Search Results (100)

In this study, we examined the oxidation of (E)-2-hydroxy-1-naphthaldehyde oxime with lead tetraacetate in tetrahydrofuran that produced novel (E)-7a,8,9,10-tetrahydro-12H-naphtho[1,2-e]pyrrolo[2,1-b][1,3]oxazin-12-one oxime and 1-(pyrrolidin-1-yl)naphtho[1,2-d]isoxazole and known 7a,8,9,10-tetrahydro-12H-naphtho[1,2-e]pyrrolo-[2,1-b][1,3]oxazin-12-one in 15, 18, and 10% yields, respectively. The oxime is partially hydrolyzed to its corresponding ketone. Modifying the oxidants and reaction conditions did not improve the product yields. Based on previous studies in our laboratory, we proposed that the reactions proceed via the formation of an o-naphthoquinone nitrosomethide intermediate; 1D and 2D NMR, HRMS, IR, and UV-VIS spectra provided information that supported the structure of the products. Full article

In this study, a novel bio-based oxazine resin was synthesized through the reaction of naturally renewable materials: cardanol and furfurylamine. The molecular structure of the target product was confirmed via comprehensive characterization techniques, including Fourier-transform Infrared Spectroscopy (FT-IR), Gel Permeation Chromatography (GPC), Mass Spectrometry (MS), and Nuclear Magnetic Resonance (NMR). Differential Scanning Calorimetry (DSC) revealed that the curing process of cardanol-furfurylamine oxazine (CFZ) exhibited three exothermic peaks (~140, ~240, ~270 °C), which not only helped to optimize the processing conditions but also effectively enhanced the material properties. In the modification experiments, CFZ had been blended and cured with benzoxazine (BZ) at the mass ratios of 2:98, 5:95, 10:90, 20:80, and 40:60. Dynamic Mechanical Thermal Analysis (DMTA) further showed an elevated Loss Factor (tan δ) peak of CFZ-BZ resin, suggesting significantly enhanced toughness. Notably, when the content of the CFZ resin in the composite reached only 5%, the storage modulus achieved its maximum value, highlighting that minimal addition of CFZ resin can optimize the rigidity of the composite, which would drastically reduce material costs and simplify the process. Impact strength testing demonstrated that the impact resistance of CFZ-BZ resin was 6.42 times higher than that of pristine BZ. By integrating renewable materials with rational molecular design, this novel oxazine resin synergistically combines high-temperature resistance, superior toughness, and efficient modification at low loading, positioning it as a promising candidate to replace conventional petroleum-based resins in aerospace, renewable energy, and electronic packaging applications. Full article

The polymorphism of the ultraviolet luminescent security ink Orlyum White 520T (N-(2-(4-oxo-4H-benzo[d][3,1]-oxazin-2-yl)phenyl)naphthalene-2-sulfonamide) is revealed, obtaining two new polymorphic forms with enhanced stability. Beyond the known form (lit. mp. 184.8–185.2 °C, Form III, YOCTAO), we succeeded in gaining two new polymorphic forms, Form II and Form I, with higher melting points of 195–196 and 197–198 °C, respectively. Their elemental composition, ¹H and ¹³C NMR spectra have been found to be identical, while their powder XRD patterns and FT-IR spectra are significantly different. Based on the single-crystal structure determination of Form II and redetermination of Form III, we uncover the similarities and differences in their packing arrangement and in their secondary interaction systems, all of which affect the molecular conformations in their crystals. In order to explain their significantly distinguishable melting points, Hirshfeld surface analysis and lattice energy calculations have also been carried out. We have made efforts toward revealing the reproducible conditions under which certain polymorphs are formed. It seems that the solvents or other probable organic contaminations are more likely responsible for the formation, nucleation and growth of crystals of various polymorphic forms, traced by thermogravimetric evolved gas analysis (TG/DTA-EGA-MS). Full article

A concise, transition metal-free four-step synthetic pathway has been developed for the synthesis of tetracyclic heterosteroidal compounds, 14-aza-12-oxasteroids, starting from readily available 2-naphthol analogues. After conversion of 2-naphthols to 2-naphthylamines by the Bucherer reaction, subsequent selective C-acetylation was achieved via the Sugasawa reaction and reduction of the acetyl group using borohydride, which resulted into the corresponding amino-alcohols. The naphthalene-based amino-alcohols underwent double dehydrations and double intramolecular cyclization with oxo-acids leading to one-pot formation of a C-N bond, a C-O bond and an amide bond in tandem, to generate two additional rings completing the steroidal framework. A series of 14-aza-12-oxasteroids were synthesized using our developed synthetic strategy in moderate yields, and the structure of one of the final products, 12a-Methyl-11-phenyl-11,12a-dihydro-1H-naphtho[2,1-d]pyrrolo[2,1-b][1,3]oxazin-3(2H)-one, was further confirmed by single crystal X-ray crystallography. Full article

Capsicum annuum, commonly known as pepper, is a widely cultivated crop valued for its nutritional and economic significance. Among its varieties, the small red bell pepper, locally known as “pimienta palmera”, is a unique cultivar from La Palma in the Canary Islands, renowned for its distinctive flavor and use in traditional dishes. Despite its cultural importance, limited research exists on the chemical composition of this pepper variety. This study investigates the chemical constituents of dichloromethane and n-butanol fractions extracted from the pericarp of Capsicum annuum var. palmera. Isolation and structural elucidation of compounds were achieved using high-resolution mass spectrometry (HREIMS), nuclear magnetic resonance spectroscopy (NMR), and chromatographic techniques. A previously unreported pyrrolo-lactone compound, 2-(6-formyl-3-oxo-3,4-dihydro-1H-pyrrolo[2,1-c][1,4]oxazin-4-yl)acetic acid, was identified alongside other metabolites, including α-tocopherol, β-sitosterol, and oleic acid. This alkaloid adds to the chemical diversity of Capsicum species and highlights the unique bioactive potential of this regional pepper. These findings enhance the understanding of pimienta palmera’s composition and suggest potential applications in nutraceuticals and pharmacology due to the biological activity associated with pyrrole alkaloids. The characterization of this compound underscores the need to further explore the phytochemical richness of traditional crops with limited prior research. Full article

Studies show that compounds such as 1,3-oxazine-6-ones are promising starting reagents that allow us to obtain various acyclic and heteroaromatic systems. These substances demonstrate a wide range of biological activity. Meanwhile, it is known that depending on the 1,3-oxazine cycle number in the molecule, pharmacological activity may vary. Therefore, the purpose of our work was to study the reaction of benzene-1,4-dicarboxamide with methylmalonyl dichloride, as a rational way to obtain new compounds of a given structure. This interaction can potentially lead to both mono- and bis(1,3-oxazine-6-one) derivatives. The reaction between terephthalamide and methylmalonyl dichloride was conducted at an equimolar ratio, with a twofold excess of the latter. Syntheses were carried out in two media—absolute benzene and 1,2-dichloroethane. The reaction of equimolar amounts of reagents resulted in obtaining only one product—4-(4-hydroxy-5-methyl-6-oxo-6H-1,3-oxazine-2-yl)benzamide (1). In twofold excess of methylmalonyl dichloride, only product 1 was obtained after 24 h of refluxing; after 58 h, only 2,2′-(benzene-1,4-diyl)bis(4-hydroxy-5-methyl-6H-1,3-oxazine-6-one) (2) was formed. The determination of the partial negative charge on the nitrogen atoms of the amido groups of terephthalamide and compound 1 allowed us to confirm the sequential formation firstly of the mono- (1) and then the bis(1,3-oxazine-6-one) derivative (2) in the reaction mass. The structure of the obtained compounds was proven using NMR spectroscopy on ¹H and ¹³C nuclei. When studying solvent influence on the synthesis rate, no significant differences were noted between benzene and 1,2-dichloroethane. However, the yield of 2,2′-(benzene-1,4-diyl)bis(4-hydroxy-5-methyl-6H-1,3-oxazine-6-one) during synthesis in 1,2-dichloroethane was lower—77% compared with 85% in benzene. Full article

Polybenzoxazines (PBzs) are advanced forms of phenolic resins that possess many attractive properties, including thermally induced self-curing polymerization, which produces void-free polymer products without any by-product formation. They also possess a high T_g (glass transition temperature) and thermal stability, but the produced materials are brittle in nature, due to which the final form of their application is very difficult. Hence, in this paper, an attempt has been made to overcome the brittleness of PBz by blending it with epoxy and ε-caprolactam (CPLA) to produce free-standing PBz/Epoxy/PCLA (polycaprolactam) films. The curing process between the three components (i.e., Bzo, epoxy, and caprolactam) was monitored using differential scanning calorimetric (DSC) analysis. The results show that there is no appreciable shift in curing the exotherm observed, except a slight shift in the curing process. However, the heat liberated during the exotherm (ΔH) decreases drastically from 121 to 84 J/g, indicating that the content of benzoxazine is very important as it is involved in the polymerization process through oxazine ring-opening. The morphological studies analyzed using SEM and AFM analyses indicate that there was no observable phase separation up to 30 wt.% of CPLA loading, whereas a higher CPLA content of 50 wt.% causes agglomeration and leads to distinctive phase separation. Moreover, the thermal stability of the composite film, PBz/Epoxy/PCLA30, is also increased with a 10% degradation temperature, T₁₀, of 438 °C, when compared with an PBz/Epoxy film. From the obtained results, it is evident that the formation of a composite film through the melt blending process could produce a tough and thermally stable film without sacrificing individual properties. Full article

Due to the resistance of Gram-negative bacteria Pseudomonas aeruginosa PAO1 to most clinically relevant antimicrobials, the use of traditional antibiotic treatments in hospitals is challenging. The formation of biofilms, which is regulated by the quorum-sensing (QS) system of Pseudomonas aeruginosa (PA), is an important cause of drug resistance. There are three main QS systems in P. aeruginosa: the las system, the rhl system, and the pqs system. The inhibitors of the las system are the most studied. Previously, the compound AOZ-1 was found to have a certain inhibitory effect on the las system when screened. In this study, twenty-four compounds were designed and synthesized by modifying the Linker and Rings of AOZ-1. Using C. violaceum CV026 as a reporter strain, this study first assessed the inhibitory effects of new compounds against QS, and their SAR was investigated. Then, based on the SAR analysis of compound AOZ-1 derivatives, the parent core of AOZ-1 was replaced to explore the structural diversity. Then, nine new compounds were designed and synthesized with a new nucleus core component of 3-amino-tetrahydro-l,3-oxazin-2-one. The compound Y-31 (IC₅₀ = 91.55 ± 3.35 µM) was found to inhibit the QS of C. violaceum CV026. Its inhibitory effect on C. violaceum CV026 was better than that of compound AOZ-1 (IC₅₀ > 200 µM). Furthermore, biofilm formation is one of the important causes of Pseudomonas aeruginosa PAO1 resistance. In this study, it was found that compound Y-31, with a new nucleus core component of 3-amino-tetrahydro-l,3-oxazin-2-one, had the highest biofilm inhibition rate (40.44%). The compound Y-31 has a certain inhibitory effect on the production of PAO1 virulence factors (pyocyanin, rhamnolipid, and elastase) and swarming. When the concentration of compound Y-31 was 162.5 µM, the inhibition rates of pyocyanin, rhamnolipid, and elastase were 22.48%, 6.13%, and 22.67%, respectively. In vivo, the lifetime of wildtype Caenorhabditis elegans N2 infected with P. aeruginosa PAO1 was markedly extended by the new parent nucleus Y-31. This study also performed cytotoxicity experiments and in vivo pharmacokinetics experiments on the compound Y-31. In conclusion, this study identified a compound, Y-31, with a new nucleus core component of 3-amino-tetrahydro-l,3-oxazin-2-one, which is a potential agent for treating P. aeruginosa PAO1 that is resistant to antibiotics and offers a way to discover novel antibacterial medications. Full article

A library of regioisomeric monoterpene-based aminodiols was synthesised and applied as chiral catalysts in the addition of diethylzinc to benzaldehyde. The synthesis of the first type of aminodiols was achieved starting from (−)-8,9-dihydroperillaldehyde via reductive amination, followed by Boc protection and dihydroxylation with the OsO₄/NMO system. Separation of formed stereoisomers resulted in a library of aminodiol diastereoisomers. The library of regioisomeric analogues was obtained starting from (−)-8,9-dihydroperillic alcohol, which was transformed into a mixture of allylic trichloroacetamides via Overman rearrangement. Changing the protecting group to a Boc function, the protected enamines were subjected to dihydroxylation with the OsO₄/NMO system, leading to a 71:16:13 mixture of diastereoisomers, which were separated, affording the three isomers in isolated form. The obtained primary aminodiols were transformed into secondary derivatives. The regioselectivity of the ring closure of the N-benzyl-substituted aminodiols with formaldehyde was also investigated, resulting in 1,3-oxazines in an exclusive manner. To explain the stability difference between diastereoisomeric 1,3-oxazines, a series of comparative theoretical modelling studies was carried out. The obtained potential catalysts were applied in the reaction of aromatic aldehydes and diethylzinc with moderate to good enantioselectivities (up to 94% ee), whereas the opposite chiral selectivity was observed between secondary aminodiols and their ring-closed 1,3-oxazine analogues. Full article

A new type of benzoxazine resin has been synthesized using a natural phenol source, guaiacol, and a biomass amines, furfuramine. The synthesis conditions were optimized; when the reaction molar ratio of guaiacol, furfuramine, and polyformaldehyde was 1:1:4, the highest synthetic yield was reached. The product was characterized via testing using transform infrared spectroscopy (FT-IR), gel permeation chromatography (GPC), mass spectrogram (MS), and nuclear magnetic resonance (¹H-NMR) to confirm its molecular structure. A differential scanning calorimetry (DSC) test was conducted to analyze the thermodynamic properties of the product, and the results showed that the product decomposed and evaporated at around 180 °C, making it impossible to achieve self-curing. However, the prepared guaiacol-furfuramine benzoxazine resin (GFZ) can be blended and cured in certain proportions with bisphenol A-aniline oxazine resin (BAZ) as a GFZ/BAZ binary system (5:95, 10:90, 20:80, and 40:60). Dynamic mechanical analysis (DMA) test results showed that when the content of GFZ was 10%, the storage modulus of the copolymer resin was greatly improved. After conducting impact strength tests on the copolymer resin, it was found that the toughness of the copolymer resin had improved, and the maximum impact strength had increased by nearly three times. This indicates that the flexible long-chain structure in GFZ can effectively improve the toughness of the cured copolymer system. The reaction of active groups on benzoxazine molecules with other resins can not only improve the mechanical properties of their cured products, but also has important significance in the preparation of low-cost and environmentally friendly sustainable composite materials with excellent comprehensive performance. Full article

Naphtho[1,8-de][1,2]oxazin-4-ol and its acyl or benzyl derivatives ring open to various 2,8-dihydroxy-1-naphthonitriles, which, through (de)protection protocols and reduction, afford the target (E)-2-hydroxy-8-methoxy-1-naphthaldehyde. This was converted to its corresponding oxime, which was oxidatively o-cyclized with phenyliodine(III) diacetate (PIDA) to 9-methoxynaphtho[1,2-d]isoxazole 2-oxide. The latter, in deuterated DMSO at room temperature, was rearranged to its isomer 2-hydroxy-8-methoxy(naphthalen-1-yl)nitrile oxide. The isomerization was detected by time-course plot ¹H NMR spectroscopy and further identified from its ¹³C NMR and HRMS spectra. The nitrile oxide was stable in (non)deuterated DMSO for at least 18 h. A 3,4-bis(2-hydroxy-8-methoxynaphthalen-1-yl)-1,2,5-oxadiazole 2-oxide, as a dimerization product or an isocyanate as a rearrangement isomer, was ruled out, the former by its HRMS spectrum and the latter by its 1,3-dipolar cycloaddition reactions to substituted isoxazoles. Full article

A fluorine-containing main-chain benzoxazine (BAF-M-TB) was co-cured with biphenyl epoxy for the integrated circuit industry. The benzoxazine precursor was synthesized using 4,4′-(Hexafluoroisopropylidene)diphenol (bisphenol AF), 2,2′-Dimethyl-[1,1′-biphenyl]-4,4′-Diamine(M-TB), and paraformaldehyde. In addition, the 3,3′-(Oxybis(4,1-phenylene))bis(3,4-dihydro-2H-benzo[e][1,3]oxazine) (Benoxazine ODA-BOZ), which is a commercialized benzoxazine, was co-cured with biphenyl epoxy as a control. The two co-curing systems were referred to as EP/BAF-M-TB and EP/ODA-BOZ. The curing kinetics, rheological behavior, and thermal stability of the two co-curing systems were studied. Poly-EP/BAF-M-TB and poly-EP/ODA-BOZ quartz fiber cloth reinforced composites (QFRPs) were prepared using the prepreg laminating method in order to determine their mechanical, thermal, and dielectric properties. Both of them showed good thermal properties and dielectric properties. The dielectric constant of poly-EP/BAF-M-TB QFRP is in the range of 3.25–3.54 at the low frequency of 10 kHz–10 MHz. At the high frequency of 5 GHz, its dielectric constant is 3.16, which is better than that of poly-EP/ODA-BOZ QFRP. Additionally, the Td₅ of poly-EP/BAF-M-TB was 398 °C in a nitrogen atmosphere, which is higher than that of poly-EP/ODA-BOZ. Full article