Leucoflavonine, a new bioactive racemic flavoalkaloid from the leaves of Leucosceptrum canum

Abstract A new flavoalkaloid racemate, leucoflavonine ( 1 ), together with its flavonoid precursor pectolinarigenin ( 2 ), was isolated from the leaves of Leucosceptrum canum collected from Tibet. Its structure was established by comprehensive spectroscopic analysis. Chrial separation of the enantiomers of 1 was achieved, and their absolute configurations were determined as S -(+)- and R -(−)-leucoflavonines ((+)- 1a and (−)- 1b ) by comparison of their computational and experimental optical rotations. Biological assays indicated that both (+)- 1a and (−)- 1b exhibited inhibitory activity against acetylchlorinesterase (AChE) in vitro (IC 50  = 68.0 ± 8.6 and 18.3 ± 1.8 μM, respectively). Moreover, (−)- 1b displayed cytotoxicity against human hepatoma cells HepG2 (IC 50  = 52.9 ± 3.6 μM), and inhibited the production of interleukelin-2 (IL-2) in Jurkat cells (IC 50  = 16.5 ± 0.9 μM), while (+)- 1a showed no obvious activity in these assays.