The Flavonoids of Combretum quadrangulare: Crystal structures of the Polymorphic Forms of 5-Hydroxy-2-(4'-hydroxy-3',5'-dimethoxyphenyl)-3,7-dimethoxy-4H-1-benzopyran-4-one

Abstract

The following substituted 2-phenyl-4H-1-benzopyran-4-ones have been isolated from the dried flowers of Combretum quadrangulare Kurz ( Combretaceae ): 5-hydroxy-3,3′,4′,5′,7-pentamethoxy ( combretol ) (1), 3′,5-dihydroxy-3,4′,7-trimethoxy ( ayanin ) (2) and 4′,5-dihydroxy- 3,3′,5′,7-tetramethoxy (3). The last substance (3) was obtained as a mixture of two polymorphic forms (α and β) each of which was characterized by X-ray diffraction. Diffractometer data at 295 K were refined by full matrix least squares to residuals of 0.043 (1181 'observed' reflections) for the α-phase and 0.044 (1421) for the β phase of (3). Crystals of the α-phase of (3) are triclinic, Pī, a 12.663(6), b 9.592(4), c 7.444(4) Ǻ, α 102.48(3), β 101.39(4), γ 91.72(4)°,Z 2. Crystals of the β-phase of (3) are monoclinic P21/n, a 17.139(8), b 12.728(6), c 7.845(7) Ǻ, β 95.07(6)°, Z 4. An unambiguous synthesis of (3) was also achieved.

5-Hydroxy-3,3′,4′,5′,7-pentamethoxyflavone (combretol)

“…The interplanar dihedral angle between the two aromatic ring systems (O1/C2/ C3/C4/C4a/C5/C6/C7/C8/C8a and C1 H ±C6 H ) is 6.8 (3) , these being closely coplanar. This is also the case in the two polymorphs of the variation on (1), compound (2), lacking the methyl at the 4 H -oxygen, in which the dihedral angles are 7.8 ( polymorph) and 0.4 ( polymorph) (Castleden et al, 1985). These contrast with related hydroxylated species such as myricetin, (3) (cocrystallized with triphenylphosphine oxide), in which the angle is 36.4 (3) (Cody & Luft, 1994) and, further a®eld, in morin monohydrate (Cody & Luft, 1994) where the angles are 41.63 (8) and 48.31 (8) (two molecules).…”

l-Arginine Improves Solubility and ANTI SARS-CoV-2 Mpro Activity of Rutin but Not the Antiviral Activity in Cells

“…Such π-cation stacking interactions may hamper the formation of the π-π stacking interaction observed in crystal structures of rutin [ 35 ], as well as of other related flavonoids [ 36 ], thus contributing to the improved aqueous solubility of the RutinArg mixture. It is worth noting that l -arginine-mediated solubility improvement involves chemical features that are located on the aglycon.…”

Labdanes and Sucrose Esters from Physalis sordida

“…Purification of the EtOAc fraction (5.63 g) by several CC and preparative TLC separations yielded compound 1 (35 mg); 3,7,3′,4′-tetra- O -methylmyricetin (6 mg), mp 154−155 °C (MeOH), lit. mp 149−151 °C (C 6 H 6 ); 3,7,3′,5′-tetra- O -methylmyricetin (6 mg), mp 188−192 °C (MeOH), lit. mp 183−185 °C (MeOH); N - trans -feruloyl 3′- O -methyldopamine (10 mg); and N - trans -feruloyltyramine (19 mg) …”

“…Fractionation of the EtOAc fraction afforded compound 1, the flavonoids 3,7,3′,4′-tetra-O-methylmyricetin 17 and 3,7,3′,5′-tetra-O-methylmyricetin, 18 and the amides N-trans-feruloyl 3′-O-methyldopamine 19 and N-trans-feruloyltyramine. 20 These compounds were identified by comparison of their spectroscopic data with those described in the literature, and compound 1 was also identified by direct comparison with an authentic sample.…”