Isolation and Structure Elucidation of Two New Xanthones from Gentiana azurium Bunge (Fam. Gentianaceae)

Abstract

Two new natural xanthones, 1,3,5-trihydroxy-8-methoxyxanthone (1) and 3,5-dihydroxy-8- methoxy-1-O-β-D-glucopyranosyl xanthone (2) were isolated along with two known xanthones from Gentiana azurium Bunge (Fam. Gentianaceae). Their structures were determined on the basis of their spectral data.

New Antifungal Xanthones from the Seeds of Rhus coriaria L.

“…The 1 H NMR spectrum of 1 exhibited two one-proton broad signals at δ 6.79 and 7.87 ppm assigned to p-coupled H-1 and H-4, respectively, two one-proton doublets at δ 7.97 (J = 8.4 Hz) and 7.01 ppm (J = 3.0 Hz) ascribed to H-5 and H-8, respectively, an one-proton double doublet at δ 6.93 ppm (J = 8.4, 3.0 Hz) attributed to H-6, and a three-proton broad signal at δ 2.50 ppm accounted to C-10 methyl protons located on the aromatic nucleus. The 13 C NMR spectral data were in accordance with those of xanthone molecules (Dall'Acqua et al, 2004;Pinheiro et al, 1998;Purev et al, 2002). Protonated carbon atoms were assigned by an HMQC spectrum where crossed peaks were observed between H-8 and C-4b and C-9.…”

“…There was no bathochromic or hypsochromic shift in the presence of AlCl 3 indicating the absence of hydroxy groups at positions C-1 and C-8. The UV spectrum did not show a bathochromic shift of the longest wavelength maximum with ethanolic sodium acetate indicating the location of a glycosidic unit at C-3 (Purev et al, 2002 ). It gave effervescences with sodium bicarbonate solution supporting the presence of a carboxylic group in the molecule.…”

“…Neither bathochromic nor hypsochromic shifts were observed in the UV spectrum with AlCl 3 indicating the absence of hydroxy groups at C-1 and C-8. The UV spectrum showed a bathochromic shift of the absorption maximum at 335 to 360 with ethanolic sodium acetate, indicating the presence of 3-OH (Markham, 1982;Purev et al, 2002). The IR spectrum of 2 showed characteristic absorption bands for a carboxylic group (3280, 1690 cm -1 ), hydroxy groups (3410, 3360 cm ).…”

“…A molecular ion peak at m/z 522 was analysed by FAB MS according to the molecular formula C 23 H 22 O 14 . It turned red in the presence of MgCl 2 which is characteristic for a xanthone glucoside (Markham, 1982;Purev et al, 2002). There was no bathochromic or hypsochromic shift in the presence of AlCl 3 indicating the absence of hydroxy groups at positions C-1 and C-8.…”

Naturally Occurring Xanthones: Chemistry and Biology

“…Plants xanthones are commonly isolated by column chromatography on silica gel using different solvent mixtures with increasing polarity [52][53][54][55]. Xanthone glycosides are usually crystallized from MeOH.…”