Chemical Constituents with UT-B Inhibitory Activity from Astragalus rigidulus

The whole plant of Astragalus rigidulus Benth. ex Bunge (Fabaceae) has been employed in Tibet to clear lung heat, alleviate diarrhea and edema. In the present study, a phytochemical investigation of A. rigidulus led to the isolation of a new alkaloid, n-butyl hematinate (1), and a new benzyl ester, astrigioside A (2), along with twenty known analogs (3-22). Their structures were elucidated through comprehensive spectroscopic analysis, including 1D/2D NMR, UV, IR, HR-ESI-MS, and comparison of the spectroscopic data with those reported in literatures. The UT-B inhibitory activities of all isolates were evaluated by erythrocyte lysis assay model. As a result, compounds 7, 8, 10, and 18 possessed significant UT-B inhibitory effects, with IC₅₀ values of 22.93 ± 0.88, 26.40 ± 0.73, 21.83 ± 0.68, 29.60 ± 0.75 µM, respectively.