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Two new cycloartanes from the leaves of Combretum quadrangulare growing in Vietnam and their biological activities
⁎Corresponding authors at: CirTech Institute, Ho Chi Minh City University of Technology (HUTECH), 475 A Dien Bien Phu Street, Binh Thanh District, Ho Chi Minh City 700000, Viet Nam (N.H. Nguyen). Department of Chemistry, Ho Chi Minh City University of Education 280 An Duong Vuong Street, District 5, 748342 Ho Chi Minh City, Viet Nam (T.H. Duong). nn.hong@hutect.edu.vn (Ngoc-Hong Nguyen), huydt@hcmue.edu.vn (Thuc-Huy Duong)
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Received: ,
Accepted: ,
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.
Abstract
Abstract
Two new cycloartanes, combretanones G and H (1 and 2), were isolated from the leaves of Combretum quadrangulare. Their structures were elucidated by applying a set of spectroscopic methods, while their relative configurations were determined using DFT-NMR chemical shift calculations and subsequent assignment of DP4 probabilities. Compounds 1 and 2 are C-23/C-24 stereoisomers of the previously-reported euphonerin E. Both exhibited moderate cytotoxicity against three human cancer cell lines. Compound 2 was shown to be a potent antiparasitic. Our results confirm the traditional medicinal uses of Combretum quadrangulare in Vietnam.
Keywords
Combretaceae
Combretum quadrangulare
Cycloartane
Combretanones G and H
Cytotoxicity
Antiparasitic activity
1 Introduction
Combretum quadrangulare Kurz (Combretaceae) is a perennial tree that is widespread throughout Eastern Asia. Known as “Tram Bau” in Vietnam, this species is widely used in folk medicine and is claimed to have ethnopharmacological properties as a hepatoprotective, antipyretic, analgesic, antidysenteric, and anthelmintic. In Vietnam, the seeds of Combretum quadrangulare have traditionally been used to suppress Toxocara canis larvae. The wide ethnopharmacological use of C. quadrangulare paved the way for phytochemical investigations that reported the presence of numerous triterpenes (mostly cycloartanes, ursanes, lupanes, and oleananes), along with a limited number of flavonoids (Adnyana et al., 2000, 2001; Banskota et al., 1998, 2000a, 2000b; Ganzera et al., 1998; Toume et al., 2011). As part of our ongoing investigation of the biochemical properties of Vietnamese medicinal plants (Duong et al., 2017, 2018a, 2019; Pham et al., 2020), in this study the phytochemical properties of EtOH extracted from the leaves of C. quadrangulare were investigated using bioactive-guided isolation. We report the isolation and structural elucidation of two new cycloartanes: combretanones G and H (1–2). The relative configurations of 1 and 2 were determined using GIAO NMR chemical shift calculations followed by calculation of DP4 probability. Compounds 1 and 2 were evaluated for cytotoxicity against three human cancer cell lines and human Adipose-derived cell line (hAdCs). Compound 2 was assayed for anti-parasitic activity against Toxocara canis larvae.
2 Material and methods
2.1 General experimental procedures
The NMR spectra were recorded on a Bruker Avance III spectrometer (500 MHz for 1H NMR and 125 MHz for 13C NMR) using residual solvent signals as internal references. The HR–ESI–MS was recorded on an HR–ESI–MS MicrOTOF–Q mass spectrometer with an LC-Agilent 1100 LC-MSD Trap spectrometer. Thin layer chromatography (TLC) was carried out on precoated silica gel 60 F254 or silica gel 60 RP–18 F254S (Merck), and spots were visualized by spraying with 10% H2SO4 solution followed by heating. Gravity column chromatography was performed on silica gel 60 (0.040–0.063 mm, Himedia).
2.2 Plant material
Leaves of C. quadrangulare were collected in Duc Hoa, Long An Province in March-April 2016. The plant was identified as C. quandrangulare Kurz by Dr. Cong Luan Tran, Tay Do University, Can Tho, Vietnam. A voucher specimen (No UE-002) was deposited in the herbarium of the Department of Organic Chemistry, Faculty of Chemistry, Ho Chi Minh University of Education, Ho Chi Minh City, Vietnam.
2.3 Extraction and isolation of compounds
Dried leaves of C. quadrangulare (3.5 kg) were crushed and extracted with 10 L of EtOH (three times) at 70 °C for 8 h. The filtrated solution was evaporated to dryness under reduced pressure to obtain a crude extract (118.4 g). This crude extract was successively partitioned by n-hexane, n-hexane: EtOAc (1:1), EtOAc, and n-butanol to produce fractions H (6.1 g), HEA (54.5 g), EA (30.0 g), and BU (12.0 g), respectively. Fraction HEA (54.5 g) was subjected to silica gel column chromatography, using an isocratic mobile phase consisting of n-hexane: EtOAc: acetone (5:1:1) to obtain fractions P1 (2.95 g), P2 (0.72 g), P3 (0.94 g), P4 (0.82 g), P5 (0.69 g), P6 (0.23 g), P7 (0.2 g), P8 (0.15 g), P9 (0.3 g), P10 (0.1 g), P11 (3.0 g), P12 (6.0 g), P13 (13.1 g), and P14 (20.1 g). Fraction P12 (6.0 g) was subjected to silica gel column chromatography, using an isocratic mobile phase consisting of a n-hexane: EtOAc: acetone solvent system 5/1/1, v/v/v), affording subfractions T1 (1.3 g), T2 (200.0 mg), T3 (300.0 mg), T4 (1.0 g), T5 (1.2 g), T6 (305.0 mg), T7 (120.0 mg), and T8 (0.5 g). Subfraction T6 (305.0 mg) was subjected to CC using the solvent system n-hexane: CHCl3: EtOAc: acetone: H2O (3:1:2:2:0.01) to give subfractions T6.1 (130.0 mg), T6.2 (60.0 mg), and T6.3 (30.0 mg). Subfraction T61 was rechromatographed and eluted with the same solvent system to yield 1 (1.4 mg) and 2 (4.7 mg).
2.3.1 Combretanone G (1)
White amorphous powder; 1H NMR (CDCl3, 500 MHz) and 13C NMR (CDCl3, 125 MHz) see Table 1; HRESIMS m/z: [M + Na]+ 495.3439 for C30H48O4Na (calcd. 495.3450).
No.
1 (CDCl3)
Euphornerin E (CDCl3)27
2 (CDCl3)
2 (acetone‑d6)
δH
δC
δH
δC
δH
δC
δH
δC
1
1.60 m, 1.85 m
32.7
32.8
1.62 m, 1.89 m
32.6
1.55 m, 1.73 m
32.4
2
2.32 ddd (2.5,4.5,14.0)2.70 td (6.5, 13.5)
37.2
38.7
2.33 ddd (1,5, 3.5, 14.5)2.70 td (6.5, 14.0)
37.4
2.2 ddd (2.5, 4.5, 13.0)2.72 td (7.0, 14.0)
37.7
3
215.9
215.8
215.8
215.1
4
49.8
49.6
49.7
50.1
5
1.90 m
46.8
46.6
1.91 m
46.9
1.90 m
46.7
6
1.15 m, 1.73 m
31.3
31.1
1.15 m, 1.73 m
31.3
1.08 m, 1.68 m
29.2
7
3.65 ddd (10.5, 9.5, 4.0)
70.8
3.61 ddd (10.7, 8.9, 3.3)
70.6
3.64 m
70.8
3.73 ddd (3.0, 7.5, 12.5)
70.5
8
1.69 m
54.8
54.6
1.69 m
54.7
1.67 d (8.5)
55.3
9
21.0
20.8
21.0
21.0
10
26.7
26.5
26.5
27.3
11
1.32 m, 1.90 m
27.0
27.0
1.33 m, 1.90 m
26.6
1.28 m, 1.91 m
28.1
12
1.64 m, 1.85 m
33.0
32.5
1.63 m, 1.87 m
33.0
1.69 m
33.5
13
46.1
46.0
46.1
46.7
14
48.6
48.3
48.5
47.7
15
1.49 m, 1.60 m
37.4
37.0
1.49 m, 1.60 m
37.1
1.52 m, 1.58 m
37.6
16
1.37 m, 1.96 m
28.4
28.6
1.38 m, 1.96 m
28.9
1.39 m, 1.95 m
29.2
17
1.68 m
53.4
52.0
1.55 m
52.1
1.54 m
53.4
18
1.03 s
17.6
1.03 s
17.4
1.05 s
17.6
1.02 s
18.0
19
0.56 d (4.5)
27.7
0.56 d (4.5)
27.7
0.57 d (4.5)
27.7
0.62 d (4.0)
27.7
0.95 d (4.5)
0.95 d (4.5)
0.95 m
0.94 d (4.0)
20
1.72 m
33.5
32.5
1.75 m
32.3
1.65 m
33.0
21
0.90 d (6.5)
18.4
0.90 d (6.5)
18.1
0.92 d (6.5)
18.3
0.92 d (6.5)
19.0
22
1.15 m, 1.66 m
39.6
39.6
1.10 m, 1.56 m
37.6
0.98 m, 1.56 m
39.1
23
3.86 ddd (10.5, 9.0, 2.0)
76.4
3.70 ddd (11.0, 6.7, 2.0)
69.5
3.81 m
69.6
3.70 ddd (11.5, 7.0, 2.0)
70.1
24
3.96 d (8.5)
85.7
3.78 d (6.7)
80.2
4.09 dd (4.5, 3.5)
79.1
3.94 dd (4.5, 3.5)
80.0
25
141.9
144.6
144.5
147.0
26
4.94 brs, 5.02 s
114.3
4.93 brs, 4.99 s
114.2
4.98 brs, 5.05 brs
112.8
4.97 brs, 4.83 s
112.0
27
1.77 s
17.6
1.72 s
17.9
1.76 s
17.6
1.73 s
18.8
28
1.05 d (3.0)
22.3
1.03 d
22.6
1.05 d (2.0)
22.4
1.02 s
22.7
29
1.10 s
20.8
1.08 s
20.6
1.11 s
20.8
1.08 s
21.7
30
0.94 s
19.0
0.92 s
18.9
0.95 s
19.1
0.96 s
19.2
7-OH
3.14 d (5.5)a
23-OH
3.19 d (6.0) a
24-OH
3.79 d (4.0)
2.3.2 Combretanone H (2)
White amorphous powder; 1H NMR (CDCl3 and acetone‑d6, 500 MHz) and 13C NMR (CDCl3 and acetone‑d6, 125 MHz) see Table 1; HRESIMS m/z: [M + H]+ 473.3615 for C30H49O4 (calcd. 473.3631).
2.4 Cytotoxicity assay
The cytotoxicity of 1 and 2 was evaluated against K562 (chronic myelogenous leukemia), HepG2 (liver hepatocellular carcinoma), MCF-7 (breast cancer), and hAdCs (human Adipose-derived) cell lines cultured in RPMI 1640 and DMEM media. The method followed that in Duong et al. (2019).
2.5 Antiparasitic activity assay
Toxocara canis larvae were prepared in our laboratory using the method reported in Nguyen et al. (2017). Adult worms were collected from pubs. For egg production, male and female worms were cultured together in PBS supplemented with 1% human serum plus penicillin (100 U/mL) and streptomycin (100 µg /mL) at 37 °C under a 5% CO2 atmosphere for up to 7 days. The eggs were then collected by centrifugation and incubation in 1% formalin–PBS for 30 days at room temperature in a sterile flask. Embryonic development was determined using an inverted microscope. For hatching, eggs were incubated using 6% sterile NaClO solution for 5 min at room temperature, then washed several times with sterile PBS buffer. Eggs were incubated with sterile Hank’s balance saline solution pH 2.0 for 30 min at room temperature. The treated eggs were washed and incubated in serum-free DMEM medium supplemented with penicillin (100 U/mL) and streptomycin (100 µg/mL) at 37 °C in a 5% CO2 atmosphere. The eggs hatched within three days. Larvae were concentrated by centrifugation and living larvae were selected by passing overnight through a 40 µm cell strainer in DMEM medium. HEA extract and compound 2 were tested for in vitro antiparasitic activity against T. canis larvae, using a method adapted from 3. Briefly, twenty to thirty larvae were prepared in 200 µL of serum-free DMEM medium in each well of a 96 well–plastic cell culture plate. HEA extract and compound 2 were dissolved in DMSO at a concentration 10 mg/mL, diluted, then placed into wells at final concentrations of 250 µg/mL, 50 µg/mL, and 5 µg/mL. Albendazole and mebendazole prepared in DMSO were used as positive controls in the same concentrations, and DMSO was used as a solvent control. Larval movement was observed and scored (Table 2) on days 2 and 4 following exposure to the test substances. As shown in Table S1, the mobility index (MI) was calculated using Eq. (1), and the relative mobility (RM) using Eq. (2). The experiment was done in triplicate. aData show average of three experiments.
Compound/extract
Relative mobility (%)
Day 2
Day 4
Concentration (µg/ml)
Concentration (µg/ml)
5
50
250
5
50
250
Albendazole
100.0
97.0
102.2
98.6
93.7
70.1
Mebendazole
99.6
100.0
100.4
99.3
100.0
100.0
HEA
98.1
99.3
81.3
88.9
92.3
77.5
2
72.4
44.5
39.9
50.2
34.9
35.1
2.6 Computation
Conformational searching was performed using the xTB package. The energies of all conformers were calculated using the GFN2-xTB method. Stable conformers were identified using a quantum mechanical method at the b3lyp/6-31G(d,p) level of theory. GIAO calculations were performed at B3LYP/6-311 + G(d,p) (Grimblat et al., 2015). The DP4 probabilities were performed as reported in Duong et al. (2020a, 2020b).
3 Results and discussion
Compounds 1 and 2 were isolated from Fraction T6.1 (see the Experimental section) of the C. quadrangulare ethanol extract, based on bioactive-guided isolation (Tables 4–6). Compound 1 was determined to have the molecular formula C30H48O4, based on HRESIMS data (m/z 495.3439, calcd. for C30H48O4Na). This indicated seven degrees of unsaturation. The 1H NMR spectrum showed six methyl groups (δH 1.77, 1.10, 1.05, 1.03, 0.94, and 0.90, the latest doublet with J = 6.5 Hz), three oxymethine protons [δH 3.96 (1H, d, J = 8.0 Hz), 3.86 (1H, ddd, J = 10.5, 9.0, 4 Hz), and 3.65 (1H, d, J = 8.0 Hz)], one sp2 methylene [δH 5.02 (1H, br s) and 4.96 (1H, br s)], and two characteristically upfield-shifted doublets [δH 0.92 (1H, d, J = 4.5 Hz), and 0.57 (1H, d, J = 4.5 Hz)] assignable to cyclopropyl methylene protons. The 13C NMR spectrum and HSQC spectrum revealed 30 carbons: carbonyl carbon (δC 215.0), one sp2 quaternary carbon (δC 149.0), one sp2 methylene (δC 114.3), three oxygenated sp3 tertiary carbons (δC 85.7, 76.4, and 70.8), five sp3 quaternary carbons (δC 50.0, 49.8, 48.6, 26.6, and 20.6), four sp3 methine carbons (δC 54.6, 53.4, 46.7, and 33.3), eight sp3 methylene carbons (δC 39.6, 37.6, 37.2, 32.4 (×2), 31.1, 28.4, and 26.8), and six methyl groups (δC 22.7, 22.1, 18.8, 18.1, and 17.4 (×2)). These spectroscopic features suggested the presence of five rings and were therefore diagnostic of a cycloartane-type triterpene (Khuong-Huu et al., 1975).
Tested compounds
K562
HepG2
MCF-7
hAdCs
IC50
IC90
IC50
IC90
IC50
IC90
IC50
IC90
1
13.3 ± 1.1
23.2 ± 0.2
20.0 ± 0.4
40.5 ± 1.8
65.8 ± 3.4
96.2 ± 0.6
38.9 ± 1.9
50.2 ± 3.4
2
21.0 ± 1.2
43.6 ± 0.7
37.3 ± 2.0
76.1 ± 2.9
70.3 ± 0.7
97.7 ± 0.2
79.2 ± 3.9
>100
Doxorubicin
2.2 ± 0.7
35.2 ± 1.1
2.4 ± 0.2
26.2 ± 1.4
13.9 ± 2.2
75.3 ± 1.5
3.1 ± 0.8
46.9 ± 3.2
Extract
EtOH
EA
H
HEA
BU
IC50 (µg/mL)
46.7 ± 2.8
> 100
39.4 ± 3.5
21.7 ± 1.2
> 100
IC90 (µg/mL)
92.4 ± 0.5
> 100
82.5 ± 5.2
46.1 ± 0.8
> 100
Fraction
IC50 ± SD (µg/mL)
IC90 (µg/mL)
Fraction
IC50 ± SD (µg/mL)
IC90 ± SD (µg/mL)
P1
> 100
> 100
P9
16.3 ± 2.1
88.9 ± 5.4
P2
86.4 ± 5.3
> 100
P10
15.5 ± 2.9
88.4 ± 2.3
P3
> 100
> 100
P11
24.9 ± 1.1
56.0 ± 11.1
P4
37.5 ± 1.6
> 100
P12
25.0 ± 0.4
49.6 ± 0.1
P5
20.7 ± 1.5
> 100
P13
17.1 ± 1.7
92.0 ± 3.6
P6
15.7 ± 1.3
> 100
P14
20.2 ± 3.9
91.6 ± 2.8
P7
17.8 ± 1.4
> 100
P15
66.4 ± 0.9
95.3 ± 0.7
P8
11.3 ± 0.5
> 100
Detailed analysis of the COSY and HMBC results determined that compound 1 had a planar structure. A ketone moiety was suggested at C-3, based on HMBC correlations from the methylene protons H2-1 (δH 1.85/1.60) and H2-2 (δH 2.70/2.32), and the methyl protons H3-28 (δH 1.10) and H3-29 (δH 1.05) to C-3 (δC 215.0). The H-5/H-6, H-6/H-7, and H-7/H-8 COSY cross-peaks, along with long-range heteronuclear correlations from H-5, H-6, and H-8 to C-7 (δC 70.6) suggested the presence of a hydroxyl group at C-7. The presence of 23– and 24-OH substituents was established, based on the magnitude of the coupling constants between H-23 [δH 3.86 (1H, ddd, J = 10.5, 8.0, 2.0 Hz)] and H-24 [δH 3.96 (1H, d, J = 8.0 Hz)]. The HMBC correlations from the exo-olefinic protons at δH 5.02 and 4.94 to C-24 (δC 85.7), C-25 (δC 141.9), and C-27 (δC 17.6) ascribed this moiety to C-25. The relative configuration of 1 was assigned based on NOESY correlations and spin coupling analysis. The axial orientations of H-7 and H-8 were determined from their large coupling constants (JH-7/H-8 9.5 Hz) and this was confirmed by a NOESY correlation between H-7 and H3-30. In particular, the key NOESY cross peaks of H-19β with both H3-29 and H-8, and H-8 with H3-18, determined their β-orientation, while the key NOESY correlations of H3-28/H-5, H-5/H-7, H-7/H3-30, and H3-30/H-17 determined their α-orientation. The usual H-20β configuration of cycloartane triterpenes was assigned based on the H-18/H-20, H-12/H-21 and H-17/H3-21 NOESY cross peaks (Nuanyai et al., 2009; Truong et al., 2011; Simo Mpetga et al., 2012).
Compound 2, a white amorphous powder, had the same molecular formula as 1. Detailed comparison of Compounds 1 and 2 with euphonerin E indicated that all three shared a planar structure. However, differences in the 1H and 13C chemical shifts of CH-23/CH-24/CH-25/CH3-27 suggested that the three stereoisomers differed in their C-23 and C-24 configurations. More specifically, the CDCl3 13C chemical shifts of C-23-C-24-C-25-C-26 in Compound 2 closely matched those of euphonerin E, while those of 1 were clearly shifted [C-23/24/25: 76.4/85.7/141.9 in 1 against 69.5/79.1/144.5 in 2]. This suggested a syn configuration of C-23 and C-24 for 2, whereas euphonerin E and 1 had the anti configuration. An attempt was made to assess the relative configuration of the side chains based on the comparison of the JH-23/H-24 coupling constant. The tirucallane triterpenoid piscidinol, having syn-oriented H-23 and H-24, also had a null coupling constant, while the anti epimer–24-epi-piscidinol has a coupling constant of JH-23/H-24 8.0 Hz, validated by X-ray crystallographic analyses (McChesney et al., 1997). The syn and anti configurations of C-23 and C-24 in related side chains have similar coupling constant values: 23,24,25-trihydroxycycloartan-3-one (JH-23/H-24 ca. 0 Hz, syn) (Joycharat et al., 2008), alisols A and P (JH-23/H-24 ca. 0 Hz, both syn) (Nakajima et al., 1994; Zhao et al., 2008), cumingianols A/B (JH-23/H-24 ca. 0 Hz, both syn) (Kurimoto et al., 2011), cumingianosides G-J and L-M (JH-23/H-24 ca. 0 Hz, all syn) (Fujioka et al., 1997), alisol E (JH-23/H-24 6 Hz, anti) (Yoshikawa et al.,1993), and toonaciliatavarin E (JH-23/H-24 7.5 Hz, anti) (Zhang et al., 2012). Interestingly, when the classical gem-dimethyl substituent is converted to an isopropenyl moiety, the magnitude of the coupling constant appears to change: unnamed argenteanol B derivative (JH-23/H-24 6.5 Hz, syn) (Mohamad et al., 1997), cumingianol C (JH-23/H-24 5.5 Hz, syn), cumingianosides D and N (JH-23/H-24 6.0 and 5.5 Hz, respectively, syn) (Fujioka et al., 1997), alisol G (JH-23/H-24 6.5 Hz, syn) (Yoshikawa et al.,1993), and euphonerin E (JH-23/H-24 6.7 Hz, syn) (Toume et al., 2012). As far as we could ascertain, no anti-disposed OH groups on isopentenyl-bearing side chains have been reported. A literature review suggested that syn isomers of compounds that share a side chain with compounds 1 and 2 would be expected to have lower JH-23/H-24 values than the anti compounds. The vicinal coupling constant of compound 2 (JH-23/H-24 4.5 Hz) is consistent with a syn configuration of euphonerin E, reducing the possible candidates for compound 2 to two (2a and 2b) (Fig. 3). In the same way, two candidates, 1a or 1b, were proposed for compound 1 (Fig. 3).
The stereochemistry of the side chains of 1 and 2 was determined based on ab initio calculation of NMR shifts, and by subsequently assigning a DP4+ probability score (Smith and Goodman, 2010). This technique is increasingly used when assigning stereochemical structure to natural extracts (Duong et al. 2018b, 2018c). The DP4+ probability suggested that isomers 1b and 2b were the most likely candidates for compounds 1 and 2, being assigned a 100% probability (Fig. 2). The suggested configuration of 1 was (23S*,24R*), and that of 2 (23R*,24R*). The final elucidation of compounds 1 and 2 as combretones G and H is shown as Fig. 1.
Structures of compounds 1–2.
Key HMBC, COSY, and NOESY correlations of 1.
Four possible isomers of 1 and 2.
Both compounds were assayed for cytotoxicity against the K562 (chronic myelogenous leukemia), HepG2 (liver hepatocellular carcinoma), and MCF-7 (breast cancer) cell lines. Moderate cytotoxicity was reflected in IC50 values of 13.3–70.3 μg/mL (Table 3). Compound 2 showed clear antiparasitic activity against T. canis larvae (Table 2) through the low relative mobility suggested dose dependence. At the highest test concentration of 250 µg/mL, 80% of larvae died, giving a mobility score of 0. At the lowest concentration of 5 μg/mL, compound 2 killed 20% of larvae. As the culture medium DMEM had no effect, it was set at 100, corresponding to a mobility score of 3. In DMSO solvent the larvae retained a relative mobility (RM) of 100%, suggesting no -antiparasitic activity. Both albendazole and mebendazole had high RM values, at 3. It was recently reviewed that several natural products (lipids, phenolics, saponin, terpenoids, coumảic acid, miscellaneous) govern anthelmintic activity against nematodes including Toxocara spp. in vitro and in vivo (Liu et al. 2020). However, mechanism under this observation is still controversial. It was shown that several cycloartane triterpenes derived from leaves of Combretum quadrangulare and other plants enhanced death receptor 5 (DR5) expression which results in induction of apoptosis in cancer cells (Toume et al., 2011, 2012). Whether Toxocara spp. governs DR5 and acts in a similar pathway is unclear. Previous studies documented that the seeds and bark of Combretum quadrangulare can be effectively used to remove intestinal helminths in both animals and human (Bui et al., 1978). Our study shows for the first time that leaf extract and compound 2 of Combretum quadrangulare expresses anthelmintic activity. We therefore propose compound 2 as a natural antiparasitic that warrants further investigation.
Fraction
IC50 ± SD (µg/mL)
IC90 ± SD (µg/mL)
Fraction
IC50 ± SD (µg/mL)
IC90 ± SD (µg/mL)
T1
69.7 ± 2.7
> 100
T5
10.1 ± 1.7
42.0 ± 0.7
T2
20.4 ± 7.9
> 100
T6
14.6 ± 0.7
24.7 ± 0.5
T3
18.8 ± 1.4
> 100
T7
14.9 ± 1.1
42.4 ± 3.5
T4
7.0 ± 0.8
34.6 ± 3.4
T8
25.4 ± 1.5
47.5 ± 0.3
4 Conclusions
Two new cycloartanes, combretanones G and H (1 and 2), were isolated from the leaves of C. quadrangulare. Their structures were determined by analysis of MS and NMR data and comparison with published values. DFT-NMR chemical shift calculations and DP4/DP4+ probability assignment were used to determine the relative configurations of compounds 1 and 2. Both exhibited moderate cytotoxicity against K562, HepG2, and MCF-7, with IC50 values in the range 13.3–70.3 μg/mL. Compound 2 was shown to be a potent antiparasitic.
Acknowledgements
The study was funded by Van Lang University, Project Nr. 05/2020/HĐ-NCKH. The authors also gratefully acknowledge the chemical support from Thammasat University Research Unit in Natural Products Chemistry and Bioactivities.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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Appendix A
Supplementary material
Supplementary data to this article can be found online at https://doi.org/10.1016/j.arabjc.2021.103189.
Appendix A
Supplementary material
The following are the Supplementary data to this article:
