Flavonoid glycosides from Astragalus galegiformis leaves

Abstract

New flavonoid oligosides, the structures of which were established by chemical transformations and UV, IR, PMR, and 13 C NMR spectra, were isolated from Astragalus galegiformis leaves.We reported earlier on the isolation from Astragalus galegiformis L. (Fabaceae L.) flowers of flavonoid glycosides that were derivatives of isorhamnetin, astragalegoside and isoastragalegoside, which possess diuretic and hyponitrogenous activity [1,2].Herein we examine the structure of flavonoid glycosides isolated from leaves of A. galegiformis. They are difficult to separate by chromatography (R f 0.34 ± 0.05) and isolate in pure states. This may be due to either H-bonds between the compounds or gums in the Astragalus species.We were able to isolate six compounds by using classical separation methods for flavonoids and their modifications. Two compounds turned out to be known flavonoids that were previously isolated from other Astragalus species, astragalin (1) and kaempferol (2) [3].The other compounds were new. We called them flagalosides (2-5). They all gave a positive qualitative reaction characteristic of flavonoid glycosides [4]. Their IR spectra contained absorption bands for hydroxyls (3200-3400 cm -1 ), γ-pyrone carbonyl (1665-1660 cm -1 ), and aromatic rings (1620, 1575 cm -1 ) [5].UV spectra of 3 and 4 in ethanol with added ionizing and complexing reagents produced absorption bands that revealed the absence of substituents on C 7 , C 5 , C 4 , and C 3′ ; for 2 and 5, the presence of substituents on C 7 and C 3 , and C 3 and C 3′ , respectively.Acid hydrolysis of the glycosides produced the aglycons quercetin (from 2-4) and isorhamnetin (from 5). The yields of the aglycons indicated that 2 was a tetraoside; 3, a pentaoside; 4, a trioside; and 5, a bioside. The carbohydrate part of 2 contained D-glucose, D-galactose, L-arabinose, and L-rhamnose bonded to C 3 and C 7 of quercetin; of 3, D-glucose, D-galactose, L-arabinose, D-xylose, and L-rhamnose also bonded to C 3 of quercetin.In view of the fact that 2 and 3 were isolated in minor amounts, it was not possible to establish their complete chemical structures.The PMR spectrum of 4 recorded in CD 3 OD (Table 1) contained a strong singlet at 12.8 ppm, which is characteristic of a 5-OH group. The presence of this hydroxyl was confirmed by the UV spectrum recorded in ethanol with added AlCl 3 , in which the absorption band at 401 nm underwent a bathochromic shift of 46 nm [6]. The size of bathochromic shifts produced by adding AcONa + H 3 BO 3 and MeONa is indicative of a dihydroxy group in the 3′,4′-positions and a free 4′-OH group [6]. Signals of aromatic protons are observable at weak field in the PMR spectra at 7.65, 6.90, and 6.92 (ring B) and 6.45 and 5.25 ppm (ring A). The chemical shifts and SSCC of protons in ring B indicated that they were located on C 2′ , C 5′ , and C 6′ ( Table 1).The 13 C NMR spectra led to an analogous conclusion, where signals for secondary C atoms at C-5, C-7, C-4′, and C-3′ were clearly observed. The chemical shift of C-3 was indicative of it...

A Review of Recent Research Progress on the Astragalus Genus

“…As the summarized results shown in Table 1, Table 2 and Table 3 and Figure 1, Figure 2, Figure 3 and Figure 4, 46 kinds of Astragalus species have been studied for their chemical constituents in recent years [9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,…”

“…Just like many other herbs, Astragalus genus plants are also a rich source of flavonoids. The flavonoids in this genus include flavonols ( 162 – 182 ) [2,8,22,63,64,65,66,67,68], flavones ( 183 – 193 ) [2,8,53,63,66,69], flavonones ( 194 – 195 ) [65,70] and isoflavonoids ( 196 – 221 ) [16,50,53,65,66,70,71,72,73,74,75], which have many kinds of bioactivities.…”

Flavonoid oligosides from georgian Astragalus falcatus

“…D-Galactose and L-rhamnose are often encountered as robinobioses in flavonoid glycosides isolated by us [1, 3,11]. Apparently this is a characteristic signature of flavonoids from Astragalus growing in Georgia.…”

“…The chemical shifts of L-rhamnose C-3 and its adjacent C atoms (C-2, 75.78; C-4, 70.12 ppm) also indicated that this position was substituted [11]. This meant that the second D-glucose was bonded to L-rhamnose C-3.…”

“…The resonance of C-6 of the D-galactose unit in the 13 C NMR spectrum experienced a glycosylation effect and appeared at G 66.80 ppm. This indicated that it was substituted with a carbohydrate [9][10][11].…”