Transformation of Ginsenoside Rc into (20S)-Rg3 by the Bacterium Leuconostoc sp. BG78

Abstract

Ginsenoside (20S)-Rg 3 is one of the most active minor dammarane glycosides of Panax ginseng C. A. Meyer and exhibits a broad spectrum of biological activity including hepatoprotective, immunostimulating, neuroprotective, and antitumor. It inhibits cell growth of malignant A549 lung carcinoma, U937 lymphoma, LNCaP prostate carcinoma, and SK-HEP-1 hepatoma and is of interest in medicine as a potential antitumor agent [1]. One factor limiting the application of ginsenoside (20S)-Rg 3 is its low content in the total saponins of Panax ginseng. (20S)-Rg 3 differs from the principal dammarane glycosides Rb 1 , Rb 2 , Rc (1), and Rd (2) that have the aglycon protopanaxadiol only by the lack of a carbohydrate on C-20 [2]. This enables it to be produced by selective incomplete deglycosylation of these saponins, including by using various microorganisms [3,4].We reported earlier the use of several bacteria with E-glucosidase activity for transformation of ginsenoside Rb 1 into the minor glycoside F-2 and compound K [5] and Rd into the aforementioned ginsenoside (20S)-Rg 3 [6]. Herein we communicate data on the transformation of another principal glycoside, Rc (1) with a C-3 E-sophorose and a C-20 D-L-arabinofuranosyl-(1o6)-E-D-glucopyranoside, into (20S)-Rg 3 by the bacterium Leuconostoc sp. BG78.Standard ginsenosides Rc, Rd, and (20S)-Rg 3 were purchased (Faces Biochemical Co., Wuhan, PRC). Glycoside 1 was isolated from six-year P. ginseng roots as described before [7] using in the final step preparative HPLC over an OptimaPak C18 column (250 u 10 mm, 10 Pm). PMR, 13 C NMR, and mass spectra of isolated Rc agreed with those published for this compound [4,7]. The Rc biotransformation products were analyzed using TLC and solvent system CHCl 3 -MeOH-H 2 O (65:35:10, lower phase) and HPLC over a Zorbax Eclipse XDB-C18 reversed-phase column. Mass spectra and NMR spectra ( 1 H and 13 C) were recorded as before [8].Bacterium Leuconostoc sp. BG78 was cultivated in 200-mL Ehrlenmeyer flasks in MRS liquid growth medium for 24 h at 37°C with constant stirring. Then, cells were harvested by centrifugation (3000 g, 15 min, 4°C), rinsed twice with phosphate buffer (20 mM, pH 7.0), and suspended in the same buffer (20 mL). The resulting bacterium suspension (10 mL each) was placed into two sterile flasks and treated with freshly prepared MRS medium (40 mL) and an aqueous solution of ginsenoside Rc (50 mL, 1 mM). The first mixture was incubated for 48 h; the second, for 96 h at 37°C with constant stirring. Analytical samples were taken every 6 h. After the incubation was finished, each mixture was extracted twice with watersaturated BuOH (100 mL). The resulting extract was evaporated in vacuo. The residue was used to isolate the biotransformation products.

A review for discovering bioactive minor saponins and biotransformative metabolites in Panax quinquefolius L.

“…BG78 and Sphingopyxis sp. BG97, respectively ( Ten et al, 2014a and Ten et al, 2014b ). Sui et al (2020) demonstrated that ginsenoside Rg1 could be thoroughly converted into 20( S/R )-Rh1 and 25-OH-20( S/R )-Rh1 by Cordyceps Sinensis , with a biocatalytic pathway established as Rg1→20( S/R )-Rh1→25-OH-20( S/R )-Rh1, and the molar bioconversion rate for total 25-OH-20( S/R )-Rh1 was 82.5%.…”