Reinvestigating the reaction of 1H-pyrazol-5-amines with 4,5-dichloro-1,2,3-dithiazolium chloride: a route to pyrazolo[3,4-c]isothiazoles and pyrazolo[3,4-d]thiazoles

The Synthesis and Biological Applications of the 1,2,3-Dithiazole Scaffold

The 1,2,3-dithiazole is an underappreciated scaffold in medicinal chemistry despite possessing a wide variety of nascent pharmacological activities. The scaffold has a potential wealth of opportunities within these activities and further afield. The 1,2,3-dithiazole scaffold has already been reported as an antifungal, herbicide, antibacterial, anticancer agent, antiviral, antifibrotic, and is a melanin and Arabidopsis gibberellin 2-oxidase inhibitor. These structure activity relationships are discussed in detail, along with insights and future directions. The review also highlights selected synthetic strategies developed towards the 1,2,3-dithiazole scaffold, how these are integrated to accessibility of chemical space, and to the prism of current and future biological activities.

Synthesis and evaluation of 1,2,3-dithiazole inhibitors of the nucleocapsid protein of feline immunodeficiency virus (FIV) as a model for HIV infection

We disclose a series of potent anti-viral 1,2,3-dithiazoles, accessed through a succinct synthetic approach from 4,5-dichloro-1,2,3-dithiazolium chloride (Appel's salt). A series of small libraries of compounds were screened against feline immunodeficiency virus (FIV) infected cells as a model for HIV. This approach highlighted new structure activity relationship understanding and led to the development of sub-micro molar anti-viral compounds with reduced toxicity. In addition, insight into the mechanistic progress of this system is provided via advanced QM-MM modelling. The 1,2,3-dithiazole represents a versatile scaffold with potential for further development to treat both FIV and HIV.

Reaction of 4,5-Dichloro-1,2,3-dithiazolium Chloride with 2-(Phenylsulfonyl)acetonitrile

The reaction of 4,5-dichloro-1,2,3-dithiazolium chloride with 2-(phenylsulfonyl)acetonitrile (1 equiv) in the presence of pyridine (2 equiv) gave S-(3-chloro-5-cyanoisothiazol-4-yl)benzenesulfonothioate and (Z)-2-(4-chloro-5H-1,2,3-dithiazol-5-ylidene)-2-(phenylsulfonyl)acetonitrile in 19% and 23% yield, respectively. The compounds were fully characterized and the mechanistic rationale is proposed for the formation of the benzensulfonate.

Crystal Structure and Solid-State Packing of 4-Chloro-5H-1,2,3-dithiazol-5-one and 4-Chloro-5H-1,2,3-dithiazole-5-thione

The crystal structure and solid-state packing of 4-chloro-5H-1,2,3-dithiazol-5-one and two polymorphs of 4-chloro-5H-1,2,3-dithiazole-5-thione were analyzed and compared to structural data of similar systems. These five-membered S,N-rich heterocycles are planar with considerable bond localization. All three structures demonstrate tight solid-state packing without voids which is attributed to a rich network of short intermolecular electrostatic contacts. These include S^δ+…N^δ−, S^δ+…O^δ−, S^δ+…Cl^δ− and S^δ+…S^δ− interactions that are well within the sum of their van der Waals radii (∑_VDW). B3LYP, BLYP, M06, mPW1PW, PBE and MP2 were employed to calculate their intramolecular geometrical parameters, the Fukui condensed functions to probe their reactivity, the bond order, Bird Index and NICS(1) to establish their aromaticity.

Lyssenko K, Rakitin OA. Synthesis of 2-((2-(Benzo[d]oxazol-2-yl)-2H-imidazol-4-yl)amino)-phenols from 2-((5H-1,2,3-Dithiazol-5-ylidene)amino)phenols through Unprecedented Formation of Imidazole Ring from Two Methanimino Groups

A new synthetic pathway to four substituted imidazoles from readily available 2-((4-aryl(thienyl)-5H-1,2,3-dithiazol-5-ylidene)amino)phenols has been developed. Benzo[d]oxazol-2-yl(aryl(thienyl))methanimines were proved as key intermediates in their synthesis. The formation of an imidazole ring from two methanimine derivatives likely includes the opening of one benzoxazole ring followed by ring closure by intermolecular nucleophilic attack of the N-methanimine atom to a carbon atom of another methanimine.

Antimicrobial and Antifungal Activity of Rare Substituted 1,2,3-Thiaselenazoles and Corresponding Matched Pair 1,2,3-Dithiazoles

We report our investigations into the underlying differences between 1,2,3-dithiazole and their ultra-rare counterpart, 1,2,3-thiaselenazole. This rare 1,2,3-thiaselenazole chemotype was afforded by sulfur extrusion and selenium insertion into the preconstructed 1,2,3-dithiazoles. We built a library of matched paired compounds to compare and contrast the two ring systems. This led to the development of both narrow and broad-spectrum antimicrobial compounds with sub-micro molar potency, limited to no toxicity and a further understanding of the transition state electronics through molecular simulations. We also identified the potent 4,5,6-trichlorocyclopenta[d][1,2,3]thiaselenazole 11a, for use against Candida albicans, Cryptococcus neoformans var. grubii, Staphylococcus aureus and Acinetobacter baumannii, all of which have limited clinical treatment options. The 1,2,3-thiaselenazole represents a new class of potential compounds for the treatment of a host of multi-resistant hospital derived infections.

5-Amino-pyrazoles: potent reagents in organic and medicinal synthesis

5-Amino-pyrazoles have proven to be a class of fascinating and privileged organic tools for the construction of diverse heterocyclic or fused heterocyclic scaffolds. This review presents comprehensively the applications of 5-amino-pyrazoles as versatile synthetic building blocks in the synthesis of remarkable organic molecules with an emphasis on versatile functionalities. Following a brief introduction of synthesis methods, planning strategies to construct organic compounds, particularly diverse heterocyclic scaffolds, such as poly-substituted heterocyclic compounds and fused heterocyclic compounds via 5-amino-pyrazoles, have been summarized. Fused heterocycles are classified as bicyclic, tricyclic, tetracyclic, and spiro-fused pyrazole derivatives. These outstanding compounds synthesized via wide variety of approaches include conventional reactions, one-pot multi-component reactions, cyclocondensation, cascade/tandem protocols, and coupling reactions. 5-Amino-pyrazoles represent a class of promising functional reagents, similar to the biologically active compounds, highlighted with diverse applications especially in the field of pharmaceutics and medicinal chemistry. Notably, this critical review covers the articles published from 1981 to 2018.

Synthesis of 2-Mercapto-(2-Oxoindolin-3-Ylidene)Acetonitriles from 3-(4-Chloro-5H-1,2,3-Dithiazol-5-Ylidene)Indolin-2-ones

Alkylidene oxindoles are important functional moieties and building blocks in pharmaceutical and synthetic chemistry. Our interest in biologically active compounds focused our studies on the synthesis of novel oxindoles, bearing on the exocyclic double bond at the C8, CN, and S groups. Extending the potential applications of Appel’s salt, we developed a new synthetic approach by investigating the reactions of C5-substituted 2-oxindoles with 4,5-dichloro-1,2,3-dithiazolium chloride (Appel’s salt) to give original (Z)-3-(4-chloro-5H-1,2,3-dithiazol-5-ylidene)indolin-2-one derivatives, and new 2-mercapto-(2-oxoindolin-3-ylidene)acetonitriles via a dithiazole ring-opening reaction. The work described in this article represents further applications of Appel’s salt in the conception of novel heterocyclic rings, in an effort to access original bioactive compounds. Fifteen new compounds were prepared and fully characterized.

The Conversion of 5,5'-Bi(1,2,3-dithiazolylidenes) into Isothiazolo[5,4-d]isothiazoles

Thermolysis of 4,4'-dichloro-, 4,4'-diaryl-, and 4,4'-di(thien-2-yl)-5,5'-bi(1,2,3-dithiazol-ylidenes) affords the respective 3,6-dichloro-, 3,6-diaryl- and 3,6-di(thien-2-yl)isothiazolo[5,4-d]-isothiazoles in low to high yields. The transformation of the 4,4'-diaryl- and 4,4'-di(thien-2-yl)-5,5'-bi(1,2,3-dithiazolylidenes) occurs at lower temperatures in the presence of the thiophiles triphenylphosphine or tetraethylammonium iodide. Optimized reaction conditions and a mechanistic rationale for the thiophile-mediated ring transformation are presented.