Grossamide K exerts a particularly strong anti-melanogenic activity on the cells without high cell toxicity.

Colocasia antiquorum var. esculenta , a variant of C. antiquorum , commonly known as 'Imperial Taro', is an edible vegetable in many tropical and subtropical regions of the world. METHODS AND RESULTS:This study with the aim of evaluating the potential of C. antiquorum var. esculenta as a functional food with a depigmenting effect resulted in the identification of a new sesquilignan, named colocasinol A (1), and a new acyclic phenylpropane lignanamide, named cis-Grossamide K (2), together with 10 known compounds (3-12). The identification and structural elucidation of these compounds were based on 1D and 2D nuclear magnetic resonance (NMR) spectroscopic data analysis as well as high-resolution fast atom bombardment mass spectrometry (FABMS) and electron impact mass spectrometry (EIMS). Quantitation of the melanin contents and cell viability in murine melanocyte melan-a cells was used to assess the antimelanogenic activities of the isolated compounds. CONCLUSIONS: Among them, cis-Grossamide K (2), isoamericanol A (3), americanol A (4), 2-hydroxy-3,2'-dimethoxy-4'-(2,3-epoxy-1-hydroxypropyl)-5-(3-hydroxy-1-propenyl)biphenyl (5), and (-)-pinoresinol (6) showed inhibitory effects on melanin production. Compounds 2, 5, and 6 exerted a particularly strong antimelanogenic activity on the cells without high cell toxicity (IC(50) = 54.24, 53.49, and 56.26 microM, and LD(50) = 163.60, 110.23, and >500 microM, respectively).