Synthesis and Antimicrobial Activity of Benzofuroxans and Structurally Related N-oxide-Containing Heterocycles

Synthesis of new organic compounds possessing biological activity is very challenging and is a current trend in medicinal chemistry. In recent studies benzofuroxan derivatives have been described as drugs active against bacteria and fungi, based on the ability of these compounds to induce intracellular release of NO. Consequently, many substances arising from reactions between (di)сhloro(di)nitrobenzofuroxans and different aliphatic, aromatic amines, amino acids, aminoalcohol nitrates, sulfanilamides, polyene antibiotics and other nucleophiles have been prepared. Novel 2H-benzimidazole 1,3-dioxides were also obtained by interaction of benzofuroxans with alcohols in sulfuric or perchloric acids. We also proposed a new method for the preparation of 2H-benzimidazole 1,3-dioxides by reaction of obenzoquinonedioxime with ketones. Further nitration of compounds yielded a wide range of Sepin-1 analogues (separase inhibitors) with various substituents in the 2-position. Beside their high biological activity, 2H-benzimidazole 1,3-dioxides can be involved into thermal reactions. Heating of 2Н-benzimidazole 1,3-dioxides resulted in the formation of 3Н-[2,1,4]benzoxadiazine 4-oxides, which are unstable and easily transformed into initial 2H-benzimidazole 1,3-dioxides on exposure to sunlight. More prolonged heating of 3Н-[2,1,4]benzoxadiazine 4-oxides caused sequential elimination of the N-oxide oxygen atom to form 2H-benzimidazole mono N-oxides.


Synthesis and Antimicrobial Activity of Benzofuroxans and
Structurally Related N-oxide-Containing Heterocycles Introduction: Benzofuroxans were first synthesized about a hundred years ago, but they continue to attract attention of researchers due to their synthetic availability, rich chemistry and biological activity of most compounds of this series.In medicinal and biological fields growing interest has been devoted to this organic scaffold owing to its ability to release nitric oxide (NO) molecules under physiological conditions

Calcium channel modulators
Antioxidants Herbicides

Explosives
Immunosuppressive compounds

Liquid-crystalline materials
Purpose of study: the synthesis of new biologically active substances on the base of benzofuroxans; the study of biological activity and toxicity of obtained benzofuroxan derivatives

Results and discussion
Development of methods of functionalization of benzofuroxans, in particular, of introduction of the nitrogencontaining structural fragments is an actual problem.In this regard the doubtless interest present mono-and dinitrobenzofuroxans containing the halogen atoms in their structure.The presence in molecules of (di)nitrobenzofuroxans (1-3) one or two mobile chlorine atoms enables easy replacement of them by group providing targeted delivery while maintaining the NO-donor properties.
The interaction of 4,6-dichloro-5-nitrobenzofuroxan with amines In spite of the amine excess only the chlorine atom in the position 4 of the benzene ring takes part in the reaction.The research clearly shows that DMSO is the more appropriate solvent to isolate the substitution product in a high yield and with a high purity.

The interaction of benzofuroxans with diamines
It was found that diamines may be also successfully involved in the abovedescribed reaction.The use of diamines can lead to the formation of two kinds of products: in the ratio of 1 to 1 isomer, when one chlorine atom is replaced and in the ratio of 2 to 1 , when two molecules of benzofuroxan are reacting with one molecule of amine.Benzofuroxan 1 reacts with diaminopentane and piperazine in equimolar amount to give the products of double substitution.Interaction of 4,6dichloro-5-nitrobenzofuroxan with phenylenediamines is going along with the substitution of one chlorine atom and is leading to the formation of compounds 21-24.Reaction of 4,6-dichloro-5-nitrobenzofuroxan with aromatic diamines in different solvents leads to the formation of two kind of products: 1:1 isomer, and 2:1 isomer.

Creation of «hybrid» compounds on the base of benzofuroxans
Recently, research and development in the medicinal chemistry sphere of benzofuroxan systems have produced hybrid compounds in which benzofuroxanyl moieties together with classical drug moieties are presented in a single molecule.For example, the diclofenac derivative bearing a benzofuroxan moiety in its structure that showed anti-inflammatory activity and with better gastric tolerability with respect to that of native diclofenac, probably related to nitric oxide release ability Carvalho P.S, Maróstica M, Gambero A, Pedrazzoli J Jr., Synthesis and pharmacological characterization of a novel nitric oxide-releasing diclofenac derivative containing a benzofuroxan moiety // Eur.J. Med.Chem.2010; V. 45, I. 6. P. 2489-2493.
"Hybrid" compounds were prepared in the reaction of benzofuroxans with Ncontaining phosphonium bromides (a), antibacterial sulfonamides such as sulfanilamide (b), sulfadimezin (c) and sulfadimethoxine (d), aminoalcohol nitrates (f-g), amino acids (h-l), N-substituted naphthalimides (m-o), and antifungal polyene antibiotics such as Amphotericin B (p) and Nystatin (q) Preparation of "hybrid" compounds based on benzofuroxans 13 Importantly, by reacting of 4,6-dichloro-5-nitrobenzofuroxan with sulfanilamide at various ratios of reagents and conditions, we have a variety of products: in a ratio of 1:2, we obtained compound 25b and by performing the reaction in the presence of sodium bicarbonate reactant ratio of 1:1 was formed compound 28.
Probably, this phenomenon can be explained by the rearrangement of Boulton-Katritzky.
In contrast to 7-chloro-4,6-dinitrobenzofuroxan, the reaction of 4,6-dichloro-5nitrobenzofuroxan with 2-mercaptobenzothiazole takes place only in polar DMSO at 80-90 °C, and unexpectedly leads to the formation of a mixture of two products.We assume that the substitution of a nitro group for a chlorine atom or mercaptothiazole in this case can probably be explained by the radical mechanism of the reaction.

Synthesis of novel structural hybrids of benzofuroxan and benzothiazole derivatives
The reaction between 7-chloro-4,6-dinitrobenzofuroxan and 2aminobenzothiazole gave two products, one bearing the benzofuroxan moiety linked to the exocyclic amino nitrogen, and the second derived from the attack of two molecules of electrophile to both the nitrogen atoms of the benzothiazole reagent.Their relative ratio is modifiable by tuning the reagents ratio and the reaction time.

Preparation of "hybrid" compounds based on benzofuroxans and fluoroquinolones
As a result of reactions with the phenolic derivatives it was found that 4,6dichloro-5-nitrobenzofuroxan forms substitution products involving carbon atoms with phenolates in isopropyl alcohol medium.

Synthesis of benzotrifuroxan
Attempts to prepare 5-chloro-6-nitrobenzodifuroxan from the reaction of 5,7-dichloro-4,6-dinitrobenzofuroxan with sodium azide have failed and, surprisingly, the formation of the powerful hydrogen-free explosivebenzotrifuroxan (BTF) through spontaneous cyclization at 0 0 C was observed.This reaction takes place instantaneously, even at low temperature through a spontaneous cyclization.

Synthesis of 2H-benzimidazole 1,3-dioxides based on the interaction between benzofuroxans and isopropyl alcohol
Benzofuroxans and their derivatives are not only established themselves as biologically active substances of different spectrum of action, but also attracted attention as a precursors for the synthesis of a number of heterocyclic compounds.Novel 2H-benzimidazole 1,3-dioxides (43) were obtained upon the interaction of benzofuroxans with alcohols in sulfuric acid.

Synthesis of 2H-benzimidazole 1,3-dioxides by reaction of obenzoquinone dioximes with ketones
Future, we developed new method of synthesis of 2H-benzimidazole 1,3dioxides with help of the interaction of o-benzoquinone dioxime with ketones.Further nitration of obtained compounds makes it possible to obtain a wide range of Sepin-1 analogues, patented in the literature as a separase inhibitor, with various substituents at position 2. The interesting property of these systems is that they can be involved into thermal reactions.Heating of 2Н-benzimidazole 1,3-dioxides (43a-d) results in the formation of 3Н-[2,1,4]benzoxadiazine 4-oxides (46a-d), which are unstable and easily transformed into initial 2H-benzimidazole 1,3-dioxides on exposure to sunlight.More prolonged heating of 3Н-[2,1,4]benzoxadiazine 4-oxides (46a-d) causes sequential elimination of the N-oxide oxygen atom to form 2H-benzimidazole mono N-oxides (47a-d)

UV-activity of benzofuroxans
Ability to suppress and prevent genotoxic effects of UV-radiation in the wavelength range between 300-400 nm was shown for compound on the base of benzofuroxans and diamines.These compounds are able to protect bacterial cells from destructive effects of the UV-radiation.Comparing the results obtained for various benzofuroxans to those obtained for the natural antioxidant alpha -tocopherol (vitamin E) and for the synthetic antioxidant trolox, which are references in this domain, we have shown that some benzofuroxans quantitatively exhibit a similar protective effect, and that compounds prepared from the reaction between 4,6-dichloro-5-nitrobenzofuroxan and ethylenedianiline possess potent protective potential The maximum protective effect of benzofuroxans and antioxidants on Е.coli MG1655 (pKatG-lux) in the wavelength range between 300-400 nanometers

Biological activity of benzofuroxans
The in vitro antibacterial and antifungal activity of the benzofuroxans was investigated against several pathogenic representative Gram-negative and Gram-positive bacteria moulds and yeast.Benzofuroxans exhibit good bacteriostatic and fungistatic activity.The screening data show that benzofuroxans exhibit activity towards gram-positive bacteria especially Staphylococcus aureus and fungi especially Candida albicans with the MICs values comparable with reference drugs.Safety of the benzofuroxans derivatives was exclusively studied for the modeled object -various bacterial biosensors.It was found that benzofuroxan derivatives do not belong to the class of the substances damaging DNA and proteins.The toxicity of the more effective benzofuroxan derivatives has been determined in mice.According to levels of acute toxicity for mammals, the benzofuroxan derivatives can be considered as moderately toxic compounds.•Substances, possessing antibacterial and antifungal activity, were prepared on the basis of the interaction of (di)сhloro(di)nitrobenzofuroxans with different aliphatic, aromatic amines, amino acids, aminoalcohol nitrates, sulfanilamides, polyene antibiotics and other nucleophiles.

Biological activity of benzofuroxans
•Novel 2H-benzimidazole 1,3-dioxides were prepared on the base of benzofuroxans upon the interaction with alcohols in sulfuric acid.
•A new method for the preparation of 2H-benzimidazole 1,3-dioxides by reaction of o-benzoquinonedioxime with ketones was developed.Further nitration of compounds yielded a wide range of Sepin-1 analogues (separase inhibitor) with various substituents in the 2-position.