2022 Volume 70 Issue 7 Pages 483-491
The first total syntheses of natural phenanthrene alkaloids, namely, uvariopsamine (1), noruvariopsamine (2), 8-hydroxystephenanthrine (3), 8-methoxyuvariopsine (4), thalihazine (5), and secophoebine (6), have been realized. In addition, their in vitro antimalarial activity against the multidrug-resistant K1 strain of Plasmodium falciparum and in vitro cytotoxic activity against the human nasopharynx carcinoma (KB), small cell lung cancer (NCI-H187), and breast cancer (MCF7) human cancer cell lines were investigated. All the phenanthrene alkaloids showed significant antiplasmodial activity (IC50 1.07–7.41 µM), and most compounds displayed low to no toxicity against the three cancer cell lines tested. Particularly, 3 exhibited the best antimalarial activity with an IC50 value of 1.07 µM, no toxicity to NCI-H187 (IC50 > 50 µM), and low toxicity against KB (IC50 24.53 µM) and MCF7 (IC50 42.67 µM) cell lines.
Malaria is an ancient infectious disease caused by Plasmodium spp., mainly P. falciparum, which is the deadliest parasite and known for its resistance to all antimalaria drugs. Malaria has still affected a significant proportion of the world population in the 21st century. According to the World Malaria Report, there were approximately 241 million malaria infected cases and 627000 deaths in 2020,1) resulting in health and economic burdens for many countries. Although malaria cases decreased steadily between 2000 and 2020, there are still some areas where the incidence is prevalent, particularly in the Africa region, which accounts for about 95% of global cases. The emergence of the resistant strain parasite to antimalaria artemisinin drugs is currently the major global obstacle to control and eliminate malaria. Over the past 15 years, artemisinin-based combination therapies (ACTs),2,3) a combination between an artemisinin analog and another antimalaria drug such as lumefantrine, amodiaquine, mefloquine, or piperaquine, are recommended as first line treatment of uncomplicated P. falciparum malaria.4) The alternative mechanism of action of each drug in ACTs improves efficacy for malaria treatment and delays the resistance of the parasites. Unfortunately, the failures of several ACTs have been reported in the Greater Mekong subregion (Cambodia, Thailand, Myanmar, Laos, and Vietnam), where artemisinin and ACT partner drug resistant strains of parasites have been found.5) Thus, efforts toward the discovery of novel antimalarial or partner drugs are of vital importance and are being actively pursued.
Naturally occurring alkaloids play an important role in drug discovery due to their interesting biological activities, particularly antimalarial properties. Quinine, the first alkaloid to be successfully used to treat an infectious disease, was isolated from a Cinchona tree (Fig. 1). Due to the resistance of parasites, quinine had been used for treatment of malaria until the 1940 s when it was replaced with its synthetic alkaloidal analogs such as chloroquine, amodiaquine, and mefloquine. Over the past two decades, there have been several types of alkaloids isolated from medicinal plants including indole, naphthoisoquinoline, bisbenzylisoquinoline isoquinoline, aporphine, protoberberine, phenanthroindolizine, morphinandienone, and amaryllidaceae alkaloids reported in the literature for their promising antimalarial activities.6–11) Among these, some aporphine and phenanthrene alkaloids showed significant antiplasmodial activity. For example, as shown in Fig. 1, obtusipetadione, a p-quinonoid aporphine alkaloid isolated from the twigs of Dasymaschalon obtusipetalum, exhibited in vitro antimalarial activity against the P. falciparum TM4 (IC50 2.46 µg/mL) and K1 (IC50 1.38 µg/mL) strains.12) Aporphine alkaloids roemerine, laurolitsine, and boldine, which were isolated from the leaves of Phoebe tavoyana, showed significant inhibitory activity against the P. falciparum 3D7 clone, with IC50 values of 0.89, 1.49, and 1.65 µg/mL, respectively.13) Phenanthrene alkaloids atherosperminine and 2-hydroxyathersperminine, isolated from the bark of Cryptocarya nigra, displayed strong antiplasmodial activity against the P. falciparum K1 strain with IC50 values of 5.80 and 0.75 µM, respectively.14)
Phenanthrene alkaloids are biogenetically related to the aporphines and can be formally derived from the aporphines by Hofmann degradation. Phenanthrene alkaloids are found in the same plant families as the aporphines such as Annonaceae, Ranunculaceae, Menispermaceae, Aristolochiaceae, Fumariaceae, Lauraceae, and Monimiaceae, albeit occurring in only small amounts.15) Furthermore, phenanthrene alkaloids have relevant biological activities to the aporphines and some phenanthrenes have been reported to possess significant bioactivity including antiplatelet aggregation,16) antiparkinsonian,17) antibacterial,18) antioxidant,19) and cholinesterase inhibitory activities.20–22) As part of our study on the syntheses of cytotoxic aporphine alkaloids23) and searches for new candidates for antimalarial agents, we have paid attention to phenanthrene alkaloids because of their promising antimalarial activity. Also, phenanthrene alkaloids share a structural similarity to halofantrine, a synthetic antimalarial drug with some side effects (Fig. 1). Thus, in this present study, we focus on the syntheses of natural phenanthrene alkaloids with different oxygenation, namely, uvariopsamine,24) noruvariopsamine,25) 8-hydroxystephenanthrine,26) 8-methoxyuvariopsine,25) thalihazine,27) and secophoebine.28) Furthermore, we have investigated their antimalarial activities against multidrug-resistant K1 strains of P. falciparum and their cytotoxicity against the small cell lung cancer (NCI-H187), breast cancer (MCF7), and human nasopharynx carcinoma (KB) cell lines.
Our approach to synthesizing the natural phenanthrene alkaloids uvariopsamine (1), noruvariopsamine (2), 8-hydroxystephenanthrine (3), 8-methoxyuvariopsine (4), thalihazine (5), and secophoebine (6) was based on the syntheses of the appropriate aporphine alkaloids (15) via palladium-catalyzed biaryl coupling of isoquinolines (13) under microwave irradiation followed by Hofmann degradation of the parent aporphine alkaloid precursors (Charts 1 and 2). Initially, conversion of known aldehydes (7)29,30) using a conventional method gave the acids (8).31) 6-Bromo-2,3-dimethoxyphenylacetic acid (8a)29) and 2-benzyloxy-6-bromophenylacetic acid (8b) were reacted with thionyl chloride to afford the corresponding acid chlorides, which were condensed with 3,4-dimethoxyphenethylamine (9a)32) and 3,4-methylenedioxyphenethylamine (9b)32) to give acetamides 10a and 10b, respectively. Acetamides (10) were converted into tetrahydroisoquinolines (12) via Bischler–Napieralski cyclization followed by imine reduction. Subsequent treatment of 12a with methyl chloroformate gave 13a, and treatment of 12b with formic acid in the presence of N,N′-dicyclohexylcarbodiimide (DCC) provided 13b. Next, the palladium-catalyzed coupling reaction under microwave irradiation of isoquinolines (13) afforded the expected aporphines (14) in reasonable yields. Finally, LiAlH4 reduction of the carbomethoxy group in 14a and the formyl group in 14b provided 1,2,8,9-tetramethoxyaporphine (15a) and 15b′, respectively. After, the benzyl group in 15b′ was deprotected under an acid condition to obtain 8-benzyloxy-1,2-methylenedioxyaporphine (fibrecisine, 15b) (Chart 1).
The total syntheses of 1, 2, and 3 were accomplished in a two-step sequence from aporphines 15a and 15b. However, 4, 5, and 6 were synthesized with crebanine (15c) and phobine (15d) as precursors. Both crebanine and phobine were prepared as described in a previous report.23) Aporphines 15a, 15b, 15c, and 15d were treated with methyl chloroformate in the presence of triethylamine to afford the corresponding N-carbomethoxyphenanthrenes 16a, 16b, 16c, and 16d, respectively. Compound 16b was obtained as N,O-dicarbomethoxyphenanthrene, where both the amino and phenolic hydroxy groups reacted with excess methyl chloroformate. Phenanthrenes 16a, 16b, and 16d were obtained in excellent yields (75–99%), but 16c was obtained in only 45% yield under the same reaction conditions. LiAlH4 reduction was performed on the carbamate groups of 16a, 16b, 16c, and 16d to give uvariopsamine (1, 70%), 8-hydroxystephenanthrine (3, 77%), 8-methoxyuvariopsine (4, 99%), and thalihazine (5, 59%), respectively. With the same sequence, aporphines 15a and 15d were treated with trifluoroacetic anhydride to afford the N-trifluoroacetylphenanthrenes 16a′ (99%) and 16d′ (75%), which were then converted by basic hydrolysis to give noruvariopsamine (2, 67%) and secophoebine (6, 58%), respectively. The NMR spectral data of the synthetic phenanthrenes (1–6) were in good accordance with those previously reported for the natural phenanthrene alkaloids.24–28) The total syntheses of 1–6 in essence established the correctness of the structures previously assigned to these natural alkaloids based on spectroscopic analysis.
All the synthetic phenanthrenes (1–6) were evaluated for their in vitro antimalarial activity against the K1 multidrug-resistant strains of P. falciparum by the microculture radioisotope technique as reported previously.33) The IC50 values of all compounds and mefloquine and dihydroartemisinine as positive controls are summarized in Table 1. The results showed that all six phenanthrene alkaloids showed a significantly promising antiplasmodium property with IC50 values ranging 1.07–7.41 µM. Of these, 3 showed the strongest inhibition activity with an IC50 value of 1.07 µM, in good agreement with a previous report that phenanthrene alkaloids possess strong antimalarial activity.14) However, none of the phenanthrenes were relatively as effective as the reference drugs, namely, mefloquine (IC50 0.0319 µM) and dihyroartemisinin (IC50 0.00163 µM). The preliminary structure–activity relationship of the phenanthrene alkaloids has also been investigated. Comparison of the structures of uvariopsamine (1, IC50 6.77 µM) possessing 3,4-dimethoxy groups and 8-methoxyuvariopsine (4, IC50 6.79 µM) possessing a 3,4-methylenedioxy group as substituents revealed that both compounds showed no difference in activity. This suggests that the dimethoxy and methylenedioxy substituents at the C-3 and C-4 give an equally contributing factor to this activity. Interestingly, 3 in the presence of the hydroxy group at the C-8 showed significantly good activity (IC50 1.07 µM) compared to 4 of similar structure having dimethoxy groups at the C-7 and C-8. This result indicated that the hydroxy substitution at the C-8 played an important role in the enhancement of the antimalarial activity.
| Compounds | Antimalarial activity (IC50, µM) | Cytotoxicity (IC50, µM) | ||
|---|---|---|---|---|
| KB | MCF7 | NCI-H187 | ||
| Uvariopsamine (1) | 6.77 | 37.87 | NAb) | 35.46 |
| Noruvariopsamine (2) | 7.41 | 44.06 | NA | 37.36 |
| 8-Hydroxystephenanthrine (3) | 1.07 | 24.53 | 42.67 | NA |
| 8-Methoxyuvariopsine (4) | 6.79 | 13.75 | 28.49 | 42.61 |
| Thalihazine (5) | 5.92 | 38.29 | NA | 40.68 |
| Secophoebine (6) | 5.69 | 13.67 | 22.60 | 23.58 |
| Mefloquinea) | 0.0319 | — | — | — |
| Dihyroartemisinina) | 0.00163 | — | — | — |
| Ellipticinea) | 4.28 | — | 7.52 | |
| Doxorubicina) | 1.35 | 15.22 | 0.19 | |
| Tamoxifena) | — | 20.78 | — | |
a) Positive control. b) NA: not active.
An ideal antimalarial candidate should have low or no toxicity against human cell lines. Therefore, compounds 1–6 were further evaluated for their cytotoxicity against the human nasopharynx carcinoma (KB), breast cancer (MCF7), and small cell lung cancer (NCI-H187) cell lines by the 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay.34,35) Table 1 lists the IC50 values of 1–6 and reference standard drugs ellipticine, doxorubicin, and tamoxifen. Compounds 6 and 4 showed moderate activity against the KB cell line with IC50 values of 13.67 and 13.75 µM, respectively, while compounds 1, 2, 3, and 5 displayed weak activity with IC50 values ranging 24.53–44.06 µM. Compounds 6, 4, and 3 had low cytotoxicity against the MCF7 cell line with corresponding IC50 values of 22.60, 28.49, and 42.67 µM, whereas the remaining phenanthrenes have no activity against this cell line at the levels tested (IC50 > 50 µM). Finally, all phenanthrenes exhibited weak cytotoxic activities against the NCI-H187 cell line (IC50 23.58–42.61 µM), except 3, which did not show any cytotoxicity.
We have performed the first total syntheses of six phenanthrene alkaloids, namely, uvariopsamine (1), noruvariopsamine (2), 8-hydroxystephenanthrine (3), 8-methoxyuvariopsine (4), thalihazine (5), and secophoebine (6), and established the correctness of the structures previously assigned to these alkaloids based on spectroscopic analysis. We have also evaluated their in vitro antimalarial activity against the K1 stain of P. falciparum and in vitro cytotoxic bioactivity against three tumor cell lines. This study revealed that all phenanthrenes 1–6 had a strong antiplasmodial effect with IC50 values in the range of 1.07–7.41 µM with moderate to non-cytotoxicity. Particularly, 3 with 3,4-methylenedioxy and 8-hydroxy groups as substituents showed the strongest antimalarial activity with an IC50 value of 1.07 µM, and its C-8 aromatic hydroxy group was conceivably crucial for increasing this activity. Furthermore, compound 3 displayed weak or noncytotoxicity against the tested human cancer cell lines, suggesting that 3 has promising potential to be developed as a potent antimalarial drug.
Melting points were measured on a Kofler hot stage apparatus and are uncorrected. UV spectra were acquired on Hewlett Packard 8453 UV-vis-spectrometer. IR spectra were obtained on PerkinElmer, Inc., U.S.A. GX FT-IR spectrophotometer. 1H- and 13C-NMR experiments were recorded on a Bruker AVANCE 300 MHz spectrometer (at 300 MHz for 1H and 75 MHz for 13C) and TMS was used as an internal standard. High resolution mass spectra were obtained on a Micro TOF Brüker Daltonic mass spectrometer. Analytical TLC was performed on Merck precoated silica gel 60 F254 plates. Spots were detected under UV light at 254 nm and/or by spraying with a solution of 1% vanillin/0.1 M sulfuric acid in methanol (W/V) followed by heating. Purification of synthetic compounds was carried out using silica gel 60 (230–400 mesh, Merck, Germany) column chromatography. Reagents were obtained from commercial sources and were used without further purification.
ChemistryStarting materials (8a, 9a, and 9b) and alkaloids 15c–15d were synthesized according to literature procedures.23,29,32)
2-Benzyloxy-6-bromophenylacetic acid (8b): Compound 8b was prepared from 2-(benzyloxy)-6-bromobenzaldehyde (7b)30) using procedures reported previously.31) Compound 8b was obtained as a white solid, mp 112–115 °C. 1H-NMR (CDCl3) δ: 7.42–7.28 (5H, m, PhH), 7.19–7.09 (2H, m, ArH), 6.97 (1H, d, J = 7.8 Hz, ArH), 5.11 (2H, s, OCH2Ph), 3.83 (2H, s, CH2); 13C-NMR (CDCl3) δ: 172.3, 157.5, 136.5, 128.9, 128.4, 127.8, 127.0, 125.9, 124.7, 124.4, 110.9, 70.2, 35.5; High resolution electrospray ionization (HRESI)MS: m/z [M + Na]+ 342.9950 (Calcd for C15H13BrO3Na 342.9946).
2-(6-Bromo-2,3-dimethoxyphenyl)-N-(3,4-dimethoxyphenethyl)acetamide (10a): A mixture of thionyl chloride (13.30 g, 111.79 mmol) and 8a (12.33 g, 44.82 mmol) in benzene (70 mL) was refluxed for 1 h. Removal of the solvent under reduced pressure gave a residue which was dissolved in ethanol-free chloroform (150 mL) and added to a mixture of 9a (8.12 g, 44.82 mmol) in ethanol-free chloroform (35 mL) and 15% sodium hydrogen carbonate (150 mL). The mixture was stirred at room temperature for 2 h. The chloroform layer was washed with 10% sodium hydrogen carbonate (200 mL × 3), water (200 mL), 10% hydrochloric acid (200 mL × 3) and water (200 mL × 3), then dried over anhydrous sodium sulfate. Removal of the solvent under reduced pressure gave a residue which was recrystallized from ethanol to give 10a as a white solid (18.27 g, 93%), mp 132–134 °C. IR (CH2Cl2-film) cm−1: 3290, 2939, 1645, 1516, 1472, 1261, 1140, 1070, 1005, 937, 798; 1H-NMR (CDCl3) δ: 7.26 (1H, d, J = 8.7 Hz, ArH), 6.75 (1H, d, J = 8.7 Hz, ArH), 6.73 (1H, d, J = 8.4 Hz, ArH), 6.64 (1H, s, ArH), 6.63 (1H, d, J = 8.4 Hz, ArH), 5.52 (1H, br s, NH), 3.85 (6H, s, 2xOCH3), 3.84 (3H, s, OCH3), 3.79 (3H, s, OCH3), 3.75 (2H, s, CH2), 3.45 (2H, apparent q, J = 6.9 Hz, CH2), 2.70 (2H, t, J = 6.9 Hz, CH2); 13C-NMR (CDCl3) δ: 169.5, 152.2, 148.9, 148.4, 147.5, 131.4, 129.4, 127.8, 120.6, 115.7, 112.7, 111.9, 111.4, 60.8, 55.9, 55.8, 55.8, 40.9, 38.0, 35.1; HRESIMS: m/z [M + Na]+ 460.0732 (Calcd for C20H24BrNO5Na 460.0736).
2-(6-Bromo-2,3-dimethoxyphenyl)-N-(3,4-methylenedioxyphenethyl)acetamide (10b): Compound 10b was prepared by a similar procedure to 10a. White solid, yield 81%, mp 120–124 °C. IR (CH2Cl2-film) cm−1: 3401, 3293, 2917, 1645, 1444, 1247, 1038, 930, 731; 1H-NMR (CDCl3) δ: 7.40–7.30 (5H, m, PhH), 7.21 (1H, dd, J = 8.1, 0.9 Hz, ArH), 7.10 (1H, t, J = 8.1 Hz, ArH), 6.88 (1H, dd, J = 8.1, 0.9 Hz, ArH), 6.61 (1H, d, J = 7.8 Hz, ArH), 6.52 (1H, d, J = 1.8 Hz, ArH), 6.43 (1H, dd, J = 7.8, 1.8 Hz, ArH), 5.89 (2H, s, OCH2O), 5.43 (1H, br s, NH), 5.05 (2H, s, OCH2Ph), 3.83 (2H, s, CH2), 3.37 (2H, apparent q, J = 6.6 Hz, CH2), 2.59 (2H, t, J = 6.6 Hz, CH2); 13C-NMR (CDCl3) δ: 169.5, 157.4, 147.7, 146.0, 136.2, 132.6, 129.3, 128.7, 128.2, 127.1, 126.4, 125.5, 124.4, 121.5, 111.2, 109.0, 108.3, 100.8, 70.6, 40.8, 38.0, 35.2; HRESIMS: m/z [M + Na]+ 490.0636 (Calcd for C24H22BrNO4Na 490.0630).
The preparation of compounds 11, 12, 13, 14, 15a, and 15b′ were achieved according to procedures that had been previously reported.20)
1-(2-Bromo-5,6-dimethoxybenzyl)-6,7-dimethoxy-3,4-dihydroisoquinoline (11a): Pale-yellow solid, yield 94%, mp 130–134 °C. IR (CH2Cl2-film) cm−1: 2938, 1604, 1573, 1512, 1471, 1356, 1273, 1229, 1143, 1076, 1009, 859, 810, 596; 1H-NMR (CDCl3) δ: 7.27 (1H, d, J = 8.7 Hz, ArH), 7.12 (1H, s, ArH), 6.71 (1H, d, J = 8.7 Hz, ArH), 6.70 (1H, s, ArH), 4.24 (2H, s, ArCH2), 3.91 (3H, s, OCH3), 3.89 (3H, s, OCH3), 3.83 (3H, s, OCH3), 3.78 (3H, s, OCH3), 3.60 (2H, t, J = 7.2 Hz, CH2), 2.62 (2H, t, J = 7.2 Hz, CH2); 13C-NMR (CDCl3) δ: 164.0, 152.1, 150.6, 148.5, 147.4, 132.5, 131.6, 127.6, 122.2, 116.2, 111.9, 110.2, 108.7, 60.8, 56.2, 55.9, 55.8, 47.2, 37.4, 25.8; HRESIMS: m/z [M + H]+ 420.0810 (Calcd for C20H23BrNO4 420.0810).
1-(2-Benzyloxy-6-bromobenzyl)-6,7-methylenedioxy-3,4-dihydroisoquinoline (11b): Brown solid, yield 74%, mp 80–86 °C. IR (CH2Cl2-film) cm−1: 2935, 2895, 1571, 1484, 1445, 1375, 1265, 1239, 1038, 933, 864, 735, 697; 1H-NMR (CDCl3) δ: 7.30–7.25 (5H, m, PhH), 7.21 (1H, dd, J = 8.1, 0.9 Hz, ArH), 7.12 (1H, s, ArH), 7.06 (1H, t, J = 8.1 Hz, ArH), 6.86 (1H, dd, J = 8.1, 0.9 Hz, ArH), 6.65 (1H, s, ArH), 5.97 (2H, s, OCH2O), 5.06 (2H, s, OCH2Ph), 4.24 (2H, s, ArCH2), 3.52 (2H, t, J = 7.5 Hz, CH2), 2.50 (2H, t, J = 7.5 Hz, CH2); 13C-NMR (CDCl3) δ: 163.7, 157.6, 148.8, 146.3, 136.7, 133.2, 128.4, 127.7, 127.4, 126.9, 126.4, 125.1, 123.5, 111.1, 107.7, 105.6, 101.2, 70.4, 46.7, 36.7, 26.2; HRESIMS: m/z [M + H]+ 450.0708 (Calcd for C24H21BrNO3 450.0705).
1-(6-Bromo-2,3-dimethoxybenzyl)-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline (12a): Brown solid, yield 95%, mp 106–107 °C. IR (CH2Cl2-film) cm−1: 3329, 2937, 1610, 1572, 1513, 1468, 1412, 1263, 1225, 1110, 1078, 1010, 859, 798, 613; 1H-NMR (CDCl3) δ: 7.29 (1H, d, J = 8.7 Hz, ArH), 6.79 (1H, s, ArH), 6.73 (1H, d, J = 8.7 Hz, ArH), 6.59 (1H, s, ArH), 4.29 (1H, dd, J = 9.9, 3.6 Hz, H-1), 3.85 (6H, s, 2xOCH3), 3.82 (3H, s, OCH3), 3.80 (3H, s, OCH3), 3.38–2.64 (6H, 4m, 3xCH2), 2.18 (1H, br s, NH); 13C-NMR (CDCl3) δ: 152.2, 148.6, 147.5, 147.0, 133.4, 130.8, 127.8, 127.2, 115.8, 111.9, 111.7, 110.0, 60.5, 55.8, 55.1, 39.4, 37.1, 29.3; HRESIMS: m/z [M + H]+ 422.0960 (Calcd for C20H25BrNO4 422.0967).
1-(2-Benzyloxy-6-bromobenzyl)-6,7-methylenedioxy-1,2,3,4-tetrahydroisoquinoline (12b): Yellow semisolid, yield 96%. IR (CH2Cl2-film) cm−1: 2924, 1588, 1569, 1483, 1445, 1263, 1038, 934, 865, 737, 698; 1H-NMR (CDCl3) δ: 7.43–7.33 (5H, m, PhH), 7.22 (1H, d, J = 8.1 Hz, ArH), 7.07 (1H, t, J = 8.1 Hz, ArH), 6.91 (1H, d, J = 8.1 Hz, ArH), 6.61 (1H, s, ArH), 6.51 (1H, s, ArH), 5.88 (2H, s, OCH2O), 5.06 (2H, d, J = 3.9 Hz, OCH2Ph), 4.28 (1H, dd, J = 10.5, 3.0 Hz, H-1), 3.39–3.10 and 2.83–2.48 (6H, 4m, 3xCH2), 2.25 (1H, br s, NH); 13C-NMR (CDCl3) δ: 158.1, 146.1, 145.8, 136.5, 131.3, 128.8, 128.5, 128.4, 128.0, 127.8, 127.1, 126.3, 125.4, 110.9, 108.6, 107.0, 100.7, 70.8, 55.2, 39.2, 36.9, 29.4; HRESIMS: m/z [M + H]+ 452.0866 (Calcd for C24H23BrNO3 452.0861).
1-(6-Bromo-2,3-dimethoxybenzyl)-2-carbomethoxy-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline (13a): White solid, yield 87%, mp 107–110 °C. IR (CH2Cl2-film) cm−1: 2943, 1698, 1611, 1574, 1519, 1469, 1448, 1413, 1361, 1258, 1225, 1103, 1077, 1012, 857, 797, 611; 1H-NMR (CDCl3) :δ 7.24 (1H, d, J = 8.7 Hz, ArH), 6.70 (1H, d, J = 8.7 Hz, ArH), 6.67 (1H, s, ArH), 6.62 (1H, s, ArH), 5.61–5.57 and 5.49–5.44 (total 1H, 2m, H-1 of both conformers), 4.30–4.25 and 4.10–4.05 (total 1H, 2m, H-3α of both conformers), 3.86 (3H, s, OCH3), 3.84 (3H, s, OCH3), 3.81 (3H, s, OCH3), 3.79 (3H, s, OCH3), 3.58 and 3.30 (total 3H, 2s, CO2CH3 of both conformers), 3.66–2.69 (5H, m, H-3β, 2xCH2); 13C-NMR (CDCl3) δ: 155.8, 152.0, 148.8, 147.9, 147.3, 132.2, 128.6, 127.1, 126.4, 116.1, 112.2, 111.5, 109.8, 60.5, 55.9, 55.8, 53.7, 52.0, 37.8, 28.1; HRESIMS: m/z [M + H]+ 480.1025 (Calcd for C22H27BrNO6 480.1022).
1-(2-Benzyloxy-6-bromobenzyl)-2-formyl-6,7-methylenedioxy-1,2,3,4-tetrahydroisoquinoline (13b): Yellow solid, yield 70%, mp 98–100 °C. IR (CH2Cl2-film) cm−1: 2927, 2881, 1670, 1569, 1483, 1444, 1263, 1217, 1037, 935, 736, 699; 1H-NMR (CDCl3) δ: 7.91 and 7.89 (total 1H, 2s, CHO of 2 conformers), 7.46–7.37 (5H, m, PhH), 7.22 (1H, dd, J = 8.1, 0.9 Hz, ArH), 7.11 (1H, t, J = 8.1 Hz, ArH), 6.92 (1H, br d, J = 8.1 Hz, ArH), 6.65 (1H, s, ArH), 6.54 (1H, s, ArH), 5.92 (2H, s, OCH2O), 5.04 (2H, s, OCH2Ph), 4.71 (1H, dd, J = 10.8, 2.4 Hz, H-1), 4.24–4.18 (1H, m, H-3α), 3.49–2.55 (5H, m, H-3β, 2xCH2); 13C-NMR (CDCl3) δ: 160.5, 157.9, 146.6, 146.2, 136.0, 129.1, 128.8, 128.6, 128.4, 128.1, 127.2, 126.0, 125.9, 125.2, 110.7, 108.4, 106.5, 100.9, 70.8, 56.4, 37.0, 34.7, 28.1; HRESIMS: m/z [M + H]+ 480.0806 (Calcd for C25H23BrNO4 480.0810).
Methyl 1,2-dimethoxy-8,9-methylenedioxynoraporphine-6-carboxylate (14a): White solid, yield 43%, mp 203–204 °C. IR (CH2Cl2-film) cm−1: 2939, 1698, 1594, 1492, 1447, 1404, 1355, 1248, 1200, 1085, 1023, 958, 807; 1H-NMR (CDCl3) δ: 8.20 (1H, d, J = 8.7 Hz, H-11), 6.90 (1H, d, J = 8.7 Hz, H-10), 6.64 (1H, s, H-3), 4.64 (1H, m, H-6a), 4.47 (1H, m, H-5α), 3.93 (3H, s, OCH3), 3.89 (3H, s, OCH3), 3.85 (3H, s, OCH3), 3.76 (1H, s, OCH3), 3.65 (3H, s, CO2CH3), 3.43 (1H, m, H-5β), 3.05–2.44 (4H, m, 2xCH2); 13C-NMR (CDCl3) δ: 156.0, 152.1, 152.0, 145.6, 145.2, 131.4, 129.5, 127.7, 125.6, 125.1, 124.9, 110.8, 110.1, 60.7, 59.9, 55.9, 55.6, 52.6, 51.6, 38.9, 30.2, 28.1; HRESIMS: m/z [M + H]+ 400.1757 (Calcd for C22H26NO6 400.1760).
6-Formyl-8-benzyloxy-1,2-methylenedioxynoraporphine (14b): Pale-brown solid, yield 75%, mp 176–177 °C. IR (CH2Cl2-film) cm−1: 2917, 1666, 1575, 1478, 1419, 1238, 1040, 941, 790, 735, 697; 1H-NMR (CDCl3) δ: 8.35 and 8.26 (total 1H, 2s, CHO of both conformers), 7.77–7.73 (total 1H, m, H-11 of both conformers), 7.46–7.22 (total 6H, m, H-10 of both conformers, PhH of both conformers), 6.93 and 6.89 (total 1H, d, J = 8.1 Hz, H-9 of both conformers), 6.59 and 6.56 (total 1H, 2s, H-3 of both conformers), 6.06 and 5.64 (total 2H, 2s, OCH2O of both conformers), 5.10 (2H, s, OCH2Ph of both conformers), 5.06–2.38 (total 7H, m, H-6a, 3xCH2 of both conformers); 13C-NMR (CDCl3) δ: (both conformers) 162.2, 162.1, 155.9, 155.5, 147.3, 147.0, 143.3, 137.2, 136.8, 131.8, 131.6, 128.7, 128.5, 128.1, 127.8, 127.7, 127.4, 127.3, 127.2, 126.4, 124.7, 124.3, 124.1, 123.5, 120.1, 119.9, 117.5, 117.1, 111.7, 111.6, 107.9, 107.6, 101.0, 100.9, 70.4, 70.3, 53.1, 49.2, 42.1, 36.1, 31.0, 30.0, 29.7, 26.2; HRESIMS: m/z [M + H]+ 400.1552 (Calcd for C25H22NO4 400.1549).
1,2,8,9-Tetramethoxyaporphine (15a): Yellow-brown semisolid, yield 92%. IR (CH2Cl2-film) cm−1: 2930, 1594, 1494, 1372, 1280, 1082, 1006, 816, 707; 1H-NMR (CDCl3) δ: 8.12 (1H, d, J = 9.0 Hz, H-11), 6.87 (1H, d, J = 9.0 Hz, H-10), 6.59 (1H, s, H-3), 3.91 (3H, s, OCH3), 3.87 (3H, s, OCH3), 3.82 (3H, s, OCH3), 3.65 (3H, s, OCH3), 3.64–2.16 (7H, m, H-6a, 3xCH2), 2.57 (3H, s, NCH3); 13C-NMR (CDCl3) δ: 151.9, 151.7, 145.3, 144.7, 130.8, 128.6, 127.3, 126.9, 125.5, 124.6, 110.6, 110.1, 62.2, 60.7, 60.0, 55.8, 55.6, 53.3, 44.0, 29.2, 27.0; HRESIMS: m/z [M + H]+ 356.1860 (Calcd for C21H26NO4 356.1862).
8-Benzyloxy-1,2-methylenedioxyaporphine (15b′): Yellow viscous oil, yield 76%. IR (CH2Cl2-film) cm−1: 2917, 2849, 2787, 1578, 1449, 1256, 1224, 1045, 942, 788, 735, 696; 1H-NMR (CDCl3) δ: 7.72 (1H, d, J = 8.1 Hz, ArH), 7.42–7.29 (5H, m, PhH), 7.22 (1H, t, J = 8.1 Hz, ArH), 6.86 (1H, d, J = 8.1 Hz, ArH), 6.52 (1H, s, H-3), 6.00 and 5.85 (2H, 2s, OCH2O), 5.09 (2H, s, OCH2Ph), 3.77 (1H, dd, J = 15.0, 4.2 Hz, H-6a), 3.17–2.21 (6H, m, 3xCH2), 2.52 (3H, s, NCH3); 13C-NMR (CDCl3) δ: 155.4, 146.6, 142.7, 137.3, 132.3, 128.5, 127.8, 127.1, 126.4, 124.4, 119.9, 116.5, 111.7, 107.5, 100.6, 70.5, 61.7, 53.5, 43.8, 29.0, 26.2; HRESIMS: m/z [M + H]+ 386.1763 (Calcd for C25H24NO3 386.1756).
8-Hydroxy-1,2-methylenedioxyaporphine (15b): A mixture of 15b′ (0.16 g, 0.42 mmol) and conc. hydrochloric acid (8 mL) in ethanol (8 mL) was refluxed for 1.5 h. The mixture was cooled to room temperature and the solvent was removed under reduced pressure. The residue was diluted with water (15 mL) and was basified with conc. ammonia solution. The residue was extracted with chloroform (10 mL ×3). The combined chloroform layer was dried over anhydrous sodium sulfate. Removal of the solvent under reduced pressure gave 15b as a brown amorphous solid (0.11 g, 89%). IR (CH2Cl2-film) cm−1: 3412, 2911, 2846, 1641, 1577, 1454, 1260, 1225, 1059, 927, 793; 1H-NMR (CH3OD) δ: 7.63 (1H, d, J = 7.8 Hz, H-11), 7.15 (1H, t, J = 7.8 Hz, H-10), 6.80 (1H, d, J = 7.8 Hz, H-9), 6.56 (1H, s, H-3), 6.07 and 5.92 (2H, 2s, OCH2O), 3.65 (1H, dd, J = 14.7, 4.8 Hz, H-6a), 3.23–3.07 and 2.70–2.21 (6H, m, 3xCH2), 2.60 (3H, s, NCH3); 13C-NMR (CH3OD) δ: 153.7, 147.0, 142.9, 132.1, 127.3, 126.4, 126.0, 121.6, 118.9, 117.0, 114.9, 107.5, 100.8, 62.0, 53.6, 43.5, 28.6, 25.9; HRESIMS: m/z [M + H]+ 296.1290 (Calcd for C18H18NO3 296.1286).
1-(N-Carbomethoxy-N-methylamino)ethyl-3,4,7,8-tetramethoxyphenanthrene (16a): To a stirred mixture of 15a (0.08 g, 0.22 mmol) and triethylamine (0.18 mL, 1.30 mmol) in dichloromethane (5 mL) at 0 °C was added dropwise methyl chloroformate (0.20 mL, 2.60 mmol). After being stirred at room temperature for 2 h, the reaction mixture was diluted with dichloromethane (10 mL) and water (20 mL). The organic layer was respectively washed with 5% sodium carbonate (20 mL), 10% hydrochloric acid (20 mL), water (20 mL), and brine then dried over anhydrous sodium sulfate. Removal of the solvent under reduced pressure gave the crude product which was purified by silica gel column chromatography using ethyl acetate-hexane (1 : 1) as an eluent. The product 16a was obtained in 89.34 mg (96% yield) as a pale brown solid, mp 115–116 °C. IR (CH2Cl2-film) cm−1: 2940, 1699, 1593, 1470, 1280, 1201, 1104, 1019, 822, 772; 1H-NMR (CDCl3) δ: 9.46 (1H, d, J = 9.6 Hz, H-5), 8.07–7.92 (1H, m, H-10 of both conformers), 8.04 (1H, s, H-2), 7.35 (1H, d, J = 9.6 Hz, H-6), 7.16 (1H, br d, H-9), 4.05, 4.04 and 4.02 (9H, 3s, 3xOCH3), 3.92 (3H, s, OCH3), 3.77 and 3.72 (3H, 2br s, CO2CH3), 3.59 (2H, br s, CH2), 3.32 (2H, br s, CH2), 2.95 and 2.87 (3H, 2br s, NCH3); 13C-NMR (CDCl3) δ: (both conformers) 156.8, 150.9, 149.6, 145.6, 143.0, 131.9, 128.4, 125.3, 125.1, 124.8, 124.6, 122.9, 122.7, 118.8, 114.2, 112.7, 61.1, 59.6, 56.4, 56.1, 52.5, 50.9, 50.0, 35.1, 34.8, 32.7, 32.0; HRESIMS: m/z [M + H]+ 414.1923 (Calcd for C23H28NO6 414.1916).
1-(N-Carbomethoxy-N-methylamino)ethyl-8-O-carbomethoxy-3,4-methylenedioxyphenanthrene (16b): Compound 16b was prepared from 15b according to a similar procedure to 16a. Brown solid, yield 82%, mp 147–149 °C. IR (CH2Cl2-film) cm−1: 2956, 2893, 1764, 1701, 1597, 1450, 1263, 1235, 1052, 940, 769; 1H-NMR (CDCl3) δ: 8.91 (1H, d, J = 8.1 Hz, H-5), 8.02–7.72 (2H, m, H-2 and H-10), 7.54 (1H, t, J = 8.1 Hz, H-6), 7.42 (1H, d, J = 8.1 Hz, H-7), 7.02 (1H, br d, H-9), 6.12 (2H, s, OCH2O), 3.97 (3H, s, OCO2CH3), 3.72 and 3.68 (3H, 2br s, CO2CH3), 3.43 (2H, br s, CH2), 3.16 (2H, br s, CH2), 2.86 and 2.77 (3H, 2br s, NCH3); 13C-NMR (CDCl3) δ: (both conformers) 156.8, 154.5, 146.7, 145.3, 142.3, 130.0, 125.9, 125.5, 124.8, 123.8, 123.5, 118.9, 117.2, 116.5, 111.1, 101.2, 55.6, 52.6, 51.1, 50.2, 35.2, 34.9, 32.3, 31.8; HRESIMS: m/z [M + H]+ 412.1388 (Calcd for C22H22NO7 412.1396).
1-(N-Carbomethoxy-N-methylamino)ethyl-7,8-dimethoxy-3,4-methylenedioxyphenanthrene (16c): Compound 16c was prepared from 15c according to a similar procedure to 16a. Off-white solid, yield 45%, mp 119–120 °C. IR (CH2Cl2-film) cm−1: 2954, 1701, 1594, 1475, 1376, 1278, 1205, 1062, 1034, 988, 817, 771; 1H-NMR (CDCl3) δ: 8.82 (1H, d, J = 9.3 Hz, H-5), 7.98 (1H, s, H-2), 7.96 and 7.86 (total 1H, 2br d, H-10 of both conformers), 7.29 (1H, d, J = 9.3 Hz, H-6), 7.06 (1H, br d, Hz, H-9), 6.21 (2H, s, OCH2O), 4.02 and 4.01 (6H, 2s, 2xOCH3), 3.74 (3H, s, CO2CH3), 3.52 (2H, br s, CH2), 3.26 (2H, br s, CH2), 2.92 and 2.82 (3H, 2br s, NCH3); 13C-NMR (CDCl3) δ: (both conformers) 156.9, 150.0, 145.0, 143.3, 142.0, 129.9, 129.7, 127.5, 125.4, 123.8, 123.6, 123.2, 122.9, 118.7, 117.1, 112.7, 110.1, 101.0, 61.3, 56.3, 52.7, 51.3, 50.4, 35.3, 35.0, 32.6, 32.0; HRESIMS: m/z [M + H]+ 398.1598 (Calcd for C22H24NO6 398.1603).
1-(N-Carbomethoxy-N-methylamino)ethyl-2,3,4-trimethoxy-6,7-methylenedioxyphenanthrene (16d): Compound 16d was prepared from 15d according to a similar procedure to 16a. Pale-yellow solid, yield 96%, mp 143–144 °C. IR (CH2Cl2-film) cm−1: 2937, 1704, 1586, 1464, 1401, 1242, 1205, 1143, 1087, 1058, 1039, 979, 879, 771; 1H-NMR (CDCl3) δ: 9.05 (1H, s, H-5), 7.99 and 7.81 (total 1H, 2br d, H-10 of both conformers), 7.60 (1H, d, J = 9.3 Hz, H-9), 7.19 (1H, s, H-8), 6.08 (2H, s, OCH2O), 4.06 (3H, s, OCH3), 4.00 (3H, s, OCH3), 3.96 (3H, s, OCH3), 3.74 (3H, s, CO2CH3), 3.46 (2H, m, CH2), 3.33 (2H, m, CH2), 2.96 (3H, br s, NCH3); 13C-NMR (CDCl3) δ: (both conformers) 156.9, 150.7, 150.4, 147.9, 146.7, 145.7, 128.7, 128.1, 126.8, 125.8, 123.2, 121.8, 120.9, 120.6, 105.6, 105.4, 101.2, 61.4, 61.2, 60.3, 52.6, 50.2, 49.4, 35.1, 24.7, 24.3; HRESIMS: m/z [M + H]+ 428.1716 (Calcd for C23H26NO7 428.1709).
1-(N-Trifluoroacetyl-N-methylamino)ethyl-3,4,7,8-tetramethoxyphenanthrene (16a'): To a stirred solution of 15a (0.40 g, 1.12 mmol) and triethylamine (0.94 mL, 6.75 mmol) in dichloromethane (15 mL) at 0 °C, was added dropwise trifluoroacetic anhydride (1.06 mL, 7.62 mmol). The mixture was allowed to stir at room temperature for 2 h and was diluted with dichloromethane (30 mL). The organic layer was washed with 10% sodium hydrogen carbonate (30 mL × 3), water (30 mL × 3), 10% hydrochloric acid (30 mL × 3), brine and then dried over anhydrous sodium sulfate. The solvent was removed under reduced pressure to give a crude product which was recrystallized from ethanol to give 16a′ as a brown semisolid (0.50 g, 99%). IR (CH2Cl2-film) cm−1: 2942, 1686, 1575, 1470, 1280, 1196, 1139, 1019, 800, 721; 1H-NMR (CDCl3) δ: 9.44 (1H, d, J = 9.6 Hz, H-5), 8.05 (1H, d, J = 9.3 Hz, H-10), 7.92 (1H, d, J = 9.3 Hz, H-9), 7.33 (1H, d, J = 9.6 Hz, H-6), 7.12 (1H, s, H-2), 4.02 and 4.00 (9H, 2s, 3xOCH3), 3.90 (3H, s, OCH3), 3.72 (2H, t, J = 7.8 Hz, CH2), 3.36 (2H, t, J = 7.8 Hz, CH2), 3.09 and 2.91 (3H, 2s, NCH3); 13C-NMR (CDCl3) δ: (both conformers) 157.1, 156.7, 151.0, 149.8, 145.9, 143.1, 130.9, 128.4, 125.3, 125.2, 124.8, 124.7, 122.5, 121.9, 119.4, 119.3, 114.6, 112.9, 61.2, 59.7, 56.4, 56.2, 51.5, 36.1, 35.2, 33.1, 30.9; HRESIMS: m/z [M + H]+ 452.1691 (Calcd for C23H25F3NO5 452.1685).
1-(N-Trifluoroacetyl-N-methylamino)ethyl-2,3,4-trimethoxy-6,7-methylenedioxyphenanthrene (16d'): Compound 16d′ was prepared from 15d according to a similar procedure to 16a′. Pale yellow crystals, yield 75%, mp 108–109 °C. IR (CH2Cl2-film) cm−1: 2939, 1693, 1586, 1503, 1464, 1401, 1243, 1192, 1141, 1097, 1057, 979, 855, 649; 1H-NMR (CDCl3) δ: 9.04 (1H, s, H-5), 7.91 (1H, d, J = 9.3 Hz, H-10), 7.60 (1H, d, J = 9.3 Hz, H-9), 7.17 (1H, s, H-8), 6.07 (2H, s, OCH2O), 4.05 (3H, s, OCH3), 4.02 and 4.01 (3H, 2s, OCH3), 3.96 (3H, s, OCH3), 3.66–3.61 (2H, m, CH2), 3.40–3.35 (2H, m, CH2), 3.15 and 3.09 (3H, 2br s, NCH3); 13C-NMR (CDCl3) δ: (both conformers) 157.2, 156.8, 151.3, 151.1, 150.5, 150.4, 148.2, 148.0, 146.9, 146.8, 145.7, 145.7, 128.8, 128.6, 128.1, 127.7, 127.2, 127.2, 125.5, 125.8, 122.2, 121.9, 121.3, 120.6, 119.7, 118.6, 118.5, 114.8, 114.7, 105.6, 105.4, 105.4, 101.3, 101.3, 61.4, 61.2, 60.3, 50.7, 35.6, 35.1, 25.3, 23.2; HRESIMS: m/z [M + H]+ 466.1470 (Calcd for C23H23F3NO6 466.1477).
Uvariopsamine (1): A mixture of 16a (0.20 g, 0.48 mmol) and lithium aluminium hydride (0.17 g, 4.35 mmol) in dry THF (40 mL) was refluxed for 1 h. The reaction mixture was allowed to cool to room temperature and was quenched with water (20 mL). To the mixture was added 10% ammonium hydroxide solution (10 mL) and the residue was filtered. The organic layer was separated and dried over anhydrous sodium sulfate and concentrated in vacuo. The crude product was purified by a silica gel column using ethyl acetate as an eluent to furnish pure 1 as a yellow viscous oil (0.12 g, 70%). UV (MeOH) λmax/nm (log ε) 225.7 (4.00), 264.3 (4.19), 271.74 (4.18), 291.8 (3.82), 307.6 (3.65), 319.9 (3.63), 348.9 (2.99), 366.7 (2.92); IR (CH2Cl2-film) cm−1: 2939, 1592, 1469, 1279, 1104, 1019, 822; 1H-NMR (CDCl3) δ: 9.43 (1H, d, J = 9.3 Hz, H-5), 8.00 (1H, d, J = 9.6 Hz, H-10), 7.86 (1H, d, J = 9.6 Hz, H-9), 7.31 (1H, d, J = 9.3 Hz, H-6), 7.16 (1H, s, H-2), 4.01 (6H, 2s, 2xOCH3), 4.00 (3H, s, OCH3), 3.89 (3H, s, OCH3), 3.25 (2H, t, J = 8.4 Hz, CH2), 2.66 (2H, t, J = 8.4 Hz, CH2), 2.38 (6H, s, N(CH3)2); 13C-NMR (CDCl3) δ: 150.9, 149.6, 145.3, 143.0, 133.3, 128.4, 125.2, 125.2, 124.9, 124.7, 123.0, 118.7, 114.0, 112.7, 61.2, 61.1, 59.6, 56.5, 56.2, 45.5, 32.5; HRESIMS: m/z [M + H]+ 370.2018 (Calcd for C22H28NO4 370.2018).
Noruvariopsamine (2): To a stirred solution of 15a′ (51.0 mg, 0.11 mmol) in MeOH-H2O (9 : 1, 10 mL) was added sodium carbonate (22.6 mg, 0.23 mmol). The reaction mixture was refluxed for 2 h. After cooling down to room temperature, the solvent was removed and the residue was diluted with water (10 mL), 10% sodium carbonate (10 mL) and extracted with dichloromethane (10 mL × 3). The combined organic layer was dried over anhydrous sodium sulfate and concentrated under reduced pressure. The resultant crude product was loaded onto a silica gel column and eluted with EtOAc to furnish 2 as a pale-yellow semisolid (26.9 mg, 67%). UV (MeOH) λmax/nm (log ε) 225.7 (4.47), 264.4 (4.72), 271.2 (4.71), 291.5 (4.27), 307.0 (4.08), 319.9 (4.08), 349.2 (2.64), 366.4 (1.51); IR (CH2Cl2-film) cm−1: 2938, 1593, 1470, 1374, 1279, 1230, 1103, 1018, 823, 797; 1H-NMR (CDCl3) δ: 9.45 (1H, d, J = 9.0 Hz, H-5), 8.00 (1H, d, J = 9.3 Hz, H-10), 7.88 (1H, d, J = 9.3 Hz, H-9), 7.32 (1H, d, J = 9.0 Hz, H-6), 7.18 (1H, s, H-2), 4.02 (9H, s, 3xOCH3), 3.90 (3H, s, OCH3), 3.27 (2H, t, J = 6.6 Hz, CH2), 2.96 (2H, t, J = 6.6 Hz, CH2), 2.46 (3H, s, NCH3); 13C-NMR (CDCl3) δ: 150.8, 149.6, 145.3, 143.0, 133.0, 128.4, 125.2, 125.2, 124.9, 124.7, 123.0, 118.6, 114.1, 112.7, 61.2, 59.6, 56.5, 56.1, 53.0, 36.5, 34.4; HRESIMS: m/z [M + H]+ 356.1862 (Calcd for C21H26NO4 356.1862).
8-Hydroxystephenanthrine (3): Compound 3 was prepared from 16b according to a similar procedure to 1. Pale-brown solid, yield 77%, mp 189–190 °C. UV (MeOH) λmax/nm (log ε) 218.1 (4.35), 240.9 (4.40), 248.1 (4.48), 254.8 (4.59), 298.1 (4.14), 315.6 (3.99), 327.8 (4.02), 356.6 (3.55), 375.2 (3.58); IR (CH2Cl2-film) cm−1: 3400, 2923, 2854, 1592, 1441, 1365, 1283, 1045, 936, 806, 754; 1H-NMR (CDCl3) δ: 8.61 (1H, d, J = 7.8 Hz, H-5), 8.07 (1H, d, J = 9.3 Hz, H-10), 7.78 (1H, d, J = 9.3 Hz, H-9), 7.42 (1H, t, J = 7.8 Hz, H-6), 7.11 (1H, s, H-2), 7.02 (1H, d, J = 7.8 Hz, H-7), 6.20 (2H, s, OCH2O), 3.25 (2H, t, J = 8.4 Hz, CH2), 2.70 (2H, t, J = 8.4 Hz, CH2), 2.44 (6H, s, NCH3); 13C-NMR (CDCl3) δ: 152.7, 144.7, 142.3, 129.9, 129.7, 126.5, 126.2, 122.0, 121.0, 119.0, 118.7, 117.1, 110.9, 110.5, 100.9, 60.5, 44.8, 31.1; HRESIMS: m/z [M + H]+ 310.1143 (Calcd for C19H20NO3 310.1143).
8-Methoxyuvariopsine (4): Compound 4 was prepared from 16c according to a similar procedure to 1. Brown solid, yield 99%, mp 93–94 °C. UV (MeOH) λmax/nm (log ε) 226.1 (4.41), 259.9 (4.55), 276.3 (4.48), 296.7 (4.27), 330.0 (4.01), 354.4 (3.38), 372.5 (3.02); IR (CH2Cl2-film) cm−1: 2941, 1594, 1474, 1447, 1375, 1278, 1191, 1063, 1036, 988, 817, 745; 1H-NMR (CDCl3) δ: 8.78 (1H, d, J = 9.0 Hz, H-5), 7.92 (1H, d, J = 9.3 Hz, H-10), 7.82 (1H, d, J = 9.3 Hz, H-9), 7.25 (1H, d, J = 9.0 Hz, H-6), 7.05 (1H, s, H-2), 6.16 (2H, s, OCH2O), 3.99 and 3.98 (6H, 2s, 2xOCH3), 3.18 (2H, t, J = 8.4 Hz, CH2), 2.60 (2H, t, J = 8.4 Hz, CH2), 2.35 (6H, s, N(CH3)2); 13C-NMR (CDCl3) δ: 149.9, 145.0, 143.2, 141.6, 131.1, 127.3, 125.0, 123.7, 123.2, 121.9, 118.4, 117.0, 112.6, 111.0, 109.9, 100.9, 61.2, 61.1, 56.2, 45.4, 32.0; HRESIMS: m/z [M + H]+ 354.1708 (Calcd for C21H24NO4 354.1705).
Thalihazine (5): Compound 5 was prepared from 16d according to a similar procedure to 1. Pale-yellow semisolid, yield 59%. UV (MeOH) λmax/nm (log ε) 220.1 (4.27), 261.8 (4.88), 284.1 (4.37), 303.0 (4.01), 315.1 (3.96), 343.5 (3.46), 360.7 (3.49); IR (CH2Cl2-film) cm−1: 2937, 1586, 1463, 1400, 1243, 1204, 1086, 1041, 980, 856, 646; 1H-NMR (CDCl3) δ: 9.06 (1H, s, H-5), 7.78 (1H, d, J = 9.0 Hz, H-10), 7.57 (1H, d, J = 9.0 Hz, H-9), 7.19 (1H, s, H-8), 6.09 (2H, s, OCH2O), 4.06 (3H, s, OCH3), 3.99 (3H, s, OCH3), 3.96 (3H, s, OCH3), 3.31–3.25 (2H, m, CH2), 2.58–2.54 (2H, m, CH2), 2.41 (6H, s, N(CH3)2); 13C-NMR (CDCl3) δ: 150.5, 150.1, 147.9, 146.7, 145.8, 128.7, 127.8, 126.7, 125.8, 124.2, 121.9, 120.8, 105.7, 105.3, 101.2, 61.5, 61.1, 60.3, 60.0, 45.2, 24.3; HRESIMS: m/z [M + H]+ 384.1812 (Calcd for C22H25NO5 384.1811).
Secophoebine (6): Compound 6 was prepared from 16d′ according to a similar procedure to 2. Pale-yellow semisolid, yield 58%. UV (MeOH) λmax/nm (log ε) 219.5 (4.32), 261.9 (4.85), 283.8 (4.40), 304.2 (4.05), 315.4 (4.00), 344.9 (3.56), 361.3 (3.59); IR (CH2Cl2-film) cm−1: 3323, 2935, 1586, 1463, 1399, 1242, 1203, 1086, 1039, 979, 880, 647; 1H-NMR (CDCl3) δ: 9.06 (1H, s, H-5), 7.79 (1H, d, J = 9.0 Hz, H-10), 7.52 (1H, d, J = 9.0 Hz, H-9), 7.14 (1H, s, H-8), 6.04 (2H, s, OCH2O), 4.05 (3H, s, OCH3), 3.98 (3H, s, OCH3), 3.95 (3H, s, OCH3), 3.29 (2H, t, J = 7.8 Hz, CH2), 2.87 (2H, t, J = 7.8 Hz, CH2), 2.49 (3H, s, NCH3), 1.89 (1H, br s, NH); 13C-NMR (CDCl3) δ: 150.5, 150.3, 147.9, 146.6, 145.8, 128.6, 127.9, 126.5, 125.8, 124.4, 121.8, 120.9, 105.6, 105.3, 101.2, 61.3, 61.1, 60.2, 52.7, 36.4, 26.5; HRESIMS: m/z [M + H]+ 370.1655 (Calcd for C21H24NO5 370.1654).
Antimalarial BioassayIn vitro antiplasmodial screening of all samples was performed at the National Center for Genetic Engineering and Biotechnology (BIOTECH), Thailand. All compounds were evaluated against the multidrug-resistant K1 strain of P. falciparum by the microculture radioisotope technique according to Desjardins et al.33) Antimalarial activity was expressed as IC50, defined as the concentration of each compound that can inhibit 50% of parasite growth. Two antimalarial drugs mefloquine and dihydroartemisinine were used as positive controls with IC50 values of 0.0319 and 0.00163 µM, respectively.
Cytotoxicity BioassayIn vitro cytotoxic evaluation was performed at BIOTECH, Thailand. All synthetic compounds were tested for human tumor cell growth inhibitory activity against the KB human nasopharynx carcinoma, MCF7 breast cancer, and NCI-H187 small cell lung cancer cell lines. The NCI-H187 (ATCC CRL-5804) was determined by the MTT assay as described previously by Plum et al.34) The MCF7 (ATCC HTB-22) and KB (ATCC CCL-17) were determined by a colorimetric cytotoxicity assay reported by Skehan et al.35) Ellipticine, doxorubicin, and tamoxifen were used as positive controls.
The work was supported by the Faculty of Science, Silpakorn University, Nakhon Pathom, Thailand (Grant No. SRF-JRG-2564-08) and Silpakorn University through the National Research Council of Thailand (Grant No. SURIC 62/02/36).
The authors declare no conflict of interest.
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