Iridoids from the aerial parts of Adenosma caeruleum with their nitric oxide inhibitory effects

Abstract

Three new iridoids, adenocaeroids A−C (1−3), and seven known analogs, umbellatolide B (4), pedicularis-lactone (5), iridolactone (6), artselaenin C (7), eucommiol (8), rehmaglutin D (9), and 3-deoxy-artselaenin C (10) were isolated from the aerial parts of Adenosma caeruleum. Their chemical structures were identified by the comprehensive spectroscopic methods, including 1D and 2D NMR and HRESI mass spectra. The relative configurations of 1−3 were established by analyzing their NOESY spectra as well as by DFT-GIAO NMR calculations followed by ML-J-DP4, DP4+, and DU8 methods. The absolute configurations of 1−3 were determined by comparing experimental and calculated ECD spectra and specific optical rotation values. All of the compounds, except 7 and 10, inhibited nitric oxide (NO) production in lipopolysaccharide (LPS)-activated BV2 microglial cells in a dose-dependent manner, with IC50 values ranging from 28.4−61.8 µM. However, none of the compounds showed inhibitory effect on protein-tyrosine phosphatase 1B (PTP1B) activity.