2 exhibited the highest cytotoxicity,

Figure 5. ORTEP drawing of 9.

Figure 6. ECD and UV spectra and octant projection of compound 10. 1783



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mg). Fraction F3c (2.5 g) was chromatographed on an RP-C18 silica gel column (MeOH/H2O, 40% → 100%) and further separated by silica gel CC (CHCl3/EtOAc, 20:1 → 1:1) to give five subfractions (F3c1−F3c5). Fraction F3c4 (41.3 mg) was further purified by semipreparative HPLC (40% MeCN/H2O) to yield compounds 3 (1.6 mg), 4 (2.3 mg), and 5 (3.1 mg). Fractions F3c5 (23.3 mg) and F3c6 (28.6 mg) were also separated using semipreparative HPLC (40% MeCN/H2O) to afford compounds 6 (4.2 mg) and 7 (1.3 mg), respectively. Fraction F3e (1.9 g) was subjected to silica gel CC eluted with petroleum ether/EtOAc (10:1 → 1:1). Further separation on an RPC18 silica gel column (MeOH/H2O, 50:50 → 100:0) gave five subfractions (F3e1−F3e5). Compound 9 (3.9 mg) recrystallized from subfraction F3e4 (102.1 mg). Subfractions F3e2 (124.3 mg) and F3e3 (145.4 mg) were both purified by silica gel CC (petroleum ether/ acetone, 15:1 → 1:1) and afforded compounds 11 (7.8 mg) and 12 (9.7 mg). Fraction F3e4 (133.6 mg) afforded compounds 8 (1.5 mg) and 10 (8.4 mg) by semipreparative HPLC (35% MeCN/H2O). Similarly, fraction F3e5 (154.4 mg) afforded compound 13 (16.8 mg). Ailanaltiolide A (1): white, amorphous powder; [α]24D −8 (c 0.1, MeOH); IR (KBr) νmax 3368, 2925, 2852, 1685, 1449, 1261, 1028, 798 cm−1; UV (MeOH) λmax (log ε) 211 (3.28) nm; HRESIMS m/z 667.3801 [M + Na]+ (calcd for C37H56O9Na, 667.3817); 1H NMR data, Table 1; 13C NMR data, Table 2. Ailanaltiolide B (2): white, amorphous powder; [α]24D +10 (c 0.1, MeOH); IR (KBr) νmax 3366, 2930, 2834, 1656, 1450, 1261, 1028, 796 cm−1; UV (MeOH) λmax (log ε) 212 (3.20) nm; HRESIMS m/z 667.3801 [M + Na]+ (calcd for C37H56O9Na, 667.3817); 1H NMR data, Table 1; 13C NMR data, Table 2. Ailanaltiolide C (3): white, amorphous powder; [α]24D +14 (c 0.1, MeOH); IR (KBr) νmax 3398, 2924, 2855, 1687, 1459, 1261, 1094, 1028, 799 cm−1; UV (MeOH) λmax (log ε) 213 (3.20) nm; HRESIMS m/z 649.3354 [M + Na]+ (calcd for C36H50O9Na, 649.3347); 1H NMR data, Table 1; 13C NMR data, Table 2. Ailanaltiolide D (4): white, amorphous powder; [α]24D +10 (c 0.1, MeOH); IR (KBr) νmax 3365, 2934, 2833, 1676, 1450, 1261, 1028, 796 cm−1; UV (MeOH) λmax (log ε) 213 (3.18) nm; HRESIMS m/z 635.3198 [M + Na]+ (calcd for C35H48O9Na, 635.3191); 1H NMR data, Table 1; 13C NMR data, Table 2. Ailanaltiolide E (5): white, amorphous powder; [α]24D +16 (c 0.1, MeOH); IR (KBr) νmax 3368, 2924, 2852, 1578, 1459, 1260, 1027, 799 cm−1; UV (MeOH) λmax (log ε) 211 (3.26) nm; HRESIMS m/z 617.3068 [M + Na]+ (calcd for C35H46O8Na, 617.3085); 1H NMR data, Table 1; 13C NMR data, Table 2. Ailanaltiolide F (6): white, amorphous powder; [α]24D −10 (c 0.1, MeOH); IR (KBr) νmax 3357, 2957, 2833, 1686, 1450, 1267, 1026, 739 cm−1; UV (MeOH) λmax (log ε) 213 (3.36) nm; HRESIMS m/z 609.3040 [M + Na]+ (calcd for C33H46O9Na, 609.3034); 1H NMR data, Table 1; 13C NMR data, Table 2. Ailanaltiolide G (7): white, amorphous powder; [α]24D +23 (c 0.1, MeOH); IR (KBr) νmax 3359, 2933, 2833, 1678, 1450, 1262, 1029, 738 cm−1; UV (MeOH) λmax (log ε) 211 (3.24) nm; HRESIMS m/z 621.3417 [M + Na]+ (calcd for C35H50O8Na, 621.3398); 1H NMR data, Table 1; 13C NMR data, Table 2. Ailanaltiolide H (8): white, amorphous powder; [α]24D −37 (c 0.1, MeOH); IR (KBr) νmax 3398, 2924, 2858, 1720, 1458, 1380, 1263, 1031, 797 cm−1; UV (MeOH) λmax (log ε) 204 (3.21) nm; HRESIMS m/z 545.3818 [M + Na]+ (calcd for C31H54O6Na, 545.3813); 1H NMR data, Table 3; 13C NMR data, Table 2. Ailanaltiolide I (9): colorless needles (chloroform); mp 215−217 °C; [α]24D +15 (c 0.1, MeOH); IR (KBr) νmax 3360, 2932, 2833, 1450, 1412, 1109, 1028, 796 cm−1; UV (MeOH) λmax (log ε) 207 (3.29) nm; HRESIMS m/z 487.3409 [M + H]+ (calcd for C30H47O5, 487.3418); 1H NMR data, Table 3; 13C NMR data, Table 2. Ailanaltiolide J (10): white, amorphous powder; [α]24D +50 (c 0.1, MeOH); IR (KBr) νmax 3396, 2961, 2926, 2854, 1703, 1459, 1261, 1030, 737 cm−1; UV (MeOH) λmax (log ε) 203 (3.25), 288 (2.42) nm; HRESIMS m/z 453.2962 [M + Na]+ (calcd for C27H42O4Na, 453.2975); 1H NMR data, Table 3; 13C NMR data, Table 2.

Table 4. Cytotoxicity Assay Results of All Compounds against Different Human Tumor Cell Lines IC50,a in μM compound

A549

786-O

HepG2

HeLa

1 2 3 4 5 6 7 8 9 10 11 12 13 colchicineb

>40 12.5 >40 >40 >40 >40 39.8 38.6 >40 >40 >40 >40 >40 0.043

>40 8.2 >40 >40 >40 >40 34.4 27.4 >40 >40 >40 >40 >40 0.022

>40 38.8 >40 >40 >40 >40 38.8 35.5 >40 >40 >40 >40 >40 0.078

>40 38.4 >40 >40 >40 >40 33.2 38.4 >40 >40 >40 >40 >40 0.027

a

IC50 = compound concentration required to inhibit tumor cell proliferation by 50% after cells were treated with compounds for 72 h. b Colchicine as a positive control.

while compound 1 did not exhibit any inhibitory activity, suggesting that the β-orientation of the 21-OMe moiety in the acetal ring may contribute to the cytotoxicity.

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EXPERIMENTAL SECTION

General Experimental Procedures. The determination of the melting point was achieved by an X-4 digital display micro melting point apparatus and was uncorrected. Optical rotations were measured at room temperature using a Perkin−Elmer 341 polarimeter. For experimental ECD data analysis, a JASCO J-720 spectropolarimeter was used. A Nicolet NEXUS 670 FT-IR spectrometer was used to acquire the IR data. The NMR spectroscopic data were acquired by Bruker Avance III-400 and Bruker DRX-800 instruments using CDCl3 as the solvent. The chemical shift values (δ) were recorded in ppm relative to the solvent signal. A Bruker APEXII instrument was used to obtain HRESIMS data. For the separation of different compounds, Sephadex LH-20, MCI gel, RP-C18 gel (Amersham Pharmacia Biotech), and silica gel purchased from Qingdao Marine Chemical Inc., China (200−300 mesh), were used. The compounds were isolated using semipreparative HPLC (Waters 1525) on a C18 ODS-A column (YMC Co. Ltd., S-5 μm, 250 × 10 mm). Plant Material. The roots of A. altissima were collected in May 2015 from Fushan County, Shanxi Province, China. The plants were authenticated by Dr. Jian-Yin Li at Lanzhou University (LZU). A sample (voucher specimen no. 20150815-4) was deposited at the Natural Product Laboratory of LZU. Extraction and Isolation. The roots of A. altissima (10.0 kg) were air-dried, powdered, and extracted with MeOH (3 × 50 L) at room temperature. After filtering the crude extract, the solvent was removed by evaporation under vacuum to obtain 460 g of extract. The extract was dissolved in 2 L of water, and the suspension extracted with EtOAc (5 × 1.5 L), which yielded 105 g of the EtOAc-soluble portion. This portion was fractionated using microporous resin eluted with EtOH/H2O. Four fractions (F1−F4) were collected based on the ratio of eluent (EtOH/H2O, 30, 50, 80, 100%). Fraction F3 (50 g, 80% EtOH/H2O) was separated on a silica gel column eluted with a mixture of petroleum ether/acetone gradient (20:1 → 1:1), which afforded six fractions, F3a−F3f. A Sephadex LH-20 column was used for the purification of fraction F3b (2.4 g). After elution with MeOH, four subfractions (F3b1−F3b4) were obtained. Fraction F3b2 (0.9 g) was subjected to an RP-C18 silica gel column (MeOH/H2O, 40% → 100%) and then purified by semipreparative HPLC (mobile phase: 45% MeCN/H2O), which yielded compounds 1 (1.8 mg) and 2 (2.1 1784



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X-ray Diffraction Analysis of Ailanaltiolide I (9). Colorless, block crystals were obtained from CHCl3, which were suitable for the further X-ray crystallography analysis. The analysis of the X-ray crystallography is described in the Supporting Information, and the key diffraction parameters of compound 9 are listed in Table S1 (Supporting Information). The crystallographic data for compound 9 have been deposited at the Cambridge Crystallographic Data Centre with deposition no. CCDC 1822668. Cytotoxicity Assays. Standard protocol was adopted for cell growth inhibition analysis.24

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Gao, K. J. Nat. Prod. 2015, 78, 1037−1044. (c) Zhao, Q. Q.; Song, Q. Y.; Jiang, K.; Li, G. D.; Wei, W. J.; Li, Y.; Gao, K. Org. Lett. 2015, 17, 2760−2763. (7) Campos, A. M.; Oliveira, F. S.; Machado, M. I. L.; Filho, B. M. R.; Matos, F. J. A. Phytochemistry 1991, 30, 1225−1229. (8) Arriaga, A. C.; De-Mesquita, A. C.; Pouliquen, Y. B. M.; Cavalcante, S. H.; Siqueira, J. A. D.; Alegrio, L. V.; Braz-Filho, R. An. Acad. Bras. Cienc. 2002, 74, 415−424. (9) (a) Nagaya, H.; Tobita, Y.; Nagae, T.; Itokawa, H.; Takeya, K.; Halim, A. F.; Halim, A. O. B. Phytochemistry 1997, 44, 1115−1119. (10) Omobuwajo, O. R.; Martin, M. T.; Perromat, G.; Sevenet, T.; Pais, M. J. Nat. Prod. 1996, 59, 614−617. (11) Joseph-Nathan, P.; Wesener, J. R.; Günther, H. Org. Magn. Reson. 1984, 22, 190−191. (12) Chen, H. Y.; Hu, Z. Y.; Tang, C. P.; Feng, Y. J.; Yao, S.; Ye, Y. Tetrahedron Lett. 2013, 54, 4150−4153. (13) Zhang, F.; Wang, J. S.; Gu, Y. C.; Kong, L. Y. J. Nat. Prod. 2012, 75, 538−546. (14) (a) Campana, P. R. V.; Coleman, C. M.; Sousa, L. P.; Teixeira, M. M.; Ferreira, D.; Braga, F. C. J. Nat. Prod. 2016, 79, 2279−2286. (b) Ren, Y. L.; VanSchoiack, A.; Chai, H. B.; Goetz, M.; Kinghorn, A. D. J. Nat. Prod. 2015, 78, 2440−2446. (15) (a) Yang, M. H.; Wang, J. S.; Luo, J. G.; Wang, X. B.; Kong, L. Y. Bioorg. Med. Chem. 2011, 19, 1409−1417. (b) Luo, X. D.; Wu, S. H.; Wu, D. G.; Ma, Y. B.; Qi, S. H. Tetrahedron 2002, 58, 6691−6695. (c) Xu, J.; Xiao, D.; Lin, Q. H.; He, J. F.; Liu, W. Y.; Xie, N.; Feng, F.; Qu, W. J. Nat. Prod. 2016, 79, 1899−1910. (16) Xie, B. J.; Yang, S. P.; Chen, H. D.; Yue, J. M. J. Nat. Prod. 2007, 70, 1532−1535. (17) (a) Zhou, Z. F.; Scafati, T. O.; Liu, H. L.; Gu, Y. C.; Kong, L. Y.; Guo, Y. W. Fitoterapia 2014, 97, 192−197. (b) Balderrama, L.; Braca, A.; Garcia, E.; Melgarejo, M.; Pizza, C.; Tommasi, N. D. Biochem. Syst. Ecol. 2001, 29, 331−333. (18) Biavatti, M. W.; Vieira, P. C.; Fernandes, J. B.; Albuquerque, S. J. Nat. Prod. 2002, 65, 562−565. (19) (a) Wang, J. R.; Liu, H. L.; Kurtan, T.; Mandi, A.; Antus, S.; Li, J. Org. Biomol. Chem. 2011, 9, 7685−7696. (b) Cui, J. X.; Deng, Z. W.; Xu, M. J.; Proksch, P.; Li, Q. S.; Lin, W. H. Helv. Chim. Acta 2009, 92, 139−150. (20) Grosvenor, S. N. J.; Mascoll, K.; McLean, S.; Reynolds, W. F.; Tinto, W. F. J. Nat. Prod. 2006, 69, 1315−1318. (21) (a) McChesney, J. D.; Dou, J.; Sindelar, R.; Goins, K. D.; Walker, L. A.; Rogers, R. D. J. Chem. Crystallogr. 1997, 27, 283−290. (b) Toume, K.; Nakazawa, T.; Ohtsuki, T.; Arai, M. A.; Koyano, T.; Kowithykorn, T.; Ishibashi, M. J. Nat. Prod. 2011, 74, 249−255. (22) Flack, H. D. Acta Crystallogr., Sect. A: Found. Crystallogr. 1983, A39, 876−881. (23) (a) Xiong, J.; Wan, J.; Ding, J.; Wang, P. P.; Ma, G. L.; Li, J.; Hu, J. F. J. Nat. Prod. 2017, 80, 2874−2882. (b) Moffitt, W.; Woodward, R. B.; Moscowitz, A.; Klyne, W.; Djerassi, C. J. Am. Chem. Soc. 1961, 83, 4013−4018. (24) Chen, J. J.; Li, W. X.; Gao, K.; Jin, X. J.; Yao, X. J. J. Nat. Prod. 2012, 75, 1184−1188.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jnatprod.8b00208. NMR, HRESIMS, UV, and IR spectra of 1−10, key COSY and HMBC correlations for 3, 6, 7, key NOESY correlations for 3, 6, 7, and ECD spectra of 2−5, 7 (PDF) Crystallographic data of 9 (CIF)

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AUTHOR INFORMATION

Corresponding Authors

*(J. Chen) E-mail: [email protected]. Tel: +86-931-8912592. Fax: 86-931-8915557. *(K. Gao) E-mail: [email protected]. Tel: +86-9318912592. Fax: 86-931-8915557. ORCID

Jian-Jun Chen: 0000-0001-5937-5569 Kun Gao: 0000-0002-3856-3672 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The National Natural Science Foundation of China (31470421, 21778027) financially supported this study. REFERENCES

(1) Chen, S. K.; Li, H.; Chen, B. Y. In Zhongguo Zhiwu Zhi; Science Press: Beijing, 1978; Vol. 43, pp 1−2. (2) Nanjing University of Chinese Medicine. In Dictionary of Traditional Chinese Materia Medica; Shanghai Scientific and Technical Press: Shanghai, 2006; pp 680, 3650. (3) (a) Wang, Y.; Wang, W. J.; Su, C.; Zhang, D. M.; Xu, L. P.; Zhang, X. Q.; Ye, W. C. Bioorg. Med. Chem. Lett. 2013, 23, 654−657. (b) Wang, R. X.; Mao, X. X.; Zhou, J.; Zhang, M. L.; Gu, Y. C. Chem. Nat. Compd. 2017, 53, 28−32. (4) (a) He, Y. D.; Peng, S. H.; Wang, J. H.; Chen, H.; Cong, X. N.; Chen, A.; Hu, M. C.; Qin, M.; Wu, H. G.; Gao, S. M.; Yi, Z. F.; Liu, M. Y. Nat. Commun. 2016, 7, 13122−13136. (b) Okunade, A. L.; Bikoff, R. E.; Casper, S. J.; Oksman, A.; Goldberg, D. E.; Lewis, W. H. Phytother. Res. 2003, 17, 675−677. (c) Ni, J. C.; Shi, J. T.; Tan, Q. W.; Chen, Q. J. Nat. Prod. Res. 2018, 32, 1−7. (d) Wang, R. X.; Mao, X. X.; Zhou, J.; Zhang, M. L.; Wu, Y. B.; Huo, C. H.; Shi, Q. W.; Sauriol, F.; Gu, Y. C. Chem. Nat. Compd. 2017, 53, 28−32. (e) Caboni, P.; Ntalli, N. G.; Aissani, N.; Cavoski, I.; Angioni, A. J. Agric. Food Chem. 2012, 60, 1146−1151. (5) (a) Hong, Z. L.; Xiong, J.; Wu, S. B.; Zhu, J. J.; Hu, J. F. Phytochemistry 2013, 86, 159−167. (b) Liu, J. M.; Zhang, Z. W.; Yao, J.; Wang, J. L.; Zhao, M.; Zhang, S. J. Chem. Ind. Fore. Prod 2013, 33, 121−127. (6) Chen, J. J.; Fei, D. Q.; Chen, S. G.; Gao, K. J. Nat. Prod. 2008, 71, 547−550. (b) Jiang, K.; Chen, L. L.; Wang, S. F.; Wang, Y.; Li, Y.; 1785


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