Purification and Separation of Eight Steroidal Plant-growth Regulators from Dolichos lablab Seed

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1 j Agric. Biol. Chem., 48 (10), , Purification and Separation of Eight Steroidal Plant-growth Regulators from Dolichos lablab Seed Takao Yokota, Jun Baba, Shigeki Koba and Nobutaka Takahashi Department of Agricultural Chemistry, The University of Tokyo, Bunkyo-ku, Tokyo 113, Japan Received May 7, 1984 Purification and separation of eight steroidal plant-growth regulators, dolicholide, dolichosterone, homodolicholide, homodolichosterone, brassinolide, castasterone, 6-deoxocastasterone and 6-deoxodolichosterone, from immature seed of Dolichos lablab were accomplished using various chromatographic techniques. The reversed-phase HPLCof a number of steroidal plant growthregulators was also studied. The extract from immature seed of Dolichos lablab contains high levels of brassinolide activity as determined by the rice-lamina inclination test. Wehave preliminarily reported the isolation and structures of new brassinolide-related steroidal growth regulators, dolicholide (2), dolichosterone (6), homodolicholide (3) and homodolichosterone (7), from the seed, as well as the identification of castasterone (5) and brassinolide (1).1~3) Wedescribe here the details of the purification procedures of the steroidal growth regulators from the Dolichos seed. Recent findings of the occurrence of 6-deoxocastasterone (9) and 6- deoxodolichosterone (10) are also described. The methanol extract obtained from D. lablab seed was partitioned between benzene and water. The water phase was again partitioned with chloroform. Using the rice lamina inclination test,4) which is very sensitive to brassinolide and related compounds,5) about 90% of the total activity was found in the benzene fraction, while the rest (10%), in the chloroform fraction. No activity was found in the aqueous residue. The benzene fraction contained a large amount of lipids and pigments, and therefore was subjected to solvent partitioning between hexane and aqueous methanol, resulting in the nearly quantitative transfer of the activity into the latter. The aqueous methanol fraction was combined with the chloroform fraction and processed as shown in Fig. 1. Upon silica gel chromatography using chloroform-methanol mixtures, a less polar fraction (fraction ) and polar fraction (fraction ) were separated as shown in Fig. 2. n this procedure, about a 20-fold reduction of the dry weight was attained. Another silica gel chromatography was carried out using a benzene-ethyl acetate mixture as the solvent, in Extract of D. lablab seed Silica gel chromatography Hydrated silica gel chromatography A B C D i L Sephadex LH-20 chromatography "i i i r A! B' C D1 i L Partisil HPLC 1 n i ' i r Att Bm C"-l C"-2 Df 1 Develosil ODS HPLC å f;-r Fig. 1. Chromatographic Separation of Steroidal Plantgrowth Regulators in the Extract of D. lablab Seed. The compoundsunderlined were isolated as crystals.

2 2530 T. Yokota et al. CD.-i_cz ~ Brassinolide 1 ppb _. - _ CD -l-i ~ >H OJ -l-> cux: CO ~ _å <_ ' ' CO "" o CO OO«rH --e à"^co ^ _ 1 Control o-l : : ;: Methanol % in chloroform Fig. 2. Distribution of Biological Activity Determined by the Rice-lamina nclination Test after Silica Gel Chromatography of the Extract of D. lablab Seed. The extract (60 g) obtained from 34kg of the seed was chromatographed on a column of silica gel (500 g) and from each fraction, a portion equivalent to 12 g fr. wt of seed was removed for bioassay. Details are shownin the text. which the silica gel was deactivated to some extent by hydration because this solvent system is weak in elution power. Fraction was thus separated into fractions A and B, and fraction, into fractions C and D. This procedure was also effective in reducing the dry weight (over a 10-fold reduction), but the elution range of the activity was rather broad. Fractions A ~ D were then separately purified by Sephadex LH-20 chromatography using 70%ethanol as the solvent. On each occasion, a discrete peak of activity was observed and the ratio of the elution volume to column volume was reproducible. Thus, fractions A', B', C and D' were obtained from fractions A, B, C and D respectively. The elution profile in the chromatography of fraction C is presented in Fig. 3. n the authors' experience, the use of a 4 : 1 mixture of methanol-chloroform as the elution solvent also gives satisfactory result: this system has been applied for other plant extracts.4'6) Fractions A', B', C, and D' were separately purified by Partisil (silica gel) HPLC with gradient systems using a chloroformisopropanol mixture. Based on a bioassay and TLCexamination, similar fractions were combined, affording fraction A" from fraction A', fraction B" from fraction B', fraction C"-l and C"-2 from fraction C and fraction D" from fraction D'. These were purified by reversed-phase HPLCusing Develosil ODSand aqueous acetonitrile. The effectiveness of this technique in purifying individual components is discussed in a later section. The fractions thus obtained were examined by a bioassay and TLC, and similar fractions were combined and subjected to crystallization from aqueous acetonitrile. Thus four new steroidal growth regulators were isolated as crystals, namely 50fig of dolichosterone (6) and 20 fig of homodolichosterone (7) from fraction B", and 12fig of homodolicholide (3) and 160 fig of dolicholide (2) from fractions C"-l and C"-2 respectively; a small amount of dolicholide was also obtained from fraction D". The structures of these compoundswere determined by mass spectrometry and 400 MHzXHNMR,1~3) and finally were confirmed by direct comparison

3 Steroidal Plant-growth Regulators CD C7> C 03 r- J3 <C -M - C n3 S- <U à"2 "^ Brassinolide 51 " 1PPb l < o fd 50- S C à"r- (U ' > > OU ^ 3 å Control U(D _ - _ - ' <c.a _ «' 0-J Fraction number Fig. 3. Distribution of biological Activity Determined by the Rice-lamina nclination Test After Sephadex LH-20 Chromatography of Fraction C. A column of LH-20 (bed vol., 145 ml) was run with 70%ethanol and the eluate was collected in 5 ml fractions. From each fraction, a portion equivalent to 68 g fr. wt of seed was removed for bioassay r- t_ ' n_n ^ Brassinolide S 0.1 ppb CD.c - _.. +-> CO c J5 ^ +J - Control +-> <-Q L 0- rn i i i i i i i i i i i Retention time (min) Fig. 4. Distribution of Biological Activity Determined by the Rice-lamina nclination Test after Reversedphase HPLCof Fraction C-l. A column of Develosil ODS(particle size, 3/mi; 0.8 x 15cm) was run with 45% acetonitrile (flow rate, 2 ml/min) and fractions were collected every 1 min. From each fraction, a portion equivalent to 340 g fr. wt of seed was removed for bioassay. By GC-MS, the following compounds were identified; 2 (tr 7 ~ % min), 3 and 6 (10~ 12min), 7 (14~ 15min) and 5 (17~ 18 min). Compound3 was isolated as crystals from the fraction with tr9-10min.

4 2532 T. Yokota et al. (400 MHzXHNMR)with synthetic compounds.7~9) The fractions which could not be crystallized were converted to bismethaneboronates and analyzed by GC-MS. Thus, 6- deoxocastasterone (9) and 6-deoxodolichosterone (10)10) were identified from fraction A", and castasterone (5) and brassinolide (1), from fractions B" and C"-2 respectively/ Some of the above compounds were also identified from fraction C"-l (Fig. 4). Since the individual steroids were effectively separated by reversed phase HPLC on Develosil ODSusing 45% acetonitrile as the mobile phase, we examined the elution profile 6'8 (22S,235)-4 i i i i i i i i i i i i i i i i i Retention time(min) Fig. 5. Reversed-phase HPLCProfile of Nine Brassinolide-related' Steroids. Sample size: 1\i% (2, 3, 6, 7), 5/ig (5, 8), 10\i% (4 and its (225,235') isomer) and 15/ig (1). A column of Develosil ODS 5 (particle size, 5/mi, 1 x 15cm) was run with 45% acetonitrile (flow rate, 3.1 ml/min). The detector was a UVDEC 100- (JASCO). in this system of a number of brassinoliderelated steroids which have been shown to be naturally-occurring, excepting (22R,23R) homobrassinolide (4) and its (225,235) isomer (Fig. 5). Functionality in the B-ring affects the elution pattern, that is, 6-ketone types are eluted more slowly than lactome-types, cf castasterone (5) vs. brassinolide (1). Compounds with a double bond in the side chain are eluted faster than the corresponding saturated compounds, cf. brassinolide (1) vs. dolicholide (2). A similar relationship is observed between 6-deoxocastasterone (9) and 6-deoxodolichosterone (10) (see Experimental). ntroduction of a methyl group in the side chain causes an increase in the retention time, cf. brassinone (8) vs. castasterone (5), and brassinolide (8) vs. (22R, 23R) homobrassinolide (4). t is also worth noting that the configuration of the hydroxyls in the side chain significantly affects the mobility, as is observed in relationship between (22R,23R) homobrassinolide (4) and its (22.5,235) isomer. Because of such a nature in this chromatography, the compounds examined could be separated, with the exception that dolichosterone (6) and brassinone (8) were coeluted. Successful applications of this technique to other plant extracts have been reported.4'10).rh y^y --./^y vxx^ LJ " R OH R OH R OH [ 1 1 R"OH R"OH R"OH R.OH HO^'^V1 H o R"= T R'"OH ' R-OH ' R'" OH R'" OH ^k^k^ 10

5 EXPERMENTAL Melting points were not corrected. EMS (direct and GC) were obtained with a JEOL DX-300 spectrometer (70eV). The weights of crystalline compounds (3, 6, 7) were roughly estimated from the GC peak areas using brassinolide bismethaneboronate as the reference compound. TLC. Merck HPTLCplate kieselgel 60 F254 was used with a solvent system of chloroform-ethanol-acetoneacetic acid, 80 : 10 : 10 : 3. Samples were visualized as a blue or purple spot under 365nm light by spraying with 70% sulfuric acid followed by heating at 110 C for 5min. Rfvalues of1, 2, and 3 were 0.19, while those of5, 6 and 7 were0.29. GC-MS. A JEOL DX-300 mass spectrometer (70eV) was used. Unless otherwise stated, a glass column packed with 2% OV-1 on Chromosorb W (2.6mmx1m) was employed at 270 C with a helium flow at 30ml/min. Prior to gas chromatography, samples were converted into bismethaneboronates after Takatsuto et al.n) Bioassay. The rice lamina inclination test Using a rice cultivar, Koshihikari, was carried out as described elsewhere.4) Extraction and solvent partitioning. mmature seeds (34kg) of D. lablab were soaked in MeOH (30 liters), homogenized with a blender and filtered by suction. The residue was further extracted with MeOH(30 liters x 4). The combined MeOHextract was concentrated in vacuo to afford the aq. residue (5.5 liters, ph 7) which was successively extracted with benzene (3 litersx 3) and CHC13 (3 liters x 3). The benzene extract was concentrated and subjected to partitioning using 1 liter each of hexane and MeOHwhich had been saturated beforehand with each other. The hexane phase was further washed with MeOH(1 liter x 2). The MeOH phases were combined and H2O (400ml) added to separate the upper and lower phases. The former was washed with 80% MeOH.The lower phases were combined and concentrated to afford an oil (56g). This was combined with the CHC13 extract (4g) for further purification. Steroidal Plant-growth Regulators 2533 fraction (2.3g). Prior to further purification, both fractions were respectively dissolved in CHC13and washed 60%-hydrated silica gel column chromatography. Fraction was dissolved in CHC13, adsorbed to Celite, dried in vacuo, and loaded on a 60%-hydrated silica gel column (91g). Water-saturated solvents were used for elution and the eluates were collected in 15 ml fractions as follows: EtOAc-benzene, 0: 100 (fr. 1-33), 10:90 (fr ), 20:80 (fr ) and 30:70 (fr ). Fractions and were respectively combined and referred as fractions A and B. Fraction was similarly purified using a 60%-hydrated silica gel column (70g). The eluate was collected in 15 ml fractions using water-saturated mixtures of EtOAcbenzene, 20:80 (fr. 1-35), 30:70 (fr ), and40:60 (fr ). Fractions 8-35 and were respectively combined and referred as fractions C and D. Purification of fraction A. Fraction A (200mg) was dissolved in a small amount of 70%EtOH. The insoluble materials were removedby centrifugation and the supernatant was chromatographed on a SephadexLH-20 column (bed volume, 500ml; 90 x 2.66cm) using 70% EtOH. The eluate was collected in 10ml fractions (flow rate, 20ml/hr). The active fraction (elution vol., ml), termed as fraction A', was dissolved in CHC13 and subjected to HPLCusing Partisil 5 (particle size 5/mi, 0.8x 15cm): flow rate, 2ml/min; mobile phase, linear gradient from 0 to 15% iso-proh in CHC13 during 25 min. Fractions in which 6-deoxocastasterone-like spots were observed on TLC were collected (tr, 9-19min) and termed as fraction A". This was dissolved in 70%MeCN and subjected to HPLCusing Develosil ODS3 (particle size 3/mi, 0.8 x 15cm): flow rate 2ml/min; mobile phase, 70% MeCN.The fractions corresponding to 6-deoxodolichosterone tr, 8-13 min) and 6-deoxocastasterone (tr, 13-16min) were collected. From the GC-MS(column temp., 280 C, 40ml/min He flow) of the former, 6-deoxodolichosterone (10) was identified as its bismethaneboronate: tr 3.82min; m/z 496 (M+, 23%), 313 (84), 273 (18), 153 (51), 124 (94), 82 (100). From a GC- MS of the latter, 6-deoxocastasterone (9) was identified as its bismethaneboronate: tr 3.85min; m/z 498 (M+, 50%), 288 (16), 273 (100), 205 (21), 155 (39). Silica gel column chromatography. The above material was dissolved in CHC13, and charged on a column of silica gel (500g). The column was eluted with CHC13 (4.5 liters), and then with mixtures of CHCl3-MeOH; 98:2 (4.5 liters), 95:5 (2 litersx2, then 1 liter), 90: 10 (1 literx5) and 85: 15 (1 literx2, then 3 liters) and 80:20 (5 liters). The 2nd and 3rd fractions of the 5% MeOHeluate and the 1st fraction of the 10% MeOHeluate were combined and termed as fraction (2.8g). The 2nd and 3rd fractions of the 10%MeOHeluate were combined and termed as Purification offraction B. Unless otherwise stated, the purification procedure was essentially the same as that employed for fraction A. Fraction B (158mg) was first subjected to a column of Sephadex LH-20 (bed vol., 145ml) and the eluate with 70% EtOH was collected in 5ml fractions. The active fraction (elution vol., ml), termed as fraction B', was purified by Partisil HPLC: flow rate, 3ml/min; mobile phase, linear gradient from 0 to 15% iso-proh in CHC13 during 15min, then 15% iso-proh in CHC13 (isocratic) during 30min.

6 2534 T. Yokota et al. The active fraction (tr 1 1 ~ 17 min), termed as fraction B", was purified by Develosil ODS 3 HPLC using 45% MeCN as the mobile phase. The fraction with a tr of 12~ 14min was crystallized from aq. MeCNto afford 50fig of dolichosterone (6), mp 233~237 C: m/z, 363 (7%), 345 (21), 327 (18), 285 (14), 269 (15) and 100 (100). The fraction with a tr 15~18min was likewise crystallized to afford 20jUg of homodolichosterone (7), mp 204~208 C: m/z, 363 (46%), 334 (50), 125 (100) and 114 (96) (data were taken from the high resolution MS). The crystals were found to contain impurities by 1H NMR. The fraction with a tr of 19~20min was subjected to GC-MS analysis, leading to the successful identification of castasterone (5) as its bismethaneboronate: tr 7.0min; m/z 512 (M+, 46%), 441 (6), 399 (8), 358 (21), 287 (24), 155 (100), 95 (42) and 85 (56). Purification of fraction C. The purification procedure employed for fraction B was applied in its entity for fraction C (97mg). After Sephadex LH-20 chromatography, the active fraction (elution vol., 95~115ml), termed as fraction C, was obtained and subjected to Partisil HPLC, yielding two active fractions, one (termed as fraction C"-l) with a tr of 16~24min and the other (termed as fraction C"-2) with a tr of 24~ 31 min. Both fractions were purified by Develosil ODS3 HPLC. Fromfraction C"-l, several active fractions were obtained (Fig. 4). Among them, a fraction with a fr of 9 ~ 10 min was crystallized from aq. MeCNto afford 12 fig of homodolicholide (3), mp 227~228 C; m/z 379 (10%), 363 (7), 345 (5), 315 (4), 303 (4), 125 (17) and 114 (100). From C"-2, the two active fractions with a tr of 8~ 10min and 10~ 15min were obtained. The former was crystallized from aq. MeCN to yield 160 /ig of dolichofide (2), mp 234~238 C: m/z 379 (21%), 361 (7), 343 (8), 325 (7) and 100 (100). GC-MS analysis of the latter fractions led to the identification of brassinolide (1) as its bismethaneboronate: tr 8.7min; m/z 528 (M+, 6%), 457 (7), 374 (36), 345 (18), 332 (26), 177 (76), 155 (100), 95 (74), 85 (84) and 81 (78). Purification offraction D. This-fraction was purified as described above, resulting in the isolation of a small amount of dolicholide. Acknowledgments. We wish to thank Professor K. Mori, Dr. K. Okada and Dr. M. Sakakibara, this Department, Professor N. kekawa, Tokyo nstitute of Technology, and Dr. F. Fujita, Zennoh Agricultural Technical Center, for generous gifts of synthetic compounds. This work was supported by a Grant-in-Aid for Cooperative Research (No ) from the Ministry of Education, Science and Culture of Japan. REFERENCES 1) T. Yokota, J. Baba and N. Takahashi, Tetrahedron Lett., 23, 4965 (1982). 2) J. Baba, T. Yokota and N. Takahashi, Agric. Biol. Client., 47, 659 (1983). 3) T. Yokota, J. Baba and N. Takahashi, Agric. Biol. Chem., 47, 1409 (1983). 4) M. Arima, T. Yokota and N. Takahashi, Phytochemistry, 23, 1587 (1984). 5) K. Wada, S. Marumo, N. kekawa, N. Morisaki and K. Mori, Plant Cell Physiol, 22, 323 (1981). 6) T. Yokota, M. Arima, N. Takahashi, S. Takatsuto, N. kekawa and T. Takematsu, Agric. Biol. Chem., 47, 2419 (1983). 7) K. Mori, M. Sakakibara and K. Okada, Tetrahedron, 40, 1767 (1984). 8) S. Takatsuto and N. kekawa, /. Chem. Soc, Perkin Trans. 1, 2133 (1983). 9) M. Sakakibara and K. Mori, Agric. Biol. Chem., 48, 745 (1984). 10) T. Yokota, M. Morita and N. Takahashi, Agric. Biol. Chem., 47, 2149 (1983). ll) S. Takatsuto, B. Ying, M. Morisaki and N. kekawa, /. Chromatogr., 239, 233 (1982).

Supporting Information

Notes Bull. Korean Chem. Soc. 2013, Vol. 34, No. 1 1 http://dx.doi.org/10.5012/bkcs.2013.34.1.xxx Supporting Information Chemical Constituents of Ficus drupacea Leaves and their α-glucosidase Inhibitory