Antineoplastic agents. 443. Synthesis of the cancer cell growth inhibitor hydroxyphenstatin and its sodium diphosphate prodrug

A structure-activity relationship (SAR) study of the South African willow t ree (Combretum caffrum) antineoplastic constituent combretastatin A-4 (3b) led to the discovery of a potent cancer cell growth inhibitor designated ph enstatin (5a). This benzophenone derivative of combretastatin A-4 showed re markable antineoplastic activity, and the benzophenone derivative of combre tastatin A-1 was therefore synthesized. The benzophenone, designated hydrox yphenstatin (6a), was synthesized by coupling of a protected bromobenzene a nd a benzaldehyde to give the benzhydrol with subsequent oxidation to the k etone. Hydroxyphenstatin was converted to the sodium phosphate prodrug (6e) by a dibenzyl phosphite phosphorylation and subsequent benzyl cleavage (6a --> 6d --> 6e). While hydroxyphenstatin (6a) was a potent inhibitor of tub ulin polymerization with activity comparable to that of combretastatin A-1 (3a), the phosphorylated derivative (6e) was inactive.