Series of new synthesized biologically active phthalazinone derivatives were obtained. Starting from the amino acid methyl esters of 4-benzyl-1(2H)-phthalazinone 2a,b which were synthesized from the aceto hydrazide of 4-benzyl-1(2H)-phthalazinone 1 via azide coupling method. The hydrazides 3a,b were prepared from hydrazinolysis of corresponding esters 2a,b. N-alkyles-2-(4-Benzyl-1-oxo-1H-phthalazin-2-yl)-methyl-acetamide 4a-f and the dipeptides methyl {2-[2-(4-Benzyl-1-oxo-1H-phthalazin-2-yl)-acetylamino]-acetylamino}-alkanoates 6a-c were obtained by the reaction of corresponding hydrazide 3a with amines and amino acid esters respectively via azide coupling method.

Similarly; N-alkyles-3-[2-(4-Benzyl-1-oxo-1H-phthalazin-2-yl)-acetylamino] 5a-f and the dipeptides methyl{3-[2-(4-Benzyl-1-oxo-1H-phthalazin-2-yl)-acetylamino]-propionylamino} alkanoates 7a-c were obtained by the reaction of corresponding hydrazide 3b with amines and amino acid esters respectively via azide coupling method