Stereoisomers of 2,4-diaminoglutaric and 2,5-diaminoadipic acids were synthesized from glutamic and 2-aminoadipic acids, respectively. The stereo, chemistry of the products was established by IH NMR spectroscopy and X-ray analysis.Key words: 2,4-diaminoglutaric acid, 2,5-diaminoadipic acid. nucleophilic substitution; stereoisomers; racemization.2,4-Diaminoglutaric acid (In) has been previously isolated as a natural product t,z and synthesized by different methods. 1"4 The (2S,4S)-enantiomer of la has been synthesized 4 and its complexing properties have been studied. 5 Methods for the synthesis of 2,5-diaminoadipic acid (lb) ~,~ and its stereoisomers s are also known. It is interesting to note that derivatives of acids la,b exhibit antitumor activity. 9,t~We have developed simple methods for the synthesis of diastereomers of compounds la,b from the corresponding monoaminodicarboxylic acids, viz., glutamic (2a) and 2-aminoadipic (2b) acids.Compound 2a is readily transformed into methyl 4-bromo-N-phthalylglutamate (3a). !1 Its reaction with potassium phthalimide (PP) in DMF followed by separation of the mixture of diastereomers afforded methyl 2,4-diphthalimidoglutarates (threo-4a and meso-4a), whose acid hydrolysis resulted in threo-and meso-la diastereomers (Scheme 1).An attempt to obtain the threo-forrn of 4a from erythro-3a was unsuccessful, since the reaction of the latter with PP in DMF ,,vas accompanied by racemization. Stirring of an equimolar mixture of meso-4aand PP in DMF for 3 h at ~ 20 ~ resulted in a mixture of diastereomers of 4a (meso/threo = 5 according to HPLC data). Evidently, PP is a very strong base, since the inversion of the carbanion follows the abstraction of the a-proton. The alternative mechanism of racemization of the phthalimide group involving nucleophilic substitution by the phthalimide ion is impossible, since heating of an equimolar mixture of meso-4aand potassium 4-nitrophthalimide in DMF for 6 h at 68 ~ did not afford (HPLC) diastereomers of methyl 2-phthalimido-4-(4-nitrophthalimido)glutarate (5),