Sesquiterpene polyol esters from Celastrus rosthornianus

Phyfochemwry,Vol. 30, No. 12, pp. 4169 4171, 1991 Printedin Great Bntain.

SESQUITERPENE

POLYOL Tu

0031.9422/91 $3.00 + 0.00 ‘c” 1991 PcrgamonPressplc

ESTERS

FROM

YONGQIANG*

and

CELASTRUS

ROSTHORNZANUS

CHEN YAOZU

Department of Chemistry, Lanzhou University, Gansu Province People’s Republic of China (Receioed 7 January 1991)

Key Word Index-Celastrus

rosthornianus; Celastraceae; root bark; sesquiterpene polyol esters; 2D NMR spectra.

Abstract-Two new sesquiterpene polyol esters with fi-dihydroagarofuran skeleton were isolated from the root bark of Celustrus rosthornianus. Their structures were elucidated, mainly on the basis of spectral analyses, as 1/3-acetoxy-8J,9adibenzoyloxy-6a-hydroxy-28(a-methylbutanoyloxy)-8-dihydroagarofuran and l/?-acetoxy-9a-benzoyloxy-8b(b-furancarbonyloxy)-6a-hydroxy-2/l (a-methylbutanoyloxy)~@-dihydroagarofuran. The complete assignments of “C NMR chemical shifts for both compounds on the basis of ’ H-’ 3C chemical-shift correlation spectrum were also carried out.

lNTRODUCITON

In previous studies of the chemical constituents from the root bark of Celustrus rosthornianus Lees., we reported two sesquiterpene polyol esters with fi-dihydroagarofuran skeleton Cl], one of which exhibits insect antifeedant activity against the larvae of Pieris rapae with a 49% antifeedant rate. A recent study has resulted in the isolation of two new sesquiterpene polyol esters (2 and 3). Both compounds are derivatives of /?-dihydroagarofuran polyol(1). We describe the structure elucidation of compounds 2 and 3. RESULTS AND DISCUSSION

Compound 2 analysed for C36H,,0,, by elementary analyses and mass spectrometry. Its IR spectrum revealed absorptions for a hydroxy group at v 3458 cm-’ ester groups at v 1742cm-’ and phenyl groups at v 1600 and 1454 cm- ‘. The mass spectrum exhibited peaks due to the losses of acetic acid (m/z 561 [M-Me - HOAc]+), benzoic acid (m/z 514 [M - PhCO,H]+) and pentanoic acid (m/z 534 [M -C,H,CO,H]’ ). In good agreement with the data above, the ‘H and lJCNMR spectra suggested the presence of one acetate ester [‘H NMR: 6 1.57 (3H, s); 13C NMR: 620.3 (Me) and 169.4 (-CO,-)], two benzoate esters [‘H NMR: 67.48-8.09 (lOH, m); “CNMR: 6128.5-133.6 (2x Ph) and 2x 164.8 (2 x -CO,-)], and one r-methylbutanoate ester [ 1H NMR: 60.90(3H,t,J=7 Hz), l.l4(3H,d,J=7 Hz), 1.48and 1.66 (each lH,m),and2.35(1H.m); 13CNMR:611.5 and 16.7 (each Me), 26.2(CH,), 41.7 (CH), 175.7(-CO,-)] [2,3]. In addition, the 13C NMR and DEPT spectra indicated that the parent skeleton consists of 15 carbons: four methyl carbons (6 19.1, 20.7, 26.0 and 31.3), one methylene carbon(6 31.3),sevenmethinecarbons(633.2,55.2,69.5,71.4, 73.2,77.0 and 77.1), and three quaternary carbons (648.8, 82.3 and 91.6). These data were in good agreement with the spectral values assigned to the 1,2,6,8,9_pentasubstituted /?-dihydroagarofuran skeleton [l, 43. Therefore, four ester groups above and one free hydroxy group were located at five carbons (C-l, C-2, C-6, C-8 and C-9) of the fl-dihydroagarofuran. PHYTO ,O:,l-”

?H

H?

1

In the ‘H NMR spectrum (see Experimental), the doublet at 6 5.57 (1H, J =4 Hz) and quartet at 65.66 (1 H, 5=4, 8 Hz) were assigned to H-l and H-2, respectively. Generally, H-l and H-6 in all compounds of this class have axial stereochemistry [S, 63, thus the coupling constant (.J=4 Hz) between Ha-l and H-2 suggested the stereochemistry of the equatorial H-2. The broad singlet at 64.99 (1H) was assigned to the axial H-6 due to the weak coupling between Ha-6 and He-7 in all compounds of this class [S, 63. The singlet at 6 5.1 I (I H) was assigned to He-9 because of the weak coupling between He-8 and He-9 [7,8]. The AB quartet at 62.53 and 5.55 (each lH, J =3 Hz) was assigned to He-7 and He-g, respectively. These assignments, together with others given in the Experimental section, were confirmed by qualitative NOE difference experiments (see structure 2). In this class of compound, when the C-6 hydroxyl group is esterified then H-6 generally has a ‘HNMR chemical shift around 66.00 [S]. Thus, the upfield value (64.99) for H-2 of 2 suggested the presence of a free C-6 hydroxyl. The location of two benzoate ester groups was based on the ‘H-“C long-range correlation (COLOC) spectrum [9], in which the correlative signals between H8 (S5.55) and the carbonyl (6 164.8) of one benzoate ester (A), and between H-9 (65.1 I) and the carbonyl(a164.8) of the second benzoate ester (B), were found. This indicated these two benzoate esters are located at C-8 and C-9, respectively. Therefore, two remaining aliphatic acid esters were located at C-l, and C-2, respectively. In the COLOC spectrum, there was no correlative signal between the carbonyls of two aliphatic acid esters and their

4169

Short Reports

e

Me

\_,/b.&J COLOC

of 2

NOE of 2

corresponding methine hydrogens (H-l and H-2). However, the correlative signal (C), between the carbonyl (6169.4) of the acetate ester and its methyl hydrogens (6 1.57). and signal (D), between the carbonyl(6 175.7) of amethylbutanoate ester and its methyl hydrogen (a 1.14), were found. The former signal (C) confirmed the reasonable assignment of the very sharp and upfield ‘H NMR signal at 6 1.57 (3H. s) to the acetate methyl. This chemical shift value was much smaller than normal (61.9-2.7), suggesting that the acetate ester is located at C-l [6]. The remaining ~-methylbutanoate ester thus was located at C-2, which was confirmed by the relatively intese McLafferty rearrangement peak at m/z534([M-C,H,CO,H]; 13%) in the mass spectrum, due to the ester McLafferty rearrangement at C-2 which is more favourable than those at other positions 12, lo]. Based on the evidence above, the structure of compound 2 was elucidated as 1bacetoxy-8P,9a-dibenzoyloxy-6a-hydroxy-Z~(~-methylbutanoyloxy)-fl-dihydroagarofuran. Compound 3 analysed for C,,H,,O, 1 by elementary analyses and mass spectrometry. Its IR, ‘HNMR, 13CNMR, and mass spectral data (see Experimental) suggested the presence of one acetate ester, one benzoate ester, one /I-furancarboxylate ester, one a-methylbutanoate ester and the 1,2,6,8,9-~ntasubstituted ~-dihydroagarofuran skeleton. In addition, the molecular composition suggested the presence of one free hydroxy group, whose presence was confirmed by the IR absorption at ~3520 cm - *. Therefore, four ester groups and one free hydroxy group were located at five carbons (C-l, C-2, C-

NOE of

3

6, C-8 and C-9, respectively) of the /?-dihydroagarofuran parent. As with com~und 2, the assignment of ‘HNMR chemical shifts for the parent hydrogens and the determination of stereochemistry of H-2, H-8 and H-9 were carried out on the basis of qualitative NOE difference experiments. The doublet at 65.56 (lH, J =4 Hz) and quartet at B5.66 (1H, J = 4, 8 Hz) were assigned to Ha-l and He-2, respectively. Two singlets at 64.93 and 5.03 (each 1H) were assigned to Ha-6 and He-9, respectively. The AB quartet at 6 2.42 and 5.47 (each 1H, J = 4 Hz) was assigned to He-7 and He-8, respectively. The assignments for other signals of the compound are summarized in the Experimental. In a qualitative NOE difference experiment, the irradiation of H-14 at S 1.53 (3H, s) caused the increase of the signal at 68.04 (2H. m) for H-2’ of benzoate ester, suggesting that the benzoate ester is located at C-9. As with 2, the upfield very sharp singlet at 6 1.57 (3H) was assigned to acetate methyl, which suggested the location of acetoxy at C-1. The upfield singlet at 54.93 for H-6 suggested the location of a free hydroxy group at C-6. The relatively intense McLafferty rearrangement peak at m/z 524 (CM-C,H,CO,H]; 13%) in the mass spectrum suggested the location of ~-methylbutanoyloxy at C-2. The remaining fl-furancarboxylate ester was located at C8. Thus, the structure of 3 is lb-acetoxy-9abenzoyIoxy 8#I (8-furancarbonyloxy)-6z-hydroxy-28(z-methylbutanoyloxy)+dihydroagarofuran. In general, the complete assignment of the r3C chemical shifts for the parent skeleton on the basis of the r3CNMR spectrum alone was very difficult, due to the fact that the methine carbons bearing ester groups or hydroxy group, such as C-l, C-2, C-6, C-8 and C-9, in compound 3, had very similar chemical shifts. However, the complete assignment (see Experimental) of “CNMR chemical shifts for compound 3 was easily carried out on the basis of the 1H-‘3C chemical-shift correlation spectrum, which signals A, 8. C, D and E showed correlations between H-l (65.56) and C-1 f&71.2), H-2 (55.66) and C-2 (S69.2), H-6 (64.93) and C-6 (S73.2), H-8 (65.47) and C-8 (S76.4), and H-9 (65.03) and C-9 (fi77.0), respectively. In comparison with 3, the complete assignments of the “C NMR chemical shifts of 2 were also carried out. EXPERIMENTAL hips: uncorr. The ‘H-‘3C chemical-shift correlation spectrum was obtained at 500 MHz with CDCI, as solvent and TMS as

4171

Short Reports int. standard. Silica gel (20@-300 mesh) and neutral alumina (100 mesh) were used for CC. Merck silica gel 60 F254 and Merck RP-18 prep. TLC plates were used for chromatography. Expe.rimental material was collected from Yunnan Province (China), and authenticated by the Department of Botanical Systematics, Kunming Institute of Botany, the Academy of Science of China. Voucher specimens are deposited at the Botanical Garden of Kunming Institute for Botany. Extraction and isolation. The air-dried and pulverized root bark (2 kg) of C. rosthornianus was extracted with Me,CO at room temp. for 2 days. Removal of the solvent under red. pres. gave a dark brown residue, which was chromatographed on an alumina column with CHCI, as eluent to give a total fraction. After concentration of the total fraction under red. pres., the residue was rechromatographed on a silica gel column with Me,CO-petrol (I : 9+ 1: I) as eluent to give 48 frs, which were combined into 3 groups. The middle polar group was chromatographed on prep. silica gel plates with Me,CO-C,H, (I : 1) as developer, and finally purified on RP-I8 prep. TLC with MeOH-H,O (4: 1) to give 2 (55 mg) and 3 (21 mg). Compound 2. Crystals, mp 225-226” (from petrol-AcOEt). Found: C, 67.90; H, 6.91 (calcd. for C,,H,,O,,: C, 67.92; H, 6.92). UV A:$“’ nm (logs): 233 (2.8333,274 (1.536). 281 (1.403). IR v:t;ccm-‘: 3458 (OH), 2966, 2931, 1742 (C=O), 1600 and 1454 (Ph), 1370, 1271, 1096,963,709. ‘H NMR: S 5.57 (IH, d, J =4 Hz H-l), 5.66 (lH, dd, J =4, 8 Hz, H-2), 1.78 and 2.46 (each l H,m,H-3),2.42(1H,m,H-4),4.99(lH,hrs,H-6),2.53(1H,d,J = 3 Hz, H-7), 5.55 (I H, d, J = 3 Hz, H-8), 5. I 1 (1 H, s, H-9), 1.45 (3H. d, J=7.3 Hz, H-12). 1.73 (3H, s, H-13). I.54 (3H. s, H-14), 1.58 (3H, s, H-15). 1.57 (3H, s, AcO), 7.48-8.09 (IOH, m, 2 x PhCO), 0.90 (3H, r, 5=7 Hz), 1.14 (3H, d, 5=7 Hz). 1.48 and 1.66 (each lH, m). and 2.35 (lH, m) (a-methylbutanoyloxy), “CNMR: 671.4 (C-l), 69.5 (C-2), 31.3 (C-3), 33.2 (C-4). 91.6 (C5), 73.2 (C-6),55.2 (C-7), 77.1 (C-8), 77.0 (C-9),48.8 (C-IO), 82.3 (Cl I), 19.1 (C-12). 20.7 (C-13), 26.0 (C-14), 31.3 (C-151, 20.3 and 169.4 (AcCO), 128.5-133.6 and 2 x 164.8 (2 x PhCO), 11.5 (Me), 16.7 (Me), 26.6 (CH,), 41.7 (CH) and 175.7 (-COz-) (a-methylbutanoyloxy). EIMS m/z (rel. int.): 636 [Ml+ (41). 621 [M -Me] * (83), 561 [621- HOAc] + (2), 534 [M - a-methylbutanoic acid]+ (13), 515 [M-PhCOz]’ (IO), 514 [M-PhCO,H]+ (3), 481 (IO), 379 (21), 249 (81, 237 (61), 215 (70). 173 (39), 105 [PhCO)’ (IOO),85 [a-methylbutanoyl]+ (43). 77 [Ph]’ (48), 69 [AcO]’ (IO), 57 [2-butyl)’ (69). 43 [AC]’ (35). Compound 3. Amorphous powder, Found: C, 65.16: H, 6.69 (calcd. for CJ4H4*01 ,: C, 65.18; H, 6.71). UV i:::” nm (logs): 232 (3.226), 275 (3.051). 282 (2.964). IR vi!: cm-‘: 3520 (OH), 2930, 1730 (C=O), 1600 and 1454 (Ph), 1385, 1365, 1076.

‘HNMR:65.56(1H,d,J=4Hz,H-l),5.66(1H,dd,5=4,8Hz, H-2). 1.79and 2.46(each lH,m, H-3). 2.42(tH,m, H-4),4.93(lH, hr s, H-6). 2.47 (IH, d, 5=4 Hz, H-7). 5.47(lH,d. 5=4 Hz, H-8), 5.03(1H.s. H-9). 1.45(3H,d,J=7.2 Hz, H-12). 1.66(3H.s, H-13). lS3(3H,s, H-14). 1.58 (3H,s, H-15), 1.57(3H, s, AcO), 7.w.04 (SH, M, PhCO), 6.78,7.48 and 8.08 (each lH, br s, ~-furancarbonyloxy), 0.90 (3H, f, J = 7 Hz), 1.14 (3H, d, J = 7 Hz), 1.48 and 1.66 (each I H, m) and 2.35 (I H, m) (a-methylbutanoyloxy). ‘% NMR: 671.2(C-1),69.4(C-2). 31.3(C-3),33.2(C-4),91.5(C-5), 73.2(C-6). 55.2 (C-7). 76.4 (C-8), 77.0 (C-9). 48.9 (C-IO), 82.3 (C-l 1). 19.1 (C12), 20.7 (C-13). 26.0 (C-14). 31.3 (C-15), 20.4 and 169.4 (AcO), 128.7-133.6 and 164.9 (PhCO), 109.8 (CH), 119.1 (quaternary carbon), 144.0 (CH), 148.0 (CH) and 161.1 (-CO,-) (~-furan~rbonyloxy), Il.6 (Me), 16.7 (Me), 26.6 (CH,), 41.7 (CH) and 175.8 (CO,-) (z-methylbutanoyloxy). EIMS m,%(rel. int.): 626 [M]’ (62). 611 [M-Me]+ (Sl), 551 [61l-HOAc]+ (2), 524 [Ma-methylbutanoic acid]’ (13). 517 [6ll -PhCO+H]+ (II), 504 [M-PhCO,H]+ (3), 481 (IO), 379 (19), 249 (IO), 237 (42). 215 (63), 173 (35), 105 [PhCO]’ (lOO),95 [/?-furancarbonyI]- (88). 85 [z-methylbutanoyl]+ (67). 77 (Ph]+ (23), 57 fisobutyl] + (67),43 [AC] + (38). Acknowledgement-We are grateful to Mr Li Zi Zhong for measurements of 2D NMR spectral data. REFERENCES

1. Tu, Y. Q. (1991) P~~~a~hern~srry 30, 1321. 2. Tu, Y. Q., Wu, D. G., Zh, I., Chen, Y. Z. and Pan, X. F. (1990) J. Nat. Prod. 53, 603. 3. Tu, Y. Q. (1990) J. Nat. Prod. 53, 915. 4. Hertog Jr, H. J., Kruk, C., Nanavati, D. D. and Dev, S.(1974) Tetrahedron Letters 2219. 5. Bruning, R. and Wagner, H. (1978) P~yf~~em~rry 17.1821. 6. Wakabayashi, N., Wu, W. J., Waters, R. M., Redfem, R. E., Mills, J. G. D., DeMilo, A. B., Lusby, W. R. and Andrzejewski, D. (1988) J. Nat. Prod. 51, 537. 7. Becorra, J., Gaete, L., Silva, M., Bohlmann, F. and Jakupovic, J. (1987) Phytochemistry 26. 3073. 8. Baudouin, G., Tillequin, F., Koch, M., Tran Huu Dau, M. E., Guilhem, J. and Jacquemin, H. (1984) Hererocyeies 22, 2221. 9. Yoshihisa, T., Kunie, U., Hiroyasu. N., Kimiko, N., Toshiaki, T., Shigetoshi, K., Koji, T. and Tohru, K. (1987) Chem. Pharm.

Bull. 35, 3534.

IO. Tu, Y. Q.. Wu, D. G., Zh. J. and Chen, Y. Z. (1990) Phylachemistry

29, 2923.