Regiospecific Prenylation of Hydroxyxanthones by a Plant Flavonoid

Note pubs.acs.org/jnp

Regiospecific Prenylation of Hydroxyxanthones by a Plant Flavonoid Prenyltransferase Ruishan Wang,† Ridao Chen,†,‡ Jianhua Li,† Xiao Liu,† Kebo Xie,† Dawei Chen,† Ying Peng,*,† and Jungui Dai*,†,‡ †

State Key Laboratory of Bioactive Substance and Function of Natural Medicines and ‡Key Laboratory of Biosynthesis of Natural Products of National Health and Family Planning Commission, Institute of Materia Medica, Peking Union Medical College and Chinese Academy of Medical Sciences, Beijing 100050, People’s Republic of China S Supporting Information *

ABSTRACT: C-Prenylated xanthones are pharmacologically attractive specialized metabolites that are distributed in plants and microorganisms. The prenylation of xanthones often contributes to the structural diversity and biological activities of these compounds. However, efficient regiospecific prenylation of xanthones is still challenging. In this study, the regiospecific prenylation of a number of structurally different hydroxyxanthones (3−10) by MaIDT, a plant flavonoid prenyltransferase with substrate flexibility from Morus alba, is demonstrated. Among the enzymatic products, 2-dimethylallyl-1,3,7-trihydroxyxanthone (3a) effectively attenuated glutamateinduced injury in SK-N-SH neuroblastoma cells. These results suggest a potential approach for the synthesis of bioactive prenylated xanthones by a substrate-relaxed flavonoid prenyltransferase.

X

cell cultures.12 Two putative XPTs, XptA and XptB, have been identified through gene deletion experiments in Aspergillus nidulans.13 Additionally, XptB has been demonstrated to only catalyze regiospecific O-prenylation of hydroxyxanthones in vitro.14 In recent years, substantial progress has been achieved in molecular biological and biochemical investigations on aromatic prenyltransferases (PTs) from bacteria, fungi, and plants.15−18 Interestingly, a number of PTs exhibit obvious substrate (aromatic acceptors and/or prenyl donors) tolerance, which renders them powerful biocatalysts for the chemoenzymatic prenylation of aromatic compounds.19−22 However, there are rare aromatic PTs with substrate promiscuity toward various xanthones and catalyzing prenylation. In the present work, the efficient regiospecific prenylation of structurally different xanthones by the promiscuous flavonoid PT MaIDT from the medicinal plant Morus alba is described.23 Our previous work identified two flavonoid prenyltransferases (FPTs), MaIDT and CtIDT, from two moraceous plants, M. alba and Cudrania tricuspidata, respectively.23 They were able to regioselectively introduce a dimethylallyl diphosphate into the ortho-position to the phenolic groups in the common 2,4-dihydroxyacetophenone substructure shared by three types of flavonoids, i.e., chalcones, isoflavones, and flavones. Natural hydroxyxanthones and benzophenones usually bear this substructure, emphasizing that MaIDT and CtIDT might catalyze regiospecific prenylation of hydroxyxanthones.

anthones are naturally occurring compounds produced by plants, lichens, fungi, and bacteria.1−4 Their common 9Hxanthen-9-one scaffold has been described as a “privileged structure” due to its potential to bind to a variety of targets; many xanthones have been proven to possess diverse biological and pharmacological activities.5,6 A host of xanthones with medicinal value are functionalized with C-prenyl groups, most commonly five-carbon dimethylallyl moieties.1−6 Decoration of xanthones by prenyl moieties often enhances the biological activities of these compounds.5,6 For example, α-mangostin, a prenylated xanthone from the mangosteen fruit, possesses multiple biological activities such as anticancer, antimycobacterial, antioxidant, and anti-inflammatory.7−10 Owing to limited resources in nature and the difficulty of regiospecificity in organic synthesis approaches, an efficient approach for the synthesis of structurally diverse prenylated xanthones for drug discovery is of specific interest and importance. Biosynthetically, xanthones result from a mixed origin including both the polyketide (A-ring) and shikimate pathways (C-ring) [Figure S1, Supporting Information (SI)].11 After the formation of the C13 framework, which is catalyzed by benzophenone synthase, the freely rotating intermediate 2,3′,4,6-tetrahydroxybenzophenone (1) undergoes a regioselective cyclization to give rise to 1,3,7-trihydroxyxanthone (3) and/or 1,3,5-trihydroxyxanthone (4), which are the precursors of most prenylated xanthones. The introduction of prenyl moieties into hydroxyxanthones may occur at the benzophenone and/or xanthone stages (Figure S1, SI). However, to date, only one xanthone prenyltransferase (XPT), HcPT, which catalyzes the regiospecific 8-prenylation of 1,3,6,7-tetrahydroxyxanthone, has been characterized from Hypericum calycinum © XXXX American Chemical Society and American Society of Pharmacognosy

Received: May 10, 2016

A

DOI: 10.1021/acs.jnatprod.6b00417 J. Nat. Prod. XXXX, XXX, XXX−XXX

Journal of Natural Products

Note

To initiate the studies, the acceptance of the defined precursor of prenylated xanthones, 2,3′,4,6-tetrahydroxybenzophenone (1) and 2,4,6-trihydroxybenzophenone (2), as well as 1,3,7-trihydroxyxanthone (3) and 1,3,5-trihydroxyxanthone (4), respectively, by MaIDT and CtIDT was tested. LC-MS analysis of the incubation mixtures revealed that both MaIDT and CtIDT accepted only 3 and 4 as substrates, and MaIDT showed significantly higher activities toward these compounds than CtIDT (Figures S2 and S3, SI). Consequently, MaIDT was chosen for further exploration of its prenylation activities toward a number of structurally different xanthones. After incubation with 100 μg of recombinant yeast microsomes containing MaIDT in a 100 μL assay at 30 °C for 16 h, 3 and 4 were converted to 3a and 4a with 55% and 43% yield, respectively. Under these conditions, 90% of isoliquiritigenin, a natural substrate of MaIDT, was converted to 3′-dimethylallylisoliquiritigenin.23 Examining 3, for example, by HPLC-UV/ESIMS analysis revealed that a product at tR 23.4 min with a 68 amu shift in its molecular ion peak was detected in the incubation mixture with the yeast cell microsomes transformed with MaIDT. In contrast, no PT activity was observed when microsomes isolated from yeast cells transformed with an empty vector or boiled recombinant protein were used. These observations indicated the monoprenylation of 3 (Figure 1). Product formation was strictly dependent on the presence of MaIDT, DMAPP, Mg2+, and 3. A linear dependence on the amount of microsomal protein for product formation was found up to 200 μg per 100 μL assay and on a reaction time up to 30 min at 30 °C. To determine the prenylation properties, the prenylated product (3a) was subsequently prepared from a scaled-up enzymatic reaction and subjected to NMR spectroscopic analysis (Figures S4 and S5, SI). In the 1H NMR spectrum, the presence of the prenyl moiety was suggested by the signals for two methyls (δH 1.65 and 1.79, s, 3H each), a methylene (δH 3.37, d, J = 7.2 Hz, 2H), and a methine (δH 5.29, t, J = 7.2 Hz, 1H). The location of the prenyl moiety at C-2 was inferred by the fact that the H-2 signal (δH 6.20) in 3 had disappeared and that the resonance of the active 1-OH proton shifted to lower field (from δH 12.70 to δH 13.27), which indicated the introduction of a prenyl substituent at the ortho-position.24 This deduction is supported by a deshielded chemical shift of C-2 from δC 97.8 in 3 to δC 111.3 in 3a (Figure S5, SI). The NMR data for 3a were in good agreement with those for 2dimethylallyl-1,3,7-trihydroxyxanthone.25 Therefore, it was proven that MaIDT promoted the specific 2-prenylation of 1,3,7-trihydroxyxanthone (3). Likewise, 4a was isolated from the preparative-scale incubation and determined to be 2dimethylallyl-1,3,5-trihydroxyxanthone by MS and NMR spectroscopic data analyses (Figures S6 and S7, SI). Notably, 3 and 4 turned out to be specifically prenylated at C-2, although their C-ring substitution patterns were different. Encouraged by the aforementioned results, the activities of MaIDT utilizing nine potential substrates including various types of hydroxyxanthones with different substituents (Figure 2) were tested. As shown in Figure 2A, all of the hydroxyxanthones with 1,3-dihydroxy substitution were accepted by MaIDT, specifically 1,3-dihydroxyxanthone (5, 51.1% yield), 1,3,6-trihydroxyxanthone (6, 19.1% yield), 1,3,8trihydroxyxanthone (7, 28.5% yield), 1,3,5,6-tetrahydroxyxanthone (8, 19.3% yield), 1,3,6,8-tetrahydroxyxanthone (9, 30.1% total yield), and 1,3,6,7-tetrahydroxyxanthone (10, 3.9% yield). In contrast, the absence of these phenolic groups inhibited

Figure 1. HPLC-DAD/ESIMS analysis of the enzymatic reaction mixture from microsomal fractions containing 3, DMAPP, and Mg2+. (A) Reaction catalyzed by recombinant MaIDT. (B) Enzymatic reaction gives 55% yield with recombinant MaIDT. (C) Enzymatic reaction with no yield using microsomes from yeast containing the empty vector. (D) Selected ion chromatogram for a prenylated product in positive mode. (E) MS spectra for 3a.

enzymatic product formation (11, 12, and 13). The data showed that the presence of C-1 and C-3 phenolic groups was crucial for the prenylation of hydroxyxanthones by MaIDT. The enzymatic products (5a, 6a, 7a, 9a, and 9b) were then prepared from large-scale reactions and subjected to MS and NMR data analyses (Figures S8−S13, SI). However, the prenylation of 1,3,5,6-tetrahydroxyxanthone (8) and 1,3,6,7tetrahydroxyxanthone (10) were confirmed using only HPLCUV/ESIMS analysis (Figures S14 and S15, SI) due to the low yields. The results clearly showed that one dimethylallyl moiety was regiospecifically introduced at C-2 of the A-ring, although the positions of the substituents on the C-ring were different. Interestingly, 1,3,6,8-tetrahydroxyxanthone (9) was diprenylated at C-2 and C-7 due to its symmetric structure, whereas 1,3,6-trihydroxyxanthone (6) and 1,3,8-trihydroxyxanthone (7) could be monoprenylated only as a result of the absence of an 8/6-OH group. This observation confirmed the importance of B

DOI: 10.1021/acs.jnatprod.6b00417 J. Nat. Prod. XXXX, XXX, XXX−XXX

Journal of Natural Products

Note

All of the enzymatic products and their corresponding substrates were evaluated for their neuroprotective effects on Lglutamic acid-induced cellular damage in SK-N-SH human neuroblastoma cells using the MTT method; resveratrol was used as a positive control. The results (Table S1, SI) indicate that the neuroprotective effects of 3a, 9a, and 9b are significantly higher than those of their corresponding substrates 3 and 9 (p < 0.05) at a concentration of 10 μM. In particular, when the cells were preincubated with 10 μM 2-dimethylallyl1,3,7-trihydroxyxanthone (3a), the cell survival rate was 82.87%, which was comparable with that for the positive control resveratrol (79.94%). In summary, the regiospecific 2-prenylation of a variety of structurally diverse hydroxyxanthones catalyzed by a plant FPT, MaIDT, was demonstrated. Seven prenylated products were efficiently obtained by incubation with MaIDT. One of the enzymatic products, 2-dimethylallyl-1,3,7-trihydroxyxanthone (3a), exhibited a strong neuroprotective effect. Thus, MaIDT should be explored as an efficient biocatalyst in combinatorial biosyntheses to create structurally various prenylated hydroxyxanthones for drug discovery due to its high efficiency and catalytic promiscuity.

■

EXPERIMENTAL SECTION

General Experimental Procedures. 1H and 13C NMR spectra were recorded on Varian NMR System 600 spectrometers (Varian Inc., Palo Alto, CA, USA). The HPLC-UV/ESIMS analyses and isolation of the enzymatic products were performed as previously described.23 Chemicals. The prenyl donor dimethylallyl diphosphate (DMAPP) was chemically synthesized as described previously.28 Benzophenones 1 and 2 were synthesized according to the literature.29,30 Hydroxyxanthones 3−9 and 12 were prepared according to the literature.31,32 Other tested substrates were purchased from J&K Chemical Ltd. (Beijing, People’s Republic of China) and BioBio-Pha (Kunming, Yunnan, People’s Republic of China). Prenyltransferase Activity. The expression of MaIDT and the preparation of the microsomal fraction from recombinant yeast YPH499 were described previously.23 A basic reaction mixture (100 μL) containing 100 mM Tris-HCl (pH 9.0), 10 mM MgCl2, 200 μM prenyl acceptor, 400 μM DMAPP, and 100 μg of recombinant yeast microsome protein was used to quantitatively determine the PT activity. The reaction mixtures were incubated at 30 °C for 16 h, and the reactions were terminated by the addition of 200 μL of MeOH. The protein was removed by centrifugation at 14000g for 20 min. The enzymatic products were analyzed by HPLC-UV/ESIMS under previously described conditions.23 Three parallel assays were routinely carried out to quantitatively measure the enzyme activity. The assays for determining the prenyl acceptors’ kinetic parameters (100 μL) contained 400 μM DMAPP, 40 μg of recombinant yeast microsome protein, and prenyl acceptors at final concentrations of 5, 10, 20, 40, 80, 160, and 400 μM. The reactions were incubated for 20 min. The resulting initial velocities were then fitted to the Lineweaver−Burk equation using OriginPro 8 (Originlab, Co., USA) to extract the Km parameters. Preparation and Identification of the Reaction Products. To prepare the enzymatic products for structural elucidation, reaction mixtures containing 100 mM Tris-HCl (pH 9.0), 10 mM MgCl2, 1 mM DMAPP, 500 μM prenyl acceptors, and 30 mg of recombinant yeast microsome protein in a total volume of 10−15 mL were incubated at 30 °C for 16 h. The reaction mixtures were subsequently extracted with EtOAc (5 × 20 mL). After evaporating the solvent, the residues were dissolved in MeOH and purified by RP semipreparative HPLC under the previously described conditions.23 The isolated products were subjected to MS and 1H and 13C NMR spectroscopic analyses.

Figure 2. Recombinant MaIDT substrate specificity. (A) Relative enzymatic activities with isoliquiritigenin and various xanthones and benzophenones acting as the prenyl acceptors and DMAPP acting as the prenyl donor. (B) The reactions catalyzed by recombinant MaIDT and the chemical structures of the substrates used for the assay.

C-1 and C-3 (or C-6 and C-8) phenolic groups for hydroxyxanthone prenylation by MaIDT. The C-prenylation catalyzed by MaIDT is essentially a Friedel−Crafts electrophilic aromatic alkylation, via the reactive carbocation generated from DMAPP at the ortho-position of electron-donating hydroxy groups, leading to regiospecific C− C bond formation.15,19−23 For example, the low electron density at C-2 of 1-hydroxyxanthone (12) in comparison with 1,3-tetrahydroxyxanthone (5) might prevent prenylation. It may also be concluded from Figure 2A that MaIDT has an apparently higher conversion rate for its natural substrate isoliquiritigenin (14) than the tested hydroxyxanthones, which is supported by the MaIDT kinetic study. The apparent MaIDT Km value for 14 was calculated as 25.9 μM, which is lower than those determined for the tested hydroxyxanthones (42.8, 70.2, 51.4, 143.6, and 104.6 μM for 3, 4, 5, 6, and 7, respectively). Therefore, the MaIDT substrate relaxation led to its robust prenylation capacity toward various hydroxyxanthones. The unique regiospecificity of MaIDT has not been demonstrated previously for other identified PTs. Furthermore, because neofunctionalization can be achieved through the exploitation of ancestral enzyme promiscuity in specific metabolism,26,27 the acceptance of hydroxyxanthones by MaIDT reveals characteristics of its promiscuous ancestor. Additionally, not only moraceous FPTs may have evolved from this promiscuous progenitor but also other unidentified moraceous XPTs. The putative homology shared by moraceous FPTs with undiscovered XPTs might be valuable for the identification of XPTs in plants. C

DOI: 10.1021/acs.jnatprod.6b00417 J. Nat. Prod. XXXX, XXX, XXX−XXX

Journal of Natural Products

Note

2-Dimethylallyl-1,3,7-trihydroxyxanthone (3a): 1H NMR (600 MHz, acetone-d6) δ 13.27 (1H, s, 1-OH), 7.58 (1H, d, J = 3.0 Hz, H8), 7.42 (1H, d, J = 9.0 Hz, H-5), 7.34 (1H, dd, J = 9.0, 3.0 Hz, H-6), 6.50 (1H, s, H-4), 5.29 (1H, t, J = 7.2 Hz, H-2′), 3.37 (2H, d, J = 7.2 Hz, H-1′), 1.79 (3H, s, H-4′), 1.65 (3H, s, H-5′); 13C NMR (150 MHz, acetone-d6) δ 181.3 (C-9), 164.0 (C-3), 161.5 (C-1), 155.7 (C4a), 154.8 (C-7), 150.8 (C-10a), 131.7 (C-3′), 125.0 (C-2′), 123.3 (C6), 122.0 (C-8a), 119.8 (C-5), 111.3 (C-2), 109.4 (C-8), 103.5 (C-9a), 94.0 (C-4), 26.0 (C-5′), 22.0 (C-1′), 18.0 (C-4′); ESIMS, m/z 312.9 [M + H]+.25 2-Dimethylallyl-1,3,5-trihydroxyxanthone (4a): 1H NMR (600 MHz, acetone-d6) δ 13.26 (1H, s, 1-OH), 7.68 (1H, d, J = 7.8 Hz, H8), 7.33 (1H, d, J = 7.8 Hz, H-6), 7.27 (1H, dd, J = 7.8, 7.8 Hz, H-7), 6.57 (1H, s, H-4), 5.29 (1H, t, J = 7.2 Hz, H-2′), 3.37 (2H, d, J = 7.2 Hz, H-1′), 1.79 (3H, s, H-4′), 1.65 (3H, s, H-5′); 13C NMR (150 MHz, acetone-d6) δ 181.6 (C-9), 164.2 (C-3), 161.6 (C-1), 156.4 (C4a), 146.9 (C-5), 146.0 (C-10a), 131.7 (C-3′), 124.7 (C-2′), 123.2 (C7), 122.3 (C-8a), 121.7 (C-6), 116.4 (C-2), 111.6 (C-8), 103.6 (C-9a), 94.3 (C-4), 25.9 (C-5′), 22.0 (C-1′), 17.9 (C-4′); ESIMS m/z 312.9 [M + H]+.25 2-Dimethylallyl-1,3-dihydroxyxanthone (5a): 1H NMR (600 MHz, acetone-d6) δ 13.21 (1H, s, 1-OH), 8.22 (1H, d, J = 8.4 Hz, H-8), 7.83 (1H, t, J = 8.4 Hz, H-6), 7.52 (1H, d, J = 8.4 Hz, H-5), 7.46 (1H, t, J = 7.8, H-7), 6.55 (1H, s, H-4), 5.29 (1H, t, J = 7.2 Hz, H-2′), 3.37 (2H, d, J = 7.2 Hz, H-1′), 1.79 (3H, s, H-4′), 1.65 (3H, s, H-5′); 13 C NMR (150 MHz, acetone-d6) δ 181.4 (C-9), 164.4 (C-3), 161.6 (C-1), 156.9 (C-4a), 156.8 (C-10a), 136.1 (C-6), 131.8 (C-3′), 126.4 (C-8), 125.0 (C-7), 121.4 (C-2′), 118.5 (C-8a), 113.4 (C-5), 111.6 (C-2), 103.8 (C-9a), 94.4 (C-4), 26.0 (C-5′), 22.0 (C-1′), 18.0 (C-4′); ESIMS m/z 312.9 [M + H]+.33 2-Dimethylallyl-1,3,6-trihydroxyxanthone (6a): 1H NMR (600 MHz, acetone-d6) δ 13.40 (1H, s, 1-OH), 8.07 (1H, d, J = 9.0 Hz, H8), 6.96 (1H, dd, J = 9.0, 2.4 Hz, H-7), 6.86 (1H, d, J = 2.4 Hz, H-5), 6.48 (1H, s, H-4), 5.28 (1H, t, J = 7.2 Hz, H-2′), 3.36 (2H, d, J = 7.2 Hz, H-1′), 1.78 (3H, s, H-4′), 1.65 (3H, s, H-5′); ESIMS m/z 312.9 [M + H]+.34 2-Dimethylallyl-1,3,8-trihydroxyxanthone (7a): 1H NMR (600 MHz, acetone-d6) δ 12.18 (1H, s, 8-OH), 11.94 (1H, s, 1-OH), 7.68 (1H, t, J = 8.4 Hz, H-6), 6.95 (1H, d, J = 8.4 Hz, H-5), 6.77 (1H, d, J = 8.4 Hz, H-7), 6.54 (1H, s, H-4), 5.27 (1H, t, J = 7.2 Hz, H-2′), 3.37 (2H, d, J = 7.2 Hz, H-1′), 1.79 (3H, s, H-4′), 1.66 (3H, s, H-5′); ESIMS m/z 312.9 [M + H]+.33 2-Dimethylallyl-1,3,6,8-tetrahydroxyxanthone (9a): 1H NMR (600 MHz, acetone-d6) δ 12.27 (1H, s, 1-OH), 12.06 (1H, s, 8OH), 6.49 (1H, s, H-4), 6.38 (1H, s, H-5), 6.24 (1H, s, H-7), 5.27 (1H, t, J = 7.2 Hz, H-2′), 3.35 (2H, d, J = 7.2 Hz, H-1′), 1.78 (3H, s, H-4′), 1.65 (3H, s, H-5′); ESIMS m/z 328.9 [M + H]+.35 2,7-Dimethylallyl-1,3,6,8-tetrahydroxyxanthone (9b): 1H NMR (600 MHz, acetone-d6) δ 12.35 (2H, s, 1-OH, 8-OH), 6.46 (2H, s, H4, 5), 5.27 (2H, t, J = 7.2 Hz, H-2′, 2″), 3.35 (2H, d, J = 7.2 Hz, H-1′, 1″), 1.78 (6H, s, H-4′, 4″), 1.65 (6H, s, H-5′, 5″); ESIMS m/z 396.8 [M + H]+. In Vitro Biassay.36 Human neuroblastoma SK-N-SH cells were grown in Dulbecco’s modified Eagle’s medium containing 10% fetal bovine serum, 100 U/mL penicillin, and 100 μg/mL streptomycin. The cell cultures were incubated at 37 °C in a humid 5% CO2/95% air environment. SK-N-SH cells were cultured in 96-well microplates at a density of 1 × 105 cells/well. The compounds were prepared in DMSO as 100 mM stock solutions. Glutamate was freshly prepared prior to each experiment. The cells were preincubated with the compounds for 4 h before 30 mM glutamate was added to the cells. After 4 h of co-incubation, MTT solution (5 mg/mL) was added for another 4 h at 37 °C. The MTT formazan crystals were solubilized with DMSO and spectrophotometrically measured at 570 nm. The cell viability was expressed as a percentage of the control group. All of the data presented in the study were obtained from at least three independent experiments and expressed as the mean ± SEM. Significant differences between groups were compared using oneway ANOVA followed by an LSD post hoc test using SPSS ver. 10.0

software. The differences were considered statistically significant at p < 0.05.

■

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jnatprod.6b00417. NMR spectra of prenylated xanthones (3a−7a, 9a, and 9b), HPLC-DAD/ESIMS analysis of enzymatic reaction mixtures of 3, 4, 8, and 10, a proposed prenylxanthone biosynthetic pathway in plants, and neuroprotective effects of 3−7 and 9 and their prenylated products (PDF)

■

AUTHOR INFORMATION

Corresponding Authors

*Tel: +86 10 6316 5173. Fax: +86 10 6301 7757. E-mail: [email protected] (Y. Peng). *Tel: +86 10 6316 5195. Fax: +86 10 6301 7757. E-mail: [email protected] (J. Dai). Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The study was supported by National Natural Science Foundation of China Grant 81273405.

■

REFERENCES

(1) El-Seedi, H. R.; El-Ghorab, D. M.; El-Barbary, M. A.; Zayed, M. F.; Goransson, U.; Larsson, S.; Verpoorte, R. Curr. Med. Chem. 2009, 16, 2581−2626. (2) Vieira, L. M. M.; Kijjoa, A. Curr. Med. Chem. 2005, 12, 2413− 2446. (3) Peres, V.; Nagem, T. J.; de Oliveira, F. F. Phytochemistry 2000, 55, 683−710. (4) Masters, K. S.; Bräse, S. Chem. Rev. 2012, 112, 3717−3776. (5) Lesch, B.; Bräse, S. Angew. Chem., Int. Ed. 2004, 43, 115−118. (6) Pinto, M. M. M.; Sousa, M. E.; Nascimento, M. S. J. Curr. Med. Chem. 2005, 12, 2517−2538. (7) Matsumoto, K.; Akao, Y.; Kobayashi, E.; Ohguchi, K.; Ito, T.; Tanaka, T.; Iinuma, M.; Nozawa, Y. J. Nat. Prod. 2003, 66, 1124− 1127. (8) Suksamrarn, S.; Suwannapoch, N.; Phakhodee, W.; Thanuhiranlert, J.; Ratananukul, P.; Chimnoi, N.; Suksamrarn, A. Chem. Pharm. Bull. 2003, 51, 857−859. (9) Jung, H. A.; Su, B. N.; Keller, W. J.; Mehta, R. G.; Kinghorn, A. D. J. Agric. Food Chem. 2006, 54, 2077−2082. (10) Chen, L. G.; Yang, L. L.; Wang, C. C. Food Chem. Toxicol. 2008, 46, 688−693. (11) El-Seedi, H. R.; El-Barbary, M. A.; El-Ghorab, D. M. H.; Bohlin, L.; Borg-Karlson, A. K.; Goransson, U.; Verpoorte, R. Curr. Med. Chem. 2010, 17, 854−901. (12) Fiesel, T.; Gaid, M.; Müller, A.; Bartels, J.; El-Awaad, I.; Beuerle, T.; Ernst, L.; Behrends, S.; Beerhues, L. Molecules 2015, 20, 15616− 15630. (13) Sanchez, J. F.; Entwistle, R.; Hung, J. H.; Yaegashi, J.; Jain, S.; Chiang, Y. M.; Wang, C. C. C.; Oakley, B. R. J. Am. Chem. Soc. 2011, 133, 4010−4017. (14) Pockrandt, D.; Ludwig, L.; Fan, A.; König, G. M.; Li, S.-M. ChemBioChem 2012, 13, 2764−2771. (15) Heide, L. Curr. Opin. Chem. Biol. 2009, 13, 171−179. (16) Yazaki, K.; Sasaki, K.; Tsurumaru, Y. Phytochemistry 2009, 70, 1739−1745. D

DOI: 10.1021/acs.jnatprod.6b00417 J. Nat. Prod. XXXX, XXX, XXX−XXX

Journal of Natural Products

Note

(17) Winkelblech, J.; Fan, A.; Li, S.-M. Appl. Microbiol. Biotechnol. 2015, 99, 7379−7397. (18) Li, W. Trends Biochem. Sci. 2016, 41, 356−370. (19) Fan, A.; Winkelblech, J.; Li, S.-M. Appl. Microbiol. Biotechnol. 2015, 99, 7399−7415. (20) Kuzuyama, T.; Noel, J. P.; Richard, S. B. Nature 2005, 435, 983−987. (21) Chen, R.; Liu, X.; Zou, J.; Yin, Y.; Ou, B.; Li, J.; Wang, R.; Xie, D.; Zhang, P.; Dai, J. Adv. Synth. Catal. 2013, 355, 1817−1828. (22) Li, J.; Chen, R.; Wang, R.; Liu, X.; Xie, D.; Zou, J.; Dai, J. ChemBioChem 2014, 15, 1673−1681. (23) Wang, R.; Chen, R.; Li, J.; Liu, X.; Xie, K.; Chen, D.; Yin, Y.; Tao, X.; Xie, D.; Zou, J.; Yang, L.; Dai, J. J. Biol. Chem. 2014, 289, 35815−35825. (24) Helboe, P.; Arends, P. Acta Chem. Scand. 1973, 27, 2237−2238. (25) Cortez, D. A. G.; Young, M. C. M.; Marston, A.; Wolfender, J. L.; Hostettmann, K. Phytochemistry 1998, 47, 1367−1374. (26) Weng, J. K.; Philippe, R. N.; Noel, J. P. Science 2012, 336, 1667− 1670. (27) Weng, J. K. New Phytol. 2014, 201, 1141−1149. (28) Davisson, V. J.; Woodside, A. B.; Poulter, C. D. Methods Enzymol. 1985, 110, 130−144. (29) Rancon, S.; Chaboud, A.; Darbour, N.; Comte, G.; Bayet, C.; Simon, P. N.; Raynaud, J.; Pietro, A. D.; Cabalion, P.; Barron, D. Phytochemistry 2001, 57, 553−557. (30) Lin, C. M.; Huang, S. T.; Lee, F. W.; Kuo, H. S.; Lin, M. H. Bioorg. Med. Chem. 2006, 14, 4402−4409. (31) Liu, Y.; Zou, L.; Ma, L.; Chen, W. H.; Wang, B.; Xu, Z. L. Bioorg. Med. Chem. 2006, 14, 5683−5690. (32) Genoux-Bastide, E.; Lorendeau, D.; Nicolle, E.; Yahiaoui, S.; Magnard, S.; Di Pietro, A.; Baubichon-Cortay, H.; Boumendjel, A. ChemMedChem 2011, 6, 1478−1484. (33) Zhang, X.; Li, X.; Ye, S.; Zhang, Y.; Tao, L.; Gao, Y.; Gong, D.; Xi, M.; Meng, H.; Zhang, M.; Gao, W.; X, X.; Guo, Q.; You, Q. Med. Chem. 2012, 8, 1012−1025. (34) Lim, C. K.; Tho, L.-Y.; Lim, Y. M.; Shah, S. A. A.; Weber, J.-F. F. Lett. Org. Chem. 2012, 9, 549−555. (35) Lim, C. K.; Tho, L.-Y.; Lim, C. H.; Lim, Y. M.; Shah, S. A. A.; Weber, J.-F. F. Lett. Drug Des. Discovery 2011, 8, 523−528. (36) Yang, L.; Wang, Z.; Lei, H.; Chen, R.; Wang, X.; Peng, Y.; Dai, J. Tetrahedron 2014, 70, 8244−8251.

E

DOI: 10.1021/acs.jnatprod.6b00417 J. Nat. Prod. XXXX, XXX, XXX−XXX