Synthesis of novel phthalazine-based derivatives with potent cytotoxicity against HCT-116 cells through apoptosis and VEGFR2 inhibition

The parent ethyl 3-(4-benzyl-1-oxophthalazin-2(1H)-yl) propanoate (3) has 25 compounds. Their respective mono, dipeptides and hydrazones derivatives were produced by chemoselective N-alkylation via addition reaction of 4-benzylphthalazin-1(2H)-one (2) with ethyl acrylate and anhydrous potassium carbonate to give ethyl 3-(4-benzyl-1-oxophthalazin-2(1H)-yl) propanoate (3). The ester 3 was hydrazinolyzed to give the corresponding hydrazide 3-(4-benzyl-1-oxophthalazin-2(1H)-yl) propanehydrazide (5), then azide 6 coupled with amino acid ester hydrochloride and/or amines to afford several parent esters 8a-c, then a series of hydrazinolyzed reactions occurred to give corresponding hydrazides 9a-c. The hydrazide 9a was subjected to the azide coupling procedure, which resulted in the formation of various dipeptides. Subsequently, it was condensed with various aldehydes to yield hydrazone derivatives 13a-d. Interestingly, compounds 9c, 12b, and 13c exhibited potent cytotoxicity with IC₅₀ values of 1.58, 0.32 and 0.64 μM compared to sorafenib (IC₅₀ = 2.93 μM). Compound 12b exhibited potent VEGFR2 inhibition by 95.2% with an IC₅₀ value of 17.8 μM compared to sorafenib (94.7% and IC₅₀ of 32.1 μM). For apoptosis activity, 12b-treatment induced apoptosis in HCT-116 cells by 21.7-fold, arresting the cell proliferation at S-phase. Finally, it formed a good binding affinity towards VEGFR2 protein with a binding energy of -10.66 kcal mol^-1, and it formed binding interactions with the key interactive amino acids.