Dendrobium crepidatum was one of the sources of Herba Dendrobii, a famous and precious traditional Chinese medicine. Indolizine-type alkaloids are the main characteristic ingredients of D. crepidatum, which possesses a variety of changeable skeletons. In the present study, we found that the total alkaloids of D. crepidatum (TAD) can inhibit the production of nitric oxide (NO) in lipopolysaccharide (LPS)-activated macrophages and showed protective effects against LPS-induced acute lung injury (ALI) in mice through downregulating the TLR4-mediated MyD88/MAPK signaling pathway. Further phytochemical study showed that six previously undescribed indolizine-type compounds, including a racemic mixture (dendrocrepidine A-E) were isolated from TAD. Meanwhile, dendrocrepidine F was separated into a pair of enantiomers by a chiral chromatography, and their absolute configurations were assigned by single-crystal X-ray diffraction analysis. The isomer (-)-dendrocrepidine F showed higher anti-inflammatory effects by inhibiting NO production in LPS-treated macrophages with an IC50 value of 13.3 mu M. Taken together, indolizine-type alkaloids are the active components of D. crepidatum through downregulating the TLR4-mediated pathway, indicating some kind of therapy of TAD for ALI treatment. (C) 2018 Elsevier Ltd. All rights reserved.