Crystal structure of 7-benzyloxy-5,6-dihydroxyflavone, C22H16O5

Abstract

Source of materialBaicalein (0.100 g, 0.370 mmol, 1 eq) and 60% NaH (0.011 g, 0.444 mmol, 1.2 eq) in DMF (8 ml) was stirred at -40°C for 20 min. The reaction mixture was then treated with benzyl bromide (0.05 ml, 0.444 mmol, 1.2 eq) at the same temperature. After 30 min stirring, the temperature was raised from -40°C to 0°C and stirred for a further 6 hrs. The crude product was extracted with EtOAc (3´20 ml), washed with water (20 ml), dried over Na 2 SO 4 and concentrated. The crude product was crystallized out with acetone and yielded 7-benzyloxy-5,6-dihydroxyflavone as brown crystals (0.030 g, 37 %).1 H NMR (600 MHz, CDCl 3 ) dH (ppm): 7.89 (d, 2 H, J 6.9 Hz, H-2' and H-6'); 7.55 (m, 3 H, OCH 2 C 6 H * 5 ); 7.49 (d, 2 H, J 7.3 Hz, H-2'' and H-6''); 7.45 (t, 2 H, J 7.3 Hz, H-3'' and H-5''); 7.40 (t, 1 H, J 7.3 Hz, H-4''); 6.70 (s, 1 H, H-3); 6.68 (s, 1 H, H-8); 5.40 (s, 1 H, OH); 5.28 (s, 2 H, OCH * 2 C 6 H 5 ).13 C NMR (600 MHz, CDCl 3 ) dC (ppm): 182.73; 164.22; 151.91; 150.54; 145.97; 135.39; 132.30; 131.45; 130.05; 129.58; 129.47; 129.31; 129.09; 128.61; 128.51; 128.32; 128.18; 128.15; 128.07; 127.19; 126.89; 126.84; 126.77; 125.87; 125.74; 106.30; 105.15; 104.80; 91.55; 91.21; 78.10; 77.63; 77.57; 71.40. IR (KBr) 3855, 3446, 2924, 1654, 1608, 1578, 1507, 1456, 1358, 1297, 1181, 1116, 1098, 1025 . Experimental detailsAll hydrogen atoms were positioned geometrically and refined using a riding model, with C-H = 0.95 Å, U iso (H)= 1.2 U eq (C) for the aromatic H, with O-H = 0.84 Å U iso (H)= 1.5 U eq (O) for the hydroxy H and with U iso (H) = 1.5 U eq (C) for methylene H atoms. The hydroxy groups were allowed to rotate with a fixed angle whilst the methylene group C-H distance was allowed to refine to best fit the experimental electron density [HFIX 147 and HFIX 24 in SHELXL97 [2]]. DiscussionPlants are an invaluable resource when used in combination with traditional environmental knowledge, researches have the opportunity to investigate and expand on this important resource. With the cataloging of various traditional medicines, scientific investigations into their combinations and active ingredients can be undertaken by the scientific community. Huang-qin (Scutellaria baicalensis Georgi) one such traditional Chinese herb has been listed in the Chinese pharmacopeia [1]. Its active ingredients have shown medicinal promise against tuberculosis, fevers, ulcers, cancers, and inflammation. One of these active components known as Baicalein was used to further functionalize the molecule by the exchange of a hydroxy with a benzyloxy moiety. The title molecule consists of a hydroxy (C5 and C6) and benzyloxy (C7) substituted flavone, the g-benzopyrone backbone including the hydroxy and carbon (C71) atom of the benzyloxy substituents was seen to be essentially planar with an r.m.s deviation of 0.0444 Å (central plane). The maximum deviation above the mean plane was observed for the carbon (C71) atom of the benzyloxy substitutent with a distance of 0.105(2) Å. The phenyl of the benzyloxy moiety was disordered ove...