Tyrosinase inhibitors from the leaves of Eucalyptus globulus

A new isoiphionane sesquiterpene, named (3S, 5S, 7S, 10R)-3, 11-dihydroxyisoiphion-4-one (1), two new phloroglucinol glycosides, named eucalglobuside A (2) and eucalglobuside B (3), along with 15 known compounds were isolated from the leaves of Eucalyptus globulus. Their structures were elucidated based on extensive spectroscopic analysis and in comparison with literature data. The absolute configuration of compound 1 was determined by ECD calculation. All isolates were evaluated their inhibitory activities against the mushroom tyrosinase. As a result, three sesquiterpenoids, 1, 5 beta, 11-dihydroxy-iphionan-4-one (5), and (-)-globulol (8), exhibited the most potent activities with IC50 values of 14.17 mu M, 10.08 mu M and 9.79 mu M, respectively.