Cucurbalsaminones A–C, Rearranged Triterpenoidswith a 5/6/3/6/5-Fused Pentacyclic Carbon Skeleton from Momordicabalsamina , as Multidrug Resistance Reversers

Three new triterpenoids, cucurbalsaminones A–C (1–3), featuring a unique 5/6/3/6/5-fused pentacyclic carbon skeleton, named cucurbalsaminane, were isolated from a methanol extract of Momordica balsamina. Their structures were elucidated by spectroscopic methods and corroborated, for 1, by structure solution using single-crystal X-ray diffraction analysis. A hypothetical biogenetic pathway for these compounds is proposed. Compounds 1–3 were evaluated for their P-glycoprotein (P-gp/ABCB1) modulation ability, using a mouse T-lymphoma MDR1-transfected cell model by the rhodamine-123 accumulation assay, and displayed potent multidrug resistance (MDR)-reversing activity.