Antineoplastic Agents, 122. Constituents of Combretum caffrum

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Abstract
An investigation of the South African tree Combretum caffrum (Combretaceae) for antineoplastic constituents was conducted by employing the astrocytoma bioassay (9ASK). By this approach and a combination of solvent partition, steric exculusion, and adsorption chromatographic procedures, a substance designated combretastatin [1a] was isolated and found to display significant (71-90% astrocyte reversal at 1-100 .mu.g/ml dose levels) astrocyte reversal and murine P-388 lymphocytic leukemia (PS) cell growth inhibition (ED50 0.011 .mu.g/ml). The structure of (-)-combretastatin was elucidated by X-ray crystal structure analysis and confirmed by total synthesis. The absolute configuration at C-10 was assigned the R-configuration on the basis of Horeau esterification techniques. Other prominent, albeit PS-inactive, constitutents were found to be 3,3'',4''-tri-O-methylellagic acid [2] and acacetin [3].