The synthesis of two new amino-acids, trans-4, 5-didehydro-DL-lysine and 4-oxo-L-lysine is described. Corrections are made concerning a previous report on the synthesis of cis-and trans-4, 5-didehydrolysine. A cyclic hemiacetal structure is proposed for threo-NN- diphthaloyl-4-hydroxy-L-lysineamide.