Design and Synthesis of Structure-Simplified ... - ACS Publications

Apr 15, 2016 - Bischromone 10 and biflavone 13 both promoted the mammalian ...... (AMED); the Program for the Promotion of Basic Research Activities f...
0 downloads 0 Views 949KB Size
Download PDF
Article pubs.acs.org/jnp

Design and Synthesis of Structure-Simplified Derivatives of Gonytolide for the Promotion of Innate Immune Responses Haruhisa Kikuchi,* Tsuyoshi Hoshikawa, Shoichiro Kurata, Yasuhiro Katou, and Yoshiteru Oshima Graduate School of Pharmaceutical Sciences, Tohoku University, Aoba-yama, Aoba-ku, Sendai 980-8578, Japan S Supporting Information *

ABSTRACT: Gonytolide A (1), a dimeric chromanone substituted with the γ-lactone, shows promoting activity of innate immune responses. However, biological studies on this compound have been limited by the low amounts of 1 available from natural resources and the difficulty of its synthesis. In this study, we designed and synthesized structure-simplified gonytolide derivatives. Bischromone 10 and biflavone 13 both promoted the mammalian TNF-α signaling pathway and Drosophila innate immunity. They did not contain a chiral center and were easy to synthesize. Hence, they can be used as lead compounds for a new type of immunostimulating drugs and as research reagents.

■

S

RESULTS AND DISCUSSION Design and Synthesis of Simplified Derivatives of Gonytolide A. Structural simplification has been applied to several biologically and pharmacologically active natural products with the aim of developing novel drugs such as Halaven (eribulin).7 Moreover, the structural simplification of the highly potent protein kinase C activators, bryostatin 1 and aplysiatoxin, provided a promising HIV eradication drug8 and an anticancer drug candidate,9 respectively. Wender demonstrated the principle of function-oriented synthesis,10 in which the function of a biologically active lead structure can be emulated by replacement with simpler scaffolds designed to incorporate the activity-determining structural features of the lead compound. Thus, we applied this concept to 1 to obtain a biologically active and simplified derivative. In our recent study,6 we revealed the structural requirements of gonytolide A (1) for innate-immunity-promoting activity by using natural gonytolides and their derivatives. As a result, we noted the following observation: (i) two symmetrical chromanone moieties through C-8 and C-8′ are crucial for the activity; (ii) the opening of γ-lactone moieties does not affect the activity; (iii) 5O,5′O-dimethylation does not affect the activity. In fact, the γ-lactone ring-opened derivative 8 exhibits innate-immunity-promoting activity (Figure 2). To increase synthetic accessibility, we then planned to remove chiral centers from 8. Specifically, removal of methoxycarbonyl groups and dehydrogenation at C-2 and C-2′ afforded bischromone-type compound 9; dehydroxylation of 9 at C-9 and C-9′ affords compound 10. Moreover, reduction of a

everal dimeric and monomeric chromanones substituted with the γ-lactone moiety have been isolated as fungal metabolites.1 They exhibit interesting biological activities such as cytotoxicity,1j,l antibacterial1d,g,k and antifungal properties,1g and anticoccidial activities1c,c as well as inhibitory activities against cytochrome P450 enzymes.1h,i However, only a few synthetic studies on monomeric-type chromanones have been reported.2 Moreover, dimeric chromanones containing γlactones have not been synthesized because of their structural complexity. Recently, the total synthesis of secalonic acids3 and rugulotrosin A,4 biogenetically related dimeric tetrahydroxanthones, has been reported. We have focused on regulators of innate immunity by developing an ex vivo culture system based on the Drosophila IMD signaling pathway to permit the screening of compounds that target the innate immune system.5,6 During screening for innate immune regulators from natural resources, we isolated and identified a dimeric chromanone, gonytolide A (1), as an innate immune promoter from the fungus Gonytrichum sp., along with its inactive derivatives, gonytolides B−G (2−7) (Figure 1).6 Gonytolide A (1) also increased TNF-α-stimulated production of IL-8 in human umbilical vein endothelial cells and represents a lead compound for novel immunostimulating agents against bacterial infections and tumors. However, biological studies on this compound are limited because of the low amounts of 1 available naturally. In addition, chemical synthesis of 1 is difficult because of its complex dimeric chromanone moiety, which includes four chiral centers and a stereogenic axis. In this study, we synthesized structuresimplified gonytolide derivatives to promote innate immune responses. © XXXX American Chemical Society and American Society of Pharmacognosy

Received: September 15, 2015

A

DOI: 10.1021/acs.jnatprod.5b00829 J. Nat. Prod. XXXX, XXX, XXX−XXX

Journal of Natural Products

Article

Figure 1. Structures of gonytolide A−G (1−7).

First, we attempted to synthesize methyl ester 10. Compound 10 was synthesized by cyclization of the α,βunsaturated ketone 18, which was prepared by chain extension of 3,3′-biphenyldicarboxylate 15 (Scheme 1). Although there are limited studies on the dimerization of 2,5-dioxybenzoate derivatives, the phenol oxidative dimerization of o-hydroxyacetophenone in a solid phase (FeCl3 on silica gel) is a method that is reported to be useful.13 We adopted the same reaction conditions and obtained 15 from monomeric benzoate 14, which was synthesized by the O-methylation of 2,6dihydroxy-4-methylbenzoic acid. HREIMS (m/z 390.1296 [M+]) of 15 indicated that it was a dimer of 14. HMBC correlation of 15 between H-5 and C-4 and between H3-10 and C-4 indicated that dimerization occurs at the ortho position of hydroxy groups and not of methoxy groups. In this dimerization reation, no isomeric dimer was obtained. After the methoxymethylation of 15, Claisen condensation with methyl dimethylphosphonate14 afforded ketophosphonate dimer 17. Horner−Wadsworth−Emmons reaction of 17 with methyl 5-oxopentanoate15 afforded α,β-unsaturated ketone 18, which was cyclized into bischromone 19 under acidic conditions. Addition and elimination of the bromine atom at C-3 and C-3′ then afforded the desired bischromone 10. Compounds 9, 11, 12, and 13 were synthesized in a route similar to that utilized to prepare 10 (Scheme 2). Compounds 9 and 11 were obtained by debenzylation and dehydration of 22 and 25, respectively, which were synthesized from the corresponding O-benzylated aldehydes, methyl (S)-4-(benzyloxy)-5-oxopentanoate (20) and 5-(benzyloxy)pentanal.16 Compound 9 existed as a diastereomeric mixture because of its 8,8′-chiral axis. Biflavone 13 was obtained from ketophosphonate dimer 17 and p-anisaldehyde. Innate-Immunity-Promoting Activities of Simplified Derivatives of Gonytolide A. We evaluated the innateimmunity-promoting activities of 1 and structure-simplified gonytolide derivatives 9−13 by using the ex vivo Drosophila culture system (Figure 3).5 As previously reported,6a gonytolide A (1) exhibited innate-immunity-promoting activity in a concentration-dependent manner, and 1 at a concentration of 10 μg/mL led to an increase of the innate immune response to greater than three times. The structure-simplified derivatives 9, 10, 12, and 13 at a concentration of 10 μg/mL also exhibited innate-immune-promoting activity without cytotoxicity. These

Figure 2. Outline of the structural simplification of gonytolide A (1).

methoxycarbonyl group afforded bis(2-(5-hydroxypentyl)chromone) 11, and acetylation of 11 afforded 12. However, many biflavones have been isolated from plants.11 However, only a few 8,8′-biflavone(cuppressuflavone)-type compounds have been reported.12 When three methylene carbons and one carbonyl carbon in 10 are replaced with a para-substituted benzene ring, 8,8′-biflavone 13 is obtained. Thus, we decided to synthesize 9−13 as simplified derivatives of gonytolide A (1). B

DOI: 10.1021/acs.jnatprod.5b00829 J. Nat. Prod. XXXX, XXX, XXX−XXX

Journal of Natural Products

Article

Scheme 1. Synthesis of bischromone 10a

Reagents and conditions: (a) pTsOMe, K2CO3, DMF, rt; (b) BCl3, CH2Cl2, −80 °C→ 0 °C (71% (two steps)); (c) FeCl3−silica gel, 40 °C (32%); (d) MOMCl, NaH, DMF, rt (91%); (e) methyl dimethylphosphonate, LHMDS, THF, rt (81%); (f) methyl 5-oxopentanoate, NaH, THF, rt (59%); (g) HCl, MeOH, reflux (43%); (h) Py·HBr3, CH2Cl2, rt; (i) DBU, benzene, reflux (55% (two steps)). a

Scheme 2. Synthesis of compounds 9 and 11−13a

a Reagents and conditions: (a) DIBAL, CH2Cl2, −78 °C (37%) ; (b) corresponding aldehydes (20, 5-(benzyloxy)pentanal or p-anisaldehyde), NaH, THF, rt (22% (for 21), 27% (for 24)); (c) HCl, MeOH, reflux (50% (for 22), 49%(for 25), 15% (for 28 (two steps from 17)); (d) H2 (baloon), Pd/C, MeOH, rt (88% (for 23), 90% (for 26)); (e) Py·HBr3, CH2Cl2, rt; (f) DBU, benzene, reflux (23% (for 9), 59% (for 11), 58% (for 13) (two steps)) ; (g) Ac2O, pyridine rt (78%).

promoting activity, indicating that the existence of a hydrophilic hydroxy group in a side chain would not be appropriate. In a similar case, gonytolide F (6) bearing a carboxyl group in a side chain did not exhibit any innate-immunity-promoting activity, as previously reported.6b

results indicate that the structure of 8,8′-bischromone bearing appropriate side chains at C-2 and C-2′ is important for innateimmunity promoting activity, whereas some substituents producing chiral centers of 1 are not crucial. Surprisingly, the activity of the biflavone-type compound 13 was comparable to that of 1. However, 11 exhibited no innate-immunityC

DOI: 10.1021/acs.jnatprod.5b00829 J. Nat. Prod. XXXX, XXX, XXX−XXX

Journal of Natural Products

Article

Figure 3. Effects of structure-simplified gonytolide derivatives on the Drosophila innate immune response. (A) Effects of compounds on the DAPtype peptidoglycan-mediated activation of Drosophila Dpt-lacZ. Activation is presented as the percentage of activity relative to the control (DMSO). (B) Drosophila S2 cell viability in the presence of 10 μg/mL of compounds. Bars indicate standard errors of three independent measurements. Symbols: * indicates p < 0.05, and ** indicates p < 0.01 vs DMSO.

Promoting Effects of Simplified Derivatives of Gonytolide A on TNF-α-Stimulated Production of IL-8 in HUVECs. The Drosophila IMD signaling pathway resembles the mammalian TNF-α signaling pathway.18 The TNF-α signaling pathway plays a critical role in host defense against several pathogens, in intrinsic tumor suppression, and in inflammatory response by NF-κB-activated production of costimulatory molecules, cytokines, chemokines, and adhesion molecules. We investigated the effect of gonytolide A (1), 10 and 13 on the TNF-α-stimulated production of IL-8, a neutrophil chemotactic factor in HUVECs. As shown in Figure 4, 10 μg/mL of 10 and 13 increased the production of IL-8, although their activities were slightly weaker than that of 1.

be used as leads for a new type of immunostimulating drugs or as research reagents.

■

EXPERIMENTAL SECTION General Experimental Procedures. Starting materials were either commercially available or prepared as reported previously in the literature. Analytical thin layer chromatography was performed on silica gel 60 F254 (Merck). Column chromatography was carried out on Silica Gel 60 (70−230 mesh, Merck). Nuclear magnetic resonance spectra were recorded on JEOL JNM ECA-600 and AL-400. Mass spectra were measured on JEOL JMS AX-500 and AX-700. Methyl 2-hydroxy-6-methoxy-4-methylbenzoate (14). To a solution of 2,6-dihydroxy-4-methylbenzoic acid (5.36 g, 31.8 mmol) in DMF (40 mL), we added potassium carbonate (15.4 g, 111 mmol) and methyl p-toluenesulfonate (14.4 mL, 95.4 mmol) at room temperature. After being stirred for 10 h, the mixture was poured into 1 M hydrochloric acid and extracted with ethyl acetate three times. The combined organic layer was washed with saturated sodium bicarbonate solution and brine, dried over anhydrous sodium sulfate, and concentrated in vacuo to afford crude methyl 2,6-dimethoxybenzoate (5.88 g). Then, 1.0 M solution of boron trichloride in pantane (33.5 mL) was added slowly to a solution of crude benzoate in dichloromethane (60 mL) at −80 °C. After being stirred for 2 h, the mixture was poured into water and extracted with ethyl acetate three times. The combined organic layer was washed with brine, dried over anhydrous sodium sulfate, and concentrated in vacuo. The residue was chromatographed over silica gel eluted by hexane-ethyl acetate (19:1) to afford 14 (4.45 g, 22.7 mmol, 71% (two steps)). Data for 14: colorless amorphous solid; 1H NMR (400 MHz, CDCl3, δ): 11.54 (s, 1H), 6.43 (s, 1H), 6.22 (s, 1H), 3.93 (s, 3H), 3.84 (s, 3H), 2.30 (s, 3H); 13C NMR (100 MHz, CDCl3, δ): 171.6, 163.5, 160.6, 146.5, 110.5, 103.4, 100.4, 56.1, 52.3, 22.2; LREIMS m/z 196 [M]+ (56%), 164 (100%), 136 (19%), 121 (11%); HREIMS m/z 196.0721 [M]+ (196.0736, calcd for C10H12O4). Dimethyl 2,2′-dihydroxy-4,4′-dimethoxy-6,6′-dimethylbiphenyl-3,3′-dicarboxylate (15). A solution of iron(III) chloride (10.6 g, 65.4 mmol) in diethyl ether (150 mL) and ethanol (10 mL) was added to silica gel (37.1 g). The solvent was removed to give a yellow solid, which was dried at 90 °C in

Figure 4. Effects of structure-simplified gonytolide derivatives on IL-8 production induced by TNF-α in HUVECs. HUVECs were treated with 10 μg/mL of each compound for 3 h prior to stimulation with TNF-α (1 ng/mL). Bars indicate standard errors of three independent measurements. Symbols: * indicates p < 0.05, and ** indicates p < 0.01 vs control (DMSO).

In conclusion, we designed and synthesized structuresimplified gonytolide derivatives, and we found that bischromone 10 and biflavone 13 promote the mammalian TNF-α signaling pathway and Drosophila innate immunity. Although the chemical synthesis of 1 is difficult because of its complex dimeric chromanone, which includes four chiral centers and a chiral axis, these structure-simplified derivatives without chiral centers can be easily synthesized and obtained. Hence, they can D

DOI: 10.1021/acs.jnatprod.5b00829 J. Nat. Prod. XXXX, XXX, XXX−XXX

Journal of Natural Products

Article

with ethyl acetate three times. The combined organic layer was washed with saturated sodium bicarbonate solution and brine, dried over anhydrous sodium sulfate, and concentrated in vacuo. The residue was chromatographed over silica gel eluted by hexane−ethyl acetate (2:1) to afford 18 (121 mg, 0.180 mmol, 59%). Data for 18: colorless oil; 1H NMR (400 MHz, CDCl3, δ): 6.65 (s, 1H), 6.57 (dt, 1H, J = 16.0, 6.8 Hz), 6.33 (d, 1H, J = 16.0 Hz), 4.67 (d, 1H, J = 5.6 Hz), 4.63 (d, 1H, J = 5.6 Hz), 3.79 (s, 3H), 3.66 (s, 3H), 3.00 (s, 3H), 2.32 (t, 2H, J = 7.6 Hz), 2.25−2.28 (m, 2H), 2.07 (s, 3H) 1.74−1.81 (m, 2H); 13C NMR (100 MHz, CDCl3, δ): 194.8, 173.5, 156.5, 153.0, 149.1, 141.0, 133.0, 123.3, 121.5, 108.5, 99.4, 56.5, 55.8, 51.5, 33.1, 31.6, 23.2, 20.7; LREIMS m/z 670 [M]+ (5%), 625 (100%), 569 (51%), 493 (79%); HREIMS m/z 670.2972 [M]+ (670.2989, calcd for C36H46O12). Dimethyl 4,4′-(5,5′-dimethoxy-7,7′-dimethyl-4,4′-dioxo8,8′-bichroman-2,2′-diyl)dibutanoate (19). Compound 18 (94.0 mg, 0.140 mmol) was dissolved in 10% hydrogen chloride in methanol (2 mL). After being stirred for 18 h at 60 °C, the solution was concentrated in vacuo. The residue was chromatographed over silica gel eluted by hexane−ethyl acetate (1:1) to afford 19 (35.0 mg, 0.060 mmol, 59%) as a diastereomeric mixture. Data for 19: colorless oil; 1H NMR (400 MHz, CDCl3) 6.47−6.48 (m 1H), 4.23−4.28 (m, 1H), 3.94 (s, 3H), 3.59−3.62 (m, 3H), 2.51−2.64 (m, 2H), 2.10− 2.18 (m, 2H), 1.98−2.01 (m, 3H), 1.48−1.60 (m, 4H); LREIMS m/z 582 [M]+ (100%), 567 (10%), 481 (18%); HREIMS m/z 582.2448 [M]+ (582.2465, calcd for C32H38O10). Dimethyl 4,4′-(5,5′-dimethoxy-7,7′-dimethyl-4,4′-dioxo4H,4′H-8,8′-bichromene-2,2′-diyl)dibutanoate (10). To a solution of 19 (22.0 mg, 0.038 mmol) in dichloromethane (2 mL), we added pyridinium bromide perbromide (24.3 mg, 0.076 mmol) at 0 °C. After being stirred for 1 h, the mixture was poured into water and extracted with ethyl acetate three times. The combined organic layer was washed with saturated sodium bicarbonate solution and brine, dried over anhydrous sodium sulfate, and concentrated in vacuo. Then, the residue was dissolved in benzene (1 mL), and DBU (20 μL, 0.134 mmol) was added to the solution at room temperature. After being stirred for 1 h, the mixture was poured into 0.5 M hydrochloric acid and extracted with ethyl acetate three times. The combined organic layer was washed with brine, dried over anhydrous sodium sulfate, and concentrated in vacuo. The residue was chromatographed over silica gel eluted by ethyl acetate-methanol (19:1) to afford 10 (12.2 mg, 0.021 mmol, 55% (2 steps)). Data for 10: colorless amorphous solid; 1H NMR (400 MHz, CDCl3, δ): 6.80 (s, 1H), 6.04 (s, 1H), 4.04 (s, 3H), 3.62 (s, 3H), 2.34 (td, 2H, J = 7.2, 1.6 Hz), 2.14 (t, 2H, J = 7.2 Hz), 2.10 (s, 3H) 1.63−1.67 (m, 2H); 13C NMR (100 MHz, CDCl3, δ): 178.1, 172.8, 165.4, 158.9, 155.8, 144.2, 115.9, 112.4, 111.4, 108.1, 56.3, 51.6, 32.5, 32.4, 21.3, 20.4; LREIMS m/z 578 [M]+ (100%), 563 (21%), 549 (21%); HREIMS m/z 578.2145 [M]+ (578.2152, calcd for C32H34O10). Methyl (S)-4-(benzyloxy)-5-oxopentanoate (20). To a solution of dimethyl (S)-2-(benzyloxy)pentanedioate17 (1.03 g, 3.87 mmol) in dichloromethane (14 mL), we added diisobutylaluminum hydride (1.0 M in toluene) (4.2 mL, 4.2 mmol) at −80 °C. After 1 h, methanol (6 mL) was added to the mixture, which was then warmed up to room temperature. Saturated potassium sodium tartarate solution (25 mL) was added, and the mixture stirred for 30 min. The mixture was extracted with ethyl acetate three times. The combined organic layer was washed with saturated sodium bicarbonate solution

vacuo. Then, a solution of 14 (4.60 g, 23.4 mmol) in dichloromethane (50 mL) was added dropwisely to the silica gel-bound iron(III) chloride. After well-mixing by rotation, the solvent was removed in vacuo, and the resultant solid was kept at 40 °C for 48 h. The solid was directly subjected to silica gel column, and compound 15 (1.46 g, 3.74 mmol, 32%) was afforded from the hexane−ethyl acetate (4:1) elutant. Data for 15: yellowish amorphous solid; 1H NMR (600 MHz, CDCl3, δ): 11.80 (s, 1H), 6.41 (s, 1H), 3.93 (s, 3H), 3.89 (s, 3H), 2.04 (s, 3H); 13C NMR (150 MHz, CDCl3, δ): 172.0, 161.0, 160.0, 146.1, 117.0, 104.0, 100.8, 56.1, 52.4, 20.7; LREIMS m/z 390 [M]+ (82%), 358 (42%), 343 (26%), 311 (100%); HREIMS m/ z 390.1296 [M]+ (390.1315, calcd for C20H22O8). Dimethyl 4,4′-dimethoxy-2,2′-bis(methoxymethoxy)-6,6′dimethylbiphenyl-3,3′-dicarboxylate (16). To a solution of 15 (2.18 g, 5.58 mmol) in DMF (40 mL), we added sodium hydride (60% oil suspension) (715 mg, 17.9 mmol) and chloromethyl methyl ether (1.36 mL, 17.9 mmol) at 0 °C. After being stirred for 3 h at room temperature, the mixture was poured into 0.5 M hydrochloric acid and extracted with ethyl acetate three times. The combined organic layer was washed with saturated sodium bicarbonate solution and brine, dried over anhydrous sodium sulfate, and concentrated in vacuo. The residue was chromatographed over silica gel eluted by hexaneethyl acetate (4:1) to afford 16 (2.42 g, 5.06 mmol, 91%). Data for 16: colorless oil; 1H NMR (400 MHz, CDCl3, δ): 6.65 (s, 1H), 4.75 (d, 1H, J = 5.6 Hz), 4.72 (d, 1H,J = 5.6 Hz), 3.87 (s, 3H), 3.84 (s, 3H), 3.00 (s, 3H), 2.05 (s, 3H); 13C NMR (100 MHz, CDCl3, δ): 166.9, 156.4, 153.4, 141.6, 123.2, 116.3, 108.5, 99.5, 56.5, 56.0, 52.3, 20.8; LREIMS m/z 478 [M]+ (15%), 402 (79%), 372 (100%); HREIMS m/z 478.1823 [M]+ (478.1839, calcd for C24H30O10). Tetramethyl 2,2′-(4,4′-dimethoxy-2,2′-bis(methoxymethoxy)-6,6′-dimethylbiphenyl-3,3′-diyl)bis(2oxoethane-2,1-diyl)diphosphonate (17). To a solution of 16 (510 mg, 1.07 mmol) in THF (20 mL), we added dimethyl methylphosphonate (0.60 mL, 5.52 mmol) and lithium bis(trimethylsilyl)amide (1.0 M solution in THF) (11.0 mL, 11.0 mmol) at 0 °C. After being stirred for 12 h at room temperature, the mixture was poured into 0.5 M hydrochloric acid and extracted with ethyl acetate three times. The combined organic layer was washed with saturated sodium bicarbonate solution and brine, dried over anhydrous sodium sulfate, and concentrated in vacuo. The residue was chromatographed over silica gel eluted by ethyl acetate−methanol (9:1) to afford 17 (578 mg, 0.872 mmol, 81%). Data for 17: colorless oil; 1H NMR (400 MHz, CDCl3, δ): 6.66 (s, 1H), 4.72 (d, 1H, J = 6.0 Hz), 4.69 (d, 1H, J = 6.0 Hz), 3.86 (s, 3H), 3.79 (d, 3H, J = 2.0 Hz), 3.75 (d, 3H, J = 2.0 Hz), 3.61 (dd, 2H, J = 20.8, 3.6 Hz), 3.01 (s, 3H), 2.06 (s, 3H); 13C NMR (100 MHz, CDCl3, δ): 194.4 (d, J = 6.6 Hz), 156.4, 153.4, 142.4, 123.5, 122.4 (d, J = 4.6 Hz), 108.6, 100.1, 56.4, 55.8, 52.8 (d, J = 6.6 Hz), 52.7 (d, J = 6.0 Hz), 42.7 (d, J = 131.0 Hz), 20.8; LREIMS m/z 662 [M]+ (13%), 617 (18%), 586 (57%), 556 (100%); HREIMS m/z 662.1878 [M]+ (662.1893, calcd for C28H40O14P2). Dimethyl (5E,5′E)-7,7′-(4,4′-dimethoxy-2,2′-bis(methoxymethoxy)-6,6′-dimethylbiphenyl-3,3′-diyl)bis(7-oxohept-5-enoate) (18). To a solution of 17 (200 mg, 0.302 mmol) in THF (8 mL), we added sodium hydride (60% in oil dispersion) (28.8 mg, 0.72 mmol) at 0 °C. After 30 min, methyl 5-oxopentanoate15 (156 mg, 1.20 mmol) was added to the mixture. After being stirred for 12 h at room temperature, the mixture was poured into 0.5 M hydrochloric acid and extracted E

DOI: 10.1021/acs.jnatprod.5b00829 J. Nat. Prod. XXXX, XXX, XXX−XXX

Journal of Natural Products

Article

3H), 2.38−2.49 (m, 4H), 2.11 (s, 6H), 1.77−1.85 (m, 2H), 1.57−1.64 (m, 2H); 13C NMR (100 MHz, CDCl3, δ): 178.13, 178.10, 174.69, 174.62, 165.4 (0.5C), 165.37 (0.5C), 165.36 (0.5C), 165.34 (0.5C), 159.0, 158.9, 155.93 (0.5C), 155.919 (0.5C), 155.911 (0.5C), 155.8 (0.5C), 144.28, 144.25 (0.5C), 144.24 (0.5C), 115.96, 115.94, 112.5, 112.4, 111.38, 111.34 (0.5C), 111.33 (0.5C), 108.07, 108.03, 68.99 (0.5C), 68.97 (0.5C), 68.90, 56.3 (2C), 52.89 (0.5C), 52.87 (0.5C), 52.82 (0.5C), 52.81 (0.5C), 30.4 (0.5C), 30.3 (0.5C), 30.2 (0.5C), 30.1 (0.5C), 28.92 (0.5C), 28.91 (0.5C), 28.7, 20.4, 20.3; LREIMS m/z 610 [M]+ (100%), 551 (36%); HREIMS m/z 610.2029 [M]+ (610.2050, calcd for C32H34O12). (2E,2′E)-1,1′-(4,4′-Dimethoxy-2,2′-bis(methoxymethoxy)6,6′-dimethylbiphenyl-3,3′-diyl)bis(7-(benzyloxy)hept-2-en1-one) (24). A similar procedure to the synthesis of 18 was used. From compounds 17 (272 mg, 0.411 mmol) and 5(benzyloxy)pentanal (315 mg, 1.64 mmol), compound 24 (87.2 mg, 0.110 mmol, 27%) was obtained. Data for 24: colorless oil; 1H NMR (400 MHz, CDCl3, δ): 7.25−7.33 (m, 5H), 6.64 (s, 1H), 6.60 (dt, 1H, J = 16.0, 7.2 Hz), 6.32 (d, 1H, J = 16.0 Hz), 4.66 (d, 1H, J = 5.6 Hz), 4.62 (d, 1H, J = 5.6 Hz), 4.48 (s, 2H), 3.77 (s, 3H), 3.45 (t, 2H, J = 6.4 Hz), 2.98 (s, 3H), 2.24 (dt, 2H, J = 7.2, 6.8 Hz), 2.07 (s, 3H), 1.53−1.69 (m, 4H); 13C NMR (100 MHz, CDCl3, δ): 195.0, 156.4, 153.0, 150.5, 140.8, 138.4, 132.5, 128.5 (2C), 127.5 (2C), 127.4, 123.3, 121.6, 108.5, 99.4, 72.8, 69.8, 56.4, 55.7, 32.2, 29.2, 24.6, 20.7; LREIMS m/z 794 [M]+ (5%), 749 (100%), 631 (41%), 279 (44%), 261 (40%), 91 (79%); HREIMS m/z 794.4016 [M]+ (794.4030, calcd for C48H58O10). 2,2′-Bis(4-(benzyloxy)butyl)-5,5′-dimethoxy-7,7′-dimethyl8,8′-bichroman-4,4′-dione (25). A similar procedure to the synthesis of 19 was used. From compound 24 (56.0 mg, 0.070 mmol), compound 25 (24.8 mg, 0.035 mmol, 49%) was afforded as a diastereomeric mixture. Data for 25: colorless oil; 1 H NMR (400 MHz, CDCl3, δ): 7.25−7.38 (m, 10H), 6.45 (s, 1H), 6.38 (s, 1H), 4.41−4.52 (m, 4H), 4.18−4.27 (m, 2H), 3.86−3.95 (s, 6H), 3.25−3.37 (m, 4H), 2.50−2.59 (m, 4H), 1.96−2.04 (m, 6H), 1.44−1.67 (m, 8H), 1.23−1.31 (m, 4H); LREIMS m/z 706 [M]+ (100%), 616 (28%), 543 (86%), 437 (86%); HREIMS m/z 706.3471 [M]+ (706.3506, calcd for C44H50O8). 2,2′-Bis(4-hydroxybutyl)-5,5′-dimethoxy-7,7′-dimethyl8,8′-bichroman-4,4′-dione (26). A similar procedure to the synthesis of 23 was used. From compound 25 (14.8 mg, 0.021 mmol), compound 26 (10.2 mg, 0.019 mmol, 90%) was afforded as a diastereomeric mixture. Data for 26: colorless oil; 1 H NMR (400 MHz, CDCl3, δ): 6.46 (s, 1H), 4.20−4.31 (m, 1H), 3.93 (s, 3H), 3.44−3.53 (m, 2H), 2.55 (m, 2H), 1.98− 2.05 (s, 3H), 1.58−1.65 (m, 2H), 1.34−1.47 (m, 2H), 1.22− 1.29 (m, 2H); LREIMS m/z 526 [M]+ (100%), 453 (40%); HREIMS m/z 526.2564 [M]+ (526.2567, calcd for C30H38O8). Dimethyl (4S,4′S)-4,4′-(5,5′-dimethoxy-7,7′-dimethyl-4,4′dioxo-4H,4′H-8,8′-bichromene-2,2′-diyl)bis(4-hydroxybutanoate) (11). A similar procedure to the synthesis of 10 was used. From compound 26 (7.4 mg, 0.014 mmol), compound 11 (4.3 mg, 0.008 mmol, 59%) was obtained. Data for 11: colorless amourphous solid; 1H NMR (400 MHz, CDCl3, δ): 6.78 (s, 1H), 6.04 (s, 1H), 4.03 (s, 3H), 3.46 (br. s, 2H), 2.31 (br. s, 2H), 2.12 (s, 3H), 1.60−1.69 (m, 2H), 1.32−1.39 (m, 2H); 13C NMR (100 MHz, CDCl3, δ): 178.4, 166.4, 158.9, 156.0, 144.1, 116.1, 112.5, 111.2, 107.9, 62.0, 56.3, 33.0, 31.4, 22.5, 20.4; LREIMS m/z 522 [M]+ (100%), 507 (19%), 425,

and brine, dried over anhydrous sodium sulfate, and concentrated in vacuo. The residue was chromatographed over silica gel eluted by hexane−ethyl acetate (9:1) to afford 20 (314 mg, 1.33 mmol, 37%). Data for 20: colorless oil; 1H NMR (400 MHz, CDCl3, δ): 9.70 (s, 1H), 7.29−7.35 (s, 5H), 4.70 (d, 1H, J = 11.6 Hz), 4.39 (d, 1H, J = 11.6 Hz), 3.99 (dd, 1H, J = 8.0, 4.8 Hz), 3.75 (s, 3H), 2.56 (t, 2H, J = 7.2 Hz), 2.02−2.16 (m, 2H); 13C NMR (100 MHz, CDCl3) δ 201.2, 172.5, 137.1, 128.4 (2C), 128.1 (2C), 128.0, 72.5, 72.4, 52.0, 29.2, 27.6; LREIMS m/z 218 [M-H2O]+ (4%), 193 (3%), 177 (10%), 146 (22%), 130 (43%), 91 (100%); HREIMS m/z 218.0931 [MH2O]+ (218.0943, calcd for C13H14O3). Dimethyl (4S,4′S,5E,5′E)-7,7′-(4,4′-dimethoxy-2,2′-bis(methoxymethoxy)-6,6′-dimethylbiphenyl-3,3′-diyl)bis(4(benzyloxy)-7-oxohept-5-enoate) (21). A similar procedure to that for the synthesis of 18 was used. From compounds 17 (240 mg, 0.362 mmol) and 20 (363 mg, 1.54 mmol), compound 21 (70.0 mg, 0.079 mmol, 22%) was afforded as a diastereomeric mixture. Data for 21: colorless oil; 1H NMR (400 MHz, CDCl3, δ): 7.23−7.34 (m, 5H), 6.64 (br. s, 1H), 6.53−6.60 (m, 1H), 6.31 (dd, 1H, J = 15.6, 3.2 Hz), 4.69 (d, 1H, J = 10.8 Hz), 4.60−4.66 (m, 2H), 4.39 (d, 1H, J = 10.8 Hz), 3.93−3.96 (m, 1H), 3.76 (s, 3H), 3.74 (s, 3H), 2.97 (s, 3H), 2.32−2.38 (s, 2H), 2.06 (s, 1.5H), 2.05 (s, 1.5H), 1.86− 1.91 (m, 2H); LREIMS m/z 882 [M]+ (14%), 837 (88%), 675 (100%), 631 (14%), 599 (34%), 383 (42%), 91 (56%); HREIMS m/z 882.3817 [M]+ (882.3827, calcd for C50H58O14). Dimethyl (4S,4′S)-4,4′-(5,5′-dimethoxy-7,7′-dimethyl-4,4′dioxo-8,8′-bichroman-2,2′-diyl)bis(4-(benzyloxy)butanoate) (22). A similar procedure to the synthesis of 19 was used. From compound 21 (65.4 mg, 0.074 mmol), compound 22 (28.9 mg, 0.036 mmol, 49%) was afforded as a diastereomeric mixture. Data for 22: colorless oil; 1H NMR (400 MHz, CDCl3, δ): 7.28−7.31 (m, 5H), 6.44 (br. s, 1H), 4.56−4.61 (m, 1H), 4.21−4.28 (m, 1H), 4.09−4.22 (m, 1H), 3.90−3.93 (m, 3H), 3.77−3.81 (m, 1H), 3.66−3.69 (m, 3H), 2.48−2.60 (m, 2H), 1.97−2.02 (m, 3H), 1.54−1.73 (m, 4H); LREIMS m/z 794 [M]+ (95%), 688 (22%), 673 (17%), 602 (26%), 597 (32%), 587 (57%), 481 (100%); HREIMS m/z 794.3297 [M]+ (794.3302, calcd for C46H50O12). Dimethyl (4S,4′S)-4,4′-(5,5′-dimethoxy-7,7′-dimethyl-4,4′dioxo-8,8′-bichroman-2,2′-diyl)bis(4-hydroxybutanoate) (23). Under hydrogen atmosphere, compound 22 (30.0 mg, 0.038 mmol) and 20% palladium hydroxide on carbon (6.0 mg) in methanol (1.0 mL) was stirred at room temperature for 2 h. After filtration through a Celite pad, the filtrate was concentrated in vacuo. The residue was chromatographed over silica gel eluted by hexane−ethyl acetate (1:4) to afford 23 (20.0 mg, 0.033 mmol, 88%) as a diastereomeric mixture. Data for 23: colorless oil; 1H NMR (400 MHz, CDCl3, δ): 6.43 (m, 1H), 4.13−4.28 (m, 1H), 3.75−4.00 (m, 1H), 3.88−3.91 (m, 3H), 3.64−3.68 (m, 3H), 2.47−2.62 (m, 2H), 1.91−1.98 (m, 3H), 1.58−1.70 (m, 4H); LREIMS m/z 614 [M]+ (100%), 497 (34%), 481 (33%); HREIMS m/z 614.2382 [M]+ (614.2363, calcd for C32H38O12). Dimethyl (4S,4′S)-4,4′-(5,5′-dimethoxy-7,7′-dimethyl-4,4′dioxo-4H,4′H-8,8′-bichromene-2,2′-diyl)bis(4-hydroxybutanoate) (9). A similar procedure to the synthesis of 10 was used. From compound 23 (21.2 mg, 0.034 mmol), compound 9 (4.9 mg, 0.008 mmol, 23%) was afforded as a diastereomeric mixture. Data for 9: colorless amourphous solid; 1H NMR (400 MHz, CDCl3, δ): 6.79 (s, 1H), 6.78 (s, 1H), 6.06 (s, 1H), 6.05 (s, 1H), 4.03 (s, 6H), 3.95−4.02 (m, 2H), 3.73 (s, 3H), 3.71 (s, F

DOI: 10.1021/acs.jnatprod.5b00829 J. Nat. Prod. XXXX, XXX, XXX−XXX

Journal of Natural Products

Article

BRL) in each well of a 96 well plate at 25 °C. For each condition, six females were cultured to produce six replicates. The test compounds were dissolved in DMSO and added to the culture medium. To determine the effects of the test compounds on the innate immune response, we cultured DptlacZ larvae in the presence of 100 ng/mL peptidoglycans from Escherichia coli (InvivoGen, San Diego, CA) and the compound at 25 °C for 12 h. The cultured individual larvae were sonicated with 200 μL of reaction buffer (60 mM Na2HPO4, 40 mM NaH2PO4, 10 mM KCl, and 1 mM MgCl2) using an ultrasonic processor (Misonix, New York, NY). After centrifugation (10000g) at 4 °C for 10 min, supernatant was harvested, and βgalactosidase activity and total protein amount of supernatant were determined as previously described.5a β-Galactosidase activity was normalized to total protein amount. Measurement of Cytotoxicity. Drosophila S2 cells were cultured in Schneider’s medium (Gibco-BRL) supplemented with 10% FBS and 1% antibiotics and antimycotics at 25 °C. Cytotoxicity was measured using the colorimetric thiazoyl blue coversion assay using WST-8 solution (Nacalai Tesque) as described previously.5a Chemokine Assay. The detailed procedure was described previously.5a Briefly, human umbilical vein endothelial cells (HUVECs) were purchased from Lonza (Walkersville, MA), cultured in 25 cm2 culture flasks, and maintained in EGM-2 medium (Lonza)) at 5% CO2 and 37 °C. The cells were incubated in the presence or absence of the compound in a final volume of 100 μL for 3 h with 5% CO2 at 37 °C, and then 11 μL of 10 ng/mL hTNF-α was added to each well. After 12 h of incubation with 5% CO2 at 37 °C, the HUVEC culture supernatants were harvested for enzyme-linked immunosorbent assay. Commercial enzyme-linked immunosorbent assay kits were used for immunologic quantification of hIL-8 (Biosource, Invitrogen).

(12%) 355 (26%); HREIMS m/z 522.2237 [M]+ (522.2254, calcd for C30H34O8). 4,4′-(5,5′-Dimethoxy-7,7′-dimethyl-4,4′-dioxo-4H,4′H8,8′-bichromene-2,2′-diyl)bis(butane-4,1-diyl) diethanoate (12). To a solution of 11 (2.5 mg, 0.005 mmol) in pyridine (0.5 mL), we added acetic anhydride (10 μL) at room temperature. After being stirred for 15 h, the mixture was concentrated in vacuo. The residue was chromatographed over silica gel eluted by ethyl acetate to afford 12 (2.2 mg, 0.004 mmol, 78%). Data for 12: colorless amourphous solid; 1H NMR (400 MHz, CDCl3, δ): 6.79 (s, 1H), 6.04 (s, 1H), 4.03 (s, 1H), 3.91 (t, 2H, J = 6.0 Hz), 2.30 (t, 2H, J = 7.2 Hz), 2.09 (s, 3H), 2.01 (s, 3H), 1.37−1.47 (m, 4H); 13C NMR (100 MHz, CDCl3, δ): 178.1, 170.9, 165.8, 159.0, 155.9, 144.1, 115.9, 112.5, 111.3, 107.9, 63.5, 56.3, 32.7, 27.5, 22.7, 20.8, 20.4; LREIMS m/z 606 [M]+ (100%), 591 (25%), 549 (25%), 429 (28%), 355 (33%); HREIMS m/z 606.2472 [M] + (606.2465, calcd for C34H38O10). 5,5′-Dimethoxy-2,2′-bis(4-methoxyphenyl)-7,7′-dimethyl8,8′-bichroman-4,4′-dione (28). To a solution of 17 (187 mg, 0.282 mmol) in THF (8 mL), we added sodium hydride (60% in oil dispersion) (27.6 mg, 0.691 mmol) at 0 °C. After 30 min, p-anisaldehyde (230 mg, 1.69 mmol) was added to the mixture. After being stirred for 8 h at room temperature, the mixture was poured into 0.5 M hydrochloric acid and extracted with ethyl acetate three times. The combined organic layer was washed with saturated sodium bicarbonate solution and brine, dried over anhydrous sodium sulfate, and concentrated in vacuo to give crude 27. This crude was dissolved in 10% hydrogen chloride in methanol (4 mL). After being stirred for 15 h at 60 °C, the solution was concentrated in vacuo. The residue was chromatographed over silica gel eluted by hexane−ethyl acetate (1:3) to afford 19 (25.0 mg, 0.042 mmol, 15% (2 steps)) as a diastereomeric mixture. Data for 28: yellowish amourphous solid; 1H NMR (400 MHz, CDCl3, δ): 7.00 (d, 2H, J = 8.8 Hz), 6.92−6.97 (m, 2H), 6.73 (d, 2H, J = 8.8 Hz), 6.65 (d, 1.1H, J = 8.8 Hz), 6.62 (d, 0.9H, J = 8.8 Hz), 6.43 (s, 0.6H), 6.42 (s, 0.4H), 6.41 (s, 0.6H), 6.40 (s, 0.4H), 5.25−5.32 (m, 1.1H), 5.21 (dd, 0.5H, J = 7.6, 7.6 Hz), 5.01 (dd, 0.4H, J = 12.0, 3.6 Hz), 3.89 (s, 1.5H), 3.88 (s, 2.5H), 3.87 (s, 2.0H), 3.71 (s, 1.4H), 3.69 (s, 1.6H), 3.64 (s, 1.7H), 3.63 (s, 1.3H), 2.64−2.81 (m, 4H), 1.95−2.04 (m, 6H); LREIMS m/z 594 [M]+ (100%), 431 (40%), 311 (19%); HREIMS m/z 594.2255 [M] + (594.2254, calcd for C36H34O8). 5,5′-Dimethoxy-2,2′-bis(4-methoxyphenyl)-7,7′-dimethyl4H,4′H-8,8′-bichromene-4,4′-dione (11). A similar procedure to the synthesis of 10 was used. From compound 28 (10.0 mg, 0.017 mmol), compound 13 (5.5 mg, 0.009 mmol, 58%) was obtained. Data for 13: colorless amourphous solid; 1H NMR (400 MHz, CDCl3, δ): 7.17 (d, 2H, J = 9.2 Hz), 6.81 (s, 1H), 6.71 (d, 2H, J = 9.2 Hz), 6.57 (s, 1H), 4.04 (s, 3H), 3.72 (s, 3H), 2.12 (s, 3H); 13C NMR (100 MHz, CDCl3, δ): 178.6, 162.1, 160.8, 159.0, 155.6, 144.6, 127.2 (2C), 123.2, 116.3, 114.5 (2C), 112.7, 108.1, 107.0, 56.5, 55.4, 20.6; LREIMS m/z 590 [M]+ (100%), 575 (11%), 561 (16%), 543 (6%); HREIMS m/z 590.1942 [M]+ (590.1941, calcd for C36H30O8). Ex vivo Drosophila Culture Assay. The detailed procedure was described previously.5a Briefly, the abdominal cavity of third-instar larva was opened using fine pincettes. Individual whole larval tissues were cultured in Schneider’s Drosophila medium (Gibco-BRL, Invitrogen, Carlsbad, CA) containing 20% fetal bovine serum (Valley Biomedical, Winchester, VA) and 1% antibiotics and antimycotics (Gibco-

■

ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jnatprod.5b00829. Figures showing the NMR and HMQC spectra of the new compounds. (PDF)

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Phone: +81-22-7956824. Fax: +81-22-795-6821. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This work was supported in part by Grant-in-Aid for Scientific Research (no. 23710247 and no. 25350959) from the Ministry of Education, Culture, Sports, Science, and Technology, Japan; the Platform Project for Supporting in Drug Discovery and Life Science Research from the Ministry of Education, Culture, Sports, Science, and Technology (MEXT) and the Japan Agency for Medical Research and development (AMED); the Program for the Promotion of Basic Research Activities for Innovative Biosciences (PROBRAIN); the SUNBOR GRANT from the Suntory Institute for Bioorganic Research; and the Astellas Foundation for Research on Metabolic Disorders. G

DOI: 10.1021/acs.jnatprod.5b00829 J. Nat. Prod. XXXX, XXX, XXX−XXX

Journal of Natural Products

■

Article

(13) (a) Toda, F.; Tanaka, K.; Iwata, S. J. Org. Chem. 1989, 54, 3007−3009. (b) Li, H.-Y.; Nehira, T.; Hagiwara, M.; Harada, N. J. Org. Chem. 1997, 62, 7222−7227. (14) Milburn, R. R.; McRae, K.; Chan, J.; Tedrow, J.; Larsen, R.; Faul, M. Tetrahedron Lett. 2009, 50, 870−872. (15) Seifert, T.; Malo, M.; Kokkola, T.; Engen, K.; Fridén-Saxin, M.; Wallén, E. A. A.; Lahtela-Kakkonen, M.; Jarho, E. M.; Luthman, K. J. Med. Chem. 2014, 57, 9870−9888. (16) Veerasamy, N.; Carlson, E. C.; Collett, N. D.; Saha, M.; Carter, R. G. J. Org. Chem. 2013, 78, 4779−4800. (17) Ashoorzadeh, A.; Archibald, G.; Caprio, V. Tetrahedron 2009, 65, 4671−4680. (18) (a) Silverman, N.; Maniatis, T. Genes Dev. 2001, 15, 2321−42. (b) Hoffmann, J. A.; Reichhart, J. M. Nat. Immunol. 2002, 3, 121−126.

REFERENCES

(1) (a) Franck, B.; Flasch, H. Fortschr. Chem. Org. Naturst. 1973, 30, 151−206. (b) Tabata, N.; Tomoda, H.; Matsuzaki, K.; Omura, S. J. Am. Chem. Soc. 1993, 115, 8558−8564. (c) Tabata, N.; Tomoda, H.; Iwai, Y.; Omura, S. J. Antibiot. 1996, 49, 267−271. (d) Kanokmedhakul, S.; Kanokmedhakul, K.; Phonkerd, N.; Soytong, K.; Kongsaeree, P.; Suksamrarn, A. Planta Med. 2002, 68, 834−836. (e) Rukachaisirikul, V.; Chantaruk, S.; Pongcharoen, W.; Isaka, M.; Lapanun, S. J. Nat. Prod. 2006, 69, 980−982. (f) Guo, Z.; She, Z.; Shao, C.; Wen, L.; Liu, F.; Zheng, Z.; Lin, Y. Magn. Reson. Chem. 2007, 45, 777−780. (g) Zhang, W.; Krohn, K.; Zia-Ullah; Flörke, U.; Pescitelli, G.; Di Bari, L.; Antus, S.; Kurtán, T.; Rheinheimer, J.; Draeger, S.; Schulz, B. Chem. - Eur. J. 2008, 14, 4913−4923. (h) Pontius, A.; Krick, A.; Kehraus, S.; Foegen, S. E.; Müller, M.; Klimo, K.; Gerhäuser, C.; König, G. M. Chem. - Eur. J. 2008, 14, 9860−9863. (i) Pontius, A.; Krick, A.; Mesry, R.; Kehraus, S.; Foegen, S. E.; Müller, M.; Klimo, K.; Gerhäuser, C.; König, G. M. J. Nat. Prod. 2008, 71, 1793−1799. (j) Yang, J.; Xu, F.; Huang, C.; Li, J.; She, Z.; Pei, Z.; Lin, Y. Eur. J. Org. Chem. 2010, 2010, 3692−3695. (k) Arunpanichlert, J.; Rukachaisirikul, V.; Tadpetch, K.; Phongpaichit, S.; Hutadilok-Towatana, N.; Supaphon, O.; Sakayaroj, J. Phytochem. Lett. 2012, 5, 604−608. (l) El-Elimat, T.; Figueroa, M.; Raja, H. A.; Graf, T. N.; Swanson, S. M.; Falkinham, J. O., III; Wani, M. C.; Pearce, C. J.; Oberlies, N. H. Eur. J. Org. Chem. 2015, 2015, 109−121. (2) (a) Qin, T.; Johnson, R. P.; Porco, J. A., Jr. J. Am. Chem. Soc. 2011, 133, 1714−1717. (b) Tietze, L. F.; Ma, L.; Jackenkroll, S.; Reiner, J. R.; Hierold, R. J.; Gnanaprakasam, B.; Heidemann, S. Heterocycles 2014, 88, 1101−1119. (c) Sudhakar, G.; Bayya, S.; Kadam, V. D.; Nanubolu, J. B. Org. Biomol. Chem. 2014, 12, 5601−5610. (d) Tietze, L. F.; Jackenkroll, S.; Hierold, J.; Ma, L.; Waldecker, B. Chem. - Eur. J. 2014, 20, 8628−8635. (e) Liu, J.; Li, Z.; Tong, P.; Xie, Z.; Zhang, Y.; Li, Y. J. Org. Chem. 2015, 80, 1632−1643. (3) Qin, T.; Porco, J. A., Jr. Angew. Chem., Int. Ed. 2014, 53, 3107− 3110. (4) Qin, T.; Skraba-Joiner, S. L.; Khalil, Z. G.; Johnson, R. P.; Capon, R. J.; Porco, J. A., Jr. Nat. Chem. 2015, 7, 234−240. (5) (a) Sekiya, M.; Ueda, K.; Fujita, T.; Kitayama, M.; Kikuchi, H.; Oshima, Y.; Kurata, S. Life Sci. 2006, 80, 113−119. (b) Sekiya, M.; Ueda, K.; Okazaki, K.; Kikuchi, H.; Kurata, S.; Oshima, Y. Biochem. Pharmacol. 2008, 75, 2165−2174. (c) Kikuchi, H.; Sekiya, M.; Katou, Y.; Ueda, K.; Kabeya, T.; Kurata, S.; Oshima, Y. Org. Lett. 2009, 11, 1693−1695. (d) Kikuchi, H.; Okazaki, K.; Sekiya, M.; Uryu, Y.; Ueda, K.; Katou, Y.; Kurata, S.; Oshima, Y. Eur. J. Med. Chem. 2011, 46, 1263−1273. (e) Kikuchi, H.; Sato, Y.; Kurata, S.; Katou, Y.; Oshima, Y. Tetrahedron 2013, 69, 3536−3542. (6) (a) Kikuchi, H.; Isobe, M.; Sekiya, M.; Abe, Y.; Hoshikawa, T.; Ueda, K.; Kurata, S.; Katou, Y.; Oshima, Y. Org. Lett. 2011, 13, 4624− 4627. (b) Kikuchi, H.; Isobe, M.; Kurata, S.; Katou, Y.; Oshima, Y. Tetrahedron 2012, 68, 6218−6223. (7) (a) Huyck, T. K.; Gradishar, W.; Manuguid, F.; Kirkpatrick, P. Nat. Rev. Drug Discovery 2011, 10, 173−174. (b) Kim, D.-S.; Dong, C.G.; Kim, J. T.; Guo, H.; Huang, J.; Tiseni, P. S.; Kishi, Y. J. Am. Chem. Soc. 2009, 131, 15636−15641. (8) DeChristopher, B. A.; Loy, B. A.; Marsden, M. D.; Schrier, A. J.; Zack, J. A.; Wender, P. A. Nat. Chem. 2012, 4, 705−710. (9) Nakagawa, Y.; Yanagita, R. C.; Hamada, N.; Murakami, A.; Takahashi, H.; Saito, N.; Nagai, H.; Irie, K. J. Am. Chem. Soc. 2009, 131, 7573−7579. (10) (a) Wender, P. A.; Verma, V. A.; Paxton, T. J.; Pillow, T. H. Acc. Chem. Res. 2008, 41, 40−49. (b) Wender, P. A. Tetrahedron 2013, 69, 7529−7550. (11) Kim, H. P.; Park, H.; Son, K. H.; Chang, H. W.; Kang, S. S. Arch. Pharmacal Res. 2008, 31, 265−273. (12) (a) Ilyas, M.; Usmani, J. N.; Bhatnagar, S. P.; Ilyas, M.; Rahman, W. Tetrahedron Lett. 1968, 9, 5515−5517. (b) Gadek, P. A.; Quinn, P. A. Phytochemistry 1985, 24, 267−272. (c) Inatomi, Y.; Iida, N.; Murata, H.; Inada, A.; Murata, J.; Lang, F. A.; Iinuma, M.; Tanaka, Y.; Nakanishi, T. Tetrahedron Lett. 2005, 46, 6533−6535. H

DOI: 10.1021/acs.jnatprod.5b00829 J. Nat. Prod. XXXX, XXX, XXX−XXX