Synthesis, stereochemistry and cytotoxic activity of novel steroidal 16-spiro-1,3,2-dioxaphosphorinanes

The epimeric pairs a and b of novel steroidal 16-spiro-dioxaphosphorinanes 4–8 were synthetized via the phosphorylation of 16,16-bis(hydroxymethyl)androst-4-ene-3,17-dione (2) and their stereostructures were investigated by NMR methods. The dioxaphosphorinane moiety exists mainly as one of the possible chair conformers or as a chair–twist equilibrium in solution as a consequence of the rigidity of the sterane framework. The contributions of the conformers depend strongly on the configuration of the P atom and the stereoelectronic properties of the substituents on it. The antiproliferative activities of the structurally related products were determined in vitro with the MTT assay on three malignant human cell lines (HeLa, MCF7 and A431).