Three cyclized isoprenylated flavonoids from the roots and rhizomes of Sophora tonkinensis

Two new flavanones, tonkinochromanes D (1) and E (2), and a new chalcone, tonkinochromane F (3). were isolated from the roots and rhizomes of Sophora tonkinensis. Their structures were elucidated by spectroscopic methods, including 2D-NMR and circular-dichroism (CD) techniques, in combination with HR-MS analysis. Compounds 1 - 3, as well the previously reported tonkinochromanes A - C, were shown by LC-MS analysis to be 'artifacts' resulting from acid-catalyzed electrophilic cyclization of isoprenyl side chains during extraction.