A practical protocol for the parallel synthesis and purification of amino tetrazole and [1,3,4]oxadiazol-2-one derivatives as carboxylic acid bioisosteres is described. Phenyl- and benzyl-amines, substituted with tetrazole or [1,3,4]oxadiazol-2-one, were transformed into functionally diverse and novel compounds, with p K a values ranging from 4.9 to 8.4, by two sequential reductive alkylation reactions. These series of di- and trisubstituted amino-phenyl and -benzyl derivatives were produced in solution using solid-supported reagents and were purified by solid-phase extraction (SPE) techniques.