Benzothiadiazole vs. iso-Benzothiadiazole: Synthesis, Electrochemical and Optical Properties of D–A–D Conjugated Molecules Based on Them

This paper presents an improved synthesis of 4,7-dibromobenzo[d][1,2,3]thiadiazole from commercially available reagents. According to quantum-mechanical calculations, benzo[d][1,2,3]thiadiazole (isoВТD) has higher values of ELUMO and energy band gap (Eg), which indicates high electron conductivity, occurring due to the high stability of the molecule in the excited state. We studied the cross-coupling reactions of this dibromide and found that the highest yields of π-spacer–acceptor–π-spacer type compounds were obtained by means of the Stille reaction. Therefore, 6 new structures of this type have been synthesized. A detailed study of the optical and electrochemical properties of the obtained π-spacer–acceptor–π-spacer type compounds in comparison with isomeric structures based on benzo[c][1,2,5]thiadiazole (BTD) showed a red shift of absorption maxima with lower absorptive and luminescent capacity. However, the addition of the 2,2′-bithiophene fragment as a π-spacer resulted in an unexpected increase of the extinction coefficient in the UV/vis spectra along with a blue shift of both absorption maxima for the isoBTD-based compound as compared to the BTD-based compound. Thus, a thorough selection of components in the designing of appropriate compounds with benzo[d][1,2,3]thiadiazole as an internal acceptor can lead to promising photovoltaic materials.

Bicyclic 5-6 Systems: Comprehensive Synthetic Strategies for the Annulations of Pyrazolo[1,5-a]pyrimidines

Pyrazolopyrimidines are a privileged class of 5-6 bicyclic systems with three or four nitrogen atoms, including four possible isomeric structures. The significance of this class of compounds is that they can be applied in medical and pharmaceutical fields due to their unlimited biological aptitude; hence it is the basic skeleton of several synthetic drugs. The current review aimed to highlight all the synthetic routes that have been applied to construct the pyrazolo[1,5-a]pyrimidine ring systems up to date. The sections in this study included the synthesis of pyrazolo[1,5-a]pyrimidines by condensation reactions of 5-aminopyrazoles with each of β-diketones, 1,5-diketones, β-ketoaldehydes, α-cyanoaldehydes, β-enaminones, enamines, enaminonitriles, ethers, with unsaturated ketones, unsaturated thiones, unsaturated esters, unsaturated dienones “1,2-allenic”, unsaturated aldehydes, unsaturated imines, and unsaturated nitriles. The synthesis of this class of hetereocycles was extended for ring construction from acyclic reagents and multicomponent reactions under catalytic or catalyst-free conditions.

Time grid-based isomer specific N-glycan analysis and detection of bisecting Lewis X in human brain

The importance of protein glycosylation in the biomedical field demands for methods capable of resolving and identifying isomeric structures of N-glycans. However, the unambiguous identification of isomeric structures from complex mixtures is currently not reasonably realized even by the most sophisticated approaches. Here we present a novel approach which uses stable isotope labelled reference N-glycans to establish a retention time grid (glyco-TiGr) on porous graphitized carbon. This furthermore enables retention as the primary criterion for the structural assignment of isomeric N-glycans. Moreover, we biosynthesized forty natural isomers of the fundamental N-glycan type consisting of five hexoses, four N-acetylhexosamines and one fucose residue. Nearly all of these isomers occupied unique positions on the retention time grid. Reference glycan assisted retention time determination with deci-minute accuracy narrowed the assignment space to very few, often only one possible glycan isomer. Application of the glyco-TiGr approach revealed yet undescribed isomers of Lewis x determinants in multimeric human IgA and hybrid type N-glycans in human brain with galactose and even fucose linked to the bisecting N-acetylglucosamine. Thus, the brain N-glycome displayed a degree of sophistication commensurate with this organ's role.

Synthesis of spiro pyrazolone-oxindole and bicyclic pyrazolone derivatives via solvent dependent regioselective aza-1,4/1,6-Michael and intramolecular cycloaddition under catalyst-free conditions

A solvent dependent and highly regioselective [3+2]-cycloaddition reaction of isoxazole-styrenes and azomethine imines is reported under catalyst-free conditions furnishing a library of pyrazolone-spirooxindole hybrids. Regioselectivity for the isomeric structures were achieved in good yields by the reaction of isoxazole-styrene (1) and azomethine imine (2) in different solvents and temperature. The developed method was extended for the synthesis of tri-substituted dinitrogen-fused pyrazolones for the using 1,6-Michael addition reaction. Further, the isoxazole moiety was converted into carboxylic acid as a model study via ring opening

Unravelling the structural complexity of glycolipids with cryogenic infrared spectroscopy

Glycolipids are complex glycoconjugates composed of a glycan headgroup and a lipid moiety. Their modular biosynthesis creates a vast amount of diverse and often isomeric structures, which fulfill highly specific biological functions. To date, no gold-standard analytical technique can provide a comprehensive structural elucidation of complex glycolipids, and insufficient tools for isomer distinction can lead to wrong assignments. Herein we use cryogenic gas-phase infrared spectroscopy to systematically investigate different kinds of isomerism in immunologically relevant glycolipids. We show that all structural features, including isomeric glycan headgroups, anomeric configurations and different lipid moieties, can be unambiguously resolved by diagnostic spectroscopic fingerprints in a narrow spectral range. The results allow for the characterization of isomeric glycolipid mixtures and biological applications.

Some Novel Tricyclic Caged-Nitramines - A DFT Study

A tricyclic caged-nitramine structure having embedded RDX base has been designed. It also has three etheric linkages in the cage structure. In that sense it reminds TEX structure but it has much better oxygen balance than RDX and TEX. Then two hetero atom exchange operation (N to O replacement) at a time has been carried out to produce different isomeric structures. Through optimization process (B3LYP/6-311++G(d,p)) they have yielded some conformers and stereoisomers. The effect of heteroatom replacement on various geometrical, quantum chemical and spectral properties of the isomers have been investigated and discussed.

SYNTHETIC APPROACHES TO HYDROGENIZED PYRIDYL[b]AZEPINE AND THEIR BENZENELYLATED ANALOGUES

Pyrido[b]azepines are represented in the literature by four types of isomeric structures: pyrido[3,2-b] azepines, pyrido[2,3-b]azepines, pyrido[3,4-b] azepines and pyrido[4,3-b ]azepines. They belong to the structural analogues of 1-benzazepine - an attractive class of heterocycles with a strong pharmacological profile. They are also used as important molecular platforms in the construction of bioactive compounds. Analysis of the literature has shown that compounds that contain the pyrido[b]azepine fragment demonstrate antiviral, antimicrobial, and antitumor activity. They are knownas effective inhibitors of R1P1 kinase, ubiquitin- specific proteases (USPS), cyclin-dependent kinase (CDKS), and glycogen synthase kinase 3 (GSK-3), TRPM8 protein, and angiotensin I type 2 (AT2) receptors. Over the last decade, promising pharmacological properties of pyrido[b]azepine derivatives stimulated the development of fundamentally new methods of their synthesis as well as the improvement of known synthetic approaches. In general, among the various methods for the synthesis of hydrogenated pyrido[b] azepines and their benzanelated analogues, priority is currently given to approaches that include the formation of an azepine cycle via the intermolecular formation of C-N and C-C bonds. These mainly include catalytic cyclizations using cobalt, palladium, and rhodium compounds. Reactions of intramolecular radical difluoromethylarylation and diauryl peroxide-initiated radical azepine analelenization of the pyridine fragment are also of great importance. An interesting method for the synthesis of pyrido [2,3-b] azepin-5-one derivatives was developed on the basis of the Friedel-Crafts intramolecular cycloalkylations reaction.