The chemical constituents of Bai-Hua-Qian-Hu, the root of Peucedanum praeruptorum Dunn. (Umbelliferae) - four new coumarins - Chen,Z.X.; Huang,B.S.; She,Q.L.; Zeng,G.F. (Yao Xue Xue Bao (Acta Pharmaceut, 1979)