www.mdpi.org/molecules Biological Activities of Hydrazone Derivatives

There has been considerable interest in the development of novel compounds with anticonvulsant, antidepressant, analgesic, antiinflammatory, antiplatelet, antimalarial, antimicrobial, antimycobacterial, antitumoral, vasodilator, antiviral and antischistosomiasis activities. Hydrazones possessing an azometine -NHN=CH- proton constitute an important class of compounds for new drug development. Therefore, many researchers have synthesized these compounds as target structures and evaluated their biological activities. These observations have been guiding for the development of new hydrazones that possess varied biological activities.

Iron is necessary for the biochemical reactions of living organisms.Desferrioxamine is an agent which is used for the treatment of a complication called "Iron Overload Disease".Researchers have synthesized hydrazones of INH by using various aldehydes and their iron complexes and evaluated these complexes for their antitumoral activity.The mechanism of antitumoral activity of iron complexes is the inhibition of ribonucleotide reductase, which is an important enzyme for conversion of ribonucleotides to deoxyribonucleotides. Copper complexes of INH that facilitate the intercellular transport of INH were synthesized and evaluated for their antitubercular activity.
Hydrazones containing an azometine -NHN=CH-proton are synthesized by heating the appropriate substituted hydrazines/hydrazides with aldehydes and ketones in solvents like ethanol, methanol, tetrahydrofuran, butanol, glacial acetic acid, ethanol-glacial acetic acid.Another synthetic route for the synthesis of hydrazones is the coupling of aryldiazonium salts with active hydrogen compounds.In addition, 4-acetylphenazone isonicotinoylhydrazones was prepared by Amal and Ergenç [8] by exposing an alcohol solution of 4-acetylphenazone and INH to sunlight or by mixing them with a mortar in the absence of the solvent.
Hydrazide-hydrazones compounds are not only intermediates but they are also very effective organic compounds in their own right.When they are used as intermediates, coupling products can be synthesized by using the active hydrogen component of -CONHN=CH-azometine group [9].N-Alkyl hydrazides can be synthesized by reduction of hydrazones with NaBH 4 [10], substituted 1,3,4oxadiazolines can be synthesized when hydrazones are heated in the presence of acetic anhydride [1,11,12].2-Azetidinones can be synthesized when hydrazones react with trietylamine chloro acetylchloride [13].4-Thiazolidinones are synthesized when hydrazones react with thioglycolic acid/ thiolactic acid [3,14] (Scheme 1).

Isocarboxazide Iproniazide
A number of studies have investigated the in-vitro and in-vivo metabolism of hydrazide-hydrazones.In in-vitro metabolism studies, it has been found that hydrazide-hydrazones undergo hydrolytic reactions and aromatic rings undergo aromatic hydroxylation reactions [15,16] (Scheme 2).This review critically evaluates the pharmacological activity of the hydrazones that were reported in the past ten years.

Anticonvulsant Activity
Epilepsy is a common neurological disorder and a collective term given to a group of syndromes that involve spontaneous, intermittent, abnormal electrical activity in the brain.The pharmacotherapy of epilepsy has been archieved during the last decade.Furthermore, although for the last twenty years new antiepileptic drugs have been introduced into clinical practice, the maximal electroshock (MES) test and the subcutaneous pentylenetetrazole (scPTZ) test are the most widely used animal models of epilepsy to characterize the anticonvulsant activity.
The biological results revealed that in general, the acetylhydrazones 2 provided good protection against convulsions while the oxamoylhydrazones 3 were significantly less active.[19].

3
Fifteen new hydrazones of (2-oxobenzoxazoline-3-yl)acetohydrazide 4 were synthesised and their antiepileptic activity was tested in scPTZ test.The 4-fluoro derivative was found to be more active than the others [20].
4-Aminobutyric acid (GABA) is the principal inhibitory neurotransmitter in the mammalian brain.GABA hydrazones 5 were designed and synthesized and evaluated for their anticonvulsant properties in different animal models of epilepsy such as MES, scPTZ, subcutaneous strychine (scSTY) and intraperitonal picrotoxin (ipPIC) induced seizure tests.Some of the compounds were effective in these models [21].

Antidepressant Activity
Iproniazide, isocarboxazide and nialamide, which are hydrazide derivatives, exert their action by inhibiting the enzyme monoamine oxidase (MAO).Inhibition results in increased levels of norepinephrine, dopamine, tyramine and serotonin in brain neurons and in various other tissues.There have been many reports on the antidepresant / MAO-inhibiting the activity of hydrazones derived from substituted hydrazides and reduction products.

Analgesic, Antiinflammatory and Antiplatelet Activity
Non-steroidal anti-inflammatory drugs (NSAIDs) have a wide clinical use for the treatment of inflammatory and painful conditions including rheumatoid arthiritis, soft tissue and oral cavity lesions, respiratory tract infections and fever.The two isoforms of cyclooxygenase (COX) are poorly distinguishable by most of the classical NSAIDs and these agents actually inhibit COX-1 extensively, besides COX-2, leading to gastrointestinal injury, suppression of TXA2 formation and platelet aggregation.The combination of these interactions is probably the reason for gastrointestinal bleeding as the most serious complication of these drugs.Some evidences suggest that the hydrazone moiety present in some compounds possess a pharmacophoric character for the inhibition of COX.
The most important antiinflammatory derivative 2-(2-formylfuryl)pyridylhydrazone 7 presented a 79 % inhibition of pleurisy at a dose of 80.1 μmol/kg.The authors also described the results concerning the mechanism of the action of these series of N-heterocyclic derivatives in platelet aggregation that suggests a Ca 2+ scavenger mechanism.Compound 7 was able to complex Ca 2+ in invitro experiments at 100 μM concentration, indicating that these series of compounds can act as Ca 2+ scavenger depending on the nature of the aryl moiety present at the imine subunit [22].
The evaluation of platelet antiaggregating profile let to identification of a new potent prototype of antiplatelet derivative, that is benzylidene 10H-phenothiazine-1-carbohydrazide (IC 50 =2.3μM) 10, which acts in the arachidonic acid pathway probably by inhibition of platelet COX-1 enzyme.Additionally, the change in para-substituent group of acylhydrazone framework permitted to identify a hydrophilic carboxylate derivative and a hydrophobic bromo derivative as two new analgesics that are more potent than dipyrone, which is the standard, possessing selective peripheral or central mechanism of action [25].

Antimalarial Activity
Malaria is a disease caused by parasitic protozoa of the genus Plasmodium which afflicts more than 500 million people worldwide and causes approximately 2 million deaths each year.The spread of multidrug-resistant Plasmodium falciparum has highlighted the urgent need to discover new antimalarial drugs.
A series of N 1 -arylidene-N 2 -quinolyl-14 and N 2 -acrydinylhydrazones-15 were synthesized and tested for their antimalarial properties.The new synthesized compounds, including 14d-g and 15a-c showed an antiplasmodial activity against the chloroquine-sensitive D10 strain in the same range of chloroquine (CQ).Similarly, 14f and 14g displayed the same activity as CQ against chloroquinesensitive 3D-7 strain, while compound 15b was 10 times more potent than CQ.Two analogues 15b and 15c, were more active against W2 CQ-resistant than D10 CQ-sensitive strains [29].1-Substituted phenyl-N′-[(substitutedphenyl)methylene]-1H-pyrazole-4-carbohydrazides 16 were synthesized and their leishmanicidal and cytotoxic effects were compared to the prototype drugs (ketoconazole, benznidazole, allopurinol and pentamidine) in vitro.The 1H-pyrazole-4carbohydrazide derivatives with X = Br, Y = NO 2 and X = NO 2, Y = Cl demonstrated the highest activity and they were more effective on promastigotes forms of L. amazonensis than on L. chagasi and L. braziliensis species [30].

Antimicrobial Activity
The dramatically rising prevalence of multi-drug resistant microbial infections in the past few decades has become a serious health care problem.The search for new antimicrobial agents will consequently always remain as an important and challenging task for medicinal chemists.
Ethyl 2-arylhydrazono-3-oxobutyrates 17 were synthesized in order to determine their antimicrobial properties.Compound 17d showed significant activity against S. aureus whereas the others had no remarkable activity on this strain.Compound 17e was found to be more active than the others against Mycobacterium fortuitum at a MIC value of 32 μg/ml [31].
methylene]hydrazine 18 inhibited the growth of several bacteria and fungi [3].
Nifuroxazide and six analogs 19 were synthesized by varying the substituent at the p-position of the benzene ring and the heteroatom of the heterocyclic ring.These compounds were evaluated for their antimicrobial activity against S. aureus ATCC 25923 and found to be active at concentration 0.16-63.00μg/mL [32].

29
A series of hydrazones synthesized from various cholesterol derivatives 30 were evaluated for their in vitro antimicrobial properties against human pathogens.The activity was highly dependent on the structure of the different compounds involved.The best results have been obtained with tosylhydrazone cholesterol derivatives exhibiting activities against C. albicans (CIP 1663-80) at a concentration of 1.5 μg/mL [37].

Antimycobacterial Activity
Tuberculosis is a serious health problem that causes the death of some three million people every year worldwide [39].In addition to this, the increase in M. tuberculosis strains resistant to front-line antimycobacterial drugs such as rifampin and INH has further complicated the problem, which clearly indicates the need for more effective drugs for the efficient management of tuberculosis.Meyer and Mally prepared new hydrazones by reacting isoniazid (INH) with benzaldehyde, o-chlorobenzaldehyde and vanilin [5].Shchukina et al. prepared INH hydrazide-hydrazones 1 by reacting INH with various aldehydes and ketones; the compounds were reported to have activity in mice which had been infected with various strains of M. tuberculosis, and also indicated lower toxicity than INH [5,6].
The reaction of   5-nitro-2-furyl/pyridyl/substituted-phenyl)methylene]hydrazino]carbonyl]phenyl]hydrazones 33 were synthesized.All the synthesized compounds were evaluated for their antimycobacterial activity against M. fortuitum ATCC 6841 and M. tuberculosis H37Rv.Of the compounds screened, 33e and 33g were found to be active against M. fortuitum at an MIC value of 32 μg/mL.Compound 33a, which exhibited > 90% inhibition in the primary screen at 12.5 μg/mL against M. tuberculosis H37Rv, was the most promising derivative for antituberculosis activity.Results obtained from the level II screening showed that the actual MIC and IC 50 values of 32a were 3.13 and 0.32 μg/mL, respectively.The same compound was also tested against Mycobacterium avium, which was observed not to be susceptible to 33a [2].
Isonicotinoylhydrazones have been further reacted with pyridinecarboxaldehydes to give the corresponding pyridylmethyleneamino derivatives 34.The new synthesized hydrazones and their pyridylmethyleneamino derivatives were tested for their activity against mycobacteria, Gram-positive and Gram-negative bacteria.The cytotoxicity was also tested.Several compounds showed a good activity against M. tuberculosis H37Rv and some isonicotinoylhydrazones showed a moderate activity against a clinically isolated M. tuberculosis (6.25-50 μg/mL) which was INH resistant [41].Novel coupling products 41 were synthesized and evaluated for their antimycobacterial activity against M. tuberculosis H37Rv and M. avium.Compound 41b was found to be the most potent derivatives of these series with the MIC value of 6.25 μg/mL against M. tuberculosis H37Rv [48].(3,4-diaryl-3H-thiazole-2-ylidene)hydrazide derivatives 42 were synthesized and tested for their in vitro antimycobacterial activity towards three strains.Compound 42s was exhibited at 20 μg/mL against M.tuberculosis 190, isolated from bronchial aspirates [49].
Various diclofenac acid hydrazones 53 were synthesized and evaluated for their antimycobacterial activities against M. tuberculosis in vitro and in vivo.Preliminary results indicated that most of the compounds demonstrated better in vitro antimycobacterial activity at concentrations ranging from 0.0383 to 7.53 μM [56].

Antitumoral Activity
A variety of antitumoral drugs are currently in clinical use.The search for antitumoral drugs led to the discovery of several hydrazones having antitumoral activity.Some of diphenolic hydrazones showed maximum uterotrophic inhibition of 70%, whereas compound 58 exhibited cytotoxicity in the range of 50-70% against MCF-7 and ZR-75-1 human malignant breast cell lines [60].5-Chloro-3-methylindole-2-carboxylic acid(4-nitrobenzylidene)hydrazide 63a was found to arrest T47D cells in G 2 /Mphase of the cell cycle and to induce apoptosis as measured by the flow cytometry analysis.A 20-fold increase of apoptotic activity was achieved from the screening hit to 5-methyl-3phenylindole-2-carboxylic acid(4-methylbenzylidene) hydrazide 64a and 5-chloro-3-phenylindole-2carboxylic acid(4-nitrobenzylidene)hydrazide 64b, with EC 50 values of 0.1 μM in the caspase activation assay in T47D breast cancer cells.Compound 64b also was found to be highly active in a standard growth inhibition assay with a GI 50 value of 0.9 μM in T47D cells.Compound 63a and its analogs were found to inhibit tubulin polymerization, which is the most probable primary mechanism of the action of these compounds [65].

Antiviral Activity
HIV infection and AIDS represent one of the first diseases for which the discovery of drugs was performed entirely via a rational drug design approach.Current treatment regimens are based on the use of two or more drugs that belong to group of inhibitors termed as highly active antiretroviral therapy (HAART).Some thiourea compounds were reported to be non-nucleoside inhibitors (NNIs) of the reverse transcriptase (RT) enzyme of the human immunodeficiency virus (HIV).Such hydrazones have been reported to be the potent inhibitors of ribonucleotide reductase activity.
N-Arylaminoacetylhydrazones and O-acetylated derivatives of sugar N-arylaminoacetyl hydrazones were synthesized and evaluated for their antiviral activity against Herpes simplex virus-1 (HSV-1) and hepatitis-A virus (HAV).Some compounds revealed the highest antiviral activity against HAV-27 and HSV-1 [73].

Schistosomiasis
Schistosomiasis or bilharzia is a parasitic disease caused by several species of flatform.Currently, schistosomiasis affects roughly 200 million people in tropical countries, and in certain African communities the process of overcoming schistosomiasis is an important rite of passage.Schistosomiasis causes debilitating nutritional, hematologic and cognitive deficits, with substantial morbidity and mortality in populations.There are five species of flatworms that cause schistosomiasis.Schistosoma mansoni, S. intercalatum, S. haematobium, S. japonicum and S. mekongi.Schistosoma mansoni and S. intercalatum, S. japonicum and S. mekongi cause intestinal and Asian intestinal schistosomiasis, respectively.S. haematobium resides in the venous plexus, which causes urinary schistosomiasis [74].9-Acridanone hydrazones have been developed by Hoffmann-La Roche (Basel-Switzerland).One of these compounds (RO 15-5458/000) was administered at two dose levels 25 mg and 15 mg/kg body-weight to S. mansoni infected vervet-monkeys [75].In addition, same compounds were found to be effective against S. mansoni in mice, killing almost all the skin schistosomules, when administered at the dose of 100mg/kg.In experiments carried out with Cebus monkeys, the compound RO 15-5458 / 000 was shown to be fully effective at 25 mg/kg [76].

Review articles related with hydrazones
There critical reviews have been published recently, and they may give an outlook on the latest research developments on antimycobacterial substances [77][78][79].
effective compounds, such as iproniazide and isocarboxazide, are synthesized by reduction of hydrazide-hydrazones. Iproniazide, like INH, is used in the treatment of tuberculosis.It has also displays an antidepressant effect and patients appear to have a better mood during the treatment.Another clinically effective hydrazide-hydrazones is nifuroxazide, which is used as an intestinal antiseptic.
{1-[2-hydroxy-3-(piperazine-1-yl-methyl)phenyl]ethylidene}isonicotinohydrazide 43 was found to be the most active compound with the MIC of 0.56 μM, and it was more potent than INH (MIC of 2.04 μM).After 10 days of treatment, same compound decreased the bacterial load in murine lung tissue by 3.7-log10 as compared to controls, which was equipotent to INH[50].
compounds were found to possess antiproliferative properties.The most active compound of the series was the 3-and 5-methylthiophene-2-carboxaldehyde α-(N)heterocyclichydrazones derivatives 62, which exhibited tumor growth inhibition activity against all cell lines at GI 50 values between 1.63 and 26.5 μM[64].

64b65f 66
Demirbaş et al. synthesized the new hydrazide-hydrazones containing 65 5-oxo-[1,2,4]triazole ring.Some of these compounds had inhibitory effect on mycelial growth whereas Compounds 65c and 65f were found to possess antitumor activity in breast cancer.[66].Hydrazinopyrimidine derivatives 66 were evaluated for their in vitro antitumoral activity in nine different types of human cancers.Some of the newly prepared compounds demonstrated inhibitory effects on the growth of a wide range of cancer cell lines generally at 10 −5 M to 10 −7 M concentrations [Several benzo[d]isothiazole hydrazones have been tested for antitumoral activity.Compound 67h, bearing a hydroxy group at o-position of the benzylidene moiety, was the most potent, with the IC50 against the various cell lines ranging between 0.5 and 8.0 μM, thus acting equally potent as 6mercaptopurine against the haematological tumors[68].