Aquilanols A and B, Macrocyclic Humulene-Type Sesquiterpenoids

Oct 30, 2017 - †College of Pharmacy and ‡Department of Agricultural Biotechnology, College of Agriculture and Life Sciences, Seoul National Univer...
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Note Cite This: J. Nat. Prod. 2017, 80, 3043-3048

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Aquilanols A and B, Macrocyclic Humulene-Type Sesquiterpenoids from the Agarwood of Aquilaria malaccensis Chi Thanh Ma,†,§ Taeyong Eom,⊥ Eunji Cho,‡ Bo Wu,▽ Tae Ryong Kim,† Ki Bong Oh,‡ Sang Beom Han,⊥ Sung Won Kwon,† and Jeong Hill Park*,† †

College of Pharmacy and ‡Department of Agricultural Biotechnology, College of Agriculture and Life Sciences, Seoul National University, Seoul 08826, Korea ▽ Department of Chemistry, China Medical University, Shenyang, Liaoning 110122, People’s Republic of China ⊥ College of Pharmacy, Chung Ang University, Seoul 06974, Korea § Faculty of Pharmacy, University of Medicine and Pharmacy, Ho Chi Minh City, 700000, Vietnam S Supporting Information *

ABSTRACT: Four new and five known sesquiterpenoids were isolated from the agarwood of Aquilaria malaccensis. Aquilanols A and B (1 and 2) have an unprecedented macrocyclic humulene structure with a bicyclic 7/10 ring system. Compound 2 was obtained as a scalemic mixture that was resolved by HPLC analysis using a chiral column. Their structures were deduced based on spectroscopic data analysis, and the absolute configurations were unambiguously determined by X-ray crystallographic data and ECD spectroscopic analysis. A putative biosynthetic pathway of these sesquiterpenoids is proposed.

A

seven fractions (E1−E7). Fraction E3 (3.36 g) was fractionated by a silica gel column, semipreparative RP-HPLC (MeOH/ H2O), and a Sephadex LH-20 column (MeOH) to afford 1 (23.6 mg), 2 (11.1 mg), 6 (11.1 mg), 8 (13.1 mg), and 9 (27.3 mg). Fraction E4 (7.6 g) was applied to a silica gel column and semipreparative RP-HPLC to obtain 3 (34.7 mg), 4 (40.4 mg), 5 (9.0 mg), and 7 (3.4 mg).

garwood is a dark aromatic resin produced inside the heartwood of various Aquilaria and Gyrinops species when insects, wounds, or microbial infections injure them.1−3 It is used as an incense for cultural and religious ceremonies. It has also been used as an analgesic and a sedative and for the treatment of digestive disorders in Southeast Asia and India.3 Its essential oil has been used as perfume. Currently, more than 150 sesquiterpenoids and chromone derivatives have been identified from agarwood.4 In recent studies, these compounds were reported to have antineuroinflammatory,5 antibacterial,6,7 α-glucosidase inhibitory,8 cytotoxic,8 acetylcholinesterase inhibitory,6−9 neuroprotective,10 and antidepressant activities.11 Our previous study on agarwood chips led to the isolation of a multitude of sesquiterpenoids and chromones.12,13 In the course of a continuous study on agarwood, four new and five known sesquiterpenoids were isolated from the ether extract of agarwood. Aquilanols A and B (1 and 2) possess an unprecedented macrocyclic humulene structure with a bicyclic 7/10 ring system. Compound 2 was obtained as a scalemic mixture. Herein, the isolation and structure interpretation of the compounds are reported along with a plausible biosynthetic pathway. The agarwood chips of A. malaccensis (9.0 kg) were extracted with 70% MeOH. The solvent was evaporated, and the residue was extracted with Et2O, EtOAc, and n-BuOH. The Et2O fraction (30 g) was subjected to a silica gel column to obtain © 2017 American Chemical Society and American Society of Pharmacognosy

Aquilanol A (1) was isolated as colorless plate crystals with a specific rotation [α]20D +3 (c 0.3, MeOH). Its molecular formula was deduced as C15H24O2 from HRESI/TOFMS based on the ion at m/z 259.1662 [M + Na]+ (calcd for C15H24O2Na, 259.1674). The IR spectrum suggested a hydroxy group (3420 cm−1), a double bond (1452 cm−1), and an ethereal Received: May 30, 2017 Published: October 30, 2017 3043

DOI: 10.1021/acs.jnatprod.7b00462 J. Nat. Prod. 2017, 80, 3043−3048

Journal of Natural Products

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functionality (1083 cm−1). The 13C NMR and HSQC data exhibited 15 carbon signals (Table 1) including two double Table 1. 1H and 13C NMR Spectroscopic Data of Aquilanols A (1) and B (2) in CDCl3 1a no.

δH (mult, J, Hz)

2b δC

1α 1β

1.63 (dd, 12.8, 6.4) 1.69 (dd, 12.8, 10.4)

38.5 (t)

2 3 4α 4β 5α 5β

5.20 (dd, 10.4, 6.4)

123.0 (d) 142.2 (s) 30.7 (t)

6 7 8α 8β 9 10 11 12α 12β 13 14 15

2.17 (m) 2.42 (td, 11.2, 3.2) 2.12 (m) 1.77 (ddt, 14.4, 11.2, 3.2) 3.71 (dd, 4.8, 2.4) 2.39 (dd, 14.4, 4.8) 2.52 (dd, 14.4, 10.4) 5.14 (ddd, 16.0, 10.4, 4.8) 5.18 (d, 16.0) 4.49 3.89 1.27 1.11 0.90

(d, 12.8) (d, 12.8) (s) (s) (s)

35.6 (t)

74.4 (d) 79.9 (s) 42.7 (t)

123.6 (d) 138.4 (d) 41.1 (s) 67.6 (t) 29.9 (q) 30.2 (q) 22.3 (q)

δH (mult, J, Hz) 1.73 (dd, 13.5, 6.5) 2.25 (dd, 13.5, 10.5) 5.36 (dd, 10.5, 6.5) 2.16 2.43 2.17 1.69

(m) (m) (m) (m)

3.76 (dd, 5.0, 2.5) 2.36 (dd, 15.0, 2.5) 1.36 (dd, 15.0, 10.5) 2.92 (dt, 10.5, 2.5) 2.62 (d (3.0) 4.63 4.11 1.28 1.11 0.67

(d, 14.0) (d, 14.0) (s) (s) (s)

δC 37.2 (t)

124.1 (d) 140.9 (s) 30.5 (t) 34.8 (t)

74.3 (d) 80.9 (s) 42.8 (t)

52.6 (d) 67.9 (d) 36.3 (s) 66.2 (t)

Figure 1. Key HMBC, 1H−1H COSY, and NOESY correlations of 1− 3 and 6.

30.1 (q) 29.4 (q) 17.1 (q)

to H-6/H2-8/H2-12, from H-12α to H-1β/H-8β/H-10/H3-13, and from H-12β to H-1β/H-4β/H-5α/H3-13. The aforementioned data suggested that the ether bridge and 6-OH are βoriented, whereas H-6 is in the α-orientation. The absolute configuration was determined by X-ray crystallographic analysis with graphite-monochromated Cu Kα radiation (χ = 1.541 84 Å) at 100 K (Figure 2a). Thus, the absolute configuration of the two stereogenic centers in 1 was established as (6S, 7R). Aquilanol B (2) was isolated as colorless needles. The molecular formula was determined as C15H24O3 from the positive ion at m/z 253.1793 [M + H]+ (calcd for C15H25O3, 253.1804) in the HRESI/TOFMS spectrum, which implied four indices of hydrogen deficiency. The increase of 16 mass units of 2 compared to the molecular weight of 1 suggested the addition of a hydroxy functionality in the structure of 2. The IR spectrum showed a hydroxy group (3446 cm−1), a double bond (1452 cm−1), an asymmetric ether group (1082 cm−1), and an oxirane moiety (877 cm−1). The IR and NMR spectral data were similar to those of 1, indicating that it possesses the same structural scaffold as aquilanol A. The 13C NMR data (Table 1) showed three oxymethine carbons (δC 74.3, 67.9, 52.6) compared with only one (δC 74.4) in 1. In the 1H NMR data, the Δ9,10 olefinic bond in 1 was replaced by an epoxide moiety in 2. The configuration of 2 was determined from the NOESY data. The small coupling constant between H-9 and H10 (J = 3.0 Hz) indicates their trans orientation.14 Hence, the 2D structure of aquilanol B (2) was determined as shown in Figure 1b. Single-crystal X-ray diffraction data showed the space group P121/n1, a = 11.6837(3) Å, b = 6.4948(2) Å, c = 18.4991(6) Å, which indicates a mixture of two enantiomers. Therefore, its absolute configuration was unambiguously determined as (6S, 7R, 9S, 10S) (2a) and (6R, 7S, 9R, 10R) (2b) (Figure 2b). HPLC analysis using a chiral-phase column (Chiralpak AD-H, n-hexane/isopropyl alcohol, 80:20, v/v)

a Data were measured at 800 MHz (1H) and 200 MHz (13C). bData were measured at 500 MHz (1H) and 125 MHz (13C).

bonds (δC 142.2, 123.0, 138.4, 123.6), three oxygen-bearing carbons (δC 79.9, 74.4, 67.6), and three methyl carbon signals (δC 30.2, 29.9, 22.3). The 1H NMR spectroscopic data showed three olefinic protons (δH 5.20, 5.18, 5.14), four methylene groups (δH 2.52−1.63), one oxymethine proton (δH 3.71), one oxymethylene (δH 4.49, 3.89), and three methyl groups (δH 1.27, 1.11, 0.90). The 1H−1H COSY spectrum of 1 showed three spin-coupling systems. First, two geminal protons, H-1α (δH 1.63, dd, J = 12.8, 6.4 Hz) and H-1β (δH 1.69, dd, J = 12.8, 10.4 Hz), showed correlations with olefinic proton H-2 (δH 5.20, dd, J = 10.4, 6.4 Hz). Second, two adjacent methylene protons, H-4α (δH 2.17, m), H-4β (δH 2.42, td, J = 11.2, 3.2 Hz), H-5α (δH 2.12, m), and H-5β (δH 1.77, ddt, J = 14.4, 11.2, 3.2 Hz), were correlated with the oxymethine proton H-6 (δH 3.71, q, J = 2.4 Hz). Third, H-9 (δH 5.14, ddd, J = 16.0, 10.4, 4.8 Hz) was correlated with H-8α (δH 2.39, dd, J = 14.4, 4.8 Hz), H-8β (δH 2.52, dd, J = 14.4, 10.4 Hz), and H-10 (δH 5.18, d, J = 16.0 Hz). Cross-peaks from H-2 to C-1/C-3/C-4/C-12, from H2-5 to C-3/C-4/C-6/C-7, from H2-8 to C-6/C-7/C-9/C-10/ C-13, from H-9 to C-7/C-8/C-10, and from H-10 to C-8/C-11 were observed in the HMBC spectrum. HMBC correlations from H2-12 to C-7 suggested the ether bridge between C-3 and C-7 via methylene C-12. Therefore, the 2D structure of 1 was elucidated as a macrocyclic humulene-type sesquiterpenoid as depicted in Figure 1a. The relative configuration and orientation of the ether bridge were assigned from NOESY experiments by the correlations between H-6, H2-12, and H3-13. Key NOESY correlations observed are from H-6 to H-5/H-8α/H-9/H3-13, from H3-13 3044

DOI: 10.1021/acs.jnatprod.7b00462 J. Nat. Prod. 2017, 80, 3043−3048

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Table 2. 1H (500 MHz) and 13C (125 MHz) NMR Spectroscopic Data of Daphnauranol D (3) and Chamaejasmone E (6) in CDCl3 3 no. 1 2α 2β 3α 3β 4 5 6α 6β 7 8 9 10 11 12α 12β 13 14 15 −OCH3

δH (mult, J in Hz) 1.65 1.87 1.88 1.37 2.23 2.03 1.52 1.90

(m) (m) (m) (m) (m) (dq, 11.0, 1.5) (dd, 13.0, 9.5) (m)

6.04 (d, 1.5)

2.99 (dd, 11.0, 2.5) 1.96 (dd, 14.5, 2.5) 2.11 (dd, 14.5, 11.0) 1.98 (d, 1.5) 0.99 (d, 7.0) 3.57 (s)

6 δC

δH (mult, J in Hz)

51.8 (s) 34.8 (t) 33.3 (t) 35.2 (d) 47.0 (d) 32.5 (t) 80.3 (s) 202.2 (s) 127.5 (d)

δC 143.0 (s) 204.6 (s)

2.64 (dd, 16.5, 7.0) 2.05 (d, 16.5) 2.66 m 2.34 (d, 20.0) 2.70 (d, 20.0)

2.45 (d, 18.5) 2.37 (d, 18.5)

45.1 (t) 34.3 (d) 174.9 (s) 36.1 (t) 81.9 (s) 215.0 (s) 50.7 (t)

171.4 (s) 48.1 (d) 31.6 (t)

1.23 (s)

41.9 (s) 59.5 (s) 10.0 (q)

173.8 (s) 22.8 (q) 17.7 (q) 52.0 (q)

1.48 (s) 1.16 (d, 7.0) 3.74 (s)

174.4 (s) 15.4 (q) 18.5 (q) 52.4 (q)

system like daphnauranol D have been reported from Daphne aurantiaca15 and Gnidia polycephala.16 Chamaejasmone E (6) was obtained as a colorless oil with a specific rotation [α]20D −129 (c 0.4, MeOH). The molecular formula was determined as C16H20O5 from HRESI/TOFMS by an ion at m/z 315.1214 [M + Na]+ (calcd for C16H20O5Na, 315.1208), indicating seven indices of hydrogen deficiency. The IR spectrum showed hydroxy (3502 cm−1), carbonyl (1756 cm−1), and olefinic (1703 cm−1) signals. The 13C NMR spectrum showed the presence of 16 carbons including two olefinic, an oxygenated, three methylene, an aliphatic methine, an O-methyl, and three methyl carbons. The 1H and 13C NMR data (Table 2) of 6 were similar to those of chamaejasmone A,17 a rare 5/6/7 tricyclic sesquiterpenoid that was isolated from Stellera chamaejasme. However, the hydroxymethyl group at C-11 of chamaejasmone A was replaced by a hydroxycarbonyl moiety (δC 174.4) in 6. The 2D structure of 6 was elucidated via the HSQC, 1H−1H COSY, and HMBC data (Figure 1d). The HMBC cross-peaks from H3-12 to C-7/C-10/ C-11/C-13 and from H3-14 to C-1/C-9/C-10/C-11 suggested a carbon bridge from C-7 to C-10 via C-11. The β-orientation of the C-7/C-11/C-10 carbon bridge was established by the NOESY cross-peaks of H3-12/H3-14/H-6β/H3-15.17 The absolute configuration of 6 was unambiguously determined as (4S, 7S, 10S, 11S) by the calculated and experimental ECD spectroscopic data analysis (Figure 3). The five known sesquiterpenoids were identified as daphnauranol B (4),15 daphnauranol C (5),15 chamaejasmone D (7),18 auranticanol A (8),19 and 12-hydroxyhumula2Z,6E,9E-triene (9)20 by comparison of experimental and reported physical data. A putative biosynthesis pathway toward 1 and 2 is shown in Scheme 1 (Scheme S1 for 3−8, Supporting Information). The biosynthesis of the precursor and intermediates could be traced

Figure 2. ORTEP diagram of 1 (a), 2a (6S,7R,9S,10S), 2b (6R,7S,9R,10R) (b), and 3 (c).

showed two peaks with a peak area ratio of 48/52 (Figure S23, Supporting Information). Comparison of the calculated and experimental electronic circular dichroism (ECD) data suggests that enantiomer 2b predominates in the scalemic mixture (Figure S24, Supporting Information). Macrocyclic humulene-type sesquiterpenoids possessing an asymmetric ether bridge such as in 1 and 2 have not been described yet. Daphnauranol D (3) was obtained as colorless needles, [α]20D +47 (c 0.6, MeOH). The positive-ion HRESI/TOFMS displayed an [M + H]+ (100%) at m/z 279.1485 (calcd for C16H23O4, 279.1596), consistent with a molecular formula of C16H22O4. The IR spectrum showed hydroxy (3492 cm−1), carbonyl (1744 cm−1), and α,β-unsaturated carbonyl (1655 and 1647 cm−1) signals. The 1H NMR spectrum displayed signals of a secondary methyl group (δH 0.99, H3-15), a tertiary methyl group (δH 1.98, H3-14), an olefinic methine (δH 6.04, H-9), and an O-methyl (δH 3.57). The 13C NMR of 3 showed 16 carbon signals including three methyl, four methylene, four methine, and five nonprotonated carbons. The 1H and 13C NMR data of 3 (Table 2) were similar to those of daphnauranol A,15,16 a sesquiterpenoid with a rare 5/6/7 ring skeleton, which was isolated from Daphne aurantiaca and Gnidia polycephala. Unlike daphnauranol A, a carbonyl signal at δC 173.8 arising from C-13 was observed in the 13C NMR spectrum of 3. The NOESY correlations of H-11/H-6β/H3-15 (Figure 1c) suggested a βorientation of the carbon bridge C-7/C-11/C-12/C-1.15 The absolute configuration of 3 was determined as (1R, 4S, 5S, 7S, 11S) by X-ray crystallographic analysis (Figure 2c). Only three sesquiterpenoids (daphnauranols A−C) with a 5/6/7 ring 3045

DOI: 10.1021/acs.jnatprod.7b00462 J. Nat. Prod. 2017, 80, 3043−3048

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NMR spectra were recorded on Bruker ASCENE (800 MHz) and Bruker ADVANCE 500 MHz FT-NMR spectrometers (Germany); NMR solvents were purchased from Sigma-Aldrich (USA). HRESIMS data were acquired on an Agilent 6350 Q-TOF mass spectrometer (Agilent, USA). The X-ray crystallographic data were measured on a SuperNova X-ray diffractometer (Agilent, USA). An Agilent 1260 Infinity HPLC system (USA) with a DAD and a Phenomenex Luna 100 RP-C18 (250 × 4.6 mm i.d., 5 μm) column was used for the analaytical HPLC analaysis. A Gilson 321 pump and a Gilson UV/vis155 detector system (Gilson, Middleton, WI, USA) with a Phenomenex Luna 100 RP-C18 (250 × 10 mm i.d., 5 μm) column were used for the semipreparative HPLC. Silica gel 60 (0.040−0.063 mm; Merck, Germany) and Sephadex LH-20 (Amersham Bioscience AB, Sweden) were used for the column chromatography. Solvents for HPLC were from J.T. Baker (USA). Plant Material. The agarwood chips of A. malaccensis were from Industrial Plantation Co. (Vientiane, Laos). A voucher specimen (AM2010-01) is deposited at the Herbarium of Seoul National University, Korea. Extraction and Isolation. The agarwood chips of A. malaccencis (9.0 kg) was ground and extracted with 70% MeOH under reflux (3 × 20 L, 3 h each). The solvent was evaporated in vacuo to obtain a total extract (864 g). The total extract was suspended in H2O and successively extracted with Et2O, EtOAc, and n-BuOH, affording 225, 155, and 289 g of extract, respectively. The Et2O fraction (30 g) was applied on a silica gel column (300 g) and eluted with n-hexane/EtOAc (40:1 → 1:1, v/v) to obtain seven fractions (E1−E7). Fraction E3 (3.36 g) was separated by a silica gel column (100 g) using n-hexane/EtOAc as the mobile phase (95:5 → 7:3, v/v) to afford nine subfractions (E3a−E3i). Subfraction E3c (450 mg) was further separated by semipreparative RP-HPLC (65% aqueous MeOH) and by a Sephadex LH-20 (MeOH) column. Compounds 2 (11.1 mg), 6 (11.1 mg), and 8 (13.1 mg) were obtained. Fraction E3d (237 mg) was applied to a Sephadex LH-20 column (MeOH) to give five subfractions (E3d1−E3d5). Compound 1 (23.6 mg) was obtained from E3d5 (71.5 mg) by semipreparative HPLC (60% aqueous MeOH). Fraction E3e was subjected to a Sephadex LH-20 column (MeOH) to give five subfractions, and 9 (27.3 mg) was obtained from subfraction E3e3. Fraction E4 (7.6 g) was applied to a silica gel column (200 g), eluting with n-hexane/ EtOAc (95:5 → 1:1, v/v); 10 subfractions (E4a−-E4k) were obtained. Subfractions E4e (1.45 g) and E4f (781 mg) were further separated by semipreparative HPLC (65% aqueous MeOH) to afford 3 (34.7 mg) and 5 (9.0 mg), respectively. Compounds 4 (40.4 mg) and 7 (3.4 mg) were obtained from subfraction E6g (814.5 mg) by using semipreparative HPLC (65% aqueous MeOH). Chiral-phase HPLC separations were conducted with an LC 20A prominence HPLC system (Shimadzu) using a Chiralpak AD-H column (250 mm × 4.6 mm i.d., 5 μm, Daicel Chiral Technologies, Ltd.) at 40 °C and detection at 210 nm. n-Hexane/isopropyl alcohol (80/20, v/v) at a flow rate of 1.0 mL/min under isocratic conditions was employed as a mobile phase. The chromatogram showed one peak with tR 4.58 min for 1 and two peaks with tR 5.79 and 6.36 min for 2. X-ray Crystallographic Data Analysis of 1−3. X-ray data were measured with Cu Kα radiation (χ = 1.541 84 Å) and the Olex222 program. The structure was solved with ShelXT using direct methods and refined with ShelXL using least squares minimization. Crystallographic data for 1−3 have been deposited at the Cambridge Crystallographic Data Centre (1: CCDC 1553076, 2a: CCDC 1553078, 2b: CCDC 1553077, 3: CCDC 1553079). Copies of the data can be obtained free of charge by application to the Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: + 44(0)1223-336033 or e-mail: [email protected]). Crystallographic data of 1: C15H24O2 (M = 236.34 g/mol), monoclinic, space group P21/c (no. 14), a = 11.34029(10) Å, b = 10.58915(8) Å, c = 11.42721(11) Å, β = 103.6427(9)°, V = 1333.51(2) Å3, Z = 4, T = 99.9(3) K, μ(Cu Kα) = 0.592 mm−1, Dcalc = 1.177 g/cm3, 27 083 reflections measured (8.022 ≤ 2Θ ≤ 153.234), 2806 unique (Rint = 0.0285, Rsigma = 0.0123). The final R1 was 0.0367 (I > 2σ(I)) and wR2 was 0.1005.

Figure 3. Calculated and experimental ECD spectra of 6.

Scheme 1. Plausible Biosynthesis Pathway for 1 and 2

back to farnesyl diphosphate (FPP).21 Compounds 1 and 2 possess the same structural framework, suggesting that these compounds might have originated from the same precursors, 12-hydroxyhumula-2Z,6E,9E-triene (9) (Supporting Information) and the humulyl cation, which is a precursor of many sesquiterpenoids.21 The FPP precursor cyclizes to the humulyl cation intermediate, which is deprotonated to produce αhumulene. Oxidation would generate intermediate 12-hydroxyhumula-2Z,6E,9E-triene, which upon oxidization and cyclization affords compound 1. Compound 2 may be derived from 1 through epoxidation of the Δ9,10 double bond. The conversion of 1 to the scalemic mixture 2 is currently not understood. Agarwood is produced inside Aquilaria trees as a selftreatment mechanism to suppress or fight microbial infection.4 The isolated compounds were tested for antibacterial activity against Gram-positive and Gram-negative pathogenic bacteria. However, these compounds did not display antibacterial activity against Staphylococcus aureus, Enterococcus faecalis, E. faecium, Salmonella enterica, Klebsiella pneumoniae, and Escherichia coli (MIC > 128 μg/mL, 430−580 μM). They were also tested for antifungal effects against the pathogenic fungi Aspergillus f umigatus, Trichophyton rubrum, T. mentagrophytes, and Candida albicans using amphotericin B as a positive control. These compounds did not show any significant inhibitory activities against these fungi strains (MIC > 128 μg/mL, 430−580 μM) under the test conditions.

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EXPERIMENTAL SECTION

General Experimental Procedures. Melting points were measured using a Mitamura Riken melting point apparatus (Japan) and are not corrected. The optical rotations were measured on a JASCO P-2000 polarimeter (Japan) at 20 °C. IR spectra were measured on FT/IR 4200 (JASCO, Japan). The UV and ECD spectra were obtained on a Chirascan Plus (Applied Photophysics Ltd., UK). 3046

DOI: 10.1021/acs.jnatprod.7b00462 J. Nat. Prod. 2017, 80, 3043−3048

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Crystallographic data of (±)-2: C15H24O3 (M = 252.34 g/mol), monoclinic, space group P21/n (no. 14), a = 11.6837(3) Å, b = 6.4948(2) Å, c = 18.4991(6) Å, β = 100.765(3)°, V = 1379.07(7) Å3, Z = 4, T = 295.0(2) K, μ(Cu Kα) = 0.660 mm−1, Dcalc = 1.215 g/cm3, 8935 reflections measured (8.308 ≤ 2Θ ≤ 152.758), 2865 unique (Rint = 0.0213, Rsigma = 0.0205). The final R1 was 0.0394 (I > 2σ(I)) and wR2 was 0.1147. Crystallographic data of 3: C16H22O4 (M = 278.33 g/mol), monoclinic, space group P21 (no. 4), a = 12.01771(12) Å, b = 6.66052(7) Å, c = 18.21093(19) Å, β = 98.0021(9)°, V = 1443.49(3) Å3, Z = 4, T = 100.0(4) K, μ(Cu Kα) = 0.740 mm−1, Dcalc = 1.281 g/ cm3, 29 447 reflections measured (7.428 ≤ 2Θ ≤ 153.192), 5952 unique (Rint = 0.0296, Rsigma= 0.0198). The final R1 was 0.0263 (I > 2σ(I)) and wR2 was 0.0687. Aquilanol A (1): colorless plates (petroleum ether/EtOAc, 8:1); mp 66−67 °C; [α]20D +3 (c 0.3, MeOH); UV (MeOH) λmax (log ε) 227 (5.01); IR (film) νmax 3420, 2955, 2861, 2348, 1508, 1452, 1364, 1083, 1051, 993 cm−1; 1H NMR and 13C NMR data see Table 1; HRESIMS m/z 259.1662 [M + Na]+ (calcd for C15H24O2Na, 259.1674). Aquilanol B (2): colorless needles (petroleum ether/EtOAc, 12:1); mp 86−87 °C; [α]20D +2 (c 1, MeOH); UV (MeOH) λmax (log ε) 208 (6.24), 227 (4.88); IR (film) νmax 3446, 2965, 2866, 1452, 1386, 1116, 1082, 1034, 877 cm−1; 1H NMR and 13C NMR data see Table 1; HRESIMS m/z 253.1793 [M + H]+ (calcd for C15H25O3, 253.1804). Daphnauranol D (3): colorless needles (petroleum ether/EtOAc, 12:1); mp 53−54 °C; [α]20D +47 (c 0.6, MeOH). UV (MeOH) λmax (log ε) 243 (5.97), 300 (5.02); IR (film) νmax 3492, 2953, 2878, 1744, 1665, 1647, 1508, 1432, 1375, 1210, 1105, 1031 cm−1; 1H NMR and 13 C NMR data see Table 2; HRESIMS m/z 279.1485 [M + H]+ (calcd for C16H23O4, 279.1596). Chamaejasmone E (6): colorless oil; [α]20D −129 (c 0.4, MeOH); UV (MeOH) λmax (log ε): 237 (6.17), 295 (5.04); IR (film) νmax 3502, 2928, 2853, 1756, 1703, 1628, 1508, 1456, 1288, 1127, 1065 cm−1; 1H NMR and 13C NMR data see Table 2; HRESIMS m/z 315.1214 [M + Na]+ (calcd for C16H20O5Na, 315.1208). ECD Calculations. The absolute configuration of compound 6 was determined by using density functional theory (DFT) calculations and carried out with the Turbomole 6.5 program. The conformational studies were performed using the MMFF94 force field to obtain energy minimization by the ChemBio3D Ultra 13.0 software. The MMFF94 conformers were further optimized using the DFT/B3LYP exchange−correlation function with the basis set 6-31G(d)/def2TZVPP for compound 2 and def-SV(P) for compound 6. The ECD spectra were simulated by overlapping Gaussian functions for each transition, where σ is the width of the band at 1/e height and ΔEi and Ri are the excitation energies and rotatory strengths for transitions i, respectively. In this case, the value of σ = 0.10 eV was used. The ground-state geometries and the calculated ECD data were obtained using the TMolex4.0 software package.

Δϵ(E) =

1 2.297 × 10−39

1 2πσ

A

Note

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jnatprod.7b00462. Detailed experimental procedure, 1D and 2D NMR, IR, UV, ECD, MS spectra data of 1−3 and 6 (PDF) X-ray crystallography data for 1−3 (CIF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Chi Thanh Ma: 0000-0003-4058-3354 Sung Won Kwon: 0000-0001-7161-4737 Jeong Hill Park: 0000-0003-3077-7673 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the National Research Foundation of Korea (NRF) under a grant of the Korean government (MSIP) (No. 2009-0083533) and the Bio-Synergy Research Project of the Ministry of Science, ICT. This project was also funded by Future Planning through the National Research Foundation (NRF-2012M3A9C4048796) and the BK21 Plus Program in 2017.

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REFERENCES

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2

∑ ΔEiR ie[−(E −ΔEi /2σ)] i

Antibacterial Activity Assay. Gram-positive bacteria (S. aureus ATCC 25923, E. faecalis ATCC 19433, and E. faecium ATCC 19434) and Gram-negative bacteria (S. enterica ATCC 14028, K. pneumoniae ATCC 10031, and E. coli ATCC 25922) were used for antibacterial activity assays according to a reported procedure.23 These compounds did not show antibacterial activity (MIC > 128 μg/mL = 430−580 μM). Antifungal Activity Assay. C. albicans ATCC 10231, A. f umigatus HIC 6094, T. rubrum NBRC 9185, and T. mentagrophytes IFM 40996 were used for the antifungal activity assay according to a reported procedure.23 These compounds did not show antifungal activity (MIC > 128 μg/mL = 430−580 μM). 3047

DOI: 10.1021/acs.jnatprod.7b00462 J. Nat. Prod. 2017, 80, 3043−3048

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