## 3 Results  
### Isolation and Structure Elucidation  
Compounds **1** and **2** were isolated from acetone-water (70:30, \(v/v\)) extract of the rhizome of _G. vivax_ in three simple steps. The extraction solvent was selected to limit co-extraction of ballast substances. The purification procedure was fairly uncomplicated due to the specific physical properties of the compounds, especially their solubility profile. The crude acetone-water extract was first fractionated by liquid-liquid partitioning with ethyl acetate to remove less polar constituents such as lipophilic terpenoids, free phenolic acids, flavonoids, and low molecular weight proanthocyanidins. The mixture of the target analytes was next obtained by spontaneous crystallisation from the water residue reconstituted beforehand in hot methanol. The pure compounds **1** and **2** were finally separated by open column gel permeation chromatography on Sephadex LH-20 with the recalculated isolation yield of 2.80 mg/g and 3.20 mg/g dw of the plant material, respectively. Compounds **1** and **2** were obtained as whitish amorphous powders that were very soluble in water and hardly soluble in methanol. Their UV-Vis spectra with maxima at 245, 362 nm and 246, 361 nm, respectively, were closely similar to that of ellagic acid (253, 334 nm). The aqueous solution of both compounds revealed the presence of potassium ion by flame atomic absorption while aqueous hydrolysate after mild acidic hydrolysis (0.1 N HCl, 100 \({}^{\circ}\)C, 2 min) gave white precipitate with barium chloride (BaCl\({}_{2}\)) indicating the presence of a sulphate ion. These were strong indicators that both compounds are potassium salts of sulphate derivatives. The molecular formula of compound **1** was established to be C\({}_{16}\)H\({}_{9}\)O\({}_{11}\)S by HR-ESI-TOF-MS (negative-ion mode) accurate mass measurement (observed 408.9869 [M-K]\({}^{\prime}\), calculated 408.9877). The fragmentation ion resulting from the cleavage of a sulphate group [M-80] was also observed at 329.0129 \(m/z\). The \({}^{1}\)H NMR spectrum of **1** in D\({}_{2}\)O (Table 1) revealed the presence of four signals, including two resonances of aromatic protons at \(\delta_{H}\) 7.8 (1H, \(s\)) and \(\delta_{H}\) 7.0 (1H, \(s\)), which corresponded to H-C(5) and H-C(5\({}^{\prime}\)), respectively, as well as two three-proton singlets observed at \(\delta_{H}\) 4.1 and \(\delta_{H}\) 4.2, and identified as the signals of methoxy groups. The \({}^{1}\)H-\({}^{1}\)H COSY spectrum showed no couplings between the protons. As compared to the corresponding resonances of free ellagic acid and its methyl ethers [12,14], the large downfield shift (\(\Delta\delta_{H}=+\) 0.4) observed for H-C(5) indicated the anisotropic effect of a strong electronegative group in the _ortho_-position and suggested thereby the substitution of the sulphate moiety at C(4) [14]. The HMQC spectrum of **1** displayed cross-peaks between the methoxy proton singlets listed above and carbon resonances found in the \({}^{13}\)C NMR spectrum at \(\delta_{C}\) 62.3 and \(\delta_{C}\) 61.6, respectively. Both were located relatively downfield, suggesting their attachment to an aromatic ring carbon which has adjacent oxygenated ring carbons on both sides and thus confirming their position at C(3) and C(3\({}^{\prime}\)), respectively [12]. Based on the HMQC and HMBC spectra, the carbon resonances for C(1), C(1\({}^{\prime}\)), C(4), C(4\({}^{\prime}\)), C(5), and C(5\({}^{\prime}\)) were next unambiguously assigned (Table 1). As for the C-4 carbon signal the large upfield shift (\(\Delta\delta_{C}=-3.1\)) was found in comparison with that of the corresponding signal of free ellagic acid [12], the proposed substitution position of the sulphate group was further confirmed.