Synthesis of (±)-Isocombretastatins A-C

Abstract

With the African bush willow (Combretum caffrum) constituent R(-)-combretastatin (1a) as a model syntheses of iso-combretastatins A(1b), B(1c) AND C(1d) were completed. Reaction (ultrasound promoted) between the lithium derivative of benzyl bromide 2b and silyl protected isovanillin 3a was illustrative of the general synthetic approach. Racemic isocombretastatin A was found to significantly inhibit (ED₅₀ 0.19–0.25 μg/ml) growth of the P388 lymphocytic leukemia cell line.