Tetrahydroxycalixarene methylenebisphosphonic acids: synthesis, stereochemistry, and aminoacids complexations

Interaction of the ready available monoformyl or diformyltetrahydroxycalixarenes with excess of diisopropylphosphite sodium salt gives isopropyl esters of tetrahydroxycalixarene methylenebisphosphonic acid or dimethylenebisphosphonic acid respectively with preparative yields. α-Hydroxymethylenephosphonates and phosphonyl quinon methids are formed as intermediates in the reaction. The obtained esters converts with quantitative yields into corresponding free acids by sequential treatment with trimethylbromosilane and methanol. The tetrahydroxycalixarene methylenebisphosphonic acids exist in the cone-shaped conformation and selectively form stable host-guest supramolecular complexes with aminoacids.