Isolation of rhododaurichromanic acid B and the anti-HIV principles rhododaurichromanic acid A and rhododaurichromenic acid from Rhododendron dauricum

Two novel chromane derivatives (1 and 2) and the known chromene (3) were isolated from the leaves and twigs of Rhododendron dauricum. The absolute stereostructure of 1 was established by spectroscopic examination and X-ray crystallographic analysis. The absolute stereostructures of 2 and 3 were also confirmed by photochemical conversion of 3 into 1 and 2. Daurichromenic acid (3) demonstrated potent anti-HIV activity with an EC50 value of 0.00567 μg/mL and therapeutic index (TI) of 3,710. Rhododaurichromanic acid A (1) also showed relatively potent anti-HIV activity with an EC50 value of 0.37 μg/mL, and a TI of 91.9, whereas rhododaurichromanic acid B (1) displayed no anti-HIV activity.