Structure of cycloquivinoside a from the aerial part of Astragalus chivensis

Article abstract of DOI:10.1007/s10600-012-0389-8

The new cycloartane glycoside cycloquivinoside A, 24S-25-methoxycycloartan- 3β,6α,16β,24,25-pentaol 3-O-β-D-glucopyranoside, was isolated from the aerial part of Astragalus chivensis Bunge (Leguminosae). The structure was established based on chemical transformations and 2D spectra (TOCSY, ROESY, HMBC, HSQC, COSY).

Full text of DOI:10.1007/s10600-012-0389-8

Chemistry of Natural Compounds, Vol. 48, No. 5, November, 2012 [Russian original No. 5, September–October, 2012]
STRUCTURE OF CYCLOQUIVINOSIDE A FROM
THE AERIAL PART OF Astragalus chivensis
1
2
1†
T. Kh. Naubeev, K. K. Uteniyazov, M. I. Isaev,
UDC 547.918:547.926
3
3
V. V. Kachala, and A. S. Shashkov
The new cycloartane glycoside cycloquivinoside A, 24S-25-methoxycycloartan-3ꢀ,6ꢁ,16ꢀ,24,25-pentaol
3-O-ꢀ-D-glucopyranoside, was isolated from the aerial part of Astragalus chivensis Bunge (Leguminosae).
The structure was established based on chemical transformations and 2D spectra (TOCSY, ROESY, HMBC,
HSQC, COSY).
Keywords: cycloquivinoside A, Astragalus chivensis Bunge, Leguminosae, cycloartane triterpenoids,
13
cyclocanthogenin, PMR and C NMR spectra, TOCSY, ROESY, HMBC, HSQC, COSY.
In continuation of research on cycloartane triterpenoids from plants of the genus Astragalus (Leguminosae) [1], we
isolated from the EtOAc extract of the aerial part of A. chivensis Bunge a new glycoside and called it cycloquivinoside A (1).
OH
21
18
20
17
23
26
24
OCH
3
OH
11
27
19
13
15
1
9
7
3
CH OH
2
28
5
O
OH
30 29
OH
HO
1
OH
The PMR spectrum of 1 had 1H doublets at strong field of 0.23 and 0.54 ppm for an AX system and resonances for
seven methyls at 1.03, 1.10, 1.23, 1.29, 1.34, 1.41, and 2.0 ppm that indicated that this compound was a cycloartane triterpenoid.
13
This was consistent with resonances for C-9, C-10, and C-19 that appeared at 21.35, 29.28, and 29.95 ppm in the C NMR
spectrum of 1 (Table 1).
Paper chromatography (PC) detected D-glucose in the acid-hydrolysis products of 1.
13
The presence in the PMR and C NMR spectra of resonances for one anomeric proton and one anomeric C atom at
5.01 and 106.96 ppm suggested that 1 was a glycoside and monoside. PC of the monosaccharide part of the acid-hydrolysis
products of 1 established that the carbohydrate part consisted of D-glucose. The chemical shifts of the carbohydrate H atoms
and the SSCC of the monosaccharide unit indicated that the D-glucose had the pyranose form and was bonded to the genin
through a ꢀ-glycoside bond to a non-tertiary hydroxyl group. The PMR spectrum of 1 contained also a 3H singlet at 3.21 ppm
for a methoxyl located obviously on the genin part of the molecule.
13
A comparison of the PMR and C NMR spectra of 1, cycloasgenin C, and cyclocanthogenin showed that the genin
of new glycoside 1 was the mono-O-methyl derivative of one of the aforementioned genins.
______
†
Deceased.
1) S. Yu. Yunusov Institute of the Chemistry of Plant Substances, Academy of Sciences, Tashkent, Republic of
Uzbekistan, fax: (99871) 120 64 75; e-mail: timan05@mail.ru; 2) Berdakh Karakalpak State University, 700742, Nukus,
Ul. Ch. Abdirova, 1, Republic of Uzbekistan; 3) N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences,
Moscow, Leninskii Pr., 47. Translated from Khimiya Prirodnykh Soedinenii, No. 5, September–October, 2012, pp. 722–723.
Original article submitted April 16, 2012.
©
810
0009-3130/12/4805-0810 2012 Springer Science+Business Media New York

13
ÒÀÁËÈÖÀ 1. PMR and C NMR Spectral Data of Cycloquivinoside A (1) (C D N, ꢃ, ppm, TMS = 0)
5
5
C atom
C atom
ꢃH
ꢃC
ꢃH
ꢃC
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
1.56; 1.16
2.47; 1.95
3.66
32.46
30.21
89.09
42.66
54.11
67.96
38.44
47.00
21.35
29.28
26.32
33.06
45.75
46.82
48.34
72.00
57.40
18.94
29.95
20
21
22
23
24
25
26
27
28
2.38
1.10
2.28; 1.70
1.90; 1.71
3.88
–
1.29
1.23
1.03
2.00
1.34
3.21
ꢀ-D-Glc
5.01
28.77
18.33
33.21
27.59
75.30
77.77
21.34
20.45
20.17
28.95
16.75
49.18
–
1.76
3.76
1.82; 1.66
1.96
–
–
29
30
ÎÌå
1.93; 1.24
1.48
–
–
p
1
2
3
4
5
6
106.96
75.97
78.79
71.92
78.19
63.11
2.16; 1.74
4.72
1.83
1.41
0.54; 0.23
4.08
4.24
4.24
3.96
4.56; 4.41
The C atoms of the genin that were bonded to O resonated at 89.09, 67.96, 72.00, 75.30, and 77.77 ppm and belonged
to C-3, C-6, C-16, C-24, and C-25. Therefore, the D-glucose was situated on C-3 and the methoxyl, on C-25. The presence of
correlation peaks between resonances of CH -26, CH -27 (1.29 and 1.23 ppm), CH O (3.21), and C-25 (77.77) in the HMBC
3
3
3
spectrum provided additional confirmation of the location of the methoxyl. Correlations were observed in the same HMBC
spectrum between resonances for H-3 (3.66) and the anomeric C atom (106.96) and between those for the anomeric proton
(5.01) and C-3 of the aglycon (89.09).
These facts also indicated that the D-glucose was located on C-3.
As already noted, the genin of 1 was the 25-O-methyl derivative of either cycloasgenin C or cyclocanthogenin, which
differ by the configuration at C-24. Therefore, the genin of 1 also contained 3ꢀ,6ꢁ,16ꢀ hydroxyls. The configuration of C-24
remained to be explained.
13
Atoms C-24 and C-25 resonated at 80.52 and 72.64 ppm, respectively, in the C NMR spectrum of cycloasgenin C.
The corresponding atoms of cyclocanthogenin were observed at 77.22 and 72.49 ppm; of 1, at 75.30 and 77.77. If 1 were a
derivative of cycloasgenin C, i.e., had the 24R-configuration, then the ꢁ- and ꢀ-effect of the 25-methoxyl would be
ꢂꢃ
+5.13 ppm and ꢂꢃ
–5.22 ppm. For the 24S-configuration, i.e., if 1 were a derivative of cyclocanthogenin, the
C-25
C-24
ꢁ- and ꢀ-effect of the 25-methoxyl would be ꢂꢃ
+5.28 and ꢂꢃ
–1.92. It can be seen that the ꢀ-effect for a 25-methoxyl
C-24
C-25
(5.22) would be greater than that of the ꢁ-effect (5.13) for the R-configuration of C-24. This seemed improbable. However,
the ꢀ-effect of a 25-methoxyl (1.92) for the S-configuration was 2.8 times less than that of the ꢁ-effect (5.28). This seemed
logical. These facts defined unambiguously the S-configuration of C-24 for 1 and; therefore, that it was a derivative of
cyclocanthogenin [2].
Thus, 1 was 24S-25-methoxycycloartan-3ꢀ,6ꢁ,16ꢀ,24,25-pentaol 3-O-ꢀ-D-glucopyranoside.
EXPERIMENTAL
General comments were published [1].
Isolation of Cycloartanes. The EtOAc fraction was chromatographed over a column using CHCl :MeOH (9:1).
3
Cycloquivinoside A (1). 65 mg (0.0033%, here and henceforth calculated for air-dried raw material), C H O ,
37 64 10
13
mp 296–298°C (MeOH). PMR and C spectra (Bruker, DRX-500, 500.13 and 125.76 MHz, respectively, C D N, ꢃ, ppm,
5
5
J/Hz, 0 = TMS) are given in Table 1.
811

Acid Hydrolysis. Compound 1 (20 mg) was hydrolyzed in methanolic H SO (10 mL, 0.25%) at 70°C for 3 h,
2
4
cooled, and treated with H O (30 mL). The MeOH was distilled off. The resulting precipitate was filtered off and dried. The
2
hydrolyzate was neutralized with BaCO and evaporated. PC (n-BuOH:Py:H O, 6:4:3) and comparison with an authentic
3
2
sample detected glucose in the hydrolyzate.
REFERENCES
1.
2.
T. Kh. Naubeev, K. K. Uteniyazov, V. V. Kachala, and A. S. Shashkov, Khim. Prir. Soedin., 138 (2007).
Yu. M. Fadeev, M. I. Isaev, Yu. A. Akimov, P. K. Kintya, M. B. Gorovits, and N. K. Abubakirov, Khim. Prir. Soedin.,
817 (1987).
812