The Dimroth rearrangement as a probable cause for structural misassignments in imidazo[1,2-a]pyrimidines: A N-labelling study and an easy method for the determination of regiochemistry

Microwave-assisted synthesis and functionalization of 2-arylimidazo[1,2-a]pyrimidin-5(8H)-ones

Despite the limited applications and scarcity of commercial examples of imidazo[1,2-a]pyrimidines, their exceptional properties hold great potential, representing a significant challenge in discovering more critical applications. Herein, we present a microwave-assisted approach for preparing 2-arylimidazo[1,2-a]pyrimidin-5(8H)-ones and their alkylation and bromination products using easily accessible and inexpensive reagents, thus offering a promising avenue for further search. Notably, the photophysical properties of an N-alkyl derivative were investigated, and the results highlight the high potential of these compounds as modular fluorophores. All the products were obtained with high yields using highly efficient protocols, and the regioselectivity of the reactions was determined on the basis of NMR measurements and X-ray diffraction analysis.

Single-Scan Heteronuclear 13C-15N J-Coupling NMR Observations Enhanced by Dissolution Dynamic Nuclear Polarization

Heteronuclear 13C-15N couplings were measured in single-scan nuclear magnetic resonance (NMR) experiments for a variety of nitrogen-containing chemical compounds with varied structural characteristics, by using a one-dimensional (1D) 13C-15N multiple-quantum (MQ)-filtered experiment. Sensitivity limitations of the MQ filtering were overcome by the combined use of 15N labeling and dissolution dynamic nuclear polarization (dDNP), performed at cryogenic conditions and followed by quick and optimized sample melting and transfer procedures. Coupling information could thus be obtained from nucleotide bases, amino acids, urea, and aliphatic and aromatic amides, including the measurement of relatively small J-couplings directly from the 1D filtered spectra. This experiment could pave the way for NMR-based analytical applications that investigate structural and stereochemical insights into nitrogen-containing compounds, including dipeptides and proteins, while relying on heteronuclear couplings and nuclear hyperpolarization.

Imidazo[1,2-b]pyridazines as inhibitors of DYRK kinases

Selective inhibitors of DYRK1A are of interest for the treatment of cancer, Type 2 diabetes and neurological disorders. Optimization of imidazo [1,2-b]pyridazine fragment 1 through structure-activity relationship exploration and in silico drug design efforts led to the discovery of compound 17 as a potent cellular inhibitor of DYRK1A with selectivity over much of the kinome. The binding mode of compound 17 was elucidated with X-ray crystallography, facilitating the rational design of compound 29, an imidazo [1,2-b]pyridazine with improved kinase selectivity with respect to closely related CLK kinases.

On the Conformation of Dimeric Acceptors and Their Polymer Solar Cells with Efficiency over 18

The determination of molecular conformations of oligomeric acceptors (OAs) and their impact on molecular packing are crucial for understanding the photovoltaic performance of their resulting polymer solar cells (PSCs) but have not been well studied yet. Herein, we synthesized two dimeric acceptor materials, DIBP3F-Se and DIBP3F-S, which bridged two segments of Y6-derivatives by selenophene and thiophene, respectively. Theoretical simulation and experimental 1D and 2D NMR spectroscopic studies prove that both dimers exhibit O-shaped conformations other than S- or U-shaped counter-ones. Notably, this O-shaped conformation is likely governed by a distinctive "conformational lock" mechanism, arising from the intensified intramolecular π-π interactions among their two terminal groups within the dimers. PSCs based on DIBP3F-Se deliver a maximum efficiency of 18.09 %, outperforming DIBP3F-S-based cells (16.11 %) and ranking among the highest efficiencies for OA-based PSCs. This work demonstrates a facile method to obtain OA conformations and highlights the potential of dimeric acceptors for high-performance PSCs.

Pilot Study to Quantify Palladium Impurities in Lead-like Compounds Following Commonly Used Purification Techniques

Palladium-catalyzed reactions are among the most commonly used procedures in organic synthesis. The products have a range of uses, including as intermediates in total synthesis and as screening compounds for drug discovery or agrochemical projects. Despite the known and potentially deleterious effects of low-level metal impurities in biological assays, the quantification of metal remaining in reaction products to verify the effective removal of the transition element is rarely reported. Using palladium as an exemplar, we describe a pilot study that for the first time quantifies residual metal levels in reaction products following increasingly rigorous purification protocols. Our results demonstrate that significant levels of residual palladium can remain in isolated reaction products following chromatographic purification, and only by using a subsequent metal scavenging step are they reliably reduced to a low level. Finally, we provide a set of simple guidelines that should minimize the potential for issues associated with residual palladium in reaction products.

The Dimroth Rearrangement in the Synthesis of Condensed Pyrimidines - Structural Analogs of Antiviral Compounds

The review discusses the use of the Dimroth rearrangement in the synthesis of condensed pyrimidines which are key structural fragments of antiviral agents. The main attention is given to publications over the past 10 years. The bibliography includes 107 references.

15N labeling and analysis of 13C–15N and 1H–15N couplings in studies of the structures and chemical transformations of nitrogen heterocycles

This review provides a generalization of effective examples of ¹⁵N labeling followed by an analysis of J_CN and J_HN couplings in solution as a tool to study the structural aspects and pathways of chemical transformations in nitrogen heterocycles.