The bark extract of the Malayan Alstonia angustifolia Wall provided the spirocyclic alkaloids macrodasines A-G. The structures of the new compounds were established by analysis of the spectroscopic data and in the case of macrodasines A and B confirmed by X-ray diffraction analysis. Macrodasines A, B, C, and G incorporate fused spirocyclic tetrahydrofuran-tetrahydrofuran rings, while macrodasines D, E, and F incorporate fused tetrahydrofuran-tetrahydropyran rings. Macrodasines B, C, and E were found to show moderate levels of activity in reversing multidrug-resistance in drug-resistant KB cells. © 2011 Elsevier Ltd. All rights reserved.