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Abstract
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In this study, a new series of spiro indolin-1,2-diazepine were designed, synthesized, and screened
for their cholinesterase inhibitory activities. A novel, green, high-yielding approach was constructed
to synthesize spiro indolin-1,2-diazepine derivatives through a cascade reaction of diferent isatins,
malononitrile and 1,1-enediamines (EDAMs) via sequential four-component reactions to produce
the target compounds with good to excellent yields. Next the inhibitory potencies of all derivatives
were determined spectroscopically at 415 nm using the modifed Ellman method. The results of the
in vitro screening indicated that 5l with spiroindolin-1,2-diazepine core bearing 5-NO2 at R1
and 4-OH at R2 was the most potent and selective AChE inhibitor with an IC50 value of 3.98 ± 1.07 µM with no
signifcant inhibition against BChE while 5j was the most active analog against both AChE and BChE
enzymes. The structure–activity relationships suggested the variation in the inhibitory activities of
derivatives was afected by diferent substitutions on the indolinone ring as well as the phenyl moiety.
The enzyme kinetic studies of the most potent compound 5l at fve diferent concentrations and
acetylthiocholine substrate (0.1–1 mM) by Ellman’s method revealed that it inhibited AChE in a mixed
mode with a K of 0.044 μM. A molecular docking study was performed via induced ft docking protocol
to predict the putative binding interaction. It was shown that the moieties used in the initial structure
design play a fundamental role in interacting with the enzyme’s binding site. Further, molecular
dynamics simulations with the Schrödinger package were performed for 5l in a complex with AChE
and revealed that compound 5l formed the stable complex with the enzyme. The MTT toxicity
assessments against the neuroblastoma cell line were executed, and no toxicity was seen for 5l under
the tested concentrations.
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