Alkaloids from Pandanus amaryllifolius: Isolation and Their Plausible

Oct 13, 2015 - (synonym: P. odorus, Pandanaceae) is distributed in Southeast Asia and was introduced in southern Taiwan as a cultivated plant in the 1...
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Alkaloids from Pandanus amaryllifolius: Isolation and Their Plausible Biosynthetic Formation Yu-Chi Tsai,†,# Meng-Lun Yu,†,# Mohamed El-Shazly,†,‡ Ludger Beerhues,§ Yuan-Bin Cheng,† Lei-Chin Chen,⊥ Tsong-Long Hwang,∥ Hui-Fen Chen,∇ Yu-Ming Chung,† Ming-Feng Hou,ο Yang-Chang Wu,*,†,σ,δ,ϕ and Fang-Rong Chang*,†,ο,ϖ,ξ †

Graduate Institute of Natural Products, Kaohsiung Medical University, Kaohsiung 807, Taiwan Department of Pharmacognosy and Natural Products Chemistry, Faculty of Pharmacy, Ain-Shams University, Organization of African Unity Street, Abassia, Cairo 11566, Egypt § Institut fur Pharmazeutische Biologie, Technische Universitat Braunschweig, Mendelssohnstrasse 1, D-38106 Braunschweig, Germany ⊥ Department of Nutrition, I-Shou University, Kaohsiung 840, Taiwan ∥ Graduate Institute of Natural Products, College of Medicine, Chang Gung University, Taoyuan 333, Taiwan ∇ Department of Medical and Applied Chemistry, Kaohsiung Medical University, Kaohsiung 807 Taiwan ο Cancer Center, Kaohsiung Medical University Hospital, Kaohsiung 807, Taiwan σ Chinese Medicine Research and Development Center, China Medical University Hospital, Taichung 404, Taiwan δ Center for Molecular Medicine, China Medical University Hospital, Taichung 404, Taiwan ϕ School of Chinese Medicine, College of Chinese Medicine, China Medical University, Taichung 404, Taiwan ϖ Research Center for Natural Product and New Drug, Kaohsiung Medical University, Kaohsiung 807, Taiwan ξ Department of Marine Biotechnology and Resources, National Sun Yat-sen University, Kaohsiung 804, Taiwan ‡

S Supporting Information *

ABSTRACT: Pandanus amaryllifolius Roxb. (Pandanaceae) is used as a flavor and in folk medicine in Southeast Asia. The ethanolic crude extract of the aerial parts of P. amaryllifolius exhibited antioxidant, antibiofilm, and anti-inflammatory activities in previous studies. In the current investigation, the purification of the ethanolic extract yielded nine new compounds, including N-acetylnorpandamarilactonines A (1) and B (2); pandalizines A (3) and B (4); pandanmenyamine (5); pandamarilactones 2 (6) and 3 (7), and 5(E)pandamarilactonine-32 (8); and pandalactonine (9). The isolated alkaloids, with either a γ-alkylidene-α,β-unsaturated-γ-lactone or γ-alkylidene-α,β-unsaturated-γ-lactam system, can be classified into five skeletons including norpandamarilactonine, indolizinone, pandanamine, pandamarilactone, and pandamarilactonine. A plausible biosynthetic route toward 1−5, 7, and 9 is proposed.

T

are categorized into pandamarine, pandarilactone, pyrrolidinone, pandamarilactonine, norpandamarilactonine, pandanamine, and pyrrolidine derivatives with either a γ-alkylideneα,β-unsaturated-γ-lactone or a γ-alkylidene-α,β-unsaturated-γlactam moiety.13 The diversity of pharmacologically active alkaloids separated from Pandanus sp., encouraged us to investigate the secondary metabolites of a common species P. amaryllifolius grown in Southeast Asia. The ethanolic extract of the aerial parts of P. amaryllifolius was partitioned and separated into EtOAc, CHCl3, and H2O fractions by an acid−base extraction method.

he tropical shrub Pandanus amaryllifolius Roxb. (synonym: P. odorus, Pandanaceae) is distributed in Southeast Asia and was introduced in southern Taiwan as a cultivated plant in the 1980s. It is used as a flavor in sweets, bakery products, and even home cooking. In folk medicine, it is used as a remedy for the treatment of hyperglycemia, liver protection, and inhibition of tumor growth.1 Previous pharmacological investigations of Pandanus sp. extracts demonstrated potent antioxidant,1a,2 antidiabetic,3 antihyperglycemic,4 antiviral,5 antitubercular,6 and cytotoxic7 activities. The phytochemical analysis of Pandanus sp. extracts resulted in the isolation of alkaloids,8 benzenoids,2,9 steroids,2 flavonoids,9,10 lignans,2 and triterpenoids.11 In general, alkaloids are considered the major secondary metabolites of this genus.8,12 Pandanus alkaloids © XXXX American Chemical Society and American Society of Pharmacognosy

Received: March 23, 2015

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DOI: 10.1021/acs.jnatprod.5b00252 J. Nat. Prod. XXXX, XXX, XXX−XXX

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Table 1. 1H NMR Data for Compounds 1−5 (400 MHz, CDCl3, δH in ppm, J in Hz) position 1 4 5 6 7 8 9 10 11 12 13 -OCH3

1

2

3

4

5

δH mult (J)

δH mult (J)

δH mult (J)

δH mult (J)

δH mult (J)

6.57, q (1.6)

6.44, q (1.6)

7.12, m 5.15, m 1.88, d (1.6) 3H

7.12, m 5.50, m 1.94, d (1.6) 3H

4.55, dt (5.6, 2.8) 2.06, m; 1.97, m 2.17, m; 1.92, m 3.43, dd (8.4, 6.0) 2H

4.32, dt (8.4, 3.6) 1.74, m; 1.58, m 2.04, m; 1.88, m 3.58, m; 3.48, m

3.63, dd (7.6, 5.6), 2H 1.91, m, 2H 2.33, m, 2H 5.42, t (4.8)

4.10, dd (12.8, 5.6); 2.72, td (12.8, 3.2) 1.80, m; 1.24, m 1.81, m; 1.67, m 2.09, dt (13.6, 3.2); 1.27, m

1.96, d (1.6) 3H

1.93, d (1.6) 3H

2.00, s, 3H

2.10, s, 3H

6.99, br d (1.6) 5.16, t (8.0) 2.40, dd (7.6, 7.2) 2H 1.69, m, 2H 3.26, dd (6.8, 6.4) 2H

1.99, s, 3H 2.00, br s, 3H 2.96, s, 3H

The CHCl3 fraction, a free-base alkaloid-rich fraction, was further purified to yield nine new compounds, including two norpandamarilactonines, N-acetylnorpandamarilactonines A (1) and B (2), two indolizinones, pandalizines A (3) and B (4), a pandanamine, pandanmenyamine (5), three pandamarilactones, pandamarilactones 2 (6) and 3 (7), and 5(E)pandamarilactonine-32 (8), together with an unusual pandamarilactonine, pandalactonine (9). The structural elucidation and absolute configuration of these compounds are discussed. Moreover, a plausible biosynthetic pathway toward the Pandanus alkaloids, 1−5, 7, and 9, is presented.

Figure 1. COSY (bold bonds) and HMBC (1H → 13C) correlations of compounds 1−9.

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the key HMBC correlations from δH 7.12 (H-4) and 1.88 (H6) to a carbonyl carbon (δC 174.3, C-2) and a quaternary carbon (δC 128.9, C-3) suggested the presence of an α-methylα,β-unsaturated-γ-lactone moiety (Figure 1). Moreover, an HMBC correlation from δH 3.43 (H2-11) to δC 56.9 (C-8) indicated the presence of a pyrrolidine ring (Figure 1). A COSY cross peak between H-5 and H-8, together with a key HMBC correlation from δH 2.06/1.97 (H2-9) to δC 83.2 (C-5), indicated the connectivity of two functional moieties to form a pyrrolidinyl-α,β-unsaturated-γ-lactone system. The structure was also confirmed by comparing the above data with the NMR data of a related compound, norpandamarilaconine-B.8d Furthermore, an acetyl group (δC 170.4, C-12; δH 2.00, δC 22.7, CH3-13) was found to be connected to the nitrogen atom as indicated by the IR (1643 cm−1) and 13C NMR data of 1, which was further confirmed by comparing the experimental data with those of N-acetylpyrrolidine. 14 The 2D structure was established as 5-(1-acetylpyrrolidine-2-yl)-3-methylfuran-2one. To determine the absolute configuration of compound 1, calculated electronic circular dichroism (ECD) spectra were used to predict the Cotton effect (CE) of the possible structures. The ECD spectra (Figure 2A) were calculated at the B3LYP/6-311++G(2d,2p)//BY3YP/6-31++G(dd) level by the GAUSSIAN 09 program. When comparing the experimental data with the calculated ECD data, 1 exhibited a positive CE at λmax 228 nm and negative CEs at 208 and 255 nm (Figure 2B). Therefore, the absolute configuration of 1 was defined as

RESULTS AND DISCUSSION

Compound 1 was isolated as a yellowish oil. Its molecular formula was calculated as C11H15NO3 by the analysis of its 13C NMR and HRESIMS data (found m/z 232.0948 [M + Na]+, calcd for 232.0950), which suggested five indices of hydrogen deficiency. The IR spectrum indicated the presence of lactone carbonyl (1757 cm−1) and amide carbonyl (1643 cm−1) functionalities. The 1H NMR data are presented in Table 1. In the 13C and DEPT NMR spectra, two methyl, three methylene, three methine, one quaternary olefinic, and two carbonyl carbons were observed (Table 3). A series of COSY correlations were detected beginning from a methyl group (δH 1.88, H3-6), through an allylic coupling to an olefinic methine (δH 7.12, H-4) and an oxygenated methine (δH 5.15, H-5), and then connected to the proton sequence of a nitrogen-bearing methine (δH 4.55, H-8)/two methylenes (δH 2.06 and 1.97, H29; δH 2.17 and 1.92, H2-10)/a nitrogen-bearing methylene (δH 3.43, H2-11) (Figure 1). These COSY correlations along with B

DOI: 10.1021/acs.jnatprod.5b00252 J. Nat. Prod. XXXX, XXX, XXX−XXX

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Figure 2. Calculated and experimental ECD spectra of 1 and 2.

Figure 3. Calculated and experimental ECD spectra of 4.

(5R,8R), and the compound was named, N-acetylnorpandamarilactonine-A. The molecular formula of compound 2 was calculated as C11H15NO3 by the analysis of its 13C NMR and HRESIMS data (found m/z 232.0949 [M + Na]+, calcd for 232.0950), suggesting five indices of hydrogen deficiency. The IR spectrum indicated the presence of lactone carbonyl (1756 cm−1) and amide carbonyl (1631 cm−1) functionalities. Comparing the 1D (Tables 1 and 3) and 2D (Figure 1) NMR data of 2 with those of 1, indicated a similar 2D structure, 5-(1-acetylpyrrolidine-2yl)-3-methylfuran-2-one. In order to determine the absolute configuration of 2, the experimental ECD spectrum was compared with the calculated ECD data (Figure 2A). Compound 2 exhibited significant positive CEs at 236 and 276 nm and a negative CE at 209 nm (Figure 2C), suggesting that 2 and 1 are epimers. Therefore, the configuration of 2 was defined as (5R,8S) and named as N-acetylnorpandamarilactonine-B. Compound 3 was isolated as a yellowish oil. Its molecular formula was calculated as C9H11NO by the analysis of its 13C NMR and HRESIMS data (found m/z 172.0939 [M + Na]+, calcd for 172.0738), suggesting five indices of hydrogen deficiency. The IR spectrum indicated the presence of a lactam carbonyl group (1708 cm−1). In the NMR spectra, one methyl, three methylene, two olefinic methine, one nitrogen-bearing olefinic tertiary carbon, one carbonyl, and one olefinic quaternary carbon were observed (Tables 1 and 3). The key HMBC correlations from an olefinic methine (δH 6.57, H-1) to a carbonyl carbon (δC 169.5, C-3)/a nitrogen-bearing olefinic tertiary carbon (δC 137.9, C-8a) and a methyl (δH 1.96, H3-10) to a carbonyl carbon (δC 169.5, C-3)/a quaternary carbon (δC 133.9, C-2), along with a long-range COSY correlation (an allylic coupling) from δH 1.96 to δH 6.57, suggested the presence of an α-methyl-α,β-unsaturated-γ-lactam moiety (Figure 1). Additional COSY cross peaks between an olefinic methine (δH 5.42, H-8), two methylenes (δH 2.33, H2-7; δH 1.91, H2-6), and a nitrogen-bearing methylene (δH 3.63, H2-5)

were also observed. A tetrahydropyridine system was suggested on the basis of the key HMBC correlations from δH 3.63 and 2.33 to δC 137.9 (C-8a) and the indices of hydrogen deficiency (Figure 1). These data suggested that the α-methyl-α,βunsaturated-γ-lactam moiety is fused to the tetrahydropyridine ring in 3. Thus, the structure of compound 3 was established as 2-methyl-6,7-dihydroindolizin-3(5H)-one and named as pandalizine-A. Compound 4 was isolated as a yellowish oil. Its molecular formula was calculated as C10H15NO2 by the analysis of the 13C NMR and HRESIMS data (found m/z 204.2211 [M + Na]+, calcd for 204.2214), suggesting four indices of hydrogen deficiency. The IR spectrum indicated the presence of a lactam carbonyl functionality (1701 cm−1). The NMR data of 4 were similar to those of 3. However, one fewer index of hydrogen deficiency and a methoxy group (δH 2.96, δC 49.8) were observed in 4 compared with 3. Moreover, changes in the chemical shift values of C-1 (deshielded to δC 140.7), C-8 (shielded to δC 34.8), and C-8a (shielded to δC 89.1) were detected in the 13C NMR data of 4. On the basis of the above data, the structure of 4 was suggested as an indolizinone derivative with a methoxy substituent. The indolizinone system was further confirmed by the analyses of COSY and HMBC correlations (Figure 1). An HMBC correlation from δH 2.96 (−OCH3) to C-8a (δC 89.1) indicated that the methoxy group is connected to C-8a. The 2D structure of 4 was established as 8a-methoxy-2-methyl-6,7,8,9-tetrahydroindolizin-3(5H)-one. To determine the absolute configuration of 4, its ECD spectrum was compared with the calculated ECD spectrum (Figure 3). The ECD spectrum of compound 4 exhibited significant positive CEs at λmax 246 and 350 nm, and a negative CE at 300 nm. Comparison of the experimental ECD spectrum of 4 was consistent with the calculated spectrum and permitted definition of the absolute configuration of 4 8aR. The compound was assigned the trivial name pandalizine-B. Compound 5 was isolated as a colorless oil. The molecular formula was calculated as C11H15NO3 by the analysis of the 13C C

DOI: 10.1021/acs.jnatprod.5b00252 J. Nat. Prod. XXXX, XXX, XXX−XXX

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NMR and HRESIMS data (found m/z 232.0951 [M + Na]+, calcd for 232.0950), suggesting five indices of hydrogen deficiency. The IR spectrum indicated the presence of lactone carbonyl (1764 cm−1) and amide carbonyl (1660 cm−1) functionalities. In the 13C and DEPT NMR spectra, two methyl, three methylene, two methine, one oxygenated olefinic tertiary carbon, two carbonyl, and one olefinic quaternary carbon were observed (Table 3). A long-range COSY cross peak between a methyl group (δH 2.00, H3-13) and an olefinic methine (δH 6.99, H-4), together with the key HMBC correlations from δH 6.99 and 2.00 to a carbonyl carbon δC 170.9 (C-2) and a quaternary carbon δC 129.4 (C-3), indicated the presence of an α-methyl-α,β-unsaturated-γ-lactone moiety. Additional COSY correlations were also observed from an olefinic methine (δH 5.16, H-6) and two methylenes (δH 2.40, H2-7; δH 1.69, H2-8), to a nitrogen-bearing methylene (δH 3.26, H2-9). Moreover, an HMBC correlation from δH 5.16 to δC 137.6 (C-4) suggested a γ-alkylidene-α,β-unsaturated-γ-lactone system in 5 (Figure 1). The structure was also confirmed by comparing the above data with those of pandamarilactam-3y.12i Furthermore, a methyl group (δH 1.99, H3-12) as well as a nitrogen-bearing methylene (δH 3.26, H2-9) showed HMBC correlations to a carbonyl carbon δC 170.2 (C-11), indicating the presence of an N-acetyl fragment on the γ-alkylidene-α,βunsaturated-γ-lactone moiety. The configuration of the Δ5,6 double bond was determined as Z by comparing the NMR data with those of pandamarilactam-3y,12i and a NOESY cross peak between δH 6.99 (H-4) and 5.16 (H-6) (Figure 4). Therefore, the structure of compound 5 was established as (6Z)-3-methyl5-butylidene-9-N-acetylfuran-2-one, and named as pandanmenyamine.

1.88 to a carbonyl carbon (δC 171.6, C-18) and a quaternary carbon (δC 131.1, C-17), and from δH 6.91 to a carbonyl carbon (δC 171.6, C-18) and a nitrogen-bearing oxygenated secondary carbon (δC 101.1, C-15). A series of COSY correlations from a nitrogen-bearing methylene (δH 2.80, H2-11) and two methylenes (δH 1.72, H2-12; δH 1.72, H2-13), to a methylene group (δH 1.72, H2-14) as well as an HMBC correlation from δH 2.48 (H-9) to δC 48.4 (C-11) suggested the presence of a piperidine ring which was linked to the γ-alkylidene-α,βunsaturated-γ-lactone system and α-methyl-α,β-unsaturated-γlactone ring (Figure 1). The structure was further confirmed by comparing the NMR data with those of a 5Z-pandamarilactone, pandamarilactone-1.8b However, the chemical shifts of the H-4 and H-6 signals of 6 were different from the corresponding signals in 6Z-pandamarilactone compounds.8b,c Therefore, the Δ5,6 configuration of 6 was considered as E. The NMR data were further compared with a reference compound, pandamarilaconine-C (5E-configuration), suggesting that 6 is the 5E isomer of pandamarilactone-1.8b,12b The E configuration was also suggested by the absence of an NOE correlation between H-4 and H-6. Thus, the structure of compound 6 was established and named as pandamarilactone-2. Compound 7 was isolated as a colorless oil. Its molecular formula was calculated as C18H24N2O3 by the analysis of the 13 C NMR and HRESIMS data (found m/z 317.1862 [M + H]+, calcd for 317.1865), suggesting eight indices of hydrogen deficiency. The IR spectrum suggested the presence of lactone carbonyl (1763 cm−1) and lactam carbonyl (1682 cm−1) functionalities. The 13C NMR data of 6 and 7 (Table 3) were similar, except for the signals of C-9, C-15, and C-16. These differences indicated a change in the C-15 stereogenic center. The spiro-structure comprising the α-methyl-α,β-unsaturated-γlactam and piperidine moieties in 7 was confirmed by analyzing the NMR data, and the structure was closely similar to pandamarine.8a Comparing the NMR data with those of 6, it was suggested that 7 possesses a γ-alkylidene-α,β-unsaturated-γlactone system. However, a significant NOESY correlation was observed between δH 6.99 (H-4) and δH 5.23 (H-6) suggesting a 5Z configuration (Figure 4). Therefore, the structure of compound 7 was established and named as pandamarilactone3. Compound 8 was isolated as a yellowish oil. The molecular formula was calculated as C18H21NO3 by the analysis of its 13C NMR and HRESIMS data (found m/z 322.1420 [M + Na]+, calcd for 322.1420), suggesting nine indices of hydrogen deficiency. The IR spectrum indicated the presence of lactone carbonyl (1764 cm−1) and olefinic (1551 cm−1) functionalities. Comparing the 1D (Tables 2 and 3) and 2D (Figure 1) NMR data of 8 with those of 6, suggested that 8 possesses a piperidinyl-γ-alkylidene-α,β-unsaturated-γ-lactone system. A long-range COSY correlation from a methylene (δH 3.14, H216) to protons of an exo- double bond (δH 5.91, 5.14, H2-19), as well as HMBC correlations from δH 3.14 to a quaternary carbon (δC 143.3, C-17) and a nitrogen-bearing tertiary carbon (168.5, C-15), and from δH 5.91 and 5.14 to a carbonyl carbon (δC 184.5, C-18) suggested the presence of a 5-methylene-2cyclopentenone ring (Figure 1). The 5-methylene-2-cyclopentenone ring was connected to the piperidine system as indicated by the key HMBC correlations from δH 3.30 (H-9) and δH 3.31 (H-11) to δC 168.5 (C-15), and δH 1.93 (H-12) and δH 2.27 (H-13) to δC 113.2 (C-14). The structure of 8 was further confirmed by comparing the spectroscopic data with those of a similar compound, pandamarilactone-32.8b However,

Figure 4. Selected NOESY (1H ←→ 1H) correlations of compounds 5, 7, and 9.

Compound 6 was isolated as a yellowish oil. The molecular formula was calculated as C18H23NO4 by the analysis of its 13C NMR and HRESIMS data (found m/z 318.1704 [M + H]+, calcd for 318.1705), suggesting eight indices of hydrogen deficiency. The IR spectrum suggested the presence of a lactone carbonyl functionality (1760 cm−1). The 1H NMR data are shown in Table 2. In the 13C and DEPT NMR spectra, two methyl, seven methylene, one nitrogen-bearing oxygenated secondary carbon, three methine, one oxygenated olefinic tertiary carbon, two carbonyl, and two olefinic quaternary carbons were observed (Table 3). A γ-alkylidene-α,β-unsaturated-γ-lactone system was suggested as a partial structure of 6 by comparing the 13C (Table 3) and 2D (Figure 1) NMR data with those of 5. An additional α-methyl-α,β-unsaturated-γlactone ring was also confirmed by an allylic coupling between a methyl group (δH 1.88, H3-20) with an olefinic methine (δH 6.91, H-16), as well as the key HMBC correlations from δH D

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Table 2. 1H NMR Data for Compounds 6−9 (δH in ppm, J in Hz) 6a

a

7b

8d

9d

position

δH mult (J)

δH mult (J)

δH mult (J)

δH mult (J)

4 5 6 7 8 9 11 12 13 14 16 19 20 21

7.25, br d (1.6)

6.99, br d (1.6)

7.21, br d (1.6)

7.00, br d (1.6)

5.27, t (7.6) 2.32, dd (7.6, 1.6) 2H 1.57, m, 2H 2.48, t (4.8), 2H 2.80, t (4.0), 2H 1.72, m, 2Hc 1.72, m, 2Hc 1.72, m, 2Hc 6.91, q (1.6)

5.23, t (7.6) 2.40, dt (7.6, 7.2) 2H 1.88, mc; 1.75, m 3.28, m; 3.38, m 3.04, m; 2.94, m 1.88, mc; 1.59, mc 1.69, m; 1.58, mc 1.41, m; 1.88, mc 7.19, q (1.6)

5.56, t (7.6) 2.37, br t (4.4), 2H 1.87, m, 2H 3.30, t (6.4), 2H 3.31, t (5.2), 2H 1.93, m, 2H 2.27, br t (5.2), 2H

5.20, t (7.8) 2.54, m; 2.49, m 1.87, m; 1.62, m 3.07, dd (8.6, 5.1) 3.61, dd (15.0, 7.8); 3.03, m 2.58, m; 1.51, m 2.16, m; 1.82, m 2.50, m 6.82, q (1.8)

1.88, br s, 3H 1.95, br s, 3H

1.88, d (1.6) 3H 1.99, br s, 3H

3.14, m, 2H 5.14, br s; 5.91, br s 2.00, br s, 3H

1.92, d (1.6) 3H 2.01, d (1.6) 3H

400 MHz in methanol-d4; b400 MHz in CDCl3; csignals overlapping; d600 MHz in CDCl3.

Table 3. 13C NMR Data for Compounds 1−9 (δC in ppm) position 1 2 3 4 5 6 7 8 8a 9 10 11 12 13 14 15 16 17 18 19 20 21 -OCH3 a

1a

2a

3a

4a

5a

6b

7a

8c

9c

δC, type

δC, type

δC, type

δC, type

δC, type

δC, type

δC, type

δC, type

δC, type

174.3, C 128.9, C 147.5, CH 83.2, CH 10.5, CH3

174.4, C 130.8, C 146.9, CH 80.0, CH 10.7, CH3

127.8, CH 133.9, C 169.5, C

140.7, CH 137.1, C 169.5, C

56.9, CH

57.8, CH

38.0, CH2 21.7, CH2 22.8, CH2 110.1, CH 137.9, C

36.8, CH2 24.9, CH2 19.3, CH2 34.8, CH2 89.1, C

170.9, C 129.4, C 137.6, CH 148.8, C 112.8, CH 23.3, CH2 28.7, CH2

171.2, C 129.9, C 139.6, CH 148.9, C 115.4, CH 24.7, CH2 28.0, CH2

171.5, C 129.6, C 137.9, CH 148.7, C 113.9, CH 24.1, CH2 28.6, CH2

170.2, C 131.4, C 132.9, CH 148.9, C 111.0, CH 23.4, CH2 28.1, CH2

171.1, C 129.6, C 137.5, CH 149.5, C 112.5, CH 23.9, CH2 32.1, CH2

27.2, CH2 24.4, CH2 48.5, CH2 170.4, C 22.7, CH3

23.9, CH2 24.8, CH2 48.0, CH2 170.1, C 23.0, CH3

38.7, CH2

50.6, CH2

38.6, CH2

50.1, CH2

73.6, CH

10.9, CH3

10.9, CH3 170.2, C 23.2, CH3 10.5, CH3

48.4, CH2 21.7, CH2 26.0, CH2 37.3, CH2 101.1, C 151.4, CH 131.1, C 171.6, C

44.2, CH2 22.8, CH2 24.8, CH2 32.5, CH2 77.2, C 141.3, CH 134.2, C 170.3, C

56.5, CH2 18.2, CH2 28.1, CH2 47.5, CH 114.4, C 145.9, CH 131.1, C 170.8, C

10.7, CH3 10.3, CH3

11.1, CH3 10.6, CH3

47.6, CH2 21.2, CH2 18.0, CH2 113.2, C 168.5, C 30.9, CH2 143.3, C 184.5, C 108.1, CH2 10.9, CH3

10.2, CH3 10.6, CH3

49.8, CH3

100 MHz in CDCl3; b100 MHz in methanol-d4; c150 MHz in CDCl3.

presence of a lactone group (1765 cm−1). In the 13C and DEPT NMR spectra, two methyl, five methylene, one dioxygenated secondary carbon, five methine, one oxygenated olefinic tertiary carbon, two carbonyl, and two olefinic quaternary carbons were observed (Table 3). A γ-alkylidene-α,β-unsaturated-γ-lactone system was suggested by comparing the 13C (Table 3) and 2D NMR (Figure 1) data of 9 with those of 5. An allylic coupling of a methyl group (δH 1.92, H3-20) with an olefinic methine (δH 6.82, H-16), along with the key HMBC correlations from δH 1.92 to a carbonyl carbon (δC 170.8, C-18)/a quaternary carbon (δC 131.1, C-17) and δH 6.82 to a dioxygenated secondary carbon (δC 114.4, C-15), suggested the presence of an α-methyl-α,β-unsaturated-γ-lactone ring (C-15 − C-20) (Figure 1). COSY correlations from a nitrogen-bearing

the proton signals of H-4 and H-6 in 8 showed different chemical shifts compared with the corresponding signals in pandamarilactone-32 (5Z geomerical isomer).8b The NMR data were further compared with a reference compound, pandamarilaconine-C (5E-isomer), which together with the absence of NOE cross peak between H-4 and H-6, suggested that 8 is the 5E isomer of pandamarilactone-32.8b,12b Thus, the structure of compound 8 was defined and named as 5(E)-pandamarilactonine-32. Compound 9 was isolated as a yellowish oil. Its molecular formula was calculated as C18H21NO5 on the basis of the analysis of the 13C NMR and HRESIMS data (found m/z 332.1500 [M + H]+, calcd for 332.1496), suggesting nine indices of hydrogen deficiency. The IR spectrum indicated the E

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Figure 5. Proposed biosynthesis of Pandanus alkaloids, starting from glutamic acid and leucine.

The closely related structures of the isolated alkaloids suggested a common biosynthetic route. A plausible biogenetic pathway for 1−5, 7, and 9 is depicted in Figure 5. Previous findings suggested that the amino acids, glutamic acid and leucine, serve as biosynthetic precursors.8c,12d,13,16 Glutamic acid appears to be converted to γ-aminobutyric acid (GABA), N-acetyl-GABA, and N-carboxypropyl-GABA, all of which can undergo condensation with 4-hydroxy-4-methylglutamic acid, which is derived from leucine. The combination of GABA and 4-hydroxy-4-methylglutamic acid generates an amine X. Compound XIII is formed via decarboxylation of X, dehydration of XI, and cyclization of XII. Pandalizines A (3) and B (4) are formed from XIII via dehydration and Omethylation, respectively. Compound XIV, which is produced by the combination of the N-acetyl-GABA and 4-hydroxy-4methylglutamic acid, is cyclized and deaminated to form pandanmenyamine (5). Furthermore, N-acetylnorpandamarilactonines A (1) and B (2) are produced by the cyclization of 5. Amine XV is formed from the combination of the Ncarboxypropyl-GABA and 4-hydroxy-4-methylglutamic acid. The conversion of XV into XVI involves dehydration and condensation with a 4-hydroxy-4-methylglutamate moiety. Amine XVII, is formed from the decarboxylation of XVI, which is transformed to XVIII and XX through cyclization and hydrogenation, respectively. Pandalactonine (9) is formed through the reduction and cyclization of XVIII and XIX. The formation of pandamarilactone-3 (7) is accomplished by the reduction and cyclization of XX and XXI.

methylene (δH 3.61, 3.03, H2-11) and two methylenes (δH 2.58, 1.51, H2-12; δH 2.16, 1.82, H2-13) to a nitrogen-bearing methine (δH 2.50, H-14) were observed. Furthermore, the key HMBC correlations from H-13 (δH 2.16 and 1.82) to C-15 (δC 114.4) and H-14 to C-15 indicated that a pyrrolidinyl-α,βunsaturated-γ-lactone is the core moiety of 9. In general, the nitrogen-bearing C-9 methylene (δH ca. 2.8 and 2.4, δC ca. 55) and the C-15 oxygenated methine (δH ca. 4.8, δC ca. 83)8c are found in the NMR data of similar Pandanus alkaloids, such as pandamarilactonine-A, the structure of which comprised a γalkylidene-α,β-unsaturated-γ-lactone and a pyrrolidinyl-α,βunsaturated-γ-lactone moieties. However, the order of carbons and chemical shifts of C-9 (methylene → methine, δH 3.07, δC 73.6) and C-15 (methine → dioxygenated secondary carbon, δC 114.4) in 9 was different, suggesting that C-9 and C-15 are linked. Moreover, the molecular formulas of 9 and pandamarilactonine-A revealed the presence of one more oxygen atom in 9 compared with pandamarilactonine-A. Therefore, the presence of an ether-bridge between C-9 and C-15 was suggested. The linkage was further confirmed by a key HMBC correction from H-9 to C-15 (Figure 1). The NOESY spectrum showed a cross peak between H-4 and H-6 indicating a 5Z configuration of 9. Furthermore, NOE cross peaks were observed between H-14, H-16 and H-9. The configuration of 9 was suggested as 9R*,14R*,15S*. The absolute configuration is still undefined. Thus, the structure of compound 9 was established and named as pandalactonine. Compound 9 possesses an unusual fused triple ring structure with spirolactone and pyrrolo[1,2-c]oxazole functionalities; suggesting that 9 is a new type of Pandanus alkaloid. F

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EXPERIMENTAL SECTION General Experimental Procedures. Optical rotations were measured with a JASCO P-1020 digital polarimeter (JASCO Inc., Tokyo, Japan). The UV spectra were measured on a JASCO V-530 UV/vis spectrophotometer (JASCO Inc., Tokyo, Japan). The ECD spectra were measured with a JASCO J-180 spectrophotometer (JASCO Inc., Tokyo, Japan). The IR spectra were measured on a Mattson Genesis II TM FT-IR spectrophotometer (Mattson Instruments, Madison, WI). 1H and 13C NMR spectra were recorded on Varian VNMRS 600 MHz FT-NMR, Varian Unity-plus 400 MHz FT-NMR (Varian Inc., Palo Alto, CA), and JNM-ECS 400 NMR spectrometer (JEOL Ltd., Tokyo, Japan). Chemical shifts are reported in parts per million (δ), and coupling constants (J) are expressed in Hertz. LRESIMS were measured on a Waters micromass ZQ mass spectrometer (Waters Corporation, Milford, MA). HRESIMS were measured on a Bruker Daltonics APEX II 30e mass spectrometer (Bruker Instruments, Billerica, MA). Silica gel (Kieselgel 60, 70−230 and 230−400 mesh, Merck KGaA, Darmstadt, Germany) and Sephadex LH-20 gel (Pharmacia Fine Chemicals AB, Uppsala, Sweden) were used for column chromatography. TLC analyses were carried out using Si gel (Kieselgel 60, F254, Merck KGaA, Darmstadt, Germany) and RP-18 (F254s, Merck KGaA, Darmstadt, Germany) precoated plates and compounds were detected by spraying with 50% H2SO4 followed by heating on a hot plate. HPLC analyses were performed with a Shimadzu LC-10AT VP (Shimadzu Inc., Kyoto, Japan) pump interface equipped with a Shimadzu SPD-M10A VP diode array detector using Luna Phenyl-Hexyl column (5 μm, 250 × 10 mm, Phenomenex Inc.). ACS grade n-hexane, CH2Cl2, EtOAc, acetone, MeOH, ammonia, and 95% H2SO4 were purchased from ECHO Chemical Co., Ltd. (Miaoli, Taiwan). HPLC-grade MeCN, MeOH, and CDCl3 were obtained from Merck KGaA (Darmstadt, Germany). Water for chromatographic separation was purified by a Milli-Q water Advantage A 10 water system (Merck Millipore, Temecula, CA). Plant Material. The fresh aerial parts of Pandanus amaryllifolius were collected from Kaohsiung City, Taiwan, in July 2012, and were identified by a specialist in Chinese herbal medicine, Dr. Ming-Hong Yen. A voucher specimen (PA0001) was deposited at the Graduate Institute of Natural Products, Kaohsiung Medical University, Kaohsiung, Taiwan. Extraction and Isolation. The aerial parts of P. amaryllifolius (6.0 kg) were extracted with 95% EtOH (3 × 20 L) at room temperature for 24 h. The solvent was removed under reduced pressure to yield a dried EtOH extract (100.0 g). The crude extract was partitioned using acid−base extraction method into CHCl3 layer (alkaloid rich), EtOAc layer (nonalkaloid), and water layer (quaternary alkaloid rich). The CHCl3 layer (4.2 g) was subjected to silica gel (Si) column chromatography (CC) and eluted successively with CH2Cl2:MeOH (100:0 → 80:20, 0.05% NH3) to afford seven fractions (D1 ∼ D7). Fraction D2 (1.35 g) was further separated using Si CC with gradient solvent CH2Cl2:MeOH system (100:0 → 90:10, 0.05% NH3) to yield 10 subfractions (D2-1∼10). Fraction D2-5 (748.9 mg) was subjected to Si CC with gradient solvent n-hexane:EtOAc system (50:50 → 0:100) to obtain four subfractions (D2-5-1∼4). Fraction D2-5-1 (45.2 mg) was purified by HPLC using MeOH:H2O (60:40, 0.05% NH3, pH 8−9, rate 2.5 mL/min) with Luna Phenyl-Hexyl column (5 μm, 250 × 10 mm) to afford compounds 3 (5.2

mg), 4 (4.5 mg), and 6 (0.8 mg). Fraction D2-5-3 (60.2 mg) was purified by HPLC using MeOH:H2O (30:70, 0.05% NH3, pH 8−9, rate 2.0 mL/min) with Luna Phenyl-Hexyl column (5 μm, 250 × 10 mm) to yield compounds 1 (4.8 mg), 2 (6.5 mg), and 7 (2.2 mg). Fraction D2-6 (178.7 mg) was subjected to Si CC with gradient solvent CH2Cl2:MeOH system (98:2 → 85:15, 0.05% NH3) to yield seven subfractions (D2-6-1∼7). Fraction D2-6-1 (10.0 mg) was purified by HPLC using MeOH:H2O (25:75, 0.05% NH3, pH 8−9, rate 2.0 mL/min) with Luna Phenyl-Hexyl column (5 μm, 250 × 10 mm) to yield compound 9 (1.4 mg). Fraction D2-6-6 (36.6 mg) was purified by HPLC using MeOH:H2O (45:55, 0.05% NH3, pH 8−9, rate 2.0 mL/min) with Luna Phenyl-Hexyl column (5 μm, 250 × 10 mm) to obtain compound 5 (2.5 mg). Fraction D2-7 (70.6 mg) was subjected to Si CC with gradient solvent CH2Cl2:MeOH system (96:4 → 95:5, 0.05% NH3) to yield four subfractions (D2-7-1∼4). Fraction D2-7-3 (20.4 mg) was purified by HPLC using MeOH:H2O (43:57, 0.05% NH3, pH 8−9, rate 2.0 mL/ min) with Luna Phenyl-Hexyl column (5 μm, 250 × 10 mm) to afford compound 8 (0.8 mg). N-Acetylnorpandamarilactonine-A (1). Yellowish oil; [α]25 D − 14 (c 1, MeOH); UV (MeOH) λmax (log ε) 209 (3.92) nm; ECD (MeOH, c 0.001 M) λmax (Δε): 208 (−0.18), 228 (+0.54), 255 (−1.33) nm; IR νneat max 2959, 1757, 1643, 1416, 1355, 1090, 1044 cm−1; 1H NMR data see Table 1; 13C NMR data see Table 3; ESIMS m/z 210 [M + H]+ and 232 [M + Na]+; HRESIMS m/z 232.0948 [M + Na]+ (calcd for C11H15NO3Na, 232.0950). N-Acetylnorpandamarilactonine-B (2). Yellowish oil; [α]25 D − 7 (c 0.7, MeOH); UV (MeOH) λmax (log ε) 209 (4.14) nm; ECD (MeOH, c 0.001 M) λmax (Δε): 209 (−0.60), 236 (+1.90), 276 (+2.92) nm; IR νneat max 2969, 1756, 1631, 1419, 1357, 1077, 1046 cm−1; 1H NMR data see Table 1; 13C NMR data see Table 3; ESIMS m/z 210 [M + H]+ and 232 [M + Na]+; HRESIMS m/z 232.0948 [M + Na]+ (calcd for C11H15NO3Na, 232.0949). Pandalizine-A (3). Yellowish oil; UV (MeOH) λmax (log ε) 220 (3.16), 273 (3.45) nm; IR νneat max 2932, 1708, 1410, 1363, 1240, 1192, 1142, 1057, 1002, 961 cm−1; 1H NMR data see Table 1; 13C NMR data see Table 3; ESIMS m/z 150 [M + H]+ and 172 [M + Na]+; HRESIMS m/z 172.0739 (calcd for C9H11NONa, 172.0738). Pandalizine-B (4). Yellowish oil; [α]25 D + 11 (c 1, MeOH); UV (MeOH) λmax (log ε) 209 (3.84), 245 (3.23) nm; ECD (MeOH, c 0.001 M) λmax (Δε): 246 (+4.250), 300 (−1.89), 350 (+2.41) nm; IR νneat max 2942, 1701, 1445, 1410, 1284, 1139, 1057, 965 cm−1; 1H NMR data see Table 1; 13C NMR data see Table 3; ESIMS m/z 182 [M + H]+ and 204 [M + Na]+; HRESIMS m/z 204.2211 [M + Na]+ (calcd for C10H15NO2Na, 204.2214). Pandanmenyamine (5). Colorless oil; λmax (log ε) 206 (3.72), 274 (4.06) nm; IR νneat max 2928, 1764, 1660, 1551, 1442, 1370, 1056, 990 cm−1; 1H NMR data see Table 1; 13C NMR data see Table 3; ESIMS m/z 210 [M + H]+ and 232 [M + Na]+; HRESIMS m/z 232.0951 [M + Na]+ (calcd for C11H15NO3Na, 232.0950). Pandamarilactone-2 (6). Yellowish oil; [α]25 D − 8 (c 0.3, MeOH); UV (MeOH) λmax (log ε) 205 (3.69), 276 (3.64) nm; −1 1 IR νneat max 2939, 1760, 1445, 1308, 1158, 1056, 991 cm ; H 13 NMR data see Table 2; C NMR data see Table 3; ESIMS m/z 318 [M + H]+; HRESIMS m/z 318.1704 [M + H]+ (calcd for C18H23NO4H, 318.1705). G

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Pandamarilactone-3 (7). Colorless oil; [α]25 D − 2 (c 0.7, MeOH); UV (MeOH) λmax (log ε) 207 (3.70), 275 (3.69) nm; −1 IR νneat max 2935, 1763, 1682, 1446, 1412, 1375, 1053, 990 cm ; 1 H NMR data see Table 2; 13C NMR data see Table 3; ESIMS m/z 317 [M + H]+ and 339 [M + Na]+; HRESIMS m/z 317.1862 [M + H]+ (calcd for C18H24N2O3H, 317.1865). 5(E)-Pandamarilactonine-32 (8). Yellowish oil; [α]25 D ± 0 (c 1, MeOH); UV (MeOH) λmax (log ε) 223 (3.63), 279 (3.77), 325 (3.71) nm; IR νneat max 2930, 1764, 1551, 1443, 1353, 300, 1192, 1052, 989 cm−1; 1H NMR data see Table 2; 13C NMR data see Table 3; ESIMS m/z 300 [M + H]+; HRESIMS m/z 322.1420 [M + Na]+ (calcd for C18H21NO3Na, 322.1420). Pandalatonine (9). Yellowish oil; [α]25 D − 13 (c 0.6, MeOH); UV (MeOH) λmax (log ε) 206 (3.80), 274 (3.96) −1 1 nm; IR νneat max 2947, 1765, 1444, 1268, 1157, 1055, 990 cm ; H 13 NMR data see Table 2; C NMR data see Table 3; ESIMS m/z 332 [M + H]+; HRESIMS m/z 332.1500 [M + H]+ (calcd for C18H21NO5H, 332.1496). ECD Calculations. The configuration analyses of compounds 1, 2, and 4 were conducted via Monte Carlo simulation with the MMFF94 molecular mechanics force field using Molecular Operating Environment (MOE) software (Chemical Computing Group, Montreal, Canada).17 The conformers were optimized using DFT at the BY3YP/6-31++G(dd) level in the gas phase with GAUSSIAN 09. The BY3YP/6-31++G(dd) harmonic vibrational frequencies were computed to confirm their stability and to provide their relative thermal free energy, which were used to evaluate their equilibrium populations. The energies, rotational strengths, and oscillator strengths of the 20 weakest electronic excitations of the conformers were computed utilizing the TDDFT methodology at the B3LYP/ 6-311++G(2d,2p) level in the gas phase. The ECD spectra were simulated using GaussSum 2.2.5 with a bandwidth σ of 0.20 eV.18

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Taiwan (MOHW104-TDU-B-212-124-003), National Health Research Institutes of Taiwan (NHRI-EX104-10241BI), and the grant for Health and Welfare Surcharge of Tobacco Products and Kaohsiung Medical University “Aim for the Top Universities Grant”, KMU-TP103, and in part from the grant from Chinese Medicine Research Center, China Medical University, Taiwan (the Ministry of Education, the Aim for the Top University Plan). The authors would like to thank the Center for Research Resources and Development (CRRD), Kaohsiung Medical University for the technical support and services in LC-MS and NMR analyses.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jnatprod.5b00252. 1D and 2D NMR spectra of compounds 1−9(PDF)

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REFERENCES

(1) (a) Hamid, K.; Rani, M.; Kaniz, S.; Urmi, F.; Habib, R.; Rahman, M. M. Inter. J. Appl. Biol. Pharmaceut. Technol. 2010, 1, 1364−1368. (b) Hamid, K.; Urmi, K. F.; Saha, M. R.; Zulfiker, A. H. M.; Rahman, M. M. J. Pharm. Sci. & Res. 2011, 3, 1025−1028. (c) Peungvicha, P.; Temsiririrkkul, R.; Prasain, J. K.; Tezuka, Y.; Kadota, S.; Thirawarapan, S. S.; Watanabe, H. J. Ethnopharmacol. 1998, 62, 79−84. (2) Jong, T.-T.; Chau, S.-W. Phytochemistry 1998, 49, 2145−2148. (3) (a) Peungvicha, P.; Thirawarapan, S. S.; Watanabe, H. Jpn. J. Pharmacol. 1998, 78, 395−398. (b) Sasidharan, S.; Sumathi, V.; Jegathambigai, N. R.; Latha, L. Y. Nat. Prod. Res. 2011, 25, 1982−1987. (4) Peungvicha, P.; Thirawarapan, S. S.; Watanabe, H. Biol. Pharm. Bull. 1996, 19, 364−366. (5) Ooi, L. S.; Wong, E. Y.; Sun, S. S.; Ooi, V. E. Peptides 2006, 27, 626−632. (6) Tan, M. A.; Takayama, H.; Aimi, N.; Kitajima, M.; Franzblau, S. G.; Nonato, M. G. J. Nat. Med. 2008, 62, 232−235. (7) Chong, H. Z.; Yeap, S. K.; Rahmat, A.; Akim, A. M.; Alitheen, N. B.; Othman, F.; Gwendoline-Ee, C. L. BMC Complementary Altern. Med. 2012, 12, 134−141. (8) (a) Byrne, L. T.; Guevara, B. Q.; Patalinghug, W. C.; Recio, B. V.; Ualat, C. R.; White, A. H. Aust. J. Chem. 1992, 45, 1903−1908. (b) Nonato, M. G.; Garson, M. J.; Truscott, R. J. W.; Carver, J. A. Phytochemistry 1993, 34, 1159−1163. (c) Takayama, H.; Ichikawa, T.; Kuwajima, T.; Kitajima, M.; Seki, H.; Aimi, N.; Nonato, M. G. J. Am. Chem. Soc. 2000, 122, 8635−8639. (d) Takayama, H.; Ichikawa, T.; Kitajima, M.; Nonato, M. G.; Aimi, N. J. Nat. Prod. 2001, 64, 1224− 1225. (9) Zhang, X.; Guo, P.; Sun, G.; Chen, S.; Yang, M.; Fu, N.; Wu, H.; Xu, X. J. Med. Plants Res. 2012, 6, 2622−2626. (10) Miean, K. H.; Mohamed, S. J. Agric. Food Chem. 2001, 49, 3106−3112. (11) Inada, A.; Ikeda, Y.; Murata, H.; Inatomi, Y.; Nakanishi, T.; Bhattacharyya, K.; Kar, T.; Bocelli, G.; Cantoni, A. Phytochemistry 2005, 66, 2729−2733. (12) (a) Takayama, H.; Ichikawa, T.; Kitajima, M.; Aimi, N.; Lopez, D.; Nonato, M. G. Tetrahedron Lett. 2001, 42, 2995−2996. (b) Takayama, H.; Ichikawa, T.; Kitajima, M.; Nonato, M. G.; Aimi, N. Chem. Pharm. Bull. 2002, 50, 1303−1304. (c) Salim, A. A.; Garson, M. J.; Craik, D. J. J. Nat. Prod. 2004, 67, 54−57. (d) Greger, H.; Schinnerl, J.; Vajrodaya, S.; Brecker, L.; Hofer, O. J. Nat. Prod. 2009, 72, 1708−1711. (e) Tan, M. A.; Kitajima, M.; Kogure, N.; Nonato, M. G.; Takayama, H. J. Nat. Prod. 2010, 73, 1453−1455. (f) Tan, M. A.; Kitajima, M.; Kogure, N.; Nonato, M. G.; Takayama, H. Tetrahedron Lett. 2010, 51, 4143−4146. (g) Tan, M. A.; Kitajima, M.; Kogure, N.; Nonato, M. G.; Takayama, H. Tetrahedron 2010, 66, 3353−3359. (h) Lopez, D. C.; Nonato, M. G. Philipp. J. Sci. 2005, 134, 39−44. (i) Sjaifullah, A.; Garson, M. J. ACGC Chem. Res. Commun. 1996, 5, 24−27. (13) Nonato, M. G.; Takayama, H.; Garson, M. J. In The Alkaloids: Chemistry and Biology; Cordell, G. A., Ed.; Elsevier: Amsterdam, 2008; Vol. 66, pp 215−249. (14) Croft, A. K.; Foley, M. K. Org. Biomol. Chem. 2008, 6, 1594− 1600.

AUTHOR INFORMATION

Corresponding Authors

* (F.-R.C.) E-mail: [email protected]. Tel: +886-73121101-2162. Fax: +886-7-3114773. * (Y.-C.W.) E-mail: [email protected]. Author Contributions #

These authors contributed equally to this work (Y.-C.T. and M.-L.Y.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors would like to acknowledge the grants from the Ministry of Science and Technology of Taiwan (MOST 1012325-B-039-004; 102-2628-B-037-003-MY3; MOST 102-2911I-002-303; MOST 103-2911-I-002-303; MOST 104-2911-I002-302; MOST 104-2911-I-037-501). This work was also supported by the Excellence for Cancer Research Center Grant, the Ministry of Health and Welfare, Executive Yuan, Taipei, H

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(15) Murugesan, D.; Mital, A.; Kaiser, M.; Shackleford, D. M.; Morizzi, J.; Katneni, K.; Campbell, M.; Hudson, A.; Charman, S. A.; Yeates, C.; Gilbert, I. H. J. Med. Chem. 2013, 56, 2975−2990. (16) Peterson, P. J.; Fowden, L. Phytochemistry 1972, 11, 663−673. (17) Lai, W. C.; Wu, Y. C.; Dankó, B.; Cheng, Y. B.; Hsieh, T. J.; Hsieh, C. T.; Tsai, Y. C.; El-Shazly, M.; Martins, A.; Hohmann, J.; Hunyadi, A.; Chang, F. R. J. Nat. Prod. 2014, 77, 1624−1631. (18) (a) Mazzeo, G.; Santoro, E.; Andolfi, A.; Cimmino, A.; Troselj, P.; Petrovic, A. G.; Superchi, S.; Evidente, A.; Berova, N. J. Nat. Prod. 2013, 76, 588−599. (b) Zhao, D. L.; Shao, C. L.; Gan, L. S.; Wang, M.; Wang, C. Y. J. Nat. Prod. 2015, 78, 286−293.

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