SummarySynthesis of l- [2,3,4,5-D 4 ]ornithine in which all of the diastereotopic hydrogens were stereoselectively labeled with deuterium was investigated. The chirally deuterated 3-aminopropanal derivative, a key intermediate in this synthesis, was prepared by a catalytic deuteration of an unsaturated g-lactone derived for l-glutamic acid followed by several functional group interconversions. Condensation of the obtained deuterium-labeled 3-aminopropanal derivative with a chiral glycine template afforded unsaturated ornithine. The dehydroornithine was then subjected to a catalytic deuteration followed by deprotection to give the l-[2,3,4,5-D 4 ]ornithine.