Isoconiferoside, a New Phenolic Glucoside from Seeds of Panax ginseng

A new phenolic glucoside, isoconiferoside (1), was isolated from the seeds of Panax ginseng (Araliaceae). The structure was determined to be 9-O-[β-d-glucopyranosyl-(1→6)-β-d-glucopyranosyl]-trans-coniferyl alcohol based on spectroscopic analyses (1H- and 13C-NMR, DEPT, COSY, HMQC, and HMBC) and acid hydrolysis.


Introduction
Panax ginseng (Aralicaceae), an ancient and popular herbal drug used in traditional Oriental medicine, has been used as a tonic and for the treatment of various diseases [1,2]. The primary phytochemical constituents of the roots, leaves, flower buds, and fruits of P. ginseng are dammarane-type triterpene oligoglycosides [3]. Additionally, phenolic derivatives and polyacetylenes have been isolated from the roots of P. ginseng and their biological activities have been studied [4]. Most notably, glucosylated phenolic components in cultured ginseng roots have been exhibited antioxidant and radical-scavenging activities [5].

Results and Discussion
Compound 1 was obtained as a colorless powder with an optical rotation of −37.5° (c 0.29, MeOH). Its molecular formula (C 22 H 32 O 13 ) was determined based on a peak in the HRESIMS data at  (Table 1)  , and a methoxyl group [δ C 56.5 (q)]. Based on a comparison of their NMR spectra compound 1 contained one more glucopyranose unit than trans-isoconiferin [9,10]. An HMBC experiment was conducted to determine the location of this additional glucopyranose moiety. As shown in Figure 2, the HMBC correlation between H-1'' (δ H 4.40, 1H, d, J = 8.2 Hz) and C-6' (δ C 69.8, t) indicates that the additional glucopyranose was bound to C-6' of the inner glucopyranose moiety. Thus, compound 1 was identified as 9-O-[β-D-glucopyranosyl-(1→6)-β-D-glucopyranosyl]-trans-coniferyl alcohol and was named isoconiferoside.

Plant Material
The seeds of P. ginseng were collected in Geumsan province, which is well-known for ginseng cultivation in Korea, in August 2009, and were taxonomically identified by one of the authors (Young Ho Kim). Voucher specimens (CNU09105) have been deposited at the College of Pharmacy, Chungnam National University.

Extraction and Isolation
The powdered seeds of P. ginseng

Acid Hydrolysis and Sugars Determination of Compound 1
A solution of 1 (3.0 mg) in 1.0 M HCl (3.0 mL) was heated under reflux for 4 h. The reaction mixture was then concentrated to dryness under reduced pressure. The residue was extracted with EtOAc and H 2 O (5 mL, 3 times). Next, the sugar residue, obtained by concentration of the water layer, was dissolved in dry pyridine (0.1 mL) and L-cysteine methyl ester hydrochloride in pyridine (0.06 M, 0.1 mL) was added to the solution. After heating the reaction mixture at 60 °C for 2 h, 0.1 mL of trimethylsilylimidazole was added. Heating at 60 °C was continued for another 2 h, and the reaction mixture was evaporated to give a dried product, which was then partitioned between hexane and H 2 O [11]. The hexane layer was analyzed by the GC general procedure. The peak of the hydrolysate was detected at 14.12 min for D-glucose. The retention times of authentic samples (Sigma-Aldrich), after being treated in a similar manner, were 14.12 min (D-glucose), and 14.25 min (L-glucose), respectively.

Conclusions
A new phenolic glucoside, isoconiferoside (1), was isolated from the methanol extract of P. ginseng seeds. Isoconiferoside is expected to be an antioxidant and free radical scavenger and its biological activity is currently under investigation.