In the course of our search for new melanin synthesis inhibitors from plants, 40 new flavonoids and 11 known flavonoids were isolated from the roots of Lespedeza floribunda Bunge. The structures of the new compounds were determined by MS and NMR analyses, and the absolute configurations by CD spectra. Many of the compounds inhibited melanin synthesis in normal human epidermal melanocytes (NHEM), and compounds 3, 7, 8, 11, 16, 24, 27, 29, 33, 43, 45, and 51 were particularly inhibitory. Their activities were stronger than that of hydroquinone, which is known as a major skin-lightening drug.

From the roots of Lespedeza cyrtobotrya, 45 flavonoids were isolated along with 20 new and 25 known compounds. Lipophilic flavonoids 2, 3, 7, 9, 11, 28, 30, and 39 exhibited strong inhibitory activities on melanin synthesis in normal human epidermal melanocytes.