7i phenylbuty1) phosphonous acid (6) l was coupled to the hydroxyacyl amino esters 7a-j to give phosphonous monoesters, which were subsequently oxidized to phosphonic monoesters Sa-j with sodium metaperiodate in aqueous dioxane.'V8 Removal of the N-Cbz and ester protecting groups gave the desired analogues 2a-j, isolated as their dilithium salts (Scheme I).
