| Croton laevigatus Vahl. belongs to the genus Croton of the family Euphorbiaceae, the roots and leaves of which have been generally used as traditional medicines in Dai Nationality for the treatment of injury from fall, fracture, malaria, stomachache and so on. Up to date, no phytochemical and pharmacological research has been reported on this plant. The chemical constituents of Croton laevigatus Vahl. were systematically investigated for the first time in this thesis, applying modern chromatographic techniques and separation methods with 29 compounds isolated from the methanol extract of its leaves. Based on the spectroscopic analysis (IR, UV, 1 NMR,13C NMR,'H-'H COSY, HMQC, HMBC, NOESY, EI-MS, ESI-MS, X-ray diffraction analysis, and CD spectra), their structures were identified as laevigatlactone A (CL-1), laevigatlactone B (CL-2), laevigatlactone C (CL-3), laevigatlactone D (CL-4), laevigatlactone E (CL-5), laevigatlactone F (CL-6), laevigatbenzoate (CL-7), neocrotocembraneic acid (CL-8),3'-(4"-hydroxy-3",5"-dimethoxyphenyl)-propylbenzoate(CL-9), dihydrodehydrodiconiferyl alcohol-β-D-glucoside (CL-10), myrsinionoside C (CL-11), alangionoside J (CL-12), 3,5,6,7,8,3',4'-heptamethoxyflavone (CL-13), tangeretin (CL-14), nobiletin (CL-15), crotoncaudatin (CL-16), isorhamnetin (CL-17), kaempferol (CL-18), quercetin (CL-19), kaempferol-3-O-or-L-arabinoside (CL-20), isorhamnetin-3-O (6"-O-E-caffeoyl)-β-D-galactopyranoside (CL-21), isorhamnetin-3-O-rutinoside (CL-22), kaempferol-3-O-β-D-galactoside (CL-23), kaempferol-3-O-rutinoside (CL-24), kaempferol-3-O-α-L-rhamnopyranosyl (1→2)β-D-galactopyranoside (CL-25), mauritian:kaempferol-3-O-or-L-rhamnopyranosyl (1→2) [a-L-rhamnopyranosyl (1→6)]-β-D-galactopyranoside)(CL-26), kaempferol-3-O-β-D-glucopyranosyl (1→3) [α-L-rhamnopyranosyl(1→2)][α-L-rhamnopyranosyl (1→6)]-β-D-galactopyranoside (CL-27),β-sitosterol (CL-28), and daucosterol (CL-29), respectively, wherein, seven were new compounds (CL-1～CL-7), ten compounds were firstly isolated from the genus Croton (CL-10～CL-12, CL-20～CL-23, CL-25-CL-27), and the other twelve constituents were firstly yielded from the species Croton laevigatus Vahl..Cytotoxicity of diterpenoids isolated from Croton laevigatus Vahl. were initially investigated on HeLa cell line by applying MTT methods, and all the diterpenoids except CL-4 and CL-5 showed cytotoxicity activities. Meanwhile, the Structure-Activity Relationship of cembranoid diterpenes were studied, and the locations of C-2, C-4, C-8, and C-11 were deduced to be the key sites of anti-tumor activities. The findings above supplied clues for the structure modification of the new compounds, and scientific evidences for the further research and application of Croton laevigatus Vahl..The stems and leaves of Croton caudatus Geisel. var. tomentosus Hook. (Euphorbiaceae) have been generally used in traditional Dai nationalistic medicine for the treatment of malaria, ardent fever, convulsion, rheumatic arthritis, and numbness. Continuous studies on the chemical constituents from the 75% alcohol extract of the stems led to the isolation of 19 compounds. On the basis of spectroscopic analysis (IR, UV,1H NMR,13C NMR, HMQC, HMBC, EI-MS, ESI-MS), their structures were identified to be crotoncaudatin (CT-1), isosinensetin (CT-2),3,5,6,7,8,3,4'-heptamethoxyflavone (CT-3), tangeretin (CT-4), nobiletin (CT-5),5,6,7,4'-tetramethoxyflavone (CT-6), sinensetin (CT-7), kaempferol (CT-8), tiliroside (CT-9), kaempferol-3-O-rutinoside (CT-10), rutin (CT-11),β-sitosterol (CT-12), daucosterol (CT-13), (24S)-stigmast-3β,5α,6β-riol (CT-14), vanillin (CT-15), vanillic acid (CT-16), syringic acid (CT-17), succinic acid (CT-18), and inosine (CT-19), respectively. Among them, one compound was a new peltogynoid with rare skeleton (CT-1), eight compounds were firstly isolated from the genus Croton (CT-2-CT-7, CT-17, CT-19), and two components (CT-10, CT-11) were firstly yielded from the species Croton caudatus Geisel. var. tomentosus Hook.
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