Two rare limonoids from the stem barks of Entandrophragma utile

Abstract Two rare limonoids (entanutilin A and B, 1 – 2 ) were identified from the stem barks of Entandrophragma utile collected in Ghana (Africa). Entanutilin A was isolated as the second limonoid possessing a cyclobutanyl ring incorporating C-19 and a cycloheptanyl ring C including C-30, and entanutilin B with a nicotinoyl group was also uncommon in natural products. Their structures were determined by extensive spectroscopic analyses (HR-ESI-MS, 1D/2D NMR), and the absolute configurations of 1 and 2 were determined by CD exciton chirality method.