Publisher Summary This chapter discusses the properties and preparation methods of furoxans and benzofuroxans. The history of its structure is briefly outlined. Many furoxan structures are determined by crystallographic methods, and as a result the dimensions of the heterocyclic ring are known in a wide variety of fused and substituted examples. Dynamic resonance effects (DNMR)—signal-broadening and coalescence phenomena at medium and fast exchange rates—are characteristic of furoxans fused to aromatic rings. The spectrum of benzotrifuroxan is analyzed and compared with that of the trifurazan. The methods of benzofuroxans preparation are: (1) dimerization of nitrile oxides, (2) dehydrogenataion of dioximes, (3) preparations from olefins and nitrogen oxides, (4) miscellaneous furoxan synthesis, and (5) benzofuroxans and other aromatic-ring-fused systems. The simple deoxygenation of furoxans to furazans is provided. Furoxans can be reduced in a variety of ways, depending upon the conditions used. It includes: (1) catalytic hydrogenation, (2) reduction with complex hydrides, (3) reduction with phosphorus compounds, (4) reduction with dissolving metals and metal ions, (5) electrochemical and other reducing methods. The chapter considers the principal substituent groups on the furoxan ring and the reactions they undergo.

Furoxans and Benzofuroxans

The parasites that give rise to human African trypanosomiasis (HAT) are auxotrophs for various nutrients from the human host, including purines. They have specialist nucleoside transporters to import these metabolites. In addition to uptake of purine nucleobases and purine nucleosides, one of these transporters, the P2 transporter, can carry melamine derivatives; these derivatives are not substrates for the corresponding mammalian transporters. In this paper, we report the coupling of the melamine moiety to selected nitro heterocycles with the aim of selectively delivering these compounds to the parasites. Some compounds prepared have similar in vitro trypanocidal activities as melarsoprol, the principal drug used against late-stage HAT, with 50% growth inhibitory concentrations in the submicromolar range. Selected compounds were also evaluated in vivo in rodent models infected with Trypanosoma brucei brucei and T. brucei rhodesiense and showed pronounced activity and in two cases were curative without overt signs of toxicity. Compounds were also tested against other trypanosomatid pathogens, Leishmania donovani and Trypanosoma cruzi, and significant activity in vitro was noted for T. cruzi against which various nitro heterocycles are already registered for use.

Design and synthesis of a series of melamine-based nitroheterocycles with activity against Trypanosomatid parasites.

Human organ alkaline phosphatases: discrimination by several means including starch gel electrophoresis of axtienzysie‐enzyme supernatant fluids*

This work was supported by a grant from the Swiss National Science Foundation SNF 200020_159802. M.R.A. gratefully acknowledges the opportunity and financial support from ETH Zurich as a guest professor in the laboratory of Prof. Dr. Francois Diederich in 2016, and Allegheny College for financial support.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/chem.201804261

Chalcogen Bonding “2S–2N Squares” versus Competing Interactions: Exploring the Recognition Properties of Sulfur

A number of well known polychlorinated chemicals are toxicologically and environmentally unsafe. Because of their persistence they are in the focus of public discussions against chlorine chemistry. However, chlorinated organic chemicals in the molecular weight range between 200 and 600 constitute an important and indispensable segment in the arsenal of existing biologically active chemicals used as pharmaceuticals or crop-protection agents. Over the course of time it has been found empirically that the introduction of a chlorine atom into one or more specific positions of a biologically active molecule may substantially improve the intrinsic biological activity. In some cases the presence of a chlorine atom is crucial for significant activity in compounds derived both from nature and chemical synthesis. But in other cases chlorination diminishes or abolishes biological activity, as shown for chlordane homologues. Thus a chlorine atom, like any other substituent, is a modulator of activity. Almost all non-reactive chlorinated chemicals and chlorine-free chemicals are devoid of any biological activity at the highest concentration typically used in primary screening tests for discovery of useful biological properties. The influence of a substituent such as chlorine on the biological activity of a potential drug or crop protection agent still has to be established empirically in biological experiments designed to detect desired activity or toxicological properties. Sometimes chlorine does prove to be the optimum for improvement of activity. Long-term rigorous investigations of several hundred chlorinated compounds, registered by the authorities as pharmaceutical drugs or crop-protection agents, show that the generalisation ‘all chlorinated chemicals are dangerous’, deduced from the negative toxicological properties of a hundred chlorinated and reactive compounds of low molecular weight that are relevant in terms of safe working conditions in the chemical industry and for ecological safety, is not justified. Chlorinated compounds are not necessarily toxic or dangerous. Highly reactive chemicals or polychlorinated compounds cannot be compared with regard to toxicological properties with unreactive compounds having a low degree of chlorination. The chlorine atom, as one of many possible substituents used in synthetic organic chemistry, will remain in the future one of the important tools for probing structure–activity relationships in life science research and as a molecular component in commercialised compounds, in order to provide safer, more selective and more environmentally compatible products with higher activity for medicine and agriculture.



© 1999 WILEY-VCH Verlag GmbH

Influence of chlorine substituents on biological activity of chemicals: a review.

Investigations on Herbicides IV: The synthesis of 2,6‐dichlorobenzonitrile

An improved synthesis of 4,6-dichloro-2-phenoxy-1,3,5,-triazine from cyanuric chloride and phenol in the presence of collidine (2,4,6-trimethyl-pyridine) induced us to investigate the scope and limitation of the substitution of one chlorine atom in cyanuric chloride and the influence of the base used as an acid acceptor. Phenols, thiophenols, alcohols, thiols and oximes generally reacted with cyanuric chloride in the presence of collidine giving good yields of the corresponding substitution derivatives. The herbicidal and fungicidal properties of the compounds are dealt with and are briefly discussed. The influence of the alkyl or aryl side chain on the biological activity was determined. For this reason some derivatives mentioned in the literature were included for comparison in our biological tests.

Investigations on herbicides II: 2-Alkyloxy- and 2-aryloxy -4,6-dichloro-1,3,5-triazines 2-Alkylthio- and 2-arylthio-4,6-dichloro-1,3,5-triazines

In view of their herbicidal properties a number of 2-(substituted amino) −4,6-dichloro-1,3,5-triazines was synthesized by a method described in the literature. The influence of the side chain on the herbicidal properties was determined. For this reason some derivatives mentioned in the literature were included to compare them with the new compounds in our biological tests.

Investigations on herbicides I. 2‐(Substituted amino)‐4,6‐dichloro‐1,3,5‐triazines

The synthesis and test results on the herbicidal and fungicidal activities of a large number of 2,1,3-benzothiadiazoles, mainly 4,5,7-trisubstituted derivatives, are described and discussed.

The chemistry, herbicidal and fungicidal activities of 2,1,3-benzothiadiazoles

The purpose of the investigation was to gather data on the course of the substitution of chlorine by dimethylamine in hexachloro-1,3,5,2,4,6-triazatriphosphorine. In the course of this reaction a geminal substitution occurs besides the consecutive substitution in the 2,4 and 6 positions. The structure of the three tetrachlorobisdimethylamino and the three trichlorotrisdimethylamino-1,3,5,2,4,6-triazatriphosphorine was determined. Contrary to previously published results1, the 2,4-bisdimethylamino derivative already described by Becke Goehring2 has the trans configuration.

The structure of the tetrachlorobisdimethylamino‐and trichlorotrisdimethylamino‐1,3,5,2,4,6‐triazatriphosphorine

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