Current Organic Chemistry - Volume 24, Issue 17, 2020

Imines, versatile intermediates for organic synthesis, can be exploited for the preparation of diverse classes of biologically active benzazoles. Because of the special characteristics of the C=N bond, imines can be simultaneously used in the synthesis of 1,3-benzazoles and 1,2-benzazoles. With the development of imine synthesis, a variety of novel cascade reactions for benzazole synthesis have been reported in the last decade. Therefore, there is a strong need to elucidate the recent progress in the formation of various classes of benzazoles, including benzimidazoles, benzoxazoles, benzothiazoles, indazoles, and benzisoxazoles, via imines obtained by condensation reactions or oxidative/ redox coupling reactions In this review, we provide a comprehensive survey of this area. In particular, various green and mild synthetic methodologies are summarized, and the multiple roles of novel catalysts and significant mechanisms for several transformations are highlighted in detail. We believe that this review will aid researchers studying the synthesis of complex molecules containing the benzazole motif via imines.

Pyrazolo-oxazine fused systems are interesting classes of heterocyclic compounds exhibiting pronounced biological applications such as anticancer, antitubercular, anti-inflammatory, antibacterial and antifungal activities as well as inhibiting COX-1 and COX-2 enzymes. Depending on the distribution position of the heteroatoms (N and O), there are fourteen different systems of pyrazolo-oxazine. Nine of them were biologically abundant in literature, for example, pyrazolo[3,4-e][1,3]oxazines are used as analogs of antibiotics Formycin, Formycin B, Oxoformycin B. This review article summarizes the concerted efforts expended on most of the synthetic routes to the various types of pyrazolo-oxazines in the literature until the first quarter of 2020. The reactions of pyrazolo-oxazines with various reagents are also outlined.

Smart materials displaying changes in color and optical properties in response to acid stimuli are known as acidochromic materials. The recent progress and emerging trends in the field of smart organic materials with acidochromic properties, reported in the last seven years, are presented herein. The molecular design of acidochromic organic materials, the origin of the chromic and fluorochromic response to acid stimuli, and related mechanisms are also discussed. Materials and systems covered in the review are divided according to the presence of basic moiety undergoing reversible protonation/ deprotonation, such as pyridine, quinoline, quinoxaline, azole, amine derivatives, etc., in the molecules. Many donor-acceptor molecules displaying acidochromic behavior are cited. Alterations in visual color change and optical properties supporting acidochromism are discussed for each example. Mechanistic studies based on the theoretical calculations, single crystal X-ray diffraction analysis, and powder pattern diffraction analysis are also discussed here. The application of these acidochromic molecules as acid-base switches, sensor films, self-erasable and rewritable media, data security inks, data encryption, molecular logic gates, etc., are also reported. Thus, this review article aims at giving an insight into the design, characterization, mechanism, and applications of organic acidochromic materials, which will guide the researchers in designing and fine-tuning new acidochromic materials for desired applications.

Molecular rearrangements are important tools to increase the molecular diversity of new bioactive compounds, especially in the class of heterocycles. This review deals specifically with a very famous and widely applicable rearrangement known as the Dimroth Rearrangement. Although it has originally been observed for 1,2,3-triazoles, its amplitude was greatly expanded to other heterocycles, as well as from laboratory to large scale production of drugs and intermediates. The reactions that were discussed in this review were selected with the aim of demonstrating the windows that may be open by the Dimroth's rearrangement, especially in what regards the development of new synthetic approaches toward biologically active compounds.

In this study, a novel series of 2,4-dioxochroman-1,2,3-triazole hybrids 8a-l was synthesized by click reaction. These compounds were screened against α-glucosidase through in vitro and in silico evaluations. All the synthesized hybrids exhibited excellent α-glucosidase inhibition in comparison to standard drug acarbose. Representatively, 3-((((1-(3,4-dichlorobenzyl)-1H-1,2,3-triazol-4-yl)methyl)amino)methylene)chroman-2,4- dione 8h with IC50 = 20.1 ± 1.5 μM against α-glucosidase, was 37-times more potent than acarbose. Enzyme kinetic study revealed that compound 8h was a competitive inhibitor against α-glucosidase. In silico docking study on chloro derivatives 8h, 8g, and 8i were also performed in the active site of α -glucosidase. Evaluations on obtained interaction modes and binding energies of these compounds confirmed the results obtained through in vitro α-glucosidase inhibition.