Synthesis of the enantiomers of flavan-4α-ol and flavanone

Five biflavonoids from Calycopteris floribunda (Combretaceae)

“…From their biosynthetic origin, both biflavonoid skeletons should have the (2S/4R)-configuration of natural flavan-4-ols which implies levorotatory properties (Ra´kosi et al, 1970). Since the relative stereochemistry of calycopterone (6) was confirmed through a single crystal X-ray structure (Wall et al, 1994), the absolute configuration would then be as depicted (2S, 4R, 2 00 S, 8 00 S, 9 00 S), and therefore, for the calyflorenones a (2S, 4R, 2 00 S, 4 00 R, 6 00 S, 7 00 R, 8 00 R)-configuration may be assumed.…”

Chemical Components of Anaphalis Sinica Hance

“…Its UV spectrum showed absorption bands at lmax 241 and 301 nm, and IR spectrum showed carbonyl and hydroxyl absorption bands at 1668 and 3325 cm -1 , respectively, suggesting a flavanone-type skeleton. [19][20] The 1 H-NMR spectrum of 1 exhibited a nonequivalent methylene at dH 2.82 (1H, dd, J = 17.6, 2.4 Hz) and 3.22 (1H, dd, J = 17.6, 13.2 Hz), and double doublets at d H 5.48 (1H, J = 13.2, 2.4 Hz); those can be attributed to H-3 and H-2 of the flavanone skeleton, respectively. 19-20 d H 7.50 (2H, d, J = 8.4 Hz) for H-2¢, 6¢, and d H 7.48 (3H, m) for H-3¢, 4¢, 5¢, respectively, indicated the non-replacement of B-ring, and it can also be confirmed by ion peak at m/z 77.…”

“…We have carried out the chemical studies of this plant and isolated a novel flavanone and 19 known compounds. In this paper, we report the isolation and identification of these 20 compounds, that is 6-[(5-methyl-6-ethyl-4-hydroxy-pyrone-3-yl)-methylene]glabranine (1), kaempferol (2), 3 tiliroside (3), 4 quercetin (4), 5 quercetin-3-O-b-D-glucoside (5), 6 scutellarin (6), 7 5,7-dihydroxy-8-methoxyflavone (7), 8 5,7-dihydroxy-4¢methoxy-flavone-7-O-a-L-rhamnopyranosyl(1®6)-b-Dglucopyranoside (8), 9 helipyrone (9), 10 4¢-hydroxydehydrokawain (10), 11 panamin (11), 12 ursolic acid (12), 13 pomolic acid (13), 14 3-acetyloleanolic acid (14), 15 a mixture of N-(2hydroxy-acyl)-4-hydroxy-8(E)-ene-sphingenine (15), 16 Omethyl-D-inositol (16), 17 a mixture of b-sitosterol (17) and stigmasterol (18) 18 and a mixture of daucosterol (19) and stigamasterol-b-D-glucoside (20). 18 Among them, compound 1 is a new flavanone; compounds 2-20 were isolated from this plant for the first time and 13 C NMR data of compound 11 is also reported for the first time.…”

Asymmetric Methods for the Synthesis of Flavanones, Chromanones, and Azaflavanones

“…[21] After oxime formation from (±)-flavanone ( 5 ) and reduction to the secondary amine, the mixture of cis - and trans -amines could be resolved by use of (+)-camphor-10-sulfonate and (–)-dibenzoyl-tartrates. These salts could be converted into the free amines 7a and 7b , which upon deamination with nitrous acid yielded flavanols that were subsequently oxidized to give both enantiomers of flavanone.…”