Assignment of Methoxyl Resonances and Observation of Restricted Rotation of B-Ring of 2′-Methoxy Flavones by 2D-Noesy in Conjunction with Asis

Abstract

2D-NOESY in conjunction with aromatic solvent induced shifts (ASIS) allowed unequivocal assignments of methoxyl resonances in polymethoxylated pyranoflavones thus providing an additional aid for the structural elucidation of natural products. In addition, the unusual nOe interactions observed in 2′-substituted B-ring flavones with H-3 or H-4″ of the pyran ring suggested hindered rotation of the B-ring.

Key Words:

• ASIS and 2D-NOESY
• assignment of methoxyl resonances
• isoracemoflavone dimethyl ether
• isocycloartocarpesin trimethyl ether and cycloartocarpesin trimethyl ether
• hindered rotation of B-ring in 2′,4′-disubstituted flavones