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Pyrazino[1,2- a ]indoles fused with various heterocycles, such as oxazolidine, oxazinane, imidazolidine, hexahydropyrimidine and benzimidazole, were synthesized transition metal-free by domino reactions which involved the condensation of 1-(2-bromoethyl)-3-chloro-1 H -indole-2-carbaldehydes  28 – 31  with various nucleophilic amines, resulting in the formation of two new interesting fused heterocycles. The anticholinesterase, antioxidant and antibacterial activities of the compounds were evaluated. Acetylcholinesterase (AChE) inhibitory activities were tested by Ellman’s assay, antioxidant activities were detected using the 2,2-azinobis[3-ethylbenzthiazoline]-6-sulfonic acid (ABTS •+ ) free-radical scavenging method and antibacterial activities were determined by agar diffusion tests. The oxazolo-pyrazino[1,2- a ]indoles ( 8 ,  10 ), the oxazino-pyrazino[1,2- a ]indoles ( 16 ,  18 ,  19 ), the pyrimido-pyrazino[1,2- a ]indole  (22 ), and the benzoimidazo-pyrazino[1,2- a ]indole ( 27 ) possessed the highest inhibitory activity against AChE with IC 50  values in the range 20–40 μg mL −1 . The oxazolo-pyrazino[1,2- a ]indoles ( 8 ,  9 ), the imidazo-pyrazino[1,2- a ]indoles ( 12 ,  13 ), and the benzoimidazo-pyrazino[1,2- a ]indole ( 24 ) revealed the highest antioxidant values with IC 50  values less than 300 μg mL −1 . However, the oxazolo-pyrazino[1,2- a ]indole ( 11 ) and imidazo-pyrazino[1,2- a ]indoles ( 12 ,  13 ) exhibited weak to moderate bioactivities against all tested Gram-positive bacteria, namely  Staphylococcus aureus ,  Bacillus subtilis  and  Bacillus cereus .

zeitschrift für naturforschung b

A convenient one-pot approach to the synthesis of novel pyrazino[1,2- a ]indoles fused to heterocyclic systems and evaluation of their biological activity as acetylcholinesterase inhibitors