Phosphonoformic acid esters and pharmaceutical compositions containing same

A compound of the formula wherein R1, R2 and R3 are the same or different, and each is selected from the group consisting of hydrogen and phenyl groups of the formula wherein R4 and R5 are the same or different and each is selected from the group consisting of hydrogen, halogen, alkyl having 1, 2, or 3 carbon atoms, alkoxy having 1, 2, or 3 carbon atoms, alkoxycarbonyl having 2-7 carbon atoms; and alkylcarbonyl groups having 2-7 carbon atoms; or R4 and R5 together form a straight saturated alkylene chain having 3 or 4 carbon atoms and being bound to adjacent positions, i.e. 2,3- or 3,4- in the phenyl ring; provided that one of R1 and R2 is a phenyl group of the formula II when R3 is H; and physiologically acceptable salts and optical isomers thereof; methods for preparation of the compounds, pharmaceutical compositions containing them, and their medicinal use.