Structure Elucidation of the Main Tetrahydroxyxanthones ofHypericumSeeds and Investigations into the Testa Structure

Abstract

Seeds from Hypericum species have recently been identified as an interesting source of xanthone derivatives. Extraction of seeds from H. perforatum with MeOH and subsequent concentration via polyamide adsorption yielded a fraction enriched in tetrahydroxyxanthones (THX), which were further semipurified by silica gel chromatography. Based on tentative structure assignment of the two main THX X1 and X2 by NMR a total synthesis was performed for both compounds (THX 1 and 2, respectively), starting with an Ullmann ether synthesis. The synthesized 1 and 2 were characterized via 1D- and 2D-NMR methods as well as by LC/HR-MS analysis and proven to be 1,4,6,7-THX (1) and 1,2,6,7-THX (2). Final structure assignment of the natural Hypericum THX constituents was accomplished by comparing chromatographic and spectroscopic data (LC/MS and GC/MS) with those of 1 and 2 which were obtained by synthesis. Beyond, investigations into the seeds of H. perforatum and H. tetrapterum by scanning electron microscopy (SEM) provided insights of the structure of the testa (seed coat), which is established by two cell layers, with the lignified sclerenchyma presumably being the depository of the xanthones.

Polyprenylated Benzophenones and Tocotrienol Derivatives from the Edible Fruits of Garcinia oblongifolia Champ. ex Benth. and Their Cytotoxicity Activity

“…43 Furthermore, the absolute config- 1 and 2) revealed the presence of 38 carbon resonances, including 16 quaternary carbons (7 oxygenated), 7 methines, 7 methylenes, and 8 methyls. The 1 H and 13 C NMR data of 6 were similar to those of 18 34 with a classic tricyclic xanthone skeleton (Figure 1 correlations, as shown in Figure 2. Furthermore, the absolute configurations of the C-20−C-29 and C-30−C-39 moieties (two 2-isopropenyl-1-isoheptanyl groups) were determined as 21R and 31S, respectively, by X-ray crystallography [Cu Kα; CCDC 2159520].…”

“…Structural Determination. The investigation on the constituents from G. oblongifolia fruits led to the isolation of seven new compounds, garcoblones A−F (1−6) and δ-(Z)deoxy-biamplexichromanol ( 7), together with 18 known compounds (Figure 1), which were identified as sampsonione P (8), 27 7-epiclusianone (9), 27 isogarcinol (10), 28 13,14didehydoxyisogarcinol (11), 29 garcinol (12), 30 garcimultiflorone K (13), 31 gacinialone ( 14), 32 acylphloroglucinol (15), 33 GDDPPH-1 ( 16), 31 GDDPPH-2 (17), 31 1,4,6,7-tetrahydroxyxanthone (18), 34 1,7-dihydroxyxanthone ( 19), 35 3-methoxy-1,6,7-trihydroxyxanthone (20), 36 hypericorin B (21), 37 δamplexichromanol ( 22), 38 γ-amplexichromanol (23), 38 γ-(Z)deoxy-amplexichromanol (24), 38 and δ,γ-biamplexichromanol (25) 38 1 and 2. The 1 H and 13 C NMR spectra showed the presence of a characteristic enolized 1,3-dicarbonyl group (C-1−C-3), a benzoyl moiety (C-11−C-17), and two isoprenyl systems (C-18−C-22/C-29−C-33), indicating that 1 could be a polycyclic polyprenylated acylphloroglucinols (PPAPs).…”

Three New Xanthones from Hypericum scabrum and Their Quorum Sensing Inhibitory Activities against Chromobacterium violaceum

“…The UV spectrum showed absorptions at 236, 293, 332 and 383 nm, indicating that 7 was a xanthone [ 12 , 13 , 14 ]. The 1D NMR data of 7 were comparable to those of 1,2,6,7-tetrahydroxyxanthone ( 9 ) [ 15 ]. The only difference was that the hydroxyl group at C-6 in 9 was placed at C-5 in 7 , which was confirmed by analysis of HMBC data ( Figure 2 ).…”

“…In addition to 4 and 9 , the other known compounds were identified as 2-demethylkielcorin ( 3 ), cadensin G ( 5 ), 5′-demthoxycadensin G ( 6 ) [ 16 ], 1,4,5,7-tetrahydroxyxanthone ( 8 ), 1,4,6,7-tetrahydroxyxanthone ( 10 ) [ 15 ] and 3,4-dihydroxy-2-methoxyxanthone ( 11 ) [ 17 ] by comparison of their spectroscopic data with those reported. Notably, the UV, IR and NMR data of 8 are reported for the first time in this work.…”

Recent advances in the synthesis of xanthones and azaxanthones

“…Common bases for Ullmann type reactions are K 2 CO 3 and Cs 2 CO 3 and some variations in the copper catalyst include the use of CuI, 45,151 CuO, 152 CuCl 153 or Cu/Cu 2 O. 154 Since this methodology has already been extensively reviewed, recent examples are summarized in Scheme 10 and will not be widely discussed. However, it is worth mentioning a new copper-(I)-catalysed approach that, when compared to the classical Ullmann reaction protocols, requires only small amounts of copper catalyst and mild temperatures, with better overall yields, even when tested on a larger scale.…”