Total NMR assignments of new [C7-O-C7']-biflavones from leaves of the limonene-carvone chemotype of Lippia alba (Mill) N. E. Brown

Phytochemical analysis of leaves of the limonene-carvone chemotype of Lippia alba led to the isolation of two biflavonoids with a new structural pattern with an ether linkage: 5,5'-dihydroxy-6,4',6',3',4'-pentamethoxy-C(7)--O--C(7')]-biflavone (1) and 4',4,5,5'-tetrahydroxy-6,6',3'-trimethoxy-C(7)--O--C(7')]-biflavone (2). Structural elucidation of the new compounds was established on the basis of spectral data, through the use of 1D NMR and several 2D shift correlated NMR pulse sequences (COSY, HMQC, HMBC and NOESY).