r alkyl n trityl 4 oxo 5 phosphononorvalinate derivative of formula iii is treated with a suitable strong aqueous mineral acid such as hydrochloric acid hydrobromic acid sulfuric acid and the like the reactants are typically stirred together for a period of time ranging from 5 minutes to 2 hours and at a temperature range of from room temperature to reflux the resulting r 4 oxo 5 phosphononorvaline derivative of formula ib is recovered from the reaction zone as its hydrochloride salt by evaporation of the solvent it may be converted to its free base by treatment with propylene oxide as is known in the art in optional step b the carboxylate functionality of the appropriate r 4 oxo 5 phosphononorvaline derivative of formula ia is cleaved to give the r 4 oxo 5 phosphononorvaline derivative of formula ib as described previously in step a 2 the following example presents a typical method of using the r alkyl n trityl 4 oxo 5 phosphononorvalinate derivatives of formula iii in order to form the r 4 oxo 5 phosphononorvaline derivatives of formula i this example is understood to be illustrative only and is not intended to limit the scope of the present invention in any way r 4 oxo 5 phosphononorvaline add r methyl n trityl 4 oxo 5 dimethylphophono norvalinate 1 0 g 2 02 mmol to aqueous 5m hydrochloric acid 10 ml and.