Synthesis of non-peptidyl α,α-difluoromethylenephosphonic acids on a soluble polymer support

The polymer-supported syntheses of a series of biaryl derivatives bearing the alpha,alpha-difluoromethylenephosphonic acid group is reported. Non-cross-linked polystyrene (NCPS) was used as the support which enabled the reactions to be carried out under homogeneous conditions and reactions to be followed using conventional F-19 NMR. Synthesis of the biaryl phosphonic acids was initiated by attaching mono-ethyl esters of alpha,alpha-difluorophosphonic acids 11 and 12 to 3% alkylhydroxy-modified NCPS via a phosphate ester linkage. Suzuki reaction conditions were developed which allowed for the formation of a series of polymer-bound biaryl phosphonates at ambient temperature. Removal of phosphonic acids from the support and cleavage of the ethyl protecting group was achieved in a single step using TMSI or TMSBr. Yields of the phosphonic acids ranged from 43 to 89% and, in most cases, were obtained in a purity (96-99%), after cleavage from the support, that was sufficient for biological screening.