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Abstract

Objective: Determine the structure, absolute configuration, and antiproliferative activity of a new furan diterpenoid isolated from the leaves of Coulteria velutina (Britton & Rose) Sotuyo & G.P.Lewis (Fabaceae). Methods: The structures of the natural product and those of 2 derivatives were established mainly by nuclear magnetic resonance spectroscopy, while their absolute configurations were established using vibrational circular dichroism involving comparison of the experimental and calculated spectra of a rigid derivative. Results: Isolation of (−)-(4R,5R,6R,8S,9S,10R,14R)-6-[(E)-p-coumaroyloxy]vouacapan-18-oic acid (1), an undescribed secondary metabolite from the leaves of C velutina, is reported hereafter. Hydrolysis of 1 provided (+)-(4R,5R,6R,8S,9S,10R,14R)-6-hydroxyvouacapan-18-oic acid (2), identical to a diterpenoid isolated from Caesalpinia echinata, but whose absolute configuration remained undetermined. Subsequent lactonization of 2 yielded (+)-(4R,5R,6R,8S,9S,10R,14R)-vouacapan-6,18-olide (3). The absolute configurations of compounds 1–3 were established by vibrational circular dichroism studies of 3. In addition, the antiproliferative activity of the natural product 1 against HeLa, MDA-MB-231, Caco-2, and NIH/3T3 cell lines is reported. Conclusions: The leaves of C velutina yielded the new vouacapane 1. It showed weak antiproliferative activity against HeLa and MDA-MB-231 cancer cell lines (IC₅₀= 92.2 and 106.2 μg/mL, respectively), but was also weakly active against the NIH/3T3 healthy cell line (IC₅₀ value of 127.6 µg/mL). Its absolute configuration was determined by vibrational circular dichroism analysis of the conformationally rigid compound 3. This derivative can be used as a reference for the absolute configuration of related vouacapanes. In addition, this is the first phytochemical investigation of C velutina.

Keywords

Fabaceae vouacapane furan diterpenoid absolute configuration vibrational circular dichroism antiproliferative activity

Introduction

The cassane skeleton arises from the geranylgeranyl diphosphate pathway, transiting by the copalyl and pimarenyl cyclization pathways, and further molecular rearrangement to provide a tricyclic diterpene possessing an ethyl group at the C-13 and a methyl group at the C-14 positions.^1,2 Biosynthetic oxidation of the cassane skeleton can yield furan diterpene derivatives, which are known as vouacapanes.³ These compounds are peculiar secondary metabolites found in the Fabaceae family.⁴ However, the analysis of the absolute configuration of this biologically relevant class of compounds has been scarcely undertaken. The Coulteria genus belongs to the subfamily Caesalpinideae and emerged from Caesalpinia sensu lato as a generic segregate.⁵ There are currently 10 accepted species in the Coulteria genus: C cubensis, C glabra, C mollis, C platyloba, C pringlei, C pumila, C velutina,⁶ C rosalindamedinae,⁷ C delgadoana,⁸ and C sousae.⁹ Consequently, the presence of cassane-type diterpenes as the predominant class of compounds can be hypothesized according to the described phytochemical studies of the restructured genus Caesalpinia.¹⁰ Only one previous study of a Coulteria species is described and involved the leaves of Coulteria platyloba, a tree previously known as Caesalpinia platyloba.¹¹ In this work, a new vouacapane was isolated from the leaves of C velutina (Britton & Rose) Sotuyo & G.P.Lewis (Fabaceae). The absolute configuration of this natural product was determined using vibrational circular dichroism (VCD),¹² involving a comparison of the experimental and calculated spectra of a rigid derivative, thus contributing to the stereochemical knowledge of these furan diterpenoids. It is worth mentioning that this is the first study about the chemical composition and biological activity of C velutina.

Results and Discussion

The dichloromethane extract of the leaves of C velutina provided, after purification by column chromatography, the new vouacapane 1 (Figure 1) as a colorless oil, representing the major secondary metabolite in the extract mixed mainly with fatty materials, as revealed by the ¹H nuclear magnetic resonance (NMR) spectrum of the extract. Its molecular formula was determined as C₂₉H₃₄O₆ by high-resolution electrospray ionization mass spectrometry (HRESIMS), displaying a sodium adduct molecular ion at m/z 501.2249, calculated as 501.2248 for [C₂₉H₃₄O₆+ Na]⁺. Compound 1 exhibited a levorotatory-specific rotation of [α]_D −18, while the ¹H NMR spectrum displayed a pattern related to previously reported vouacapane derivatives.¹¹ The complete data of ¹H and ¹³C, given in Table 1, and together with two-dimensional (2D) NMR correlations, confirmed the presence of a vouacapane skeleton by distinctive resonances of the furan moiety at δ_H 7.21 (d, J = 1.9 Hz, H-16) and δ_H 6.16 (d, J = 1.9 Hz, H-15), and the methyl resonances at δ_H 1.34 (s, CH₃-20), δ_H 1.40 (s, CH₃-19), and δ_H 0.94 (d, J = 7.0 Hz, H-17). A broad singlet observed at δ_H 5.32 was assigned to H-6, suggesting the presence of an ester moiety with a β-orientation attached to the B ring. Its resonance pattern was related to a p-coumarate moiety, showing 2 doublet resonances at δ_H 7.56 (J = 15.8 Hz, H-3´) and δ_H 6.20 (J = 15.8 Hz, H-2´), as well as 2 aromatic proton resonances at δ_H 7.35 (d, J = 8.8 Hz, H-5´, H-9´) and δ_H 6.83 (d, J = 8.8 Hz, H-6´, H-8´). The ¹³C NMR spectrum displayed 29 resonances, including a carbonyl peak at δ_C 184.5 (C-18) attributed to a carboxylic acid. The carbon resonances for the furan moiety were observed at δ_C 149.3 (C-12), 140.7 (CH-16), 122.4 (C-13), and 109.7 (CH-15), while the aliphatic carbon resonances of the vouacapane skeleton appeared within the range of δ_C 72.9–17.9. The coumarate moiety exhibited a typical carbonyl resonance at δ_C 167.8 (C-1´), while the remaining sp² carbon resonances appeared in the range of δ_C 158.7–115.6 (Table 1). The characteristic chemical shifts and peak assignments for this ester group were supported by literature data,¹³ thus confirming the presence of the new 6-[(E)-p-coumaroyloxy]vouacapan-18-oic acid (1). Attempts to crystallize 1 were unsuccessful because this compound was relatively unstable due to the furan instability in the acidic medium generated by the carboxylic acid when samples of 1 are concentrated.

Figure 1.

Skeletal (shorthand) structures of cassane diterpenoids 1–3.

Table 1.

¹³C and ¹H Nuclear Magnetic Resonance (NMR) Data for Compounds 1 and 3 (101 and 400 MHz, Respectively, in CDCl₃).

	1		3
Position	δ_C, mult.	δ_H, mult. (J in Hz)	δ_C, mult.	δ_H, mult. (J in Hz)
1a	41.6, CH₂	1.78, brd (13.1)	40.1, CH₂	1.59, dd (12.3, 4.5)
1b		1.18, m		1.32, m
2a	17.9, CH₂	1.67, m	20.3, CH₂	2.03, m
2b		1.61, m		1.87, dd (12.0, 2.0)
3a	39.1, CH₂	1.80, m	35.2, CH₂	1.88, dd (12.0, 4.0)
3b		1.64, m		1.74, m
4	47.7, C		42.3, C
5	49.9, CH	2.08, brs	52.0, CH	2.27, d (11.0)
6	72.9, CH	5.32, brs	76.4, CH	4.53, ddd, (14.1, 11.0, 5.9)
7a	36.3, CH₂	1.91, brd (14.5)	29.0, CH₂	2.13, m
7b		1.68, m		2.00, m
8	31.6, CH	2.05, m	36.5, CH	2.28, m
9	46.0, CH	1.66, m	40.6, CH	1.74, td (10.3, 2.5)
10	37.7, C		37.8, C
11a	21.9, CH₂	2.48, dd (16.0, 10.0)	22.8, CH₂	2.55, d (8.4)
11b		2.63, d (16.0, 7.0)		1.75, m
12	149.3, C		148.9, C
13	122.4, C		122.8, C
14	31.2, CH	2.56, m	33.2, CH	2.77, m
15	109.7, CH	6.16, d (1.9)	109.7, CH	6.21, d (2.1)
16	140.7, CH	7.21, d (1.9)	141.0, CH	7.26, d (2.1)
17	17.9, CH₃	0.94, d (7.0)	17.1, CH₃	1.16, d (7.0)
18	184.5, C		181.7, C
19	18.7, CH₃	1.40, s	23.4, CH₃	1.51, s
20	18.2, CH₃	1.34, s.	17.7, CH₃	1.22, s
1´	167.8, C
2´	115.6, CH	6.20, d (15.8)
3´	145.5, CH	7.56, d (15.8)
4´	126.8, C
5´	130.4, CH	7.35, d (8.8)
6´	116.3, CH	6.83, d (8.8)
7´	158.7, C
8´	116.3, CH	6.83, d (8.8)
9´	130.4, CH	7.35, d (8.8)

Alkaline hydrolysis of 1 yielded a white solid. Its ¹H and ¹³C NMR data were consistent with those of 6β-hydroxyvouacapan-18-oic acid (2), formerly isolated from Paubrasilia echinata (Lam.) Gagnon, H.C.Lima & G.P.Lewis, previously known as Caesalpinia echinata Lam.¹⁴ The relative configuration of compound 2 was corroborated by analysis of one-dimensional (1D) and 2D NMR data and was in agreement with previous data.¹⁴ According to the biogenesis of cassane compounds, copalyl diphosphate is a key intermediate.¹⁵ Interestingly, either copalyl diphosphate or ent-copalyl diphosphate can lead to diterpenoids.¹⁶ Therefore, detailed configurational analyses should be undertaken to address stereochemical uncertainty and cogent chemotaxonomic correlations for the diterpenoids of the Caesalpinieae tribe.^6,10 In addition, the absolute configuration assignment for compound 2 was necessary to ensure the determination of the absolute configuration of its natural precursor 1. As mentioned earlier, VCD spectroscopy was selected due to its reliability in the absolute configuration determination of natural products.¹² Furthermore, the absolute configuration of other vouacapanes has been successfully defined by this methodology when combined with quantum mechanical calculations.^11,17

A lactonization reaction¹⁸ of compound 2 was done to promote the formation of the new compound 3 in 92% yield, revealing the closeness of the C-18 carboxylic acid and the C-6 hydroxy groups. Furthermore, the rigidity and the absence of critical intermolecular interactions in 3 facilitated the VCD studies. The ¹H NMR spectrum showed the H-6 signal at δ_H 4.53 as a doublet of doublet of doublet (J = 14.1, 11.0, 5.9 Hz), suggesting that conformational changes occurred at the B ring, as expected after cyclization. In this conformation, depicted in the molecular model of Figure 2, the proximity between H-6 at δ_H 4.51 and the axially oriented C-17 methyl group at δ_H 1.15 was verified by the NOESY correlation between these 2 resonances. The fully assigned ¹H and ¹³C NMR data of 3 using 2D NMR experiments are presented in Table 1. In addition, the NOESY spectra of 1–3 showed a consistent correlation between H-5 and H-6, thus confirming the alpha orientation of H-6 in the 3 compounds.

Figure 2.

Low-energy conformer of (+)-(4R,5R,6R,8S,9S,10R,14R)-vouacapan-6,18-olide (3) at the B3LYP/DGDZVP level of theory.

The experimental VCD and infrared (IR) spectra of 3 were measured for comparison with those calculated by Density Functional Theory (DFT) means. VCD and IR calculations started with the molecular model of 3, built in the Spartan'04 software, considering the relative configurations of precursors 1 and 2. The most probable absolute configuration for the model of 3 was selected according to biogenetic reasons, but was, of course, subjected to verification. A conformational distribution analysis using the Monte Carlo protocol and the Merck Molecular Force Field¹⁹ was carried out to reveal the presence of 2 conformers in the 0 to 10 kcal/mol energy window, evidencing the influence of conformational restriction in the molecule. Subsequent energy optimization of the 2 conformers was achieved by DFT using B3LYP/6-31G(d) basis set to provide only one conformer (3a) in the 0 to 3 kcal/mol energy gap. Further geometry-optimization of 3a at the B3LYP/DGDZVP level of theory, using the Gaussian 09 software,²⁰ was carried out (Figure 2), followed by VCD and IR spectroscopic calculations (Figure 3) at the same level of theory.²¹ Statistical comparison of the calculated and experimental spectra using the CompareVOA program provided quantitative spectroscopic similarities,²² in which the optimal anharmonicity factor (anH) was 0.981. The VCD spectroscopic similarities for the correct enantiomer (S_E) was 76.5, while that for the incorrect enantiomer (S_−E) was only 12.0. The enantiomer similarity index (ESI), obtained by the S_E − S_−E difference was 64.6, indicating a confidence level (C) of 100% for the (+)-(4R,5R,6R,8S,9S,10R,14R)-vouacapan-6,18-olide (3). This compound might be used as a reference for the absolute configuration of vouacapanes. Consequently, the chirality of the natural product 1 and that of its precursor 2 was defined as (−)-(4R,5R,6R,8S,9S,10R,14R)-6-[(E)-p-coumaroyloxy]vouacapan-18-oic acid (1) and (+)-(4R,5R,6R,8S,9S,10R,14R)-6-hydroxyvouacapan-18-oic acid (2).

Figure 3.

Comparison of the experimental and DFT B3LYP/DGDZVP calculated IR and VCD spectra of (+)-(4R,5R,6R,8S,9S,10R,14R)-vouacapan-6,18-olide (3). Abbreviations: DFT, Density Functional Theory; VCD, vibrational circular dichroism; IR, infrared.

Several cassane diterpenoids have shown cytotoxic activities against cancer cell lines.^{2–4,10,23–25} Therefore, exploring the preliminary in vitro cytotoxicity of the natural compound 1 was of interest because contemporary pharmacological studies are focused on the detection of new anticancer agents isolated from unexplored species. The cytotoxicity of 1 was tested by the MTT protocol due to the adequate chemical stability and solubility required for this assay.²⁶ Thus, human cervical carcinoma HeLa, human breast carcinoma MDA-MB-231, human colorectal adenocarcinoma Caco-2, and mouse embryonic fibroblast NIH/3T3 cell lines were used for the antiproliferative assays, which were carried out in triplicate at 5 concentrations of 1 to obtain the averaged IC₅₀ values and the confidence intervals (CI). The IC₅₀ values were 92.2 μg/mL (95% CI: 89.9‒119.6) for HeLa and 106.2 μg/mL (95% CI: 104.6‒125.7) for MDA-MB-231 cell lines, while the IC₅₀ value for the Caco-2 was higher than 130 μg/mL. The IC₅₀ value for a healthy cell line (NIH/3T3) was 127.6 µg/mL (95% CI: 126.8‒136.7). Methotrexate was used as the positive control and DMSO as the negative control to assess the validity of the assays. Evaluation of the NIH/3T3 healthy cell line was significant for testing the selectivity of compound 1. The results presented in Figure 4 show a certain degree of selectivity at lower doses, although when considering the whole dataset, the selectivity appears to be small.

Figure 4.

Effect of compound 1, isolated from Coulteria velutina, on the viability of HeLa, Caco-2, MDA-MB-231, and NIH/3T3 cell lines after treatment for 48 h. MTX was used as the positive reference compound at 100 µM for HeLa, MDA-MB-231, and NIH/3T3 cell lines, and at 1 µM for Caco-2 cells. The viability was determined using the MTT assay by quantification of the fluorescence intensity, showing the results as percentage of viable cells. Bars represent the mean value ± the SE of 3 independent experiments. One-way analysis of variance was carried out with Tukey's post hoc test, n = 3. Values for SE (P < .05) are shown in lowercase letters (a to f). Nonlinear regression analysis of dose-response for the inhibition of viability by compound 1, 95% confidence interval, P < .001. The IC₅₀ for HeLa cell line was 92.2 µg/mL, R²= 0.9173; for MDA-MB-231: IC₅₀= 106.2 μg/mL, R²= 0.9803; for Caco-2: IC₅₀> 130 μg/mL R² not determined; and for NIH/3T3: IC₅₀= 127.6 µg/mL, R²= 0.9901 (GraphPad Prism 5.0). Abbreviations: MTX, methotrexate; SE, standard error.

Conclusions

The first phytochemical investigation of C velutina yielded a new weakly cytotoxic vouacapane from its leaves. Its structure was determined as (−)-(4R,5R,6R,8S,9S,10R,14R)-6-[(E)-p-coumaroyloxy]vouacapan-18-oic acid (1) by 1D and 2D NMR spectroscopy, as well as by VCD analysis of the synthetic derivative 3. This conformationally rigid compound can be used as a reference for the absolute configuration of other related vouacapanes.

Material and Methods

General

Melting points were measured on a Fisher-Johns apparatus. Optical rotations were determined on a Perkin-Elmer 341 polarimeter. IR spectra were measured on a Thermo-Scientific Nicolet IS10 spectrophotometer using the ATR technique. Low-resolution mass spectra were obtained by electron impact on a Varian Saturn 2000 spectrometer, and high-resolution accurate mass data were measured by electrospray ionization on a Thermo Fisher Scientific Orbitrap Exploris 120 mass spectrometer at Laboratorios Centrales, Cinvestav, Mexico City. The NMR spectra were acquired on a Varian Mercury 400 spectrometer from CDCl₃ solutions using TMS as the internal standard. Column chromatography was carried out using Merck silica gel 60 (230-400).

Plant Material

The leaves of C velutina (Britton & Rose) Sotuyo & G.P.Lewis were collected from Panzacola village (18° 53´ 15.4´´ N, 100° 59´ 18.3´´W) near Paso de Núñez town in the municipality of Carácuaro, Michoacán, Mexico at 629 m above sea level in October 2021. The plant material was dried at room temperature for 3 days under the shade and identified by Professor Rosa Isabel Fuentes Chávez and Professor Norma Patricia Reyes Martínez. A specimen, consisting of a branch of the tree with leaves, flowers, and fruit with seeds, was deposited at Herbario de la Facultad de Biología (EBUM), Universidad Michoacana de San Nicolás de Hidalgo, with the voucher number 30779.

Extraction and Isolation

The crushed air-dried leaves (∼0.5 cm on average) of C velutina (1.2 kg) were extracted with CH₂Cl₂ (3.5 L) under reflux for 4 h. Filtration and evaporation of the extract afforded a green viscous material (85 g). A portion of the extract (35 g) was subjected to column chromatography on silica gel (250 g) using mixtures of hexanes–EtOAc (1:0, 9:1, 4:1, 3:2, and 1:1, 200 mL each). Fractions of 10 mL were collected, monitored by TLC, and analyzed by ¹H NMR spectroscopy. The fractions eluted with hexanes–EtOAc 3:2 yielded compound 1 (7.0 g) as a colorless oil. No other secondary metabolites were found in the remaining eluted fractions.

(−)-(4R,5R,6R,8S,9S,10R,14R)-6-[(E)-p-Coumaroyloxy]vouacapan-18-oic acid (1). Colorless oil. [α]_D −18, [α]₅₇₈ −19, [α]₅₄₆ −21, [α]₄₃₆ −26 (c 0.4, CHCl₃, 20 °C); IR (film): 3673–2900 (br), 1698, 1602, 1513, 1262, 1168, 1159 cm⁻¹; UV (EtOH) λ_max (log ε) 314 (4.16), 300 (4.10), 225 (4.01), 212 nm (3.98); EIMS (70 eV): m/z (%) 314 (24) [M – coumaric acid]⁺, 270 (17) [M – coumaric acid – CO₂]⁺, 199 (12), 159 (20), 147 (100), 145 (64), 120 (71), 91 (82); HRESIMS m/z 501.2249 [M + Na]⁺ calcd for [C₂₉H₃₄O₆+ Na]⁺ 501.2248; ¹H and ¹³C NMR (CDCl₃): see Table 1.

Hydrolysis of Compound 1

A solution of 1 (100 mg) in 9:1 MeOH–CH₂Cl₂ (20 mL) was treated with NaOH (50 mg) in H₂O (0.2 mL). The reaction mixture was refluxed for 15 min in a microwave reactor working at 150 W, then neutralized with aqueous HCl (2%), and extracted with EtOAc (3 × 50 mL). The organic layer was washed with H₂O, dried over Na₂SO₄, filtered, and evaporated to dryness to give compound 2 as a white solid (89%), m.p. 125 °C; [α]_D+ 30, [α]₅₇₈+ 31, [α]₅₄₆+ 36, [α]₄₃₆+ 65, [α]₃₆₅+ 119 (c 0.9, CHCl₃, 20 °C). The ¹H and ¹³C NMR data were in agreement with published values.¹⁴ The hydrolysis also proceeds under reflux for 6 h when MeOH (5 mL) is used as the solvent.

Lactonization of Compound 2

A solution of 2 (50 mg) and sodium acetate (25 mg) in acetic anhydride (4 mL) was heated to reflux for 4 h.¹⁸ The reaction mixture was then poured over ice and extracted with EtOAc. The organic layer was washed with a NaHCO₃ aqueous solution, water, and then dried over anhydrous Na₂SO₄, filtered, and evaporated to dryness to yield compound 3 (92%).

(+)-(4R,5R,6R,8S,9S,10R,14R)-Vouacapan-6,18-olide (3). White solid, m.p. 157 °C; [α]_D+ 102, [α]₅₇₈+ 106, [α]₅₄₆+ 121, [α]₄₃₆+ 208, [α]₃₆₅+ 334 (c 0.8, CHCl₃, 20 °C); IR (CHCl₃): 2923, 1770, 1657, 1014 cm⁻¹; UV (EtOH) λ_max (log ε) 280 (2.88), 246 (3.08), 218 nm (3.55); EIMS (70 eV): m/z (%) 314 (100) [M]⁺, 270 (12), 255 (24), 199 (16), 162 (29), 147 (90), 145 (47), 133 (29), 108 (70); HRESIMS m/z 337.1759 [M + Na]⁺ calcd for [C₂₀H₂₆O₃+ Na]⁺ 337.1774; ¹H and ¹³C NMR: see Table 1.

Vibrational Circular Dichroism

The VCD and IR spectra of compound 3 were determined on a BioTools dualPEM ChiralIR FT spectrophotometer. A solution of 3 (6.0 mg) in CDCl₃ (150 μL) was deposited in a BaF₂ cell with a 100 μm path length. The data were acquired at a resolution of 4 cm⁻¹ for 20 h. The baseline was obtained by subtracting the spectrum of the solvent acquired under the same conditions. The stability of 3 was ensured by ¹H NMR spectra recorded before and after the VCD and IR measurement.

Cell Cultures

The human cancer cell lines HeLa, MDA-MB-231, Caco-2, and NIH/3T3 were acquired from the American Type Culture Collection (ATCC). The cell cultures were incubated at 37 °C in an atmosphere of 5% CO_2% and 80% humidity in Dulbecco's modified Eagle's medium supplemented with 10% (v/v) fetal bovine serum and 1% antibiotic (10 000 units of penicillin, 10 mg streptomycin, and 25 μg of amphotericin B per mL) solution.

Antiproliferative Assay

The in vitro antiproliferative activity of compound 1 was determined using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT, Sigma-Aldrich Co) dye uptake assay.²⁶ HeLa, MDA-MB-231, Caco-2 and NIH/3T3 cells were individually seeded into 96-well flat-bottomed plates (Costar) at a density of 3 × 10⁴ cells per well in 200 μL of serum-enriched medium. All assays were performed in triplicate (n = 3) using increasing concentrations of compound 1 (50, 70, 90, 110, and 130 μg/mL) for 48 h. Methotrexate (MTX) was employed as the positive control at 100 µM for MDA-MB-231, HeLa, and NIH/3T3 cells and 1 µM for Caco-2 cells, while DMSO (≤0.1% in culture medium) was used as the negative control. After the treatment, a solution (10 μL) of MTT (5 mg/mL in PBS) was added to each well and incubated for 4 h at 37 °C. Consecutively, 100 μL of 2-propanol/1 M HCl (19:1 v/v) was added to dissolve the formazan crystals, and absorbance measurements were done in a microplate spectrophotometer (iMark Microplate Absorbance Reader, BIO-RAD, Hercules) at 595 nm. Averaged IC₅₀ values are reported in μg/mL, including the corresponding CIs at 95%.

Supplemental Material

sj-docx-1-npx-10.1177_1934578X241252505 - Supplemental material for Absolute Configuration and Cytotoxicity of a New Vouacapane Diterpenoid from Coulteria velutina

Supplemental material, sj-docx-1-npx-10.1177_1934578X241252505 for Absolute Configuration and Cytotoxicity of a New Vouacapane Diterpenoid from Coulteria velutina by Odessa Magallón-Chávez, Laura Hernández-Padilla, Gabriela Rodríguez-García, Armando Talavera-Alemán, Concepción Armenta-Salinas, Ernestina Gutiérrez-Vázquez, Jesús Campos-García, Rosa E. del Río, Carlos M. Cerda-García-Rojas and Mario A. Gómez-Hurtado in Natural Product Communications

Footnotes

Acknowledgments

We acknowledge CIC-UMSNH for financial support. O.M.C. is grateful to CONACYT-Mexico for scholarship number 775693. L.H.P. and A.T.A. thank CONACYT-Mexico for their postdoctoral scholarships. We are grateful to M. en C. Ma Alvina Bucio Vásquez and Q. F. B. Verónica Reyes Olivares for VCD and optical rotation measurements, respectively. We also acknowledge I.BT. Lorena Ramírez-Reyes from Unidad de Genómica, Proteómica y Metabolómica, Laboratorio Nacional de Servicios Experimentales, Cinvestav-IPN for the high-resolution mass spectrometry analyses. We are also grateful to Dra. Rosa Elvira Nuñez Anita from Facultad de Medicina Veterinaria y Zootecnia de la Universidad Michoacana de San Nicolás de Hidalgo for the valuable support in the in vitro antiproliferative assays.

Declaration of Conflicting Interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by CIC-UMSNH and CONACYT-Mexico. Coordinación de la Investigación Científica, Consejo Nacional de Ciencia y Tecnología.

ORCID iDs

Gabriela Rodríguez-García

Armando Talavera-Alemán

Rosa E. del Río

Carlos M. Cerda-García-Rojas

Mario A. Gómez-Hurtado

Supplemental Material

Supplemental material for this article is available online.

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