A total of 16 alkaloids, exemplified by mersinine A and its congeners, and constituting a new subclass of the monoterpenoid indoles, were isolated exclusively and for the first time from Kopsia singapurensis. The structures of these alkaloids were established by spectroscopic methods and in some instances confirmed by X-ray diffraction analysis. A possible biogenetic route from an aspidofractinine precursor is proposed. Compounds 1, 2, 3, 9, and 10 were found to reverse multidrug-resistance in drug-resistant KB cells. © 2007 Elsevier Ltd. All rights reserved.