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In this study, a series of novel Schiff base derivatives containing a pyrazolone ring (2a-e) were designed, successfully synthesized for the first time, and characterized by elemental analysis and some spectroscopic methods. These compounds were tested for their inhibitory activities on acetylcholinesterase (AChE), butyrylcholinesterase (BChE), and the human carbonic anhydrase isoenzymes I and II (hCA I and II). All synthesized molecules indicated significant inhibition effects with IC 50 values ranging from 14.15 to 107.62 nM against these enzymes. Compound 2d showed the most potent inhibitory activity among the tested molecules toward AChE and BChE (IC 50 = 15.07 and 14.15 nM) compared to the standard drug neostigmine. We determined that the IC 50 values of the tested molecules ranged between 16.86 and 57.96 nM for hCA I and 15.24-46.21 nM for hCA II. As a consequence, we may say that some of the Schiff base derivatives may be used as potential drug candidates in later studies.

In this research, nine novel heterocyclic Schiff base derivatives (10–18) bearing an aryl sulfonate moiety were designed, synthesized for the first time, and characterized. Then, their inhibitory effects on acetyl‐ and butyrylcholinesterase (AChE and BChE) were investigated in vitro conditions. Moreover, their antioxidant activities were examined by DPPH and ABTS methods. The results indicated that some of the tested molecules had varying enzyme inhibition and antioxidant activities. We determined that compounds 8, 9, 14, 17, and 18 indicated inhibitory effects with IC50 values ranging from 89.30 to 111.28 μM against BChE, respectively compared to standard compound galanthamine (IC50 = 125.88 μM). On the other hand, of the molecules tested, only compound 5 (IC50 = 36.64 μM) displayed inhibitory activity higher than galanthamine against AChE. In DPPH assay, compounds 15 (IC50 = 161.93 μM), 16 (IC50 = 191.76 μM) and 17 (IC50 = 107.55 μM) showed higher antioxidant activity than BHT (IC50 = 203.50 μM). On the other hand, it was determined in ABTS assay that Schiff bases 10–17 (except for compound 18) indicated higher antioxidant activity than BHT.

Alzheimer's disease, one of the diseases that still has no a specific therapy, has become a major public health issue owing to the increasing population of the elderly, particularly in rich countries. Inhibitory of cholinesterase enzymes (acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), which hydrolyze acetylcholine (ACh) and butyrylcholine (BCh) neurotransmitters, have recently become a choice for the therapy of this disease. Therefore, there is currently a great demand for novel enzyme inhibitors with desirable properties for applying in the treatment of AD. In this study, a series of ester derivatives of 4-(diethylamino)salicylaldehyde (1-5) were successfully prepared and structurally illuminated with FT-IR, 1 H-and 13 C NMR spectroscopy. The inhibitory properties of the synthesized molecules on AChE, BChE, and tyrosinase enzymes were investigated, respectively. Compound 1 indicated potent inhibitory activity against BChE with 87.28±0.87% inhibition better than galanthamine (73.83±0.25 %inhibition) employed as standard. Compound 3 showed significant inhibitory effect against tyrosinase with 87.73±0.22 % inhibition, which is better than kojic acid utilized as standard. The obtained results clearly revealed that some of these molecules have the potential to be used as potent enzyme inhibitor candidates in the future studies.

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In this study, some pyrazolone-based Schiff base derivatives 2a-e (except 2a) were synthesized for the first time and structurally illuminated by some spectroscopic techniques ( 1 H, 13 C NMR, FT-IR) and elemental analysis. All synthesized molecules were screened for their anticancer and antioxidant activities, as well as AChE, BChE, and tyrosinase inhibitory properties.The obtained results exhibited that compounds 1b (IC 50 = 9.497 μΜ) and 2a (IC 50 = 30.49 μΜ) significantly decreased the proliferation of HeLa cells. On the other hand, the apoptotic effects of these two compounds were investigated with acridine orange/propidium iodide double staining. The apoptotic cell ratios of the molecules treated with these two compounds were determined as 60 and 64%. Compound 2b (IC 50 = 17.95 ± 0.47 μΜ) was determined to be a very active substance in the ABTS assay. Compound 2e (A 0.5 = 43.75 ± 0.62 μM) indicated the closest antioxidant activity to the standard compound α-TOC (A 0.5 = 50.58 ± 0.39 μM) in the cupric reducing antioxidant capacity (CUPRAC) assay. In inhibition studies of enzymes, it was determined that compound 2c had a very active molecule in AChE, BChE, and tyrosinase inhibitory activities with 82.79 ± 1.03, 91.39 ± 1.06, and 92.60 ± 1.80% inhibition, respectively. It was determined that the target molecules 2a-e showed better antioxidant and enzyme inhibitory activities than those of ester derivatives 1a-e.

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