Design, synthesis and evaluation of new pyrazino[1′,2′:1,5]pyrrolo[2,3- <i>d</i> ]pyrimidines as tacrine-like acetylcholinesterase inhibitors

The development of acetylcholinesterase (AChE) inhibitors remains a promising research direction in drug discovery for Alzheimer's disease. A series of eighteen pyrazino[1',2':1,5]pyrrolo[2,3-<i>d</i>]pyrimidine derivatives was synthesized as novel tacrine-like AChE inhibitors. Sixteen compounds inhibited AChE in the micromolar range. Among them, 4-(dimethylamino)-7,8-dimethylpyrazino[1',2':1,5]pyrrolo[2,3-<i>d</i>]pyrimidin-6(7<i>H</i>)-one (22) exhibited the highest inhibitory activity against the enzyme with an IC₅₀ value of 0.22 ± 0.02 µM, showing mixed-type inhibition. <i>In silico</i> studies showed that 22 occupies the catalytic anionic site of hAChE and forms strong π-π stacking interactions with Trp86, similar to those of tacrine. This study demonstrates the potential use of methyl-substituted pyrazino[1',2':1,5]pyrrolo[2,3-<i>d</i>]pyrimidines in the development of potent AChE inhibitors.