Nonhydrolyzable analogues of both stereoisomers of phosphotyrosine, and a series of related aryloxy (or thio) methyl and aryloxy (or thio) ethyl phosphonic acids of the general formula RX–(CH2) n–PO3H2 (where X= O or S and n= 1 or 2), have been tested as nonhydrolyzable mimetics of phosphatase substrates. These compounds were tested against a panel of phosphatases (two alkaline phosphatases, a protein–tyrosine ...