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DOI:10.29013/AJT-24-1.2-24-27
CYCLOASCIDOSIDE D FROM ASTRAGALUS MUCIDUS
Artikbaeva Baxtibike Rasbergenovna1, Naubeev Temirbek Khasetullaevich1
1 Department "Oil & Gas Technology", Karakalpak State University
Cite: Artikbaeva B. R., Naubeev T. Kh. (2024). Cycloascidoside D from Astragalus Mucidus. Austrian Journal of Technical and Natural Sciences 2023, No 11-12. https://doi. org/10.29013/AJT-24-1.2-24-27
Abstract
A new cycloartane glycoside, cycloascidoside D which is determined as 3-O-^-D-(2-OAc)-xy-lopyranoside-24R-cycloartane-3P,6a,16P,24, 25-pentaol, was isolated from the aerial part of the plant Astragalus mucidus Bunge (Leguminosae).
Structure of this glycoside was proven by chemical transformations and on the basis of 1H and 13C NMR spectra, which were interpreted using 2D NMR.
Keywords: Triterpenoids, cycloartanes, cycloasgenin C, glycosides, cycloascidoside D, Leguminosae, Astragalus, 1H, 13C NMR spectra, HMBC
Introduction
In continuation of our studies of cycloartane triterpenoids from plants of the genus Astragalus (Leguminosae) (Naubeev, T. Kh., Uteniyazov, K. K., Isaev, M. I., 2011). We determined the structure of a new cycloartane glycoside, cycloascidoside D (1), obtained from the aerial part of Astragalus mucidus Bunge. Its structure is discussed in the article.
The 1H NMR spectrum of cycloascidoside D shows single-proton doublets of the AX system at 0.29 and 0.58 ppm with SSCC2J = = 4.5 Hz along with signals of seven methyl groups in the range of 1.05-1.86 ppm, allowing us to classify the compound under discussion as triterpenoids of the cycloartane series (Naubeev, T. Kh., Uteniyazov, K. K., Isaev, M. I., 2011; Naubeev, T. Kh., Zhan-ibekov, A. A., Isaev, M. I., 2012; Naubeev, T. Kh., Zhanibekov, A.A., Uteniyazov, K. K., Bobakulov, Kh. M., Abdullaev, N. D., 2014;
Naubeev, T. Kh., Ramazonov, N. Sh., 2021; Naubeev, T. Kh., Uteniyazov, K. K., Ramazonov, N. Sh., 2022).
Indeed, genin 2, identified with cy-cloasgenin C, was isolated from the products of acid hydrolysis of glycoside 1 (Naubeev, T. Kh., Uteniyazov, K. K., Isaev, M. I., 2011; Naubeev, T. Kh., Zhanibekov, A. A., Isaev, M. I., 2012).
D-xylose was detected in the carbohydrate part of the acid hydrolyzate after neutralization and concentration by paper chromatography (PC). The presence of signals of one anomeric proton and one anomeric carbon atom at 4.64 ppm and 104.92 ppm in the 1H and 13C NMR spectra suggests that the discussed compound 1 is of glycosidic nature and is a monoside. A set of chemical shifts of carbon and hydrogen atoms, as well as the coupling constant of protons of the monosaccharide residue indicate the pyranose form,
^-conformation and ^-configuration of D-xylose. The same conclusion emerges from the chemical shifts of the corresponding carbon atoms. Comparative analysis of the 13C NMR spectra of the new glycoside 1 and cy-cloasgenin C unambiguously determines the position of D-xylose at C-3.
Chemical correlation in the HMBC spectrum of the glycoside was observed between
the signals of H-3 (8 3.66 ppm) and the ano-meric carbon atom of D-xylose (8 104.92 ppm), as well as between the signals of the anomeric proton of the monosaccharide (8 4.64 ppm) and the C-3 atom (8 89.20 ppm) of the aglycone.
These facts also indicate the location of D-xylose at C-3.
Figure 1. Acid and alkaline hydrolysis of cycloascidoside D (1)
In the 1H NMR spectrum of the glycoside there is 1 three-proton singlet at 2.02 ppm indicates that this glycoside contains one acetyl group. As expected, the 13C NMR spectrum of new glycoside 1 shows signals from the carbon atoms of one acetyl group at 21.23 and 170.02 ppm.
Alkaline hydrolysis of cycloascidoside D leads to the formation of glycoside 3, iden-
tified with 3-O-ß-D-xylopyranoside cyclo-asgenin C (Naubeev, T. Kh., Uteniyazov, K. K., Isaev, M. I., 2011; Naubeev, T. Kh., Zhanibe-kov, A. A., Isaev, M. I., 2012; Naubeev, T. Kh., Zhanibekov, A. A., Uteniyazov, K. K., Bobaku-lov, Kh. M., Abdullaev, N. D., 2014). The place of the attachment of the acetyl group was determined by comparative study of the 13C NMR and 1H spectra and compounds 1 and 3.
Table 1. Chemical shifts of carbon atoms of compounds 1 and 3 (C5D5N, 8, ppm, J/Hz, 0-TMS)
C/H
1
8
8
H
3 [2] 8
C/H
1
8
8
3 [2] 8
1 32.95 1.22 m, 1.65 m 32.97 20 32.10 1.92 m 32.11
2 30.85 2.50 m, 1.93 m 30.85 21 19.44 1.12 d (6.3) 19.46
C/H »c 1 «H 3 [2] »C C/H »C 1 »H 3 [2] »C
3 89.20 3.66 dd (11.5, 4.4) 89.20 22 35.30 1.26 m, 2.38 m 35.31
4 43.18 - 43.20 23 29.82 1.85 m; 1.95 m 29.86
5 54.60 1.76 d (8.7) 54.61 24 81.07 3.80 q 81.07
6 68.38 3.75 td (9, 9, 3.8) 68.40 25 73.14 - 73.16
7 38.92 2.17 dt (13.1, 4, 4) 38.93 26 26.41 1.53 s 26.41
8 47.48 1.99 dd (9.8, 5.2) 47.50 27 26.62 1.50 s 26.64
9 21.82 - 21.84 28 20.69 1.04 s 20.70
10 29.69 - 29.71 29 29.34 1.86 s 29.36
11 26.76 1.70 m, 1.24 m 26.79 30 17.17 1.36 s 17.18
12 33.61 1.68 m, 33.64 ß-D-Xylp
13 46.18 - 46.19 1 104.92 4.64 d (7.5) 108.12
14 47.39 - 47.41 2 76.65 5.36 dd (8.6, 7.8) 76.13
15 49.19 1.97 dd (5.2, 12); 2.44 dd (8, 12) 49.20 3 75.59 3.97 t (8.7) 79.02
16 72.16 4.53 td (7.5, 7.5, 4.8) 72.20 4 71.73 4.17 t (9) 71.74
17 57.67 1.72 m 57.70 5 67.56 3.68 dd (11.3, 10); 4.38 dd (11.2, 5.1) 67.55
18 19.24 1.41 s 19.27 Ac 21.23 2.02 s
19 30.43 0.28 and 0.58 dd (4.5) 30.46 Ac 170.02
The C-6, C-16, C-25 atoms of the glycoside 1 molecule in the 13C NMR spectrum resonate at 68.38, respectively 72.17 and 73.14 ppm. These values practically coincide with those of the 13C NMR spectra of cyclo-asgenin C and glycoside 3. Consequently, the acetyl group is not located in the genin part of the cycloascidoside D molecule. Indeed, a one-proton doublet with a coupling constant of 3J1 = 9 and 3J2-8 Hz is noted in the 1H NMR spectrum of the latter at 5.36 ppm, belonging to the proton geminal to the acetyl group.
Additional confirmation of the conclusion about the position of the acetyl group is provided by a comparative analysis of the 13C NMR spectra of glycosides 1 and 3.
As can be seen from Table 1, upon transition from glycoside 3 to glycoside 1, the chemical shifts of carbon atoms C-1 (-2.84 ppm), C-2 (+0.52 ppm), C-3 (-2.87) of monosaccharide residue change significantly. The signs and values of these changes coincide well with the a- and ^-influences of the acetyl group located at C-2 of the P-D-xylopy-ranoside ring, and unambiguously determine the location of the acetyl residue.
Thus, the presented experimental data allow us to conclude that the new trit-erpene glycoside of the cycloartane series, cycloascidoside D, has the structure 3-O-ß-D-(2-OAc)-xylopyranoside-24R-cy-cloartane-3ß,6a,16ß,24,25- pentaol.
Experimental part. General Experimental Ptocedures (Naubeev, T. Kh., Uteniyazov, K.K., Isaev, M.I., 2011). The following solvent systems were used: 1) chloroform-methanol (9:1), 2) chloroform-methanol-water (70:12:1), 3) chloroform-methanol-water (70:23:3).
NMR spectra were recorded on a JNM-ECZ600R spectrometer (JEOL, Japan) at an operating frequency of 600 MHz, for 1H in C5D5N solutions. TMS (0 ppm) was used as an internal standard in 1H NMR spectra. In the 13C NMR spectra, the chemical shift of the solvent (C5D5N, 150.35 ppm relative to TMS) was used as an internal standard.
Extraction and isolation. Isolation method of isoprenoids from the aerial parts Astragalus mucidus Bunge were given in (Naubeev, T. Kh., Uteniyazov, K.K., Isaev, M.I., 2011). When the column was eluted with a 70:12:1 system (chloroform-methanol-wa-
ter), 84 mg of cycloascidoside D was isolated (0.0056%, the yield here and below is given based on the weight of air-dried raw material).
Cycloascidoside D (1) - substance 1, C37H62O10, m.p. 260-262°C (from methanol).
Acid hydrolysis of cycloascidoside D. Glycoside 1 (35 mg) was dissolved in 15 ml of a 0.5% methanol solution of sulfuric acid and boiled in a water bath for 1 hour, monitoring the progress of hydrolysis on TLC every 20 minutes. Then the reaction mixture was diluted with a threefold volume of water and the methanol was evaporated. The formed precipitate was filtered off, washed with water, and dried. The filtrate was neutralized with BaCO3. After removing the precipitate, the solution was concentrated and D-xylose was found by using PC in the system n-butyl alcohol-pyridine-water (6:4:3) in comparison with known samples.
The residue was chromatographed on a column, eluting with a system 1. 10 mg of genin 2, identified with cycloasgenin C C30H52O5, m.p. 250-252°C (from methanol), which was identified as a true sample according to the 1H and 13C NMR spectrum and mobility on TLC.
1H NMR spectrum of cycloasgenin C (400 MHz, C5D5N, 8, ppm, J/Hz, 0-HMDS): 0.21 and 0.49 (d, J=4, 2H-19), 0.92 (CH3, s), 1.00 (d, J=6.4, CH3-21), 1.25, 1.30, 1.36, 1.39, 1.77 (s, 5 x CH3), 3.55 (dd, J=11.4, 4.7, H-3), 3.67 (dd, J=10.4, J=2.3, H-24), 3.69 (td, J=9.4, 3.7, H-6), 4.60 (td, J=7.8, 5.0, H-16) (Naubeev, T. Kh., Uteniyazov, K.K., Isaev, M. I., 2011).
Alkaline hydrolysis of cycloascidoside D. 25 mg of cycloascidoside D (1) was saponified with 20 ml of 0.5% methanol solution of potassium hydroxide. The reaction mixture was left at room temperature for a day. Then the methanol solution was diluted with a threefold volume of water, and the methanol was evaporated. The reaction product was extracted with butanol. The butanol extract was washed with water. The dry residue after distilling off the butanol was chromatographed on a silica gel column. Eluting with system 2, 15 mg of glycoside 3 was isolated, m.p. 252-254°С (from methanol), identified with 3-O-ß-D-xylopy-ranoside cycloasgenin C (3) (Naubeev, T. Kh., Zhanibekov, А. А., Isaev, М. I., 2012).
1H NMR spectrum of 3-O-ß-D-xylopyra-noside cycloasgenin C (3) (600 MHz, C5D5N, 6, ppm, J/Hz, 0-HMDS): 0.30 and 0.58 (2H-19, d, 2J =4), 1.05 (CH3, s), 1.13 (CH3-21, d, 3J=6.4), 1.36, 1.42, 1.51, 1.53, 2.02 (5xCH3, s), 3.60 (H-5a of ß-D-xylopyranose residue, dd, 2J=11.2, 3J=9.8), 3.64 (H-3, dd, 3J1=11.7, 3J2=4.6), 3.67 (H-6, td, 3J1=3J2=9.7, 3J3=3.6), 3.75 (H-24, dd, 3J1=10.5, 3J2=2.4), 3.83 (H-2 ß-D-xylopyranose residue, dd, 3J1=8.8, 3J2=7.5), 4.06 (H-3 ß-D-xylopyranose residue, t, 3J1=3J2=8.6), 4.15 (H-4 of ß-D-xy-lopyranose residue, m), 4.36 (H-5e of ß-D-xy-lopyranose residue, dd, 2J=11.3, 3J=5), 4.71 (H -16, td, 3J1=3J2=7.7, 3J3=4.9), 4.92 (H-1 of ß-D-xylopyranose residue, d, 3J=7.5).
13C NMR spectra of the 3-O-ß-D-xylopy-ranoside cycloasgenin C (3) is given in the table 1.
References:
Naubeev, T. Kh., Uteniyazov, K.K., Isaev, M. I. (2011). Chem. Nat. Compd.,- 47.- 250 p. Naubeev, T. Kh., Zhanibekov, А.А., Isaev, М. I. (2012). Chem. Nat. Compd.,- 48.- 813 p. Naubeev, T. Kh., Zhanibekov, А.А., Uteniyazov, K. K., Bobakulov, Kh. M., Abdullaev, N. D.
(2014). Chem. Nat. Compd.,- 49.- 1048 p. Naubeev, T. Kh., Ramazonov, N. Sh. (2021). Austrian Journal of Technical and Natural Sciences,- № 7-8.- 48 p.
Naubeev, T. Kh., Uteniyazov, K. K., Ramazonov, N. Sh. (2022). Austrian Journal of Technical and Natural Sciences,- № 7-8.- 42 p.
submitted 07.02.2024; accepted for publication 26.02.2024; published 18.03.2024 © Artikbaeva B. R., Naubeev T. Kh. Contact: [email protected]
