Prenylated purine alkaloids from seeds of Gleditsia japonica

Phytochemistry 143 (2017) 145e150

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Prenylated purine alkaloids from seeds of Gleditsia japonica Yui Harauchi a, Tadashi Kajimoto b, 1, Emi Ohta a, Hiroyuki Kawachi b, Aya Imamura-Jinda b, Shinji Ohta a, * a b

Graduate School of Biosphere Science, Hiroshima University, 1-7-1 Kagamiyama, Higashi-Hiroshima 739-8521, Japan Graduate School of Bioscience, Nagahama Institute for Bioscience and Technology, 1266 Tamura-cho, Nagahama-shi, Shiga 526-0829, Japan

a r t i c l e i n f o

a b s t r a c t

Article history: Received 28 May 2017 Received in revised form 3 August 2017 Accepted 7 August 2017

Three previously undescribed isoguanine glycosides with an N3-prenyl group, designated locustoside B, saikachinoside B, and saikachinoside C, have been isolated from the seed of Gleditsia japonica Miquel (Fabaceae) along with two known compounds, locustoside A and saikachinoside A. Their structures were determined from spectroscopic data and X-ray crystallographic analysis. The inhibitory activity against acid phosphatase was evaluated. © 2017 Elsevier Ltd. All rights reserved.

Keywords: Gleditsia japonica Fabaceae Prenylated isoguanoside Locustoside B Saikachinoside B Saikachinoside C

1. Introduction The plants belonging to the genus Gleditsia have been used as local and traditional medicines in many regions for the treatment of measles, indigestion, whooping, smallpox, arthrolithiasis, constipation, diarrhea, hematochezia, dysentery, and carbuncle (Zhang et al., 2016). The Japanese honey locust, Gleditsia japonica Miquel (Fabaceae), grows in Japan, Korea, and China. The dried fruits have been used as a diuretic and an expectorant in traditional oriental medicine (Konoshima et al., 1981; Zhang et al., 2016). Its seeds have been reported to contain polyamines (Hamana et al., 1996), phenols, alkaloids, flavonoids, carbohydrates, saponins, steroids, coumarins, and amino acids (Wan et al., 2001). Our preliminary examination of the aq. portion of the MeOH extract of the seeds of G. japonica led to the isolation of two rare N3-prenylated purine alkaloid glucosides, locustoside A (4) (Kajimoto et al., 2010a) and saikachinoside A (5) (Kajimoto et al., 2010b). Further investigation of the extract resulted in the isolation of three previously undescribed compounds designated locustoside B (1), saikachinoside B

* Corresponding author. E-mail address: [email protected] (S. Ohta). 1 Present address: Central Research Laboratory, Nippon Suisan Kaisha, Ltd., Tokyo Innovation Center, 1-32-3 Nanakuni, Hachioji, Tokyo 192-0991, Japan. http://dx.doi.org/10.1016/j.phytochem.2017.08.006 0031-9422/© 2017 Elsevier Ltd. All rights reserved.

(2), and saikachinoside C (3). We report the purification, structural elucidation, and biological activity of 1e3. 2. Results and discussion The seeds (250 g, wet weight) were cut into small pieces and extracted with MeOH. The concentrated MeOH extract was suspended in water and successively partitioned with hexane and EtOAc. The aq. layer was lyophilized to yield syrup. The watersoluble portion (13.5 g) was repeatedly separated on an ODS column by using MeOHeH2O gradient mixtures to afford 1e5 (Fig. 1). Compound 1 was isolated as colorless crystals (MeOHeH2O) with an optical rotation of [a]D
27 (с 0.3, MeOH). Positive-ion HRESITOFMS analysis showed a [MþH]þ ion peak at m/z 514.2144 (calcd for C21H32N5Oþ 10, 514.2144), indicating the molecular formula of C21H31N5O10. The IR absorption bands at 3403, 3321, 1635, and 1577 cm
1 implied the presence of OH, NH, C]O, C]N, and C]C functionalities. The 13C NMR and DEPT spectra revealed the presence of 21 carbon signals including seven sp2 carbon atoms, twelve oxygen- or heteroatom-substituted carbons, and two vinylic methyls (Table 1). A characteristic downfield methine proton signal at dH 8.04 (1H, s) in the 1H NMR spectrum (CD3OD) and the UV (MeOH) absorption maxima at 247 (log ε 3.94) and 291 nm (log ε 3.89) implied compound 1 to be a 3,7-disubstituted isoguanine derivative (Stewart and Harris, 1977; Cafieri et al., 1995), which was

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Fig. 2. 1He1H COSY, HMBC, NOESY, and (þ)-ESIMS/MS key data for 1. Fig. 1. Structures of 1e5 from Gleditsia japonica.

13

confirmed by comparison of its C NMR data (C-2, C-4, C-5, C-6, and C-8) with those for isoguanine analogs previously reported in the literature (Kajimoto et al., 2010a, 2010b). A 1He1H COSY correlation between H2-10 and H-20 and HMBC correlations from H3-40 and H3-50 to C-20 and C-30 revealed the presence of an isopentenyl unit. HMBC correlations from H2-10 to C-2 and C-4 indicated the attachment of the isopentenyl unit to N-3 of the isoguanine unit (Fig. 2). Because of the overlap of some oxygenated methine and methylene signals in the 3.5e4.0 ppm region of the 1H NMR spectrum (CD3OD), the NMR spectra recorded in C5D5N were also used for further structural analysis. As a result, interpretation of 1 He1H COSY data in conjunction with vicinal coupling constants led to a b-glucopyranosyl unit (C-100 eC-600 ). Furthermore, a comparison of the 13C NMR chemical shifts for the remaining five oxygenated carbon signals with those for methyl b-D-

apiofuranoside previously reported in the literature (Kitagawa et al., 1993) revealed the presence of a b-apiofuranosyl unit (C1000 eC-5000 ). A NOESY correlation between H-2000 and H2-5000 of the bapiofuranosyl unit supported the erythro configuration of C-2000 and C-3000 (Fig. 2). An HMBC correlation from the anomeric proton (H1000 ) to C-600 and the downfield chemical shift of C-600 indicated the attachment of the b-apiofuranosyl unit to C-600 of the b-glucopyranosyl unit, which was supported by the observation of a NOESY correlation between H-1000 and H-600 . The b-glucopyranosyl unit was in turn attached to N-7 of the isoguanine unit through an N-glucosyl linkage, as indicated by HMBC correlations from H-100 to C-5 and C-8. This was supported by the observation of a NOESY correlation between H-100 and H-8. The presence of the disaccharide unit was supported by the observation of a fragment ion peak at m/z 220 [M þ He294]þ in the positive-ion ESIMS/MS spectrum (Fig. 2). These findings demonstrated compound 1 to be a 600 -O-b-apiofuranosyl analog of locustoside A (4) (Kajimoto et al., 2010a). The

Table 1 1 H and 13C NMR spectroscopic data for 1e3 in CD3OD. No

1

2

dC

dH (J in Hz)

dC

8.04 (s) 4.65 (2H, d, 6.6)

157.7 s 154.4 s 104.7 s 155.1 s 144.8 d 41.6 t

2 4 5 6 8 10

157.9 s 154.7 s 104.7 s 155.2 s 144.9 d 42.3 t

20 30 40

120.0 d 137.5 s 18.4 q

5.27 (br t, 6.6)

50 100 200 300 400 500 600

25.9 88.8 74.0 77.6 69.3 79.5 66.6

1000 2000 3000 4000

111.2 d 78.1 d 80.2 s 74.8 t

1.68 5.47 3.57 3.55 3.81 3.77 4.02 3.83 5.00 4.08

(3H, br s) (d, 8.4) (m) (m) (m) (m) (dd, 10.3, 1.5) (d, 10.3) (d, 2.6) (d, 2.6)

5000

63.5 t

3.74 4.00 3.57 3.58

(d, 9.9) (d, 9.9) (m) (m)

6000

q d d d d d t

3

1.83 (3H, br s)

dH (J in Hz)

dC

8.07 (s) 4.76 (2H, d, 7.0)

157.7 s 154.4 s 104.7 s 155.2 s 144.7 d 41.8 t

122.1 d 140.9 s 61.7 t

5.38 (br t, 7.0)

21.9 88.7 74.0 77.6 69.3 79.5 66.5

1.77 5.48 3.49 3.51 3.77 3.79 4.02 3.83 5.00 4.08

(3H, br s) (d, 8.3) (dd, 8.3, 9.1) (t, 9.1) (t, 9.1) (d, 9.1) (br d, 10.5) (br d, 10.5) (d, 2.5) (d, 2.5)

3.74 4.00 3.55 3.59

(d, (d, (d, (d,

q d d d d d t

111.1 d 78.0 d 80.1 s 74.8 t 63.5 t

4.26 (2H, br s)

9.7) 9.7) 11.0) 11.0)

dH (J in Hz)

8.08 4.82 4.74 5.52

(s) (dd, 14.7, 6.9) (dd, 14.7, 6.9) (br t, 6.9)

102.6 d 75.1 d 77.8 d 71.7 d

4.59 4.40 1.79 5.47 3.49 3.54 3.73 3.64 3.93 3.85 4.35 3.21 3.38 3.32

(d, 12.1) (d, 12.1) (3H, br s) (d, 8.2) (dd, 8.2, 9.1) (t, 9.1) (t, 9.1) (dt, 9.1, 2.2) (dd, 11.7, 2.2) (dd, 11.7, 2.2) (d, 7.8) (dd, 8.6, 7.8) (t, 8.6) (dd, 9.5, 8.6)

77.8 d

3.36 (m)

62.9 t

3.87 (dd, 11.7, 2.2) 3.68 (dd, 11.7, 5.2)

124.8 d 137.3 s 68.1 t 21.9 88.6 74.2 78.0 69.4 81.0 60.3

q d d d d d t

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Fig. 3. ORTEP diagram of 1. Solvent molecules are omitted for clarity.

structure was confirmed via X-ray crystallographic analysis of 1 (Fig. 3). In the solid state, the amino group at C-6 of 1 was intramolecularly hydrogen-bonded to the ring oxygen atom of the glucopyranosyl unit and the oxygen atoms at C-1000 and at C-5000 of the apiofuranosyl unit. In turn, the hydroxyl group at C-5000 was intermolecularly hydrogen-bonded to C-200 of the glucopyranosyl unit of another molecule. Further, the hydroxyl group at C-200 of the glucopyranosyl unit was linked to the hydroxyl group at C-3000 of the apiofuranosyl unit of another molecule of 1 via two molecules of MeOH through the intermolecular hydrogen bonds (Fig. 4). The

absolute configurations of glucose and apiose obtained after acid hydrolysis of 1 were all determined as D by GC-MS analysis of the trimethylsilyl ethers of the methyl (4R)-thiazolidine-4-carboxylate derivatives (Hara et al., 1987). Consequently, the structure of locustoside B was elucidated as 7-(b-D-apiofuranosyl-(1/6)-b-Dglucopyranosyl)-3-(3-methyl-2-butenyl)-isoguanine (1). Saikachinoside B (2) was obtained as a colorless oil and the molecular formula was established as C21H31N5O11 from positiveion HRESITOFMS data {m/z 530.2095 ([MþH]þ; calcd for 1 13 C21H32N5Oþ C NMR spectra were 11, 530.2093)}. The H NMR and

Fig. 4. Molecular packing diagram of 1.

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Fig. 5. 1He1H COSY, HMBC, NOESY, and (þ)-ESIMS/MS key data for 2.

very similar to those of 1 (Table 1), except for the absence of the signal from one of the vinylic methyls in the N3-prenyl unit and the presence of signals from an oxygenated methylene [dH 4.26 (2H, br s); dC 61.7]. HMBC correlations from the oxygenated methylene protons to C-20 , C-30 , and C-50 indicated the presence of a 4hydroxy-3-methyl-2-butenyl unit (Fig. 5). The geometry of the double bond of the unit was determined as Z on the basis of the observation of a NOESY correlation between the methyl protons (H3-50 ) and the olefinic proton (H-20 ) (Fig. 5). HMBC correlations from the allylic methylene protons (H2-10 ) to C-2 and C-4 of the purine ring indicated the attachment of the 4-hydroxy-3-methyl-2butenyl unit to the 3-nitrogen atom of the purine ring, which was supported by positive-ion ESI-MS/MS analysis (Fig. 5). All other HMBC correlations verified the proposed structure for 2. The absolute configurations of glucose and apiose obtained after acid hydrolysis of 2 were all determined as D by GC-MS analysis of the trimethylsilylated thiazolidine derivative. Consequently, the structure of saikachinoside B was elucidated as 7-(b-D-apiofuranosyl(1/6)-b-D-glucopyranosyl)-3-[(Z)-4-hydroxy-3-methyl-2butenyl]isoguanine (2). Saikachinoside C (3) was obtained as a colorless oil and the molecular formula was established as C22H33N5O12 from positiveion HRESITOFMS data {m/z 560.2197 ([MþH]þ; calcd for 1 13 C22H34N5Oþ C NMR spectra were 12, 560.2198)}. The H NMR and very similar to those of saikachinoside A (5) previously described in the literature (Kajimoto et al., 2010b), except for additional signals that were attributable to a hexose unit (Table 1). The analysis of the

1 H coupling constants of the additional hexose unit indicated that it was a b-glucopyranosyl. HMBC correlations from the anomeric proton (H-1000 ) of the additional b-glucopyranosyl unit to the oxygenated carbon (C-40 ) and a NOESY correlation between the anomeric proton (H-1000 ) and the oxygenated methylene protons (H2-40 ) indicated that the additional b-glucopyranosyl unit was attached to C-40 of the N3-prenyl unit, which was supported by positive-ion ESI-MS/MS analysis (Fig. 6). Further, a NOESY correlation between the methyl protons (H3-50 ) and the olefinic proton (H20 ) indicated the geometry of the double bond of the prenyl unit to be Z. All other HMBC correlations verified the proposed structure for 3 (Fig. 6). The hydrolysis of 3 with 1 M HCl afforded D-glucose. Consequently, the structure of saikachinoside C was elucidated as 7-(b-D-glucopyranosyl)-3-[(Z)-4-b-D-glucopyranosyloxy-3methyl-2-butenyl]isoguanine (3). Purine analogs are known to modulate the activity of acid phosphatase (Wurzinger et al., 1985). Although compounds 2e4 could not be tested in bioassay owing to the limited amount available, compounds 1 and 5 were evaluated with an inhibition assay for acid phosphatase. Locustoside B (1) exhibited weak inhibitory activity (23.9 ± 2.9%) against acid phosphatase at the concentration of 1 mM, while saikachinoside A (5) had no effect.

3. Conclusions Three previously undescribed compounds 1e3 were isolated from the seeds of G. japonica. Their structures were elucidated from spectroscopic data and X-ray crystallographic analysis. So far, N6prenylated adenine derivatives, e.g., N6-isopentenyladenine (Robins et al., 1967), have been found as plant cytokinins, and a few N3-prenylated purine alkaloids, e.g., triacanthine from the leaves of Gleditsia triacanthos (Belikov et al., 1954; Leonard and Deyrup, 1962), dioicine from the seeds of Gymnocladus dioicus (Fitch et al., 2009), and 3-(3-methylbut-2-en-1-yl)isoguanine from the whole plant of Phyllanthus reticulatus (Lan et al., 2010), have been reported. However, N3-prenylated isoguanine glycosides obtained in the present study are rare naturally occurring compounds. 4. Experimental 4.1. General experimental procedures Melting point was recorded using a Round Science RFS 10 melting point apparatus. Optical rotation was measured on an Horiba SEPA-300 polarimeter. IR spectra were recorded using a Horiba FT720 spectrometer. UV spectra were obtained using a JASCO V-630 Bio spectrophotometer. ECD spectra were measured using a JASCO J-820 spectropolarimeter. NMR spectra were acquired using a JEOL AL400 NMR spectrometer (400 MHz for 1H, 100 MHz for 13C). 1H and 13C NMR chemical shifts were referenced to residual solvent peaks: dH 3.30 and dC 49.0 for CD3OD; dH 7.55 and dC 135.5 for C5D5N. HRESITOFMS were carried out using a Shimadzu LCMS-IT-TOF mass spectrometer. EIMS and CIMS were measured on a Shimadzu GCMS-QP2010 Plus mass spectrometer. Column chromatography (CC) was performed using Wakogel 50C18 (Wako Pure Chemical Industries, Ltd, Osaka, Japan). Thin layer chromatography (TLC) was performed using pre-coated silica gel RP-18 F254s plates (Merck). 4.2. Plant material

Fig. 6. 1He1H COSY, HMBC, NOESY, and (þ)-ESIMS/MS key data for 3.

The seeds of Gleditsia japonica Miquel (Fabaceae) were collected at Nagahama City (coordinates 35.3574 N, 136.2782 E) in Shiga Prefecture, Japan, and identified as described in the literature (Kajimoto et al., 2010a). A voucher specimen has been deposited at

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the Hiroshima University Museum, Japan (registry number HUMPL-00002).

4.8. Determination of the absolute configurations of sugar moieties of 1e3

4.3. Extraction and isolation

Treatment of each sample of 1e3 (each 1 mg) with 1 M HCl (100 ml) at 60  C overnight gave a reaction mixture. The mixture, after drying, was dissolved in pyridine and L-cysteine methyl ester hydrochloride (1.6 mg) (Hara et al., 1987) in pyridine (200 ml) was added. The mixture was heated at 60  C for 1 h. The solution was then treated with 25% N,O-bis(trimethylsilyl)acetamide in acetonitrile solution (200 ml) at room temp. for 1 h. The trimethylsilyl ethers of the methyl (4R)-thiazolidine-4-carboxylate derivatives were applied to GCMS analysis [conditions: column, Rtx-5MS (Restek, USA), 30 m  0.25 mm, 1 mm; carrier gas He; injection temp. 300  C, column temp. 150  C, 10  C/min to 300  C; tR of derivatives, D-glucose 17.2 min, L-glucose 17.5 min, D-apiose 14.6 min, L-apiose 14.9 min]. The peaks corresponding to D-glucose and Dapiose derivatives were detected from 1 and 2 and that to a Dglucose derivative was detected from 3.

The seeds (250 g, wet weight) were cut into small pieces and extracted with MeOH. The concentrated MeOH extract was suspended in water and partitioned successively with hexane and EtOAc. The aq. layer was lyophilized to yield syrup. The watersoluble portion (13 g) was separated on ODS column to afford ten fractions A to J by elution with MeOHeH2O (0:100 to 100:0) gradient mixtures. Fraction B (MeOHeH2O, 1:9) (37 mg) was subjected to medium pressure column chromatography on ODS employing MeOHeH2O (1:4) to afford 3 (2 mg) and 5 (25 mg). Fraction C (MeOHeH2O, 1:4) (17 mg) was further purified by ODS column chromatography with MeCNeH2O (1:9) to afford 2 (4 mg). Fraction G (MeOHeH2O, 3:2) (120 mg) was further subjected to medium pressure ODS column chromatography employing gradient mixtures of MeOHeH2O (1:4 to 4:1) solvent system to afford 4 (7 mg) and 1 (21 mg). 4.4. Locustoside B (1) Colorless crystals. Mp 195.0e195.5  C; [a]D
27 (с 0.3, MeOH); IR (KBr) nmax 3403, 3321, 1635, 1577 cm
1; UV (MeOH) 247 nm (log ε 3.94), 291 (log ε 3.89); ECD (MeOH) Dε227 e8.6, Dε289 þ0.75; 1H NMR, see Table 1; 13C NMR, see Table 1; (þ)HRESITOFMS m/z 514.2144 [MþH]þ (calcd for C21H32N5Oþ 10: 514.2144). 4.5. Saikachinoside B (2) A colorless oil. [a]D
11 (с 0.09, MeOH); IR (film) nmax 3400, 3323, 1641, 1620, 1577 cm
1; UV (MeOH) 246 nm (log ε 3.86), 290 (log ε 3.77); ECD (MeOH) Dε226 e7.1, Dε288 þ1.0; 1H NMR, see Table 1; 13C NMR, see Table 1; (þ)HRESITOFMS m/z 530.2095 [MþH]þ (calcd for C21H32N5Oþ 11: 530.2093). 4.6. Saikachinoside C (3) A colorless oil. [a]D
31 (с 0.1, MeOH); IR (film) nmax 3392, 3325, 1635, 1624, 1577 cm
1; UV (MeOH) 248 nm (log ε 3.87), 290 (log ε 3.77); ECD (MeOH) Dε226 e5.9, Dε245 þ0.77, Dε263 e0.30; 1H NMR, see Table 1; 13C NMR, see Table 1; (þ)HRESITOFMS m/z 560.2197 [MþH]þ (calcd for C22H34N5Oþ 12: 560.2198). 4.7. X-ray crystallographic analysis of 1 Data collection was performed with a Bruker SMART-APEX II ULTRA CCD area detector with graphite monochromated Mo Ka radiation (l ¼ 0.71073 Å). The structure was solved by direct methods using SHELXS-97 (Sheldrick, 2008). Refinements were performed with SHELXL-2014 (Sheldrick, 2014) using full-matrix least squares on F2. All non-hydrogen atoms were refined anisotropically. Hydrogen atoms were refined isotropically. Crystal data: C21H31N5O10 2CH3OH, M ¼ 577.59, orthorhombic, crystal size, 0.10  0.06  0.03 mm3, space group P212121, Z ¼ 4, crystal cell parameters a ¼ 5.711 (8) Å, b ¼ 17.20 (2) Å, c ¼ 28.67 (4) Å, V ¼ 2817 (7) Å3, F(000) ¼ 1232, Dc ¼ 1.362 g/cm3, T ¼ 100 K, 13,786 reflections measured, 5140 independent reflections [R(int) ¼ 0.0646], final R indices [I > 2.0s(I)], R1 ¼ 0.0428, wR2 ¼ 0.0822, final R indices (all data), R1 ¼ 0.0765, wR2 ¼ 0.0958. CCDC-1551303 contains the supplementary crystallographic data for this paper. The data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

4.9. Acid phosphatase inhibition assay Acid phosphatase from wheat germ was purchased from Tokyo Chemical Industry Co., Ltd. (Tokyo, Japan). The enzyme activity was measured according to the reported method with a slight modification (Wurzinger et al., 1985). Briefly, an aq. solution of a test compound (10 ml) was added to a 0.1 mg/ml enzyme solution in 0.1 M sodium acetate buffer at pH 5.0 (80 ml), and preincubated for 10 min at room temp. The enzymatic reaction was initiated by the addition of 10 ml of 2 mM p-nitrophenyl phosphate (p-NPP) as the substrate. After 15 min incubation at 37  C, the reaction was terminated by the addition of 100 ml of 1 M Na2CO3 and the absorbance of released p-nitrophenolate was measured at 415 nm using a 96-well microplate reader (iMark, Bio-Rad, USA). The inactive mixture prepared by the addition of 1 M Na2CO3 prior to pNPP addition was used as a blank, water was used as a negative control, and guanine (Wako Pure Chemical Industries, Ltd., Osaka, Japan) was used as a positive control (16.1 ± 0.1% inhibition at 1 mM). Results are expressed as percentage decrease with respect to negative control values. All experiments were performed in duplicate. Acknowledgments We thank Dr. Chona D. Gelani, Mindanao State University-Iligan Institute of Technology, Philippines, for reading the manuscript. Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.phytochem.2017.08.006. References Belikov, A.S., Ban’kovskii, A.I., Tsarev, M.V., 1954. Alkaloid from Gleditschia triacanthos. Zhur. Obsch. Khim 24, 919e922. Cafieri, F., Fattorusso, E., Mangoni, A., Taglialatela-Scafati, O., 1995. Longamide and 3,7-dimethylisoguanine, two novel alkaloids from the marine sponge Agelas longissima. Tetrahedron Lett. 36, 7893e7896. Fitch, R.W., Spande, T.F., Garraffo, H.M., Chase, R.R., Clinedinst, M.A., Parkes, D.A., Reed, R., Whittaker, N.F., Daly, J.W., 2009. Dioicine: a novel prenylated purine alkaloid from Gymnocladus dioicus. Heterocycles 79, 583e598. Hamana, K., Niitsu, M., Samejima, K., 1996. Further polyamine analyses of leguminous seeds and seedlings: the occurrence of novel linear, tertiary branched and quaternary branched pentaamines. Can. J. Bot. 74, 1766e1772. Hara, S., Okabe, H., Mihashi, K., 1987. Gas-liquid chromatographic separation of aldose enantiomers as trimethylsilyl ethers of methyl 2-(polyhydroxyalkyl)thiazolidine-4(R)-carboxylates. Chem. Pharm. Bull. 35, 501e506. Kajimoto, T., Aoki, N., Ohta, E., Ohta, S., 2010a. Locustoside Aea new purine alkaloid

150

Y. Harauchi et al. / Phytochemistry 143 (2017) 145e150

glucoside from seeds of Gleditsia japonica. Phytochem. Lett. 3, 198e200. Kajimoto, T., Aoki, N., Ohta, E., Kawai, Y., Ohta, S., 2010b. Saikachinoside A, a novel 3prenylated isoguanine glucoside from seeds of Gleditsia japonica. Tetrahedron Lett. 51, 2099e2101. Kitagawa, I., Hori, K., Sakagami, M., Hashiuchi, F., Yoshikawa, M., Ren, J., 1993. Saponin and sapogenol. XLIX. On the constituents of the roots of Glycyrrhiza inflate Batalin from Xinjiang, China. Characterization of two sweet oleananetype triterpene oligoglycosides, apioglycyrrhizin and araboglycyrrhizin. Chem. Pharm. Bull. 41, 1350e1357. Konoshima, T., Fukushima, H., Inui, H., Sato, K., Sawada, T., 1981. The structure of prosapogenin obtained from the saponin of Gleditsia japonica. Phytochemistry 20, 139e142. Lan, M.-S., Ma, J.-X., Tan, C.-H., Wei, S., Zhu, D.-Y., 2010. Chemical constituents of Phyllanthus reticulatus. Helv. Chim. Acta 93, 2276e2280. Leonard, N.J., Deyrup, J.A., 1962. The chemistry of triacanthine. J. Am. Chem. Soc. 84, 2148e2160.

Robins, M.J., Hall, R.H., Thedford, R., 1967. N6-(D2-Isopentenyl)adenosine. A component of the transfer ribonucleic acid of yeast and of mammalian tissue, methods of isolation, and characterization. Biochemistry 6, 1837e1848. Sheldrick, G.M., 2008. A short history of SHELX. Acta Cryst. A 64, 112e122. Sheldrick, G.M., 2014. SHELXL-2014/6: Program for Crystal Structure Refinement. € ttingen, Go €ttingen, Germany. University of Go Stewart, R., Harris, M., 1977. Amino group acidity in nucleotide bases. Can. J. Chem. 55, 3807e3814. Wan, Y., Dong, Y., Qi, Z., Yang, R., Shi, L., Wang, Y., Fu, J., 2001. Study on chemical constituents of the seeds of Gleditsia japonica. Xibei Zhiwu Xuebao 21, 689e692. Wurzinger, K.H., Novorty, J.E., Mohrenweiser, H.W., 1985. Studies of the purine analog associated modulation of human erythrocyte acid phosphatase activity. Mol. Cell. Biochem. 66, 127e136. Zhang, J.-P., Tian, X.-H., Yang, Y.-X., Liu, Q.-X., Wang, Q., Chen, L.-P., Li, H.-L., Zhang, W.-D., 2016. Gleditsia species: an ethnomedical, phytochemical and pharmacological review. J. Ethnopharmacol. 178, 155e171.