HETEROCYCLES

Paper | Special issue | Vol. 79, No. 1, 2009, pp. 753-764
Received, 29th September, 2008, Accepted, 27th October, 2008, Published online, 31st October, 2008.
DOI: 10.3987/COM-08-S(D)40

■ Synthetic Studies on Natural Isocoumarins and Isocarbostyril Derivatives Having an Alkyl Substituent at the 3-Position: Total Synthesis of Scoparines A and B, and Ruprechstyril

Marcellino Rudyanto, Koichi Kobayashi, and Toshio Honda*

Faculty of Pharmaceutical Sciences, Hoshi University, 2-4-41 Ebara, Shinagawa-ku, Tokyo 142-8501, Japan

Abstract

Two isocoumarins, scoparines A and B, having n-propyl group at the 3-position, and a new isocarbostyril, ruprechstyril, bearing n-pentyl substituent at the 3-position were synthesized via Sonogashira coupling of the corresponding aromatic halides and alkynes, followed by regioselective 6-endo-dig cyclization.

INTRODUCTION
The isocoumarins are becoming an increasingly interesting class of naturally occurring lactones with a wide range of biological activities.1,2 The isocarbostyril derivatives, the nitrogen analogue of isocoumarins are recognized not only as bioactive natural products3 but also as potential medicinal compounds.4 Those natural products usually possess a various types of substituents such as alkyl, alkenyl, and aryl group, at their 3-positions.

Very recently, we have established5 the synthesis of an antimalarial natural alkaloid, cassiarin A, by employing sequential Sonogashira coupling6 of aromatic halides and alkynes, followed by regioselective 6-endo-dig cyclization7 of oxygen functions to carbon-carbon triple bonds, as key steps, as shown in Scheme 1. In this synthesis, both 3-substituted isocoumarin and isocarbostyril derivatives were involved as key intermediates.
As an extension of this work, we are interested in synthesizing and studying the biological activity of compounds related to the natural isocoumarin and isocarbostyril having an alkyl group at the 3-position, and report here the first syntheses of scoparines A and B having n-propyl group, and ruprechstyril bearing n-pentyl substituent at the 3-position, respectively, although a number of synthetic approaches to those classes of natural products have been appeared to date.7

RESULTS AND DISCUSSION
First, we investigated the synthesis of 3-substituted isocoumarins, scoparines A and B (Figure 1), since these isocoumarins have not been synthesized yet.
Scoparines A 1 and B 2 were isolated from the ethyl acetate extract of the root of Pituranthos scoparius, and their structures were determined by spectroscopic analyses to be 3-n-propyl-5-methoxy- 6-hydroxyisocoumarin and 3-n-propyl-5,7-dimethoxy-6-hydroxyisocoumarin, respectively.8 Pituranthos scoparius is a toxic plant and used as a decoction in the treatment of asthma and a local application of the leaves alleviates pains linked to rheumatism in traditional medicine.9

To apply the same synthetic strategy used in the preparation of cass１iarin A to the synthesis of scoparine A, the known acid 410 was reacted with diethylamine in the presence of 2-chloro-N-methylpyridinium iodide (CMPI) to give the amide 5. A site-selective iodination of the amide 5 according to Hegedus’s procedure11 gave the iodide 6. Sonogashira coupling6 of 6 with 1-pentyne in diethylamine in the presence of bis(triphenylphosphine)palladium dichloride and copper(I) iodide provided the desired alkyne 7 in quantitative yield. Treatment of 7 with trimethyloxonium tetrafluoroborate in acetonitrile, followed by further treatment with methanol afforded the ester 8, in 79% yield, accompanied with deprotection of the methoxymethyl group. Acid hydrolysis of 8 with trifluoroacetic acid gave scoparine A 1, in 78% yield, where the hydrolysis of the ester group and regioselective 6-endo-dig cyclization occurred simultaneously.7e The spectroscopic data of the synthetic compound including its melting point were identical with those reported in the literature.8
Synthesis of scoparine B was also achieved by application of the above strategy starting from methyl 3,5-dimethoxy-4-methoxymethoxy benzoate 9.12 First, we investigated a direct iodination for 9 under the various reaction conditions, however, the desired iodide could not be isolated in reasonable yields, unfortunately. Therefore, the ester 9 was converted to the bromide 10 by treatment with NBS. Attempted Sonogashira coupling of 10 with 1-pentyne under the same reaction conditions as described for the preparation of 7 at 60 °C for 8 days, provided the desired alkyne 11 in 78% yield. Since the alkyne 11 was obtained in reasonably good yield, its further conversion to the natural product was achieved by its acid hydrolysis providing scoparine B 2, whose physicochemical properties were identical with those reported in the literature.8

Although 11 could be derived from the bromide 10, the coupling with the alkyne required a relatively long reaction time. To improve the reaction conditions for Sonogashira coupling, a preparation of the corresponding iodide 15 was carried out as follows. Iodination of the alcohol 12, derived from 9 by LiAlH4 reduction, with NIS gave the iodide 13, in 82% yield, which on oxidation with pyridinium dichromate (PDC), followed by treatment of the resulting aldehyde 14 with iodine and potassium hydroxide in MeOH afforded the ester 15, in 82% yield from 13. Sonogashira coupling of 15 with 1-pentyne in diethylamine in the presence of bis(triphenylphosphine)palladium dichloride and copper(I) iodide was achieved at 60 °C for 15 h to give 11 in 90% yield.

Next, our attention was focused on the first total synthesis of a natural isocarbostyril, ruprechstyril 3, bearing n-pentyl group at the 3-position. Ruprechstyril 3 was isolated from Ruprechtia tangarana as a new isocarbostyril derivative, and its structure was determined by X-ray crystal analysis.13 As the extract of this plant exhibited anticancer activity against the KB cell line and P388 lymphocytic leukemia,13 this plant was expected to be the sources of new anticancer agents. However, further investigation of the bioactive principles for this plant revealed that ruprechstyril did not show any significant activity against the murine P388 lymphocytic leukemia cell line.13
Our synthesis of ruprechstyril 3 commenced with the use of the iodide 165a employed in the synthesis of cassiarin A. Treatment of 16 with 1-heptyne in the presence of Pd(PPh3)2Cl2 and copper(I) iodide in diethylamine gave the alkyne 17 in 96% yield. Hydrolysis of 17 with 10% NaOH solution, followed by acidic treatment afforded the coumarin derivative 18. Conversion of 18 to the isocarbostyril 19 was achieved by treatment with 25-28% ammonium hydroxide in DMF. Deprotection of the methoxymethyl groups of 19 afforded the diol 20, which on treatment with iodomethane and cesium carbonate gave ruprechstyril 3 and O-methylruprechstyril 21, in 45 and 23% yields, respectively. The physicochemical properties of the synthetic ruprechstyril were identical with those reported.13

In summary, we disclose a general synthesis of natural isocoumarin and isocarbostyril compounds by employing Sonogashira coupling and a regioselective 6-endo-dig cyclization. The strategy described here would be applicable to a preparation of medicinally important bioactive compounds structurally related to the natural products.

EXPERIMENTAL
Melting points were measured with a Yanagimoto MP apparatus and are uncorrected. IR spectra were obtained using a JASCO FT/IR-200 spectrophotometer. 1H- and 13C-NMR spectra were obtained on JEOL Bruker AV-400 (1H-NMR: 270 MHz, 13C-NMR: 67.8 MHz) instrument for solutions in CDCl3 unless otherwise noted, and chemical shifts are reported on the δ scale from internal TMS. MS spectra were measured with a JEOL JMS-D 300 spectrometer. Elemental analyses were performed on a Yanaco-MT5.
N,N-Diethyl-3-methoxy-4-(methoxymethoxy)benzamide (5). To 2-chloro-N-methylpyridinium iodide (CMPI）(14.3 g, 67.2 mmol) were successively added a solution of diethylamine (11.4 mL, 107.5 mmol) and 3-methoxy-4-methoxymethoxybenzoic acid (1)（25.8 g, 100.8 mmol）in CH2Cl2 (670 mL), and triethylamine (22.7 mL, 107.5 mmol). The mixture was stirred at rt for 1 h and at 45 °C for 5 h. After treatment with saturated aqueous NaHCO3, the mixture was extracted with Et2O. The ethereal layer was washed with brine and dried over Na2SO4. Evaporation of the solvent gave a residue, which was subjected to column chromatography on silica gel. Elution with hexane:AcOEt（4:1 to 1:1, v/v）gave the amide (5) (17.7 g, 99%) as a pale yellow oil. IR (neat) cm-1: 1627，1583. 1H NMR δ: 1.20 (6H, br s), 3.45 (4H, br s), 3.52 (3H, s), 3.89 (3H, s), 5.25 (2H, s), 6.91 (1H, dd, J = 1.9, 8.2 Hz), 6.97 (1H, d, J = 1.9 Hz), 7.14 (1H, d, J = 8.2 Hz); 13C NMR δ: 55.8, 56.1, 95.2, 110.5, 115.5, 118.9, 131.1, 147.1, 149.5, 170.9. MS (EI) m/z 267 (M+). HRMS (EI): Calcd for C14H21NO4 (M+) 267.1470, Found 267.1462．
N,N-Diethyl-2-iodo-3-methoxy-4-(methoxymethoxy)benzamide (6). To a stirred solution of 5（0.2 g, 0.75 mmol）in THF (3.8 mL) was added N,N,N’,N’-tetramethylethylenediamine (0.27 ml, 1.73 mmol) at -60 °C, and the mixture was stirred at the same temperature for further 10 min. sec-BuLi (1.74 mL, 2.5 mmol) was added to the solution and the whole was stirred at the same temperature for 5 h. To this solution was added a solution of iodine (0.48 g, 2.5 mmol) in THF (3.0 mL) dropwise, and the resulting mixture was stirred for further 2 h. After treatment with saturated aqueous NH4Cl and 10% aqueous sodium thiosulfate solution, the mixture was extracted with Et2O. The ethereal layer was washed with brine and dried over Na2SO4. Evaporation of the solvent gave a residue, which was subjected to column chromatography on silica gel. Elution with hexane:AcOEt（2:1, v/v）gave the iodide (6) (0.19 g, 63%) as a pale yellow oil. IR (neat) cm-1: 1632，1586. 1H NMR δ: 1.07 (3H, t, J = 7.1 Hz), 1.24-1.30 (4H, m), 3.11-3.17 (2H, m), 3.25-3.30 (1H, m), 3.52 (3H, s), 3.86 (3H, s), 5.23 (2H, s), 6.91 (1H, d, J = 8.4 Hz), 7.15 (1H, d, J = 8.4 Hz); 13C NMR δ: 12.2, 13.8, 38.9, 42.8, 56.3, 60.5, 91.9, 95.1, 99.7, 117.0, 122.5, 137.4, 149.7, 170.0. MS (EI) m/z 393 (M+). HRMS (EI): Calcd for C14H20NO4I (M+) 393.0437, Found 393.0456.
N,N-Diethyl-3-methoxy-4-(methoxymethoxy)-2-(pent-1-yn-1-yl)benzamide (7). To a solution of 6 (0.52 g, 1.32 mmol) in diethylamine (6.6 mL) were added 1-pentyne (0.20 mL, 1.98 mmol), Pd(PPh3)2Cl2 (47.2 mg, 0.07 mmol) and CuI (52.9 mg, 0.26 mmol) under argon, and the resulting mixture was heated in a sealed tube at 60 °C for 35 h. The mixture was concentrated by evaporation and the residue was subjected to column chromatography on silica gel. Elution with hexane:AcOEt (4:1, v/v) afforded the alkyne (7) (0.44 g, 100%) as a pale yellow oil. IR (neat) cm-1: 2230, 1634, 1593. 1H NMR δ: 1.02-1.07 (6H, m), 1.24 (3H, t, J = 7.1 Hz), 1.57-1.66 (2H, m), 1.66-1.67 (2H, m), 2.40 (2H, t, J = 7.0 Hz), 3.17-3.19 (2H, m), 3.51 (3H, s), 3.93 (3H, s), 5.21 (2H, s), 6.90 (1H, d, J = 8.4 Hz), 7.09 (1H, d, J = 8.4 Hz); 13C NMR δ: 12.7, 13.5, 14.0, 21.6, 21.9, 38.7, 42.8, 56.2, 60.9, 73.7, 95.1, 98.2, 116.3, 116.4, 121.5, 134.9, 150.1, 150.9, 169.2. MS (EI) m/z 333 (M+). HRMS (EI) Calcd for C19H27NO4 (M+) 333.1940, Found 333.1944.
Methyl 4-hydroxy-3-methoxy-2-(pent-1-yn-1-yl)benzoate (8). To a stirred solution of 7 (0.10 g, 0.30 mmol) in MeCN (1.5 mL) were added Na2HPO4 (63.9 mg 0.45 mmol) and trimethyloxonium tetrafluoroborate (0.22 g, 1.5 mmol) at rt, and the whole was stirred for further 38 h at the same temperature. After treatment of the solution with MeOH and saturated aqueous NaHCO3, the resulting mixture was stirred for 28 h and then concentrated to leave a residue, which was extracted with Et2O. The extract was washed with brine and dried over Na2SO4. Evaporation of the solvent gave a residue, which was subjected to column chromatography on silica gel. Elution with hexane:AcOEt (7:1, v/v) gave the ester (8) (58.9 mg, 79%) as a pale yellow oil. IR (neat) cm-1: 1711, 3381. 1H NMR δ: 1.02 (3H, t, J = 7.4 Hz), 1.58-1.67 (2H, m), 2.46 (2H, t, J = 7.0 Hz), 3.80 (3H, s), 3.92 (3H, s), 6.26 (1H, br s), 6.82 (1H, d, J = 8.6 Hz), 7.58 (1H, d, J = 8.6 Hz); 13C NMR δ: 13.6, 22.0, 29.6, 51.9, 61.0, 74.3, 101.8, 114.1, 118.4, 124.7, 127.7, 148.7, 152.2, 166.4. MS (EI) m/z 249 (M+). HRMS (EI) Calcd for C14H17O4 (M+) 249.1127, Found 249.1123.
Scoparine A (1). A solution of 8 (23.8 mg, 0.096 mmol) in TFA (0.12 mL) was stirred at rt for 13 h. The solution was concentrated to leave a residue, which was subjected to column chromatography on silica gel. Elution with hexane:AcOEt (9:2, v/v) gave scoparine A (1) (11.5 mg, 51%) as a colorless solid. Mp 155-156 °C [lit.,8 mp 159-160 °C ]. Spectral data (IR, NMR, MS) of the synthesized scoparine A were identical to those of the published data.8
Methyl 2-bromo-3,5-dimethoxy-4-(methoxymethoxy)benzoate (10). To a stirred solution of 9 (3.82 g, 14.9 mmol) in CHCl3:AcOH = 1:1 (30 mL) was added N-bromosuccinimide (4.06 g, 22.4 mmol) at rt and the resulting mixture was stirred for further 43 h at the same temperature. The mixture was treated with saturated aqueous NaHCO3 and extracted with CHCl3. The extract was washed with brine and dried over Na2SO4. Evaporation of the solvent gave a residue, which was subjected to column chromatography on silica gel. Elution with hexane:AcOEt (9:1, v/v) afforded the bromide (10) (3.67 g, 74%) as a yellow oil. IR (neat) cm-1: 2949, 2848, 1733, 1581, 1567. 1H NMR δ: 3.59 (3H, s), 3.88 (6H, s), 3.93 (3H, s), 5.19 (2H, s), 7.17 (1H, s); 13C NMR δ: 52.5, 56.2, 57.3, 60.9, 98.6, 109.6, 110.1, 127.9, 142.8, 151.8, 152.4, 166.4. MS (CI) m/z 335 (M++1). HRMS (CI): Calcd for C12H16 O6 (M++1) 335.0130, Found 335.0158.
Methyl 3,5-dimethoxy-4-(methoxymethoxy)-2-(pent-1-yn-1-yl)benzoate (11). To a stirred solution of 10 (2.96 g, 8.8 mmol) in diethylamine (44.2 ml) were added 1-pentyne (1.04 mL, 10.6 mmol), (tert-Bu)3P (0.2 mL, 0.88 mmol), Pd(PPh3)2Cl2 (0.32 g, 0.44 mmol) and CuI (0.35 g, 1.77 mmol) at rt under argon, and the resulting mixture was heated in a sealed tube at 60 °C for 8 days. The mixture was concentrated to leave a residue, which was subjected to column chromatography on silica gel. Elution with hexane:AcOEt (9:1, v/v) afforded the alkyne (11) (2.22 g, 78%) as a yellow oil. IR (neat) cm-1: 2962, 1733, 1713, 1591. 1H NMR δ: 1.09 (3H, t, J = 7.3 Hz), 1.64-1.73 (2H, m), 2.51 (2H, t, J = 7.0 Hz), 3.59 (3H, s), 3.89-3.94 (9H, m), 5.18 (2H, s), 7.25 (1H, s); 13C NMR δ: 13.5, 21.9, 22.1, 52.0, 56.0, 57.2, 60.9, 74.1, 98.5, 98.8, 109.3, 112.9, 128.3, 142.4, 152.3, 155.5, 166.5. MS (EI) m/z 322 (M+). HRMS (EI): Calcd for C17H22O6 (M+) 322.1416, Found 322.1403.
Scoparine B (2). A solution of 11 (0.1 g, 0.31 mmol) in TFA (0.5 mL) was stirred at rt for 7 h. After evaporation of the solvent, the residue was purified by column chromatography on silica gel. Elution with hexane:AcOEt (5:2, v/v) afforded scoparine B (2) (64 mg, 78%) as a colorless solid. Mp 148-150 °C [lit.,8 mp 151-152 °C ]. Spectral data (IR, NMR, MS) of the synthesized scoparone B were identical to those of the published data.8
3,5-Dimethoxy-4-(methoxymethoxy)benzyl alcohol (12). To a stirred suspension of lithium aluminum hydride (0.16 g, 4.29 mmol) in THF (13 mL) was added a solution of ester (9) (1.0 g, 3.9 mmol) in THF (13 mL) at 0 °C, and the resulting mixture was stirred for further 15 min at rt. After treatment with 4N NaOH and H2O, the mixture was filtered through Celite to remove the insoluble materials. The filtrate was concentrated to leave a residue, which was purified by column chromatography on silica gel. Elution with hexane:AcOEt (1:1, v/v) gave the alcohol (12) (0.87 g, 98 %) as a colorless oil. IR (neat) cm-1: 3415, 2941, 2841, 1594, 1505. 1H NMR δ: 2.51 (1H, br s), 3.59 (3H, s), 3.84 (6H, s), 4.58 (2H, s), 5.09 (2H, s), 6.57 (2H, s); 13C NMR δ: 55.9, 57.0, 65.1, 98.0, 103.6, 133.4, 137.1, 153.2. MS (EI) m/z 228 (M+). HRMS (EI) Calcd for C11H16 O5 (M+) 228.0998, Found 228.0986.
2-Iodo-3,5-dimethoxy-4-(methoxymethoxy)benzyl alcohol (13). To a stirred solution of 12 (4.5 g, 19.7 mmol) in DMF (65.7 mL) was added N–iodosuccinimide (13.3 g, 59.2 mmol) at rt, and the resulting mixture was stirred for further 5 days at the same temperature. The solution was treated with saturated aqueous NH4Cl and 10% aqueous sodium thiosulfate, and extracted with Et2O. The organic layer was washed with brine and dried over Na2SO4. Evaporation of the solvent gave a residue, which was purified by column chromatography on silica gel. Elution with hexane:AcOEt (3:1, v/v) gave the iodide (13) (5.7 g, 82%) as a pale yellow oil. IR (neat) cm-1: 3424, 2936, 1582, 1566, 1465. 1H NMR δ: 2.35 (1H, br s), 3.60 (3H, s), 3.87 (6H, s), 4.64 (2H, s), 5.12 (2H, s), 6.94 (1H, s); 13C NMR δ: 56.1, 57.3, 60.7, 69.3, 84.6, 98.5, 108.0, 137.9, 138.9, 153.1, 154.0. MS (EI) m/z 353 (M+). HRMS (EI) Calcd for C11H15 O5I (M+) 353.9964, Found 353.9951.
Methyl 3,5-dimethoxy-4-(methoxymethoxy)benzoate (15). To a stirred solution of 13 (5.7 g, 16.1 mmol) in DMF (80.5 mL) was added pyridinium dichromate (12.1 g, 32.2 mmol) portionwise at rt, and the mixture was stirred for further 1 h at the same temperature. The mixture was treated with Celite (30g) and Et2O (80.5 mL) and stirred for 3 h. After filtration, the filtrate was concentrated by evaporation of the solvent, and the residue was treated with H2O. The aqueous layer was extracted with CHCl3, and the extract was washed with brine and dried over Na2SO4. Evaporation of the solvent gave a crude aldehyde (14), which without purification, was used in the next reaction. To a stirred solution of the aldehyde in MeOH (161 mL) were successively added a solution of KOH (2.4 g, 41.9 mmol) in MeOH (52.3 mL), iodine (5.31 g, 20.9 mmol) and MeOH (41.8 mL) at 0 °C, and the whole was stirred for further 23 h at 0 °C. The solution was treated with saturated aqueous NH4Cl and 10% aqueous sodium thiosulfate, and extracted with Et2O. The organic layer was washed with brine and dried over Na2SO4. Evaporation of the solvent gave a residue, which was purified by column chromatography on silica gel. Elution with hexane:AcOEt (5:1, v/v) gave the ester (15) (5.1 g, 82%) as a pale yellow oil. IR (neat) cm-1: 2948, 1733, 1577, 1561. 1H NMR δ: 3.59 (3H, s), 3.88 (6H, s), 3.93 (3H, s,), 5.19 (2H, s), 7.17 (1H, s); 13C NMR δ: 52.5, 56.2, 57.3, 60.9, 98.6, 109.6, 110.1, 127.9, 142.8, 151.8, 152.4, 166.4. MS (EI) m/z 381 (M+). HRMS (EI): Calcd for C12H15 O6I (M+) 381.9913, Found 381.9902.
Alternative synthesis of the alkyne 11 from 15. To a stirred solution of 15 (0.1 g, 0.26 mmol) in diethylamine (1.3 mL) were added 1-pentyne (0.031 mL, 0.31 mmol), Pd(PPh3)2Cl2 (9.4 mg, 0.013 mmol) and CuI (10.6 mg, 0.052 mmol) under argon, and the resulting mixture was heated in a sealed tube at 60 °C for 15 h. Work-up was carried out by the same procedure as for the preparation of 11 from 10 to give the alkyne (11) (76.8 mg, 90%).
Methyl 6-(hept-1-yn-1-yl)-2,4-bis(methoxymethoxy)benzoate (17). To a solution of iodine compound 16 (2.05 g, 5.37 mmol) in diethylamine (35 mL) was added 1-heptyne (0.81 mL, 6.18 mmol), Pd(PPh3)2Cl2 (0.19 g, 0.27 mmol) and CuI (0.10 g, 0.54 mmol). The resulting mixture was stirred at 60 °C for 19 h. The solvent was evaporated under reduced pressure. The residue was partitioned between saturated aqueous NH4Cl solution and Et2O. After separation, the aqueous layer was extracted three times with Et2O. The combined organic layers were dried over Na2SO4 and concentrated. Purification of the crude product by column chromatography with hexane:EtOAc (4:1, v/v) as an eluent provided the alkyne 17 (1.81 g, 96%) as a colorless liquid. IR (neat) cm-1: 1732, 1597, 1216, 1149. 1H NMR δ: 0.92 (3H, t, J=7.2 Hz), 1.31-1. 45 (4H, m), 1.61-1.63 (2H, m), 2.37 (2H, t, J=7.1 Hz), 3.46 (3H, s), 3.89 (3H, s), 5.14 (2H, s), 6.76 (1H, d, J=2.2 Hz), 6.78 (1H, d, J=2.2 Hz). 13C NMR δ: 13.9, 19.3, 22.1, 28.2, 30.9, 52.2, 56.1, 56.2, 77.5, 94.3, 94.4, 94.7, 103.8, 112.4, 121.1, 123.7, 155.0, 158.5, 167.3. MS (CI) m/z 351 (M++1). HRMS Calcd for C19H27O6 (M++1): 351.1807, Found: 351.1801.
6,8-Bis(methoxymethoxy)-3-pentylisochromen-1-one (18). To a solution of compound 17 (716.4 mg, 2.04 mmol) in MeOH (25 mL) was added 20% aqueous NaOH (25 mL). The mixture was stirred at 60 °C for 23 h. After cooling to 0 °C, to the mixture was added dropwise 10% HCl solution until pH ≈3. The mixture was extracted three times with EtOAc. The extract was concentrated by evaporation of the solvent. The concentrated extract was kept overnight at rt to complete the cyclization. Column chromatography with CHCl3:MeOH (200:1, v/v) as an eluent gave the isocoumarin 18 (403.1 mg, 59%) as colorless oil. IR (neat) cm-1: 1732, 1602, 1152. 1H NMR δ: 0.88-0.92 (3H, m), 1.32-1.36 (4H, m), 1.64-1.71 (2H, m), 3.45 (2H, t, J=7.6 Hz), 3.49 (3H, s), 3.55 (3H, s), 5.23 (2H, s), 5.34 (2H, s), 6.09 (1H, s), 6.58 (1H, d, J=2.3 Hz), 6.79 (1H, d, J=2.3 Hz). 13C NMR δ: 13.9, 22.4, 26.4, 31.1, 33.2, 56.4, 56.5, 94.1, 95.1, 102.9, 103.48, 103.50, 104.6, 142.0, 159.0, 159.3, 160.7, 162.6. MS (CI) m/z 337 (M++1): HRMS Calcd for C18H25O6 (M++1): 337.1651, Found: 337.1629.
6,8-Bis(methoxymethoxy)-3-pentyl-2H-isoquinolin-1-one (19). Isocoumarin 18 (302.2 mg, 0.90 mmol) was dissolved in DMF (7 mL) in a round bottom flask. To the solution was added NH4OH (25-28% solution in water, 7 mL), and then the flask was sealed with rubber septum. The mixture was stirred at rt for 60 h. After removing the septum, the mixture was stirred at 90-100 °C for 2 h. The solvent was removed by distillation under reduced pressure to give crude product. Column chromatography of the crude product with CHCl3:MeOH (30:1, v/v) as an eluent gave the isocarbostyril 19 (266.8 mg, 89%) as white prisms (recrystallized from methanol), mp 93-95 °C. IR (neat) cm-1: 3171, 1646, 1605, 1152. 1H NMR δ: 0.87-0.91 (3H, m), 1.32-1.38 (4H, m), 1.67-1.75 (2H, m), 2.55 (2H, t, J=7.6 Hz), 3.50 (3H, s), 3.58 (3H, s), 5.24 (2H, s), 5.33 (2H, s), 6.14 (1H, s), 6.72 (1H, d, J=2.3 Hz), 6.75 (1H, d, J=2.3 Hz), 10.52 (1H, s). 13C NMR δ: 13.9, 22.4, 27.6, 31.2, 32.9, 56.3, 56.4, 94.1, 95.9, 103.6, 103.7, 103.9, 110.4, 142.8, 143.1, 159.7, 166.6, 162.7. MS (CI) m/z 336 (M++1). HRMS Calcd for C18H26NO5 (M++1): 336.1811, Found: 336.1807. Anal Calcd for C18H25NO5: C 64.46, H 7.51, N 4.18; Found: C 64.29, H 7.44, N 4.09.
6,8-Dihydroxy-3-pentyl-2H-isoquinolin-1-one (20). Compound 19 (232.6 mg, 0.69 mmol) was dissolved in a MeOH (5 mL). To the solution was added 6 drops of concentrated HCl, and the resulting mixture was stirred at 50 °C for 24 h. The solvent was evaporated in reduced pressure. The residue was purified by column chromatography with CHCl3:MeOH (30:1, v/v) as an eluent to give the diol 20 (165.0 mg, 80%) as white needles (recrystallized from MeOH), mp 170-172 °C. IR (neat) cm-1: 3297, 3168, 3067, 1653. 1H NMR δ: 0.92 (3H, t, J=6.8 Hz), 1.35-1.38 (4H, m), 1.64-1.71 (2H, m), 2.50 (2H, t, J=7.6 Hz), 6.21 (1H, s), 6.28 (1H, d, J=2.1 Hz), 6.33 (1H, d, J=2.1 Hz). 13C NMR δ: 13.0, 21.8, 27.5, 30.6, 32.3, 99.6, 100.4, 103.8, 104.5, 140.9, 131.1, 162.1, 162.5, 166.1. MS (CI) m/z 228 (M++1). HRMS Calcd for C14H18NO3 (M++1):248.1286, Found: 248.1293.
Ruprechstyril (3) and O-methylruprechstyril (21). Compound 20 (102.8 mg, 0.42 mmol) was dissolved in acetone (8 mL). To the solution were added iodomethane (25.9 μL, 0.42 mmol) and cesium carbonate (135.5 mg, 0.42 mmol). The resulting mixture was stirred at rt for 23 h. The solvent was evaporated in reduced pressure. To the residue were added saturated aqueous NH4Cl solution and a mixture of CHCl3:MeOH (10:1, v/v). After separation, the aqueous layer was extracted three times with CHCl3:MeOH (10:1, v/v). The organic layers were combined, washed with brine, dried over Na2SO4, and concentrated. Purification by column chromatography with CHCl3:MeOH (50:1, v/v) as an eluent provided ruprechstyril (3) (49.0 mg, 45%) (white solids), mp 138-140 °C [lit.,13 mp 139-141 °C ]., along with O-methylruprechstyril (21) (25.9 mg, 23%) and recovered 20 (22.4 mg, 22%) (white solid). Spectral data (IR, NMR, MS) of the synthesized ruprechstyril (3) are identical to those of the published data.13
Spectral data of O-methylruprechstyril (21): IR (neat) cm-1: 3073, 1652, 1600, 1162. 1H NMR δ: 0.91-0.95 (3H, m), 1.34-1.43 (4H, m), 1.62-1.69 (2H, m), 2.60 (2H, t, J=7.8 Hz), 3.52 (3H, s), 3.84 (3H, s), 6.27 (1H, s), 6.31 (1H, d, J=2.3 Hz), 6.41 (1H, d, J=2.3 Hz), 13.07 (1H, s). 13C NMR δ: 13.9, 22.4, 27.9, 29.7, 31.4, 33.3, 55.3, 98.2, 99.5, 105.4, 106.4, 139.0, 143.3, 162.8, 164.4, 166.1. MS (EI) m/z 275 (M+). HRMS Calcd for C16H21NO3 (M+): 275.1521, Found: 275.1545.

ACKNOWLEDGEMENTS
This research was supported financially in part by a grant for the Open Research Center Project and a Grant-in-Aid from the Ministry of Education, Culture, Sports, Science and Technology of Japan.

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