Pyridine derivatives are the most common and significant heterocyclic compounds, which play an important role in various fields ranging from medicinal to chemosensing applications. Pyridine derivatives possess different biological activities such as antifungal, antibacterial, antioxidant, antiglycation, analgesic, antiparkinsonian, anticonvulsant, anti-inflammatory, ulcerogenic, antiviral, and anticancer activity. Furthermore, these derivatives have a high affinity for various ions and neutral species and can be used as a highly effective chemosensor for the determination of different species. In this review article, generally used synthetic routes of pyridine, structural characterization, medicinal applications, and potential of pyridine derivatives in analytical chemistry as chemosensors have been discussed. We hope this study will support the new thoughts to design biological active compounds and highly selective and effective chemosensors for the detection of various species (anions, cations, and neutral species) in various samples (environmental, agricultural, and biological). Graphical Abstract

In this work, a novel series of pyridazinone derivatives (3–17) were synthesized and characterized by NMR (¹H and ¹³C), FT-IR spectroscopies, and ESI-MS methods. All synthesized compounds were screened for their antibacterial activities against Staphylococcus aureus (Methicillin-resistant), Escherichia coli, Salmonella typhimurium, Pseudomonas aeruginosa, and Acinetobacter baumannii. Among the series, compounds 7 and 13 were found to be active against S. aureus (MRSA), P. aeruginosa, and A. baumannii with the lowest MIC value range of 3.74–8.92 µM. Afterwards, DFT calculations of B3LYP/6-31++G(d,p) level were carried out to investigate geometry structures, frontier molecular orbital, molecular electrostatic potential maps, and gap energies of the synthesized compounds. In addition, the activities of these compounds against various bacterial proteins were compared with molecular-docking calculations. Finally, ADMET studies were performed to investigate the possibility of using of the target compounds as drugs.

A comparative study between two stability-indicating chromatographic methods for the assay of brinzolamide and timolol maleate in the co-existence of the probable carcinogenic oxidative degradation product of timolol maleate in their ophthalmic formulation was demonstrated. The first method established the thin-layer chromatography coupled with the densitometric determination of the analyzed spots, using silica gel TLC aluminum plates F254 and a developing system of chloroform: methanol: ammonia (6:1:0.1, in volumes) at room temperature to give good separation for the three investigated components, where retardation factors for the oxidative degradation product of timolol maleate, brinzolamide and timolol maleate were (Rf 0.21), (Rf 0.46), and (Rf 0.55), respectively. The linear ranges were 2–10 and 3–16 μg/band for brinzolamide and timolol maleate, respectively. In the second method, high performance liquid chromatography (HPLC), photo diode array detection was used on a Eurospher 5 µm C18 100 Å (4.6 × 250 mm) column, using triethylamine pH 3.5, adjusted by glacial acetic acid: acetonitrile (20:80, v/v) at a rate of 0.5 mL per minute. An acceptable separation was achieved, where the retention times for timolol maleate, the oxidative degradation product of timolol maleate and brinzolamide, were (Rt 3.6), (Rt 4.7), and (Rt 5.6), respectively. Linearity covered a range of 20–120 μg/mL for both drugs. It has been proved previously that timolol maleate is liable to oxidation, giving a high-probability carcinogenic product in female mice. The validation for the new proposed stability-indicating methods was optimized in line with the ICH guidelines with good outcomes. It is worth noting that the HPLC-DAD method showed superior separation, economic and time-saving results, while TLC method was more sensitive.

Male infertility is significantly influenced by the plasma-protein sex hormone-binding globulin (SHBG). Male infertility, erectile dysfunction, prostate cancer, and several other male reproductive system diseases are all caused by reduced testosterone bioavailability due to its binding to SHBG. In this study, we have identified 345 phytochemicals from 200 literature reviews that potentially inhibit severe acute respiratory syndrome coronavirus 2. Only a few studies have been done using the SARS-CoV-2 inhibitors to identify the SHBG inhibitor, which is thought to be the main protein responsible for male infertility. In virtual-screening and molecular-docking experiments, cryptomisrine, dorsilurin E, and isoiguesterin were identified as potential SHBG inhibitors with binding affinities of −9.2, −9.0, and −8.8 kcal/mol, respectively. They were also found to have higher binding affinities than the control drug anastrozole (−7.0 kcal/mol). In addition to favorable pharmacological properties, these top three phytochemicals showed no adverse effects in pharmacokinetic evaluations. Several molecular dynamics simulation profiles’ root-mean-square deviation, radius of gyration, root-mean-square fluctuation, hydrogen bonds, and solvent-accessible surface area supported the top three protein–ligand complexes’ better firmness and stability than the control drug throughout the 100 ns simulation period. These combinatorial drug-design approaches indicate that these three phytochemicals could be developed as potential drugs to treat male infertility.

In this study analogues of compounds based on pyrano[2,3-d]pyrimidine were synthesized. 1,3-dimethyl-5- (thiomethyl)-2,4,7-trioxo-1,3,4,7-tetrahydro-2H-pyrano[2,3-d]pyrimidine-6-carboxylic acid 3 and 1,3-dimethyl-5- (thiomethyl)-2H-pyrano[2,3-d]pyrimidine-2,4,7(1H,3H)-trione 4 were obtained by the treatment of Triethylammonium 5- [(2,2-dimethyl-4,6-dioxo-1,3-dioxan-5-ylidene)(thiomethyl)methyl]-1,3-dimethylpyrimidine-2,4,6-trionate 1 with methyl sulfonic acid and pyridine, respectively. 5,5-dianilino-1,3-dimethyl-5,6-dihydro-2H-pyrano[2,3-d]pyrimidine- 2,4,7(1H,3H)-trione 6 was obtained after oxidizing compound 4 to produce 1,3-dimethyl-5-(methylsulfinyl)-2Hpyrano[ 2,3-d]pyrimidine-2,4,7(1H,3H)-trione 5 , then the sulfoxide group on compound 5 was replaced by aniline group.

The formation of stable binary water-soluble sub-micellar aggregates of cetyltrimethylammonium bromide-copper-pyrocatechol violet complex (CTAB-Cu-PCV) diminishes the stability and absorbance of the Cu-PCV complex. A new flow injection spectrophotometric sensing strategy used for the determination of CTAB in commodity personal care antiseptics and water samples has been established relying on the above-mentioned concept. Based on the reduction of the absorption of the Cu-PCV solution by the injection of CTAB solution at pH 6.0 and 430 nm, a linear absorbance decrease was observed over the CTAB concentration range of 2.0 to 100.0 µg mL⁻¹ (r = 0.987). The analysis method showed limits of detection (3.3 ơ) and quantification (10 ơ) of 0.08 and 0.27 µg mL⁻¹, respectively. The precision (RSD) for five replicate determinations was 7.9 and 3.7% at 10 and 50 µg mL⁻¹, respectively. The developed method was applied successfully to the determination of CTAB in personal care products, namely skin lotion and vaginal wash, in addition to water samples. The corresponding RSD (n = 5) values were ≤8.2%.