Thus, the new triterpene cycloartane glycoside askendoside K (1) was 23R,24R-cycloartan-3ꢀ,6ꢁ,16ꢀ,23,24,25-hexaol
3-O-[(ꢁ-L-arabinopyranosyl)(1ꢂ2)-ꢀ-D-xylopyranoside],23-O-[(ꢀ-D-glucuronopyranosyl)(1ꢂ2)-ꢀ-D-glucopyranoside].
EXPERIMENTAL
General comments have been published [12]. The following solvent systems were used: CHCl :MeOH:H O (65:35:7,
3
2
13
1); CHCl :MeOH (10:1, 2); n-BuOH:Py:H O (6:4:3, 3); CHCl :MeOH:H O (70:12:1, 4); 70:25:4, 5). PMR and C NMR
3
2
3
2
spectra were obtained on UNITYplus 400 (Varian) and DRX-500 (Bruker) spectrometers from Py-d solutions of the compounds.
5
13
Data for spectra of 1 that were obtained with added trifluoroacetic acid are also given. C NMR spectra were recorded with
full C–H decoupling and under DEPT conditions. 2D spectra of 1 were taken using standard Varian programs. Chemical
shifts of protons are given versus HMDS; of C atoms, relative to the resonance of the ꢀ-C atoms of Py-d (ꢃ 123.493 vs. TMS).
5
Isolation and separation of triterpenoids from Astragalus taschkendicus Bunge were reported [13–15]. Fractions
eluted after askendoside H and several more polar glycosides that contained askendoside K (1) were combined and
rechromatographed over a column using system 1 to isolate 1 (1.5 g, 0.0285% of air-dried raw material).
13
Askendoside K (1), C H O , white non-crystalline powder. Table 1 lists the PMR and C NMR spectra.
52 86 25
Cycloorbigenin C (2) from 1. Compound 1 (300 mg) was hydrolyzed by methanolic H SO (30 mL, 0.5%) on a
2
4
boiling-water bath for 6 h. The mixture was diluted with H O. The MeOH was evaporated. The resulting solid was filtered
2
off, washed with H O, and dried. The dry solid was chromatographed over a column of silica gel with elution by system 2 to
2
afford genin 2 (120 mg), C H O , mp 256–258°C (MeOH), which was identified as cycloorbigenin C [6, 7].
30 52
6
2
PMR spectrum of cycloorbigenin C (400 MHz, C D N, ꢃ, ppm, J/Hz, 0 = HMDS): 0.19 and 0.47 (d, J = 4, 2H-19),
5
5
3
3
3
0.90 (s, CH ), 1.08 (d, J = 6.4, CH -21), 1.26, 1.27, 1.57, 1.61, 1.79 (s, 5 ꢄ CH ), 3.56 (dd, J = 11.5, J = 4.7, H-3), 3.65
3
3
3
1
2
3
3
3
3
3
3
3
3
3
(d, J = 8.5, H-24), 3.70 (td, J = J = 9.4, J = 3.8, H-6), 4.22 (td, J = J = 8.7, J = 2, H-23), 4.59 (td, J = J = 7.8,
1
2
3
1
2
3
1
2
3
13
J = 4.9, H-16). Table 1 lists the C NMR spectrum of cycloorbigenin C.
3
The filtrate was evaporated to a small volume and heated on a water bath for 1 h to destroy methylglycosides. The
solution was cooled and neutralized with BaCO . A precipitate formed. The aqueous solution was concentrated and analyzed
3
by PC using system 3 and comparison with authentic samples. PC detected D-glucose, D-xylose, D-glucuronic acid, and
13
L-arabinose. PMR and C NMR spectra of 1 showed that these monosaccharides were present in the glycoside in a 1:1:1:1
ratio.
Partial Hydrolysis of 1. Compound 1 (500 mg) was hydrolyzed by methanolic H SO (50 mL, 0.25%) for 8 h at
2
4
40°C. The mixture was diluted with H O. The MeOH was evaporated. The aqueous solution was treated with n-BuOH. The
2
BuOH extract was washed with H O and evaporated to dryness. The dry solid was chromatographed over a column with
2
elution by system 2 to afford 2 (90 mg), which was identified as cycloorbigenin C by direct comparison and PMR spectral
data.
Further elution of the column by system 4 produced progenin 3 (27 mg). Continued elution of the column by system
5 gave progenin 4 (35 mg). Further elution of the column by the same solvent system isolated progenin 5 (30 mg).
23R,24R-Cycloartan-3ꢀ,6ꢁ,16ꢀ,23,24,25-hexaol 3-O-ꢀ-D-Xylopyranoside or Cycloorbicoside D (3) from 1.
28
Progenin 3, C H O , mp 285–287°C (MeOH), [ꢁ]
0
3° (c 0.44, MeOH), identified as cycloorbicoside D based on
35 60 10
D
spectral data and comparison with an authentic sample [7–9].
2
PMR spectrum of cycloorbicoside D (400 MHz, C D N, ꢃ, ppm, J/Hz, 0 = HMDS): 0.13 and 0.42 (d, J = 4, 2H-19),
5
5
3
3
3
0.88 (s, CH ), 1.06 (d, J = 6.6, CH -21), 1.21, 1.24, 1.56, 1.60, 1.88 (s, 5 ꢄ CH ), 3.52 (dd, J = 11.6, J = 4.4, H-3),
3.61 (dd, J = 11.6, J = 10, D-xylose H-5a), 3.64 (m, H-6), 3.64 (d, J = 8.4, H-24), 3.95 (dd, J = 8.8, J = 7.2, D-xylose
3
3
3
1
2
2
3
3
3
3
1
2
3
3
2
3
H-2), 4.05 (t, J = J = 8.8, D-xylose H-3), 4.13 (m, D-xylose H-4), 4.21 (m, H-23), 4.25 (dd, J = 11.2, J = 5.2, D-xylose
1
2
3
3
3
3
13
H-5e), 4.58 (td, J = J = 7.3, J = 4.7, H-16), 4.79 (d, J = 7.5, D-xylose H-1). Table 1 lists the C NMR spectrum of
1
2
3
cycloorbicoside D.
23R,24R-Cycloartan-3ꢀ,6ꢁ,23,24,25-hexaol 23-O-[(ꢀ-D-Glucuronopyranosyl)(1ꢂ2)-ꢀ-D-glucopyranoside] (4)
28
from 1. Progenin 4, C H O , [ꢁ] –7.4 2° (c 1.35, MeOH).
42 70 17
D
2
PMR spectrum of progenin 4 (500 MHz, C D N, ꢃ, ppm, J/Hz, 0 = HMDS): 0.14 and 0.40 (d, J = 4, 2H-19),
5
5
3
3
3
0.82 (s, CH ), 1.21 (d, J = 6, CH -21), 1.25, 1.28, 1.56, 1.57, 1.79 (s, 5 ꢄ CH ), 3.55 (dd, J = 12, J = 4, H-3), 3.64 (td,
J = J = 9, J = 3, H-6), 4.56 (m, H-16), 4.75 (m, H-23), 5.51 (d, J = 7, D-glucuronic acid H-1). The resonance of
3
3
3
1
2
3
3
3
3
1
2
3
13
D-glucose H-1 overlapped the H O resonance at ꢃ 5.28. Table 1 lists the C NMR spectrum of progenin 4.
2
590