6-Fused Triterpenoid Acids from ... - ACS Publications

Article pubs.acs.org/jnp

Rearranged 6/6/5/6-Fused Triterpenoid Acids from the Stems of Kadsura coccinea Zheng-Xi Hu,†,‡ Kun Hu,‡ Yi-Ming Shi,‡ Wei-Guang Wang,‡ Xue Du,‡ Yan Li,‡ Yong-Hui Zhang,*,† Jian-Xin Pu,*,‡ and Han-Dong Sun‡ †

Hubei Key Laboratory of Natural Medicinal Chemistry and Resource Evaluation, School of Pharmacy, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, People’s Republic of China ‡ State Key Laboratory of Phytochemistry and Plant Resources in West China, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650201, People’s Republic of China S Supporting Information *

ABSTRACT: Fourteen new rearranged 6/6/5/6-fused triterpenoid acids, namely, kadcoccine acids A−N (1−14), were isolated from an EtOAc-soluble extract of the stems of Kadsura coccinea. Their structures were characterized mainly by analyzing 1D and 2D NMR and HRESIMS data and were shown to feature a rare 14(13→12)-abeo-lanostane skeleton. Compounds 7 and 8 represented the first examples of a 5-substituted 2(5H)-furanone motif on the C-17 side chain of this skeleton. The absolute configurations of C-23 for compounds 1, 7, and 8 were determined by comparison of their experimental electronic circular dichroism spectra. All the isolates were screened for their in vitro cytotoxicity against six human tumor cell lines (HL-60, SMMC7721, A-549, MCF-7, SW-480, and HeLa), and compounds 2 and 8 exhibited weak inhibitory effects with IC50 values ranging from 3.11 to 7.77 μM.

H

Guangxi Province. Also reported were six lanostane-related triterpenoids, kadcoccinones A−F, possessing 6/6/5/6-, 6/6/ 9-, 18(13→12)-abeo-6/6/6/5-, and 6/6/6/5-fused ring systems from K. coccinea collected in the Menglun district of Yunnan Province. In the present work, an EtOAc-soluble extract of the stems of K. coccinea was investigated, resulting in the isolation of 14 new rearranged 6/6/5/6-fused triterpenoid acids, kadcoccine acids A−N (1−14). All the isolates are structurally characterized by a rare 14(13→12)-abeo-6/6/5/6-fused rearranged lanostane-type triterpenoid skeleton, which occurred mainly in the C/D-ring systems via a Wagner−Meerwein rearrangement reaction.1 Only 11 triterpenoids possessing this unique tetracyclic carbocyclic core have been reported to date.1,14,15 Importantly, a pair of C-23 epimeric molecules (7 and 8) represented the first examples of rearranged 6/6/5/6fused triterpenoids featuring a 5-substituted 2(5H)-furanone motif on the C-17 side chain. In this report, the isolation and structure identification of new compounds 1−14, as well as their in vitro cytotoxicity, are discussed.

istorically, members of the genus Kadsura (Schisandraceae) were economically and medicinally valuable plants,1 and the stems and roots of Kadsura species have been commonly applied in traditional Chinese medicines (TCMs) for the treatment of blood deficiency, numb hands and feet, arthralgia, and irregular menstruation.2 Most notably, Kadsura interior has been used as a major ingredient in one of the TCMs, colloquially called “Dian-ji-xue-teng”, and is recorded in the Chinese Pharmacopeia.3 Previous phytochemical investigations on this genus revealed that it was a rich source of lignans and triterpenoids, many of which showed a wide array of biological activities, including antitumor,4 antilipid peroxidative,5 anti-HIV,6 antihepatitis,7 and neuroprotective activities.8 Kadsura coccinea (Lem.) A. C. Smith, a climbing plant distributed in southwest China, has been widely used to treat cancer and dermatosis and as an anodyne.9 As part of a systematic search for naturally occurring bioactive agents from this species,10−16 some schinortriterpenoids (SNTs) and cycloartane-related triterpenoids were obtained from K. coccinea collected in the Honghe Prefecture of Yunnan Province, and some rearranged lanostane-related triterpenoids with diverse skeletal types, such as 6/6/5-, 6/6/6-, 6/6/5/5-, 6/6/5/6-, 2,3seco-6/6/5/6-, and 3,4-seco-6/6/5/6-fused ring systems, were obtained from K. coccinea collected in the Ziyuan Prefecture of © 2016 American Chemical Society and American Society of Pharmacognosy

Received: June 3, 2016 Published: October 5, 2016 2590

DOI: 10.1021/acs.jnatprod.6b00508 J. Nat. Prod. 2016, 79, 2590−2598

Journal of Natural Products

Article

Chart 1

Table 1. 1H NMR Spectroscopic Data of Kadcoccine Acids A−G (1−7) (δ in ppm, J in Hz) 1a,d

no. 1 2 3 5 6 7 9 11 12

1.01, m; 1.76, m 1.61, m; 1.76, m 4.84, br s 1.52, dd (5.0, 10.8) 1.92, m 5.52, m 2.66, br t (10.3) 1.77, m 2.25, m

15 16 17 18

1.23, m; 1.98, m 1.63, m; 1.97, m 2.00, m 4.92, br s

19 20 21 22 23 24 26 27 28 29 30 −OAc

1.17, 0.88, 0.92, 2.12,

2b,d

4a,d

5c,d

6c,d

1.02, 1.56, 4.59, 1.26,

m; 1.55, m m; 1.83, m br s m

1.16, 1.76, 3.68, 1.82,

m; 2.33, m m; 2.02, m br s m

1.39, 1.84, 3.51, 1.10,

m; 1.45, m m; 1.90, m dd (4.1, 11.4) m

1.11, 1.68, 4.80, 2.69,

m; 1.84, m m; 1.91, m br s s

1.39, dd (3.8, 11.2)

1.84, 5.35, 2.18, 1.38, 2.10,

m m m m; 1.48, m m

2.05, 5.59, 2.52, 1.66, 2.15,

m m br t (10.4) m; 1.85, m dd (4.3, 12.4)

2.09, 5.55, 2.47, 1.56, 2.20,

m m m m m

5.92, 2.91, 1.78, 2.26,

br d (1.2) m m; 1.96, m m

1.96, 5.51, 2.51, 1.46, 2.18,

1.05, m; 1.58, m 1.55, m; 1.69, m 1.82, m 4.65, d (2.2); 4.72, d (2.2) 1.04, s 0.97, s 2.51, m 1.72, m 1.29, d (6.4) 0.96, m 1.18, m; 2.23, m 1.55, m; 2.23, m 5.04, m 7.54, br d (8.1) 6.79, s 2.19, s 1.83, s s s s s

3a,d

1.00, 0.92, 0.83, 2.00,

s s s s

1.57, m; 1.61, m 2.26, m; 2.73, m

1.15, 1.80, 3.69, 1.81,

m; 2.35, m m; 2.05, m br s m

1.24, m; 1.86, m 1.61, m; 1.94, m 1.95, m 4.78, d (2.6); 4.83, d (2.6) 1.17, s 1.95, m 1.09, d (5.5) 1.25, m; 1.83, m 2.84, m; 2.90, m 6.03, t (7.1)

1.24, m; 1.82, m 1.62, m; 1.92, m 1.96, m 4.83, d (2.4); 4.92, d (2.4) 1.11, s 1.92, m 1.12, m 1.25, m; 1.84, m 2.82, m; 2.91, m 6.02, t (7.1)



2.04, m 5.57, m 2.46, br t (10.3) 1.61, m; 1.84, m 2.13, dd (3.5, 12.3) 1.20, m; 1.77, m 1.58, m; 1.74, m 1.94, m 4.78, br s; 4.85, br s 1.18, s 1.94, m 1.07, d (3.7) 1.47, m; 1.90, m 5.08, m 7.21, m

2.19, 1.15, 1.00, 1.26,

2.18, 1.15, 1.16, 1.31,

2.17, 1.09, 1.43, 1.34, 2.13,

2.19, 1.14, 1.08, 1.22,

1.89, 1.12, 1.00, 1.26,

s s s s

s s s s

s s s s s

m; 2.06, m br d (6.9) br t (10.3) m; 1.53, m m

7a,d

s s s s

s s s s

Recorded at 600 MHz in pyridine-d5. bRecorded at 600 MHz in CDCl3. cRecorded at 400 MHz in pyridine-d5. d“m” means overlapped or multiplet with other signals.

a

2591



Article

Table 2. 1H NMR Spectroscopic Data of Kadcoccine Acids H−N (8−14) (δ in ppm, J in Hz) 8a,c

no.

9b,c

10a,c

11a,c

12a,c

1

1.20, m; 2.33, m

1.40, m; 1.56, m

1.09, m; 1.76, m

1.57, m

1.04, m; 1.68, m

2

1.75, m; 2.02, m

2.18, m; 2.70, m

1.59, m; 1.76, m

2.19, m; 2.65, m

1.55, m; 1.72, m

3 5

3.67, br s 1.81, m

1.55, m

4.81, br s 1.47, m

1.34, dd (3.6, 11.8)

6 7 9 11

2.03, 5.56, 2.57, 1.65,

1.89, 3.36, 2.53, 1.64,

1.92, 5.58, 2.40, 1.89,

1.94, 5.55, 2.43, 1.62,

12 15

2.15, dd (3.9, 12.2) 1.19, m; 1.77, m

2.33, dd (6.1, 11.8) 1.28, m; 1.97, m

16

1.55, m; 1.70, m

17 18

m; 2.03, m m m m; 1.75, m

4.78, br s 1.45, dd (3.9, 11.7) 1.91, m 5.59, m 2.20, m 1.64, m; 2.04, m

2.68, br d (9.3) 1.46, m; 1.81, m

2.65, m 1.45, m; 1.79, m

2.80, br d (8.9) 1.37, m; 1.80, m

1.55, m; 1.95, m

2.02, m

2.02, m

2.21, m

1.98, m 4.84, d (2.2); 4.93, d (2.2) 1.29, s 1.95, m 1.11, d (6.0) 1.25, m; 1.83, m

4.44, d (12.0); 4.80, d (12.0) 1.03, s 3.19, m 1.08, d (6.5) 1.55, m; 1.66, m

4.40, d (12.0); 4.79, d (12.0) 1.14, s 3.19, m 1.08, d (6.8) 1.55, m; 1.67, m

10.53, s

19 20 21 22

1.88, m 4.79, d (2.3); 4.85, d (2.3) 1.24, s 2.21, m 1.10, d (6.5) 1.32, m; 1.71, m

23

5.05, m

2.77, m; 2.93, m

2.78, m

2.78, m

2.74, m

24 27 28 29 30 −OAc

7.10, 1.86, 1.13, 0.98, 1.25,

6.02, 2.18, 0.79, 0.99, 1.21,

6.08, 2.13, 1.14, 0.87, 0.89, 2.01,

6.10, 2.14, 1.13, 1.03, 1.18,

6.02, 2.13, 1.08, 0.84, 0.88, 1.99,

a

m m br t (10.4) m; 1.84, m

m s s s s

m m br t (10.4) m; 1.70, m

t (7.3) s s s s

m br d (5.4) m m

t (6.8) s s s s s

t (7.2) s s s s

1.00, 3.72, 1.08, 1.58,

s m m m; 1.71, m

t (7.3) s s s s s

13a,c 1.13, m; 1.84, m 1.68, m; 1.85, m 4.84, br s 1.53, m 1.93, m 5.50, m 2.12, m 1.55, m; 2.18, m 2.03, m 1.37, m; 1.68, m 1.54, m; 1.96, m 1.86, m 1.46, s 1.05, s 2.37, m 1.27, d (6.9) 1.43, m; 1.93, m 2.86, m; 2.96, m 6.12, t (7.1) 2.15, s 1.34, s 0.91, s 0.89, s 2.06, s

14a,c 1.11, m; 1.79, m 1.64, m; 1.79, m 4.83, br s 1.51, dd (4.1, 11.0) 1.94, m 5.71, m 2.11, m 2.18, m; 2.84, m

1.56, m; 1.65, m 1.80, m; 1.85, m 2.64, m 4.69, br s 0.95, 2.55, 1.11, 1.28,

s m d (6.7) m; 1.80, m

2.85, m 6.06, 2.07, 1.16, 0.86, 0.90, 2.06,

t (7.0) s s s s s

Recorded at 600 MHz in pyridine-d5. bRecorded at 500 MHz in pyridine-d5. c“m” means overlapped or multiplet with other signals.

■

RESULTS AND DISCUSSION Compound 1 was obtained as a white, amorphous powder, and its molecular formula was deduced to be C32H48O5 based on the HRESIMS ion at m/z 535.3391 ([M + Na]+, calcd for 535.3394) and 13C NMR data. The 1H NMR data (Table 1) showed the characteristic signals attributable to one methyl doublet at δH 1.29 (d, J = 6.4 Hz, H3-21); six methyl singlets at δH 1.04 (H3-19), 2.19 (H3-26), 1.17 (H3-28), 0.88 (H3-29), 0.92 (H3-30), and 2.12 (−OAc); two oxygenated methines at δH 4.84 (br s, H-3) and 5.04 (m, H-23); and four olefinic protons at δH 5.52 (m, H-7), 4.92 (2H, br s, H2-18), and 7.54 (br d, J = 8.1 Hz, H-24). Examination of the 13C NMR (Table 3) and DEPT spectroscopic data disclosed 32 carbon resonances corresponding to one acetoxy group, six methyls (one secondary and five tertiary), eight methylenes (one olefinic), nine methines (two oxygenated and two olefinic), six quaternary carbons (three olefinic), and one carboxyl group. The presence of three double bonds and two carbonyls accounted for five of the nine indices of hydrogen deficiency required by its molecular formula, illustrating the presence of a tetracyclic ring system for 1. Analysis of the NMR and HRESIMS data of 1 implied that its structural features were similar to those of the known compound kadcoccinone A,15 whose absolute configuration was confirmed by single-crystal X-ray crystallographic analysis. The corresponding 1H−1H COSY and HMBC correlations (Figure 1) of 1 further confirmed its 2D structure and indicated

that the structures of these two compounds were consistent with a 14(13→12)-abeo-6/6/5/6-fused rearranged lanostanetype triterpenoid skeleton, in which the configurations of the A/B/C/D-ring systems remained intact, differing only in the absolute configurations of C-23. This assumption was confirmed by comparison of the electronic circular dichroism (ECD) spectra (Figure S8, Supporting Information), showing an opposite Cotton effect at approximately 214 nm ascribable to the adjacent α,β-unsaturated hydroxycarbonyl unit. Therefore, the absolute configuration of C-23 in 1, kadcoccine acid A, was established as R. Compound 2, obtained as a white, amorphous powder, had a molecular formula of C32H46O5 based on its HRESIMS analysis (m/z 509.3261, [M − H]−, calcd for 509.3272), which was two mass units less than that of 1. Comparison of the NMR spectroscopic data of 2 with those of 1 (Tables 1 and 3) revealed that they possessed identical carbocyclic cores, with the only difference being at C-23 (δC 66.6 for 1, 207.7 for 2), showing that the hydroxy group was replaced by a carbonyl group in 2 and giving rise to the H-24 olefinic signal resonating as a singlet at δH 6.79 (s, H-24). The ROESY spectrum (Figure S15, Supporting Information) showed that the relative configuration of 2 was identical to that of 1. Accordingly, the structure of 2, kadcoccine acid B, was defined as shown. Compounds 3 and 4, obtained as white, amorphous powders, were assigned the same molecular formula C30H46O3 (eight indices of hydrogen deficiency) by analyzing the HRESIMS and 2592


a

2593

30.8, CH2 23.4, CH2 79.1, CH 36.7, C 41.0, CH 23.3, CH2 115.1, CH 152.1, C 51.6, CH 35.1, C 32.0, CH2 51.2, CH 152.1, C 44.5, C 31.1, CH2 25.5, CH2 49.4, CH 112.3, CH2 23.8, CH3 28.4, CH 19.3, CH3 41.7, CH2 66.6, CH 146.9, CH 128.1, C 13.7, CH3 171.4, C 24.7, CH3 23.0, CH3 28.7, CH3 170.8, C 21.5, CH3

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 −OAc

30.3, CH2 22.7, CH2 79.1, CH 36.2, C 40.3, CH 22.6, CH2 114.5, CH 151.1, C 51.0, CH 34.4, C 30.7, CH2 50.7, CH 150.1, C 43.8, C 30.4, CH2 24.8, CH2 48.2, CH 112.0, CH2 23.4, CH3 27.9, CH 21.1, CH3 42.4, CH2 207.7, C 147.5, CH 131.9, C 11.1, CH3 172.1, C 23.9, CH3 22.6, CH3 28.2, CH3 171.0, C 21.4, CH3

2b,c

30.6, CH2 26.8, CH2 76.1, CH 37.9, C 40.3, CH 23.6, CH2 115.9, CH 152.0, C 52.1, CH 35.4, C 31.9, CH2 51.5, CH 151.9, C 44.6, C 31.1, CH2 25.5, CH2 48.8, CH 112.1, CH2 24.3, CH3 31.6, CH 19.1, CH3 34.1, CH2 27.4, CH2 142.6, CH 129.6, C 171.1, C 22.2, CH3 24.6, CH3 23.7, CH3 30.0, CH3

3a,c 36.1, CH2 28.7, CH2 79.1, CH 39.5, C 45.9, CH 23.8, CH2 115.4, CH 151.9, C 51.8, CH 35.5, C 31.7, CH2 51.3, CH 151.9, C 44.5, C 31.1, CH2 25.5, CH2 48.7, CH 112.1, CH2 24.3, CH3 31.6, CH 19.1, CH3 34.0, CH2 27.4, CH2 142.7, CH 129.5, C 171.1, C 22.2, CH3 24.6, CH3 17.3, CH3 29.8, CH3

4a,c 30.7, CH2 22.8, CH2 79.4, CH 36.3, C 51.9, CH 200.8, C 120.1, CH 171.2, C 52.2, CH 34.5, C 28.7, CH2 50.7, CH 150.3, C 44.8, C 30.3, CH2 25.0, CH2 48.2, CH 112.7, CH2 25.6, CH3 32.0, CH 19.1, CH3 33.9, CH2 27.4, CH2 142.5, CH 129.7, C 171.2, C 22.2, CH3 23.9, CH3 22.6, CH3 28.5, CH3 170.6, C 21.5, CH3

5a,e 36.4, CH2 35.5, CH2 215.7, C 48.0, C 47.5, CH 24.4, CH2 114.9, CH 152.2, C 51.2, CH 35.1, C 31.1, CH2 51.3, CH 151.5, C 44.5, C 31.1, CH2 25.4, CH2 48.6, CH 112.1, CH2 23.1, CH3 31.8, CH 19.2, CH3 34.1, CH2 27.5, CH2 142.6, CH 129.6, C 171.1, C 22.2, CH3 24.6, CH3 23.1, CH3 26.5, CH3

6a,e 30.7, CH2 26.8, CH2 76.0, CH 37.9, C 40.3, CH 23.6, CH2 116.0, CH 151.7, C 52.1, CH 35.4, C 31.7, CH2 51.3, CH 151.1, C 44.5, C 31.0, CH2 25.5, CH2 48.8, CH 112.4, CH2 24.3, CH3 29.6, CH 20.0, CH3 38.4, CH2 81.1, CH 150.1, CH 130.2, C 174.6, C 11.2, CH3 24.5, CH3 23.7, CH3 30.0, CH3

7a,c 30.6, CH2 26.8, CH2 76.1, CH 37.9, C 40.3, CH 23.5, CH2 115.8, CH 151.9, C 52.0, CH 35.3, C 32.1, CH2 51.2, CH 151.5, C 44.4, C 31.1, CH2 25.4, CH2 48.8, CH 112.2, CH2 24.2, CH3 29.3, CH 18.9, CH3 38.4, CH2 79.9, CH 150.9, CH 129.7, C 174.6, C 11.2, CH3 24.7, CH3 23.7, CH3 30.0, CH3

8a,c

9a,d 37.1, CH2 34.9, CH2 215.3, C 47.9, C 44.6, CH 23.8, CH2 55.8, CH 71.8, C 46.9, CH 34.4, C 28.7, CH2 49.1, CH 150.3, C 43.0, C 26.8, CH2 24.3, CH2 49.1, CH 113.3, CH2 22.4, CH3 31.8, CH 19.2, CH3 34.4, CH2 27.6, CH2 142.6, CH 129.6, C 171.1, C 22.1, CH3 21.3, CH3 22.6, CH3 25.7, CH3

Recorded in pyridine-d5. bRecorded in CDCl3. cRecorded at 150 MHz. dRecorded at 125 MHz. eRecorded at 100 MHz.

1a,c

no.

Table 3. 13C NMR Spectroscopic Data of Kadcoccine Acids A−N (1−14) (δ in ppm) 31.1, CH2 23.5, CH2 79.0, CH 36.8, C 41.8, CH 23.3, CH2 115.5, CH 153.0, C 53.1, CH 35.1, C 32.1, CH2 46.9, CH 135.4, C 41.9, C 34.8, CH2 21.5, CH2 137.8, C 61.1, CH2 24.2, CH3 35.3, CH 20.0, CH3 35.7, CH2 29.2, CH2 143.0, CH 129.3, C 171.4, C 22.1, CH3 26.8, CH3 23.1, CH3 28.8, CH3 170.8, C 21.5, CH3

10a,c 36.4, CH2 35.5, CH2 215.8, C 48.0, C 48.4, CH 24.5, CH2 115.2, CH 153.3, C 52.7, CH 35.1, C 31.6, CH2 46.9, CH 135.4, C 41.9, C 34.7, CH2 21.4, CH2 137.9, C 61.0, CH2 23.3, CH3 35.3, CH 20.0, CH3 35.7, CH2 29.2, CH 143.2, CH 129.2, C 170.9, C 22.0, CH3 27.1, CH3 23.1, CH3 26.6, CH3

11a,c 30.9, CH2 23.4, CH2 78.9, CH 36.8, C 41.9, CH 23.3, CH2 116.7, CH 152.0, C 53.8, CH 35.1, C 34.1, CH2 43.0, CH 138.8, C 41.4, C 33.9, CH2 23.4, CH2 163.4, C 191.2, CH 24.2, CH3 33.9, CH 20.0, CH3 35.2, CH2 28.9, CH2 142.0, CH 129.9, C 170.7, C 22.0, CH3 27.2, CH3 23.0, CH3 28.8, CH3 170.7, C 21.4, CH3

12a,c 31.4, CH2 23.5, CH2 79.1, CH 36.8, C 40.8, CH 23.3, CH2 114.6, CH 153.2, C 53.4, CH 35.0, C 28.5, CH2 58.2, CH 76.0, C 43.5, C 32.5, CH2 21.8, CH2 48.3, CH 20.6, CH3 23.9, CH3 33.5, CH 21.7, CH3 35.0, CH2 28.9, CH2 143.0, CH 129.3, C 171.3, C 22.0, CH3 28.8, CH3 23.0, CH3 28.8, CH3 170.7, C 21.5, CH3

13a,e

31.5, CH2 23.6, CH2 78.9, CH 37.0, C 43.3, CH 23.3, CH2 118.0, CH 153.2, C 57.9, CH 35.3, C 32.8, CH2 146.0, C 130.5, C 42.3, C 34.1, CH2 19.8, CH2 39.6, CH 61.9, CH2 24.0, CH3 34.8, CH 19.4, CH3 32.2, CH2 29.2, CH2 143.3, CH 129.2, C 171.0, C 22.0, CH3 27.3, CH3 23.2, CH3 29.0, CH3 170.7, C 21.5, CH3

14a,e

Journal of Natural Products Article



Article 13

C NMR data, suggesting 10 indices of hydrogen deficiency. Comparison of the 1D and 2D NMR spectra of 5 with those of kadcoccinone B15 indicated that these compounds possessed identical scaffolds and substitution patterns, with the only difference that 5 had a carbonyl group replacing an sp3 methylene function. Furthermore, the UV spectrum (Figure S45, Supporting Information) of 5 displayed an absorption maximum at approximately 239 nm, consistent with an α,βunsaturated hydroxycarbonyl group. The significant downfield shifts of C-5 (δH 2.69, s; δC 51.9), C-7 (δC 120.1), and C-8 (δC 171.2) in conjunction with the HMBC correlations (Figure S41, Supporting Information) from H-5 and H-7 to C-6 (δC 200.8) demonstrated that a conjugated carbonyl group was attached to C-6. The ROESY spectrum (Figure S43, Supporting Information) of 5 revealed that the relative configurations of the stereogenic carbons were similar to those of kadcoccinone B. Therefore, the structure of 5, kadcoccine acid E, was established as shown. Compound 6 was isolated as a white, amorphous powder, and its HRESIMS data revealed a positive molecular ion peak at m/z 453.3361 ([M + H]+, calcd for 453.3363), corresponding to a molecular formula of C30H44O3, which was two mass units less than that of 3 and 4. The 1H and 13C NMR spectroscopic data (Tables 1 and 3) of 6 strongly resembled those of 3 and 4, except for the presence of a carbonyl group (δC 215.7) in 6 instead of the oxygenated methines (δC 76.1 and 79.1) in 3 and 4, respectively. In the HMBC spectrum (Figure S50, Supporting Information), H3-29 (δH 1.08) and H3-30 (δH 1.22) correlated with C-3 (δC 215.7), C-4 (δC 48.0), and C-5 (δC 47.5), demonstrating that the carbonyl group was located at C-3. Similar ROESY correlations (Figure S52, Supporting Information) showed that the relative configuration of 6 was the same as that of 4. Accordingly, the structure of 6, kadcoccine acid F, was determined as shown. Compounds 7 and 8 were determined to have the same molecular formula, C30H44O3, according to the 13C NMR and HRESIMS data, indicative of nine indices of hydrogen deficiency. The NMR spectroscopic data (Tables 1−3) of 7 and 8 revealed similar structures, with the largest variation being the chemical shifts of C-23 (ΔδC 1.2 ppm), implying that these compounds are a pair of C-23 epimers. Comparison of the NMR spectroscopic data of compounds 7 and 3 revealed that they possessed identical A/B/C/D-ring systems and differed only as far as the C-17 side chain was concerned. In comparison to 3, an additional degree of unsaturation, a deshielded oxymethine (δC 81.1, C-23), and the molecular formula for 7 indicated the presence of a ring system on the side chain. A 5-substituted 2(5H)-furanone motif was inferred by the 1H−1H COSY correlations (Figure 2) of H3-21/H-20/ H-22/H-23/H-24 and the HMBC correlations (Figure 2) of H3-27 (δH 1.89) with C-24 (δC 150.1), C-25 (δC 130.2), and C-

Figure 1. 1H−1H COSY and HMBC correlations of compound 1. 13

C NMR data. The 1H and 13C NMR spectroscopic data of 3 and 4 (Tables 1 and 3) were closely related to those of kadcoccinone B,15 with the only difference being the presence of a hydroxy group at C-3 in 3 and 4 rather than an acetoxy group in kadcoccinone B. This conclusion was confirmed by the HMBC correlations (Figures S23 and S32, Supporting Information) of H3-29 and H3-30 with C-3 (δC 76.1 for 3, 79.1 for 4). The chemical shift of C-5 (δC 40.3) in 3 was close to that of kadcoccinone B (δC 41.1), indicating the presence of a γ-steric compression effect between HO-3 and H-5α; thus, HO3 was determined to be α-oriented in 3, which was supported by the ROESY correlations (Figure 3) of H-3/H3-29, H-3/H3-

Figure 2. 1H−1H COSY and HMBC correlations of compound 7.

30, H-3/H-2β, H-3/H-2α, H3-29/H-2β, H-2β/H3-19β, and H5α/H3-30. On the contrary, the chemical shift of C-5 (δC 45.9) in 4 was significantly different (ΔδC 4.8 ppm) relative to that of kadcoccinone B, indicating the absence of a γ-steric compression effect of HO-3/H-5α, and thus, HO-3 was determined to be β-oriented in 4. This was supported by the ROESY correlations (Figure 3) of H-3/H-5α, H-3/H3-30, H5α/H3-30, and H-3/H-2α, but there was no ROESY correlation of H-3/H-2β. Consequently, the structures of 3 and 4 were identified as C-3 epimers, and these compounds were named kadcoccine acids C and D, respectively. Compound 5 had a molecular formula of C32H46O5 based on the m/z 511.3414 [M + H]+ ion in the positive HRESIMS and

Figure 3. ROESY correlations of compounds 3, 4, and 9. 2594



Article

Table 4. Cytotoxicity of Compounds 1−14 against Human Tumor Cell Linesa compound

HL-60

SMMC-7721

A-549

MCF-7

SW-480

HeLa

2 7 8 cisplatinb paclitaxelb

3.11 10.40 7.36 1.93 40 11.83 40 12.40

6-Fused Triterpenoid Acids from ... - ACS Publications

Recommend Documents