The anomeric protons of D-xylose, D-glucose, and L-arabinose resonated in the PMR spectrum of 1 as doublets at
3
4
ꢃ 4.81, 5.02, and 5.11. Their SSCC ( J = 7, 7.7, 6.6 Hz) also indicated that they had the pyranose form, the C -conformation,
1
and the ꢀ-configuration for D-xylose and D-glucose and the ꢁ-configuration for L-arabinose.
The genin, which was identified as cycloorbigenin C (2), was isolated from the genin part of the acid hydrolysis
products [5, 6].
13
A comparison of C NMR spectra of cycloorbigenin C and askendoside H showed that C-3 and C-23 of the genin
and C-2 of D-xylose experienced a glycosylation effect in the latter. These resonated at ꢃ 88.50, 82.77, and 83.62, respectively.
Therefore, the new glycoside 1 was a bisdesmoside glycoside, the carbohydrate constituents of which were located on C-3 and
C-23 of cycloorbigenin C and the D-glucose and L-arabinose of which were terminal.
Nuclear Overhauser Effect (NOE) difference measurements with pre-irradiation of the D-glucose anomeric proton
revealed an Overhauser effect on the H-23 resonance. This determined unambiguously the location of the D-glucose on C-23.
This meant that the biose located on C-3 was (ꢁ-L-arabinopyranosyl)(1ꢂ2)- ꢀ-D-xylopyranose.
The difference PMR spectrum with irradiation of the D-xylose anomeric proton (ꢃ 4.81) revealed a negative NOE on
the resonance of the genin H-3 (ꢃ 3.36) [7, 8], which confirmed the conclusion about the attachment of D-xylose to C-3.
Thus, the experimental results led to the conclusion that the new triterpene glycoside 1 was 23R,24R-cycloartan-
3ꢀ,6ꢁ,16ꢀ,23,24,25-hexaol 3-O-[(ꢁ-L-arabinopyranosyl)(1ꢂ2)- ꢀ-D-xylopyranoside] 23-O-ꢀ-D-glucopyranoside.
EXPERIMENTAL
General comments have been published [9]. The following solvent systems were used: CHCl :MeOH:H O
3
2
(70:23:4, 1), CHCl :MeOH (10:1, 2), n-BuOH:Py:H O (6:4:3, 3). NMR spectra were recorded in Py-d on a UNITYplus 400
3
2
5
13
(Varian) spectrometer. C NMR spectra were obtained with full C–H decoupling and under DEPT conditions. 2D spectra of
1 were recorded using standard Varian programs. Chemical shifts of protons in 1 and 2 are given vs. HMDS. Chemical shifts
13
of C atoms in C NMR spectra of 1 and 2 are given vs. resonances of the ꢀ-C atoms of deuteropyridine (ꢃ 123.493 vs. TMS).
Isolation and Separation of Triterpenoids from A. taschkendicus [10–12]. Fractions that eluted after askendoside
G and contained askendoside H were combined and rechromatographed over a column using system 1 to afford 1 (170 mg,
0.0033% of air-dried raw material).
13
Askendoside H (1), C H O , white non-crystalline compound. Table 1 presents the PMR and C NMR spectra
46 78 19
of 1.
Cycloorbigenin C (2) from 1. Askendoside H (140 mg) was hydrolyzed by methanolic H SO (15 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 precipitate was
2
filtered off, washed with H O until neutral, and dried. The dry product was chromatographed over a column with elution by
2
system 2 to afford 2 (25 mg), C H O , mp 256–258°C (MeOH).
30 52
6
2
PMR spectrum of 2 (400 MHz, C D N, ꢃ, ppm, J/Hz, 0 = HMDS): 0.19 and 0.47 (d, J = 4, 2H-19), 0.89 (s, CH ),
5
5
3
3
3
3
3
1.07 (d, J = 6.7, CH -21), 1.26, 1.27, 1.57, 1.61, 1.79 (s, 5 ꢄ CH ), 3.56 (dd, J = 11.6, J = 4.7, H-3), 3.65 (d, J = 8.5,
H-24), 3.69 (td, J = J = 9.3, J = 3.8, H-6), 4.22 (td, J = J = 8.7, J = 2, H-23), 4.59 (td, J = J = 7.6, J = 4.7,
3
3
1
2
3
3
3
3
3
3
3
3
3
1
2
3
1
2
3
1
2
3
H-16).
13
Table 1 presents the C NMR spectrum for 2.
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 . The precipitate was removed. The solution was evaporated to a small
3
volume. PC using system 3 and comparison with authentic samples detected D-glucose, D-xylose, and L-arabinose. PMR and
13
C NMR spectra provided evidence that the aforementioned monosaccharides were present in a 1:1:1 ratio in 1.
ACKNOWLEDGMENT
The work was supported financially by the Republic of Uzbekistan State Foundation for Basic Research (Grant FA-
FZ-T-044) and GNTP (Grant FA-A12-T-101).
413
Isaev
