The conversion of amino diols to aminohy-droxy acids by oxidation of the primary hydroxy group mediated by homogeneous and heterogeneous TEMPO (2,2,6,6-tetramethylpiperidine 1-oxyl radi-cal) is reported. The synthesis uses NaOCl as primary oxidant and TEMPO, either dissolved in the homoge-neous phase or entrapped in a sol-gel matrix, as cata-lytic mediator. Homogeneous TEMPO is suitable for the oxidation of aliphatic methylamino diols, while the hybrid organic-inorganic silica sol-gel catalysts are more selective mediators for the oxidation of ben-zylic amino diols like the potent antibiotic chloram-phenicol which, under homogeneous conditions, are unselectively oxidized to benzoic acids.