As part of the continuing work of the International Cooperative Biodiversity Group (ICBG), plant extracts were received from Madagascar. The extracts were screened for cytotoxicity using the A2780 human ovarian cancer cell line bioassay. The crude extract of Casearia nigrescens was fractionated and yielded five known compounds and one new compound that were cytotoxic. Mass spectrometry and 1D and 2D NMR techniques were used to determine the structure of the isolated compounds. The dichloromethane fraction of Casearia nigrescens was weakly active in the A2780 human ovarian cancer cell line bioassay. Further separation of the dichloromethane fraction resulted in the isolation of five known compounds (casearlucin A, caseamenbrol A, rel-18(S),19(R)-diacetoxy-18,19-epoxy-6(R)-hydroxy-2(S)-(2ξ-methylbutanoyloxy)-5(R),8(S),9(S),10(R)-cleroda-3,13(16),14-triene, casearlucin B, and rel-18(S),19(R)-diacetoxy-18,19-epoxy-2(S)-(2ξ-ethylbutanoyloxy)-5(R),8(S),9(S),10(R)-cleroda-3,13(16),14-triene) and one new compound (casearlucin L). Based on the available literature this was the first investigation of the natural products of Casearia nigrescens. The structure of the known compounds was determined by comparison of the NMR, MS, optical rotation, UV, and IR data with the data found in the literature. The structure of casearlucin L was determined by NMR data and comparison with the NMR data for similar known compounds. / Master of Science

Through the ICBG (International Cooperative Biodiversity Group) program and a continuing search for anticancer compounds, plant extracts were obtianed from Suriname and Madagascar and screened for cytotoxic activity in the A2780 human ovarian cancer cell line. Fractionation of a leaf and flower extract of Casearia nigrescens led to the isolation of six new clerodane diterpenes. Four were new natural products and the other two were previously unreported hydrolysis products. Their structures were determined using mass spectrometry and 1-D and 2-D NMR. All six compounds were cytotoxic in the A2780 human ovarian cancer cell line. Fractionation of a leaf extract of Vernonia pachyclada led to the isolation of four new sesquiterpene lactones. Their structures were determined using mass spectrometry, 1-D and 2-D NMR, and (in one case) single crystal X-ray diffraction. All four compounds were cytotoxic in the A2780 human ovarian cancer cell line. Fractionation of an extract of Casimirella ampla led to the isolation of three new diterpenes and two known diterpenes. Their structures were determined using mass spectrometry and 1-D and 2-D NMR. All five compounds were cytotoxic in the A2780 human ovarian cancer cell line. Fractionation of root and stem extracts of Mendoncia cowanii led to the isolation of two new naphthaquinones, and two known naphthaquinones. Their structures were determined using mass spectrometry and 1-D and 2-D NMR. All four compounds were cytotoxic in the A2780 human ovarian cancer cell line and three compounds exhibited weak inhibition of Akt kinase. The fractionation of five additional extracts resulted in the isolation of twelve known compounds. Their structures were determined using mass spectrometry, 1-D and 2-D NMR, and comparison to literature data. All twelve compounds were cytotoxic in the A2780 human ovarian cancer cell line. / Ph. D.