Abstract
There has been substantial interest over the past many years in the design of novel chemical compounds containing the azomethine group (-NH-N=CH) and exhibiting various medicinal properties such as antibacterial, antiviral, antifungal, and anti-inflammatory activities. Herein, hydrazones were synthesized via the chemical reaction of substituted aromatic hydrazides with various aromatic aldehydes. The obtained products were confirmed using different physical and spectroscopic techniques, such as m.p., IR, 1H-NMR and 13C-NMR. The present study was designed to synthesize different aromatic hydrazones assembled by various combinations of aromatic hydrazides and aromatic benzaldehydes containing different substituents such as hydroxyl and polyhydroxyl groups as key structural features. Thus, incorporating such moieties and simultaneously creating highly-conjugated systems was expected to create novel species to mimic as much as possible natural phenolics, chalcones and stilbenes. Compounds of aromatic hydrazones synthesized in the present study were tested in vitro for their direct and indirect antioxidant activities using different methods such as DPPH, ABTS and FTC. The antioxidant activities of the new compounds ranged from very weak to very high activity. In addition, the inhibition of tyrosinase and cholinesterase by these compounds was tested. The new compounds containing two or three hydroxyl groups attached to aldehyde rings exhibited significantly greater inhibition effects on tyrosinase or cholinesterase activities in comparison to other compounds of the same series containing only one hydroxyl group.
Highlights
The hydrazone function is a privileged moiety and plays a noteworthy role in the area of medicinal chemistry
The aromatic hydrazones obtained in the present investigation were tested in vitro whether they have direct or indirect antioxidant activities using different methods, such as, DPPH, ABTS and ferric thiocyanate (FTC)
The direct antioxidant activities of hydrazones as measured by the DPPH method (Table 1) ranged from very low to very high (1.19–89.51). These results have shown that the greater the number of hydroxyl groups (4–5 groups) attached to aromatic rings and their locations in orthopositions relative to each other may be responsible for this high biological activity
Summary
The hydrazone function is a privileged moiety and plays a noteworthy role in the area of medicinal chemistry. The chemotherapeutic potential of this class of organic compounds provided the impetus that attracted many researchers involved in drug discovery and development to explore the synthesis and testing of their biological activity in the hope of finding some hydrazones with potent bioactivities. Aromatic hydrazones are compounds derived from phenolic acid hydrazides and aromatic aldehydes. These compounds contain the azomethine group (-NH-N1⁄4CH-) and are prepared by refluxing stoichiometric amounts of the aromatic hydrazide and aldehyde or ketone dissolved in a suitable solvent. Hydrazides and hydrazones are nowadays of considerable technical and commercial importance due to their wide utilization as drugs in medicine and as versatile ligands in coordination chemistry (Hueso-Urena et al, 1999; O€ zdemir and Gülçin, 2008). It is noted that the growing interest in the chemistry of hydrazones is related to their wide spectrum of bioactivities
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