Bioactive rearranged limonoids from the Chinese mangrove Xylocarpus granatum Koenig

Two new pyridine-containing limonoids, xylogranatopyridines A and B (I and 2) and their formal precursor, prexylogranatopyridine (3) were isolated from the twigs and leaves of the Chinese mangrove, Xylocarpus granatum. Xylogranatopyridine B (2) possesses an unprecedented rearranged B-ring together with a seco-ring A, supporting the biogenetic connection of 1-2 with 3. The chemical structures were elucidated by means of detailed spectroscopic analysis and X-ray single-crystal diffraction. The absolute configurations were assigned using electronic solid-state circular dichroism (ECD) supported by time-dependent density functional theory (TDDFT) ECD calculations and X-ray analysis. Xylogranatopyridine A (1) exhibited a significant inhibitory activity against protein tyrosine phosphatase 1B (PTP1B) with an IC50 value of 22.9 mu M. This is the first report of PTP1B inhibitory activity of limonoids. (C) 2014 Elsevier Ltd. All rights reserved.