Pyran Moiety Research Articles

Solution Versus On‐Surface Synthesis of Peripherally Oxygen‐Annulated Porphyrins through C−O Bond Formation

AbstractThis study investigates the synthesis of tetra‐ and octa‐O‐fused porphyrinoids employing an oxidative O‐annulation approach through C−H activation. Despite encountering challenges such as overoxidation and instability in conventional solution protocols, successful synthesis was achieved on Au(111) surfaces under ultra‐high vacuum (UHV) conditions. X‐ray photoelectron spectroscopy, scanning tunneling microscopy, and non‐contact atomic force microscopy elucidated the preferential formation of pyran moieties via C−O bond formation and subsequent self‐assembly driven by C−H⋅⋅⋅O interactions. Furthermore, the O‐annulation process was found to reduce the HOMO–LUMO gap by lifting the HOMO energy level, with the effect rising upon increasing the number of embedded O‐atoms.

Solution Versus On-Surface Synthesis of Peripherally Oxygen-Annulated Porphyrins through C-O Bond Formation.

This study investigates the synthesis of tetra- and octa-O-fused porphyrinoids employing an oxidative O-annulation approach through C-H activation. Despite encountering challenges such as overoxidation and instability in conventional solution protocols, successful synthesis was achieved on Au(111) surfaces under ultra-high vacuum (UHV) conditions. X-ray photoelectron spectroscopy, scanning tunneling microscopy, and non-contact atomic force microscopy elucidated the preferential formation of pyran moieties via C-O bond formation and subsequent self-assembly driven by C-H⋅⋅⋅O interactions. Furthermore, the O-annulation process was found to reduce the HOMO-LUMO gap by lifting the HOMO energy level, with the effect rising upon increasing the number of embedded O-atoms.

An Unexpected Lewis Acid-Catalyzed Cascade during the Synthesis of the DEF-Benzoxocin Ring System of Nogalamycin and Menogaril: Mechanistic Elucidation by Intermediate Trapping Experiments and Density Functional Theory Studies.

An unexpected Lewis acid-catalyzed carbohydrate rearrangement of a 1,5-bis-glycopyranoside to the product of a formal intramolecular C-aryl glycosylation reaction is reported. Mechanistic studies based mainly on intermediate trapping experiments and density functional theory (DFT) calculations reveal a cascade process involving three transient (a)cyclic oxocarbenium cations, the breaking of three single C(sp3)-O bonds, and the formation of three single bonds (i.e., exo-, endo-, and C-glycosidic bonds), leading to the 2,6-epoxybenzoxocine skeleton of bioactive natural glycoconjugates related to serjanione A and mimocaesalpin E. DFT calculations established that the generation of the pyran moiety embedded in the bridged benzoxocin ring system is likely to proceed through an unusual ring-closure of an ortho-quinone methide intermediate in which the attacking nucleophile is a carbonyl oxygen.

Indium(III)-Catalyzed Benzannulation of 3-Formyl-4-pyrones with Terminal Aryl Alkynes: Regioselective Synthesis of Functionalized Salicylaldehydes with ortho-Terphenyl Frameworks.

An effective and unprecedented In(III)-catalyzed [4 + 2] benzannulation of 3-formyl-4-pyrones with simple arylacetylenes is reported, which enables their conversion into structurally diverse salicylaldehyde-bearing ortho-terphenyl frameworks. This transformation is achieved via an In(III)-catalyzed C-O bond extrusion and proceeds without the requirement for an external oxidant. This protocol directly provides aromatic compounds from 4-pyrones. Isotopic substitution experiments suggest that the reaction proceeds via a stepwise sequence involving the addition of an alkyne to the pyran moiety followed by cyclization, oxidation, decarboxylation, and aromatization. The synthetic utility of this protocol is demonstrated by the transformation of the obtained product into molecules with bisindole, chromene, and oxime moieties.

Influence of alkyl chain length on the photovoltaic properties of dithienopyran-based hole-transporting materials for perovskite solar cells

A tailored design of asymmetric hole-transporting materials (HTMs) is reported with the synthesis of a family of new HTMs based on the use of the 5H-dithieno[3,2-b:2′,3′-d]pyran (DTP) moiety endowed with donor p-methoxytriphenylamines.

Mechanical Force Enables an Anomalous Dual Ring-Opening Reaction of Naphthodipyran.

Multimodal mechanophores that exhibit complex mechanochromic behavior beyond the typical binary response are capable of distinguishing between multiple stress states through discrete changes in color. Naphthodipyran photoswitches contain two pyran rings fused to a central naphthalene core and represent a potentially promising framework for multimodal reactivity. However, the concurrent ring opening of both pyran moieties has previously proven inaccessible via photochemical activation. Here, we demonstrate that mechanical force supplied to naphthodipyran through covalently linked polymer chains generates the elusive dual ring-opened dimerocyanine product with unique near-infrared absorption properties. Trapping with boron trifluoride renders the merocyanine dyes thermally persistent and reveals apparent sequential ring-opening behavior that departs from the reactivity of previously studied mechanophores under the high strain rates imposed by ultrasound-induced solvodynamic chain extension.

Phytochemical and bioactive compounds identification of Ficus auriculata fig methanolic extraction and its antioxidant activity

In the current investigation, a new phytoconstituent was isolated and identified from a methanolic extract of Ficus auriculata Lour figs. Naturally occurring phytoconstituents have been used to treat ailments for a long time and have served as a source of structural variety for natural product chemists. Natural products are frequently mentioned as a rich source of chemical variation when looking for new pharmacological leads or molecules. The analysis of the chemical components of the methanolic extract led to the discovery of a new phytoconstituent, 5-hydroxy-2-(4-hydroxy-2-methyl-2H-pyran-6-yl)-9-methyl-2H,3H,4H-naphtho[1,2-b] pyran-4-one, with pyran as a basic nucleus. Ficus auriculata Lour figs were collected and sun-dried. Dried Ficus auriculata Lour figs were extracted using menthol. Ficus auriculata Lour figs methanolic extract conducted a preliminary phytochemical study. Ficus auriculata Lour figs methanolic extract novel phytoconstituent isolated and identified by using FT-IR, 1HNMR, 13CNMR, and MS were used to determine the compound's structure. Methanolic extract conducted antioxidant activity by the DPPH method. Preliminary screening confirmed that methanolic extract contains flavonoids and phenols. The purity of the 5-hydroxy-2-(4-hydroxy-2-methyl-2H-pyran-6-yl)-9-methyl-2H,3H,4H-naphtho[1,2-b] pyran-4-one compound was confirmed by RP-HPLC. 5-hydroxy-2-(4-hydroxy-2-methyl-2H-pyran-6-yl)-9-methyl-2H,3H,4H-naphtho[1,2-b]pyran-4-one compound were novel and first reported in Ficus auriculata Lour methanolic extract in the Ficus family. Based on previous studies, pyran moieties have a significant role in biological activities. Methanolic extract showed good antioxidant activity as compared to ascorbic acid. From the methanolic extract of the Ficus auriculata Lour fig, the chemical A, 5-hydroxy-2-(4-hydroxy-2-methyl-2H-pyran-6-yl)-9-methyl-2H,3H,4H-naphtho[1,2-b] pyran-4-one, was successfully isolated and identified. FT-IR, 1HNMR, 13CNMR, and LC-MS/MS spectral data were used to determine the novel compound's structure. Methanolic extract of Ficus auriculata Lour fig showing good antioxidant activity.

OSMAC strategy integrated with molecular networking discovery peniciacetals A−I, nine new meroterpenoids from the mangrove-derived fungus Penicillium sp. HLLG-122

Nine new highly oxygenated meroterpenoids, peniciacetals A−I (1–9), along with five known analogues (10–14) were isolated from the mangrove-derived fungus Penicillium sp. HLLG-122 based on the guidance of molecular networking and OSMAC approach. Peniciacetals A−B (1–2) were characterized with a unique 6/6/6/6/5 pentacyclic system possessing an unusual 4,6-dimethyl-2,5-dioxohexahydro-6-carboxy-4H-furo[2,3-b]pyran moiety. Peniciacetals C−D (3–4) possessed an uncommon 3,6-dimethyldihydro-4H-furo[2,3-b]pyran-2,5-dione unit with 6/6/6/5/6 fused pentacyclic skeleton. The structures and absolute configurations of new compounds were elucidated by HR-ESI-MS, 1D and 2D NMR spectroscopic data, X-ray diffraction analysis, and quantum chemical electronic circular dichroism (ECD) calculation. The plausible biosynthetic pathway of 1–9 were also proposed. Compound 14 showed good cytotoxicity against HepG2, MCF-7, HL-60, A549, HCT116 and H929 cell with IC50 values of 6.6, 14.8, 3.2, 5.7, 6.9 and 3.0 μM, respectively. Further research showed that the compound 14 induced necrosis or late apoptosis contributes to the HL-60 cells toxicity.

Combined experimental and TD-DFT/DMOl3 investigations, optical properties, and photoluminescence behavior of a thiazolopyrimidine derivative

We present here the FT-IR, DFT computation, XRD, optical, and photophysical characterization of a heterocyclic compound with thienopyrimidine and pyran moieties. TD-DFT/DMOl3 and TD-DFT/CASTEP computations were used to study the geometry of isolated and dimer molecules and their optical behavior. The indirect (3.93 eV) and direct (3.29 eV) optical energy bandgaps, HOMO–LUMO energy gap (3.02 eV), and wavelength of maximum absorption (353 nm) were determined in the gas phase with M062X/6-31+G (d, p). A thin film of the studied molecule was studied using XRD, FT-IR, and UV–Vis spectroscopy. The average crystallite size was found as 74.95 nm. Also, the photoluminescence spectroscopy revealed that the compound exhibited different emission bands at the visible range with different intensities depending on the degree of molecular aggregation. For instance, solutions with different concentrations emitted blue, cyan, and green light. On the other hand, the solid-state material produced a dual emission with comparable intensities at λmax = 455, 505, and 621 nm to cover the entire visible range and produce white emission from a single material with CIE coordinates of (0.34, 0.32) that are very similar to the ideal pure white light. Consequently, these findings could lead to the development of more attractive new luminous materials.

A near-infrared fluorescence probe for the detection of bisulfite in vivo and food samples

The evaluation of the HSO3− levels in the biological systems and food samples is of great significance in the understanding its physiological/pathological roles and realizing food security supervision. In this work, a near-infrared (NIR) emitted fluorescence probe (QNP) has been successfully developed to detect HSO3− in live animals and food samples. QNP was designed with a large π-conjugation structure by conjugating of quinolinium with 3H-naphtho[2,1-b]pyran moiety through a reactive C=C double bond. Spectroscopic titration, high resolution mass spectrometry (HR MS), 1H NMR titration and theoretical computation indicates that HSO3− attacks to the C=C double bond through an established 1,4-nucleophilic addition reaction leads to the interruption of the π-conjugation system of QNP, resulting in dramatic decline of the UV–vis absorption and fluorescence spectra. QNP was featured with near infrared emission (centered at 690 nm), high water-solubility (98% water), large Stokes shift (218 nm), perfect selectivity, fast response time (within 50 s) to HSO3−, reliability in broad pH range (6.5–11.5) and low cytotoxicity. The application of QNP in biological systems has been demonstrated by the monitoring of exogenous HSO3− in live adult zebrafish and nude mouse. Furthermore, the evaluation of HSO3− level in several food samples including sugar, white wine, canned fruits and jasmine tea drinks were also determined by fluorescence colorimetric method using QNP.

Influence of phenolic acids/aldehydes on color intensification of cyanidin-3-O-glucoside, the main anthocyanin in sugarcane (Saccharum officinarum L.)

Sugarcane contains various anthocyanins, which are responsible for the colors present in sugarcane. In this study, the color intensification of the major anthocyanin, cyanidin-3-O-glucoside, by phenolic acids/aldehydes (ferulic acid, vanillic acid, p-coumaric acid, syringic aldehyde and vanillic aldehyde) was investigated. The color enhancement of cyanidin-3-O-glucoside (hyperchromic effect and bathochromic shift) was affected by the temperature and concentration of phenolic acids/aldehydes present. Reactions were spontaneous and exothermic, as determined using different thermodynamic parameters (ΔG0, ΔH0, ΔS0). Quantum chemical calculations demonstrated their intermolecular interaction differences, and AIM analysis indicated that hydrogen bonds and van der Waals force interactions contributed to color. Pyranoanthocyanins derived from cyanidin-3-O-glucoside and ferulic/p-coumaric acids during storage were recognized as cyanidin-3-O-glucoside-vinylphenol and cyanidin-3-O-glucoside-vinylguaiacol, respectively, by UPLC-ESI-QTOF-MS/MS. The electron-donating substituents on the aromatic ring of ferulic/p-coumaric acids stabilized the intermediately formed carbenium ion. Decarboxylation and further oxidation of the pyran moieties to the aromatic heterocycles resulted in the final products.

Vibrational spectroscopic studies, theoretical aspects, and X‐ray analysis of xanthenodiones (1,8‐dioxooctahydroxanthenes)

AbstractCompounds containing a pyran moiety fused to two cyclohexen‐2‐one rings are collectively called xanthenodiones (1,8‐dioxooctahydroxanthenes). With the aim of increasing the knowledge about the structures of xanthenodiones, in the present investigation two xanthenodiones, namely 9‐(4‐hydroxy‐3‐methoxyphenyl)‐3,4,5,6,7,9‐hexahydro‐1H‐xanthene‐1,8(2H)‐dione (1) and 9‐(4‐hydroxyphenyl)‐3,6‐diisopropyl 3,4,5,6,7,9‐hexahydro‐1H‐xanthene‐1,8(2H)‐dione (2), were synthesized. Their structures were investigated by nuclear magnetic resonance, single‐crystal X‐ray diffraction, infrared (IR), and Raman spectroscopy techniques along with mass spectrometry. In addition, a computational study was carried out involving vibrational spectroscopy, which allowed us to assign vibrational modes and their shifts as lattice environment. Even though compound 2 has two stereocenters, it crystallized in a centrosymmetric space group (P21/c) as expected from its achiral synthesis. This compound also crystallized as monohydrate and the presence of water molecule did not change the conformation of the target compounds.

Efficient corrosion inhibition by sugarcane purple rind extract for carbon steel in HCl solution: mechanism analyses by experimental and in silico insights.

Sugarcane purple rind ethanolic extract (SPRE) was evaluated as an efficient corrosion inhibitor for carbon steel (C-steel) in 1 M HCl solution. Dynamic weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and frequency modulation (EFM) measurements were employed to evaluate the anticorrosive efficiency of SPRE, which was further validated by morphological and wettability analyses. The results of the weight loss tests showed that the inhibition efficiency (ηw) for C-steel in HCl solution increased with an increase in the concentration of SPRE. An increase in temperature moderately impaired the anticorrosive efficacy of SPRE. The maximum ηw of 96.2% was attained for C-steel in the inhibition system with 800 mg L−1 SPRE at 298 K. The polarization curves indicated that SPRE simultaneously suppressed the anodic and cathodic reactions for C-steel in HCl solution, which can be categorized as a mixed-type corrosion inhibitor with a predominant anodic effect. The corrosion current density (icorr-P) was monotonously reduced with an increase in the concentration of SPRE. The charge transfer resistance (Rct) was enhanced for C-steel in the inhibition solution with a restrained capacitive property due to the adsorption of SPRE. A high temperature caused partial desorption of SPRE on the C-steel surface and a slight increase in icorr-P and decrease in Rct. However, SPRE still fully maintained its morphology and wettability at 328 K. The electrochemical kinetics of C-steel in HCl solution without and with SPRE was also supported by EFM spectra. The adsorption of SPRE conformed to the Langmuir isotherm and increased the corrosion activation energy of C-steel. Complementing the experimental observations, calculations based on density functional theory indicated that the hydroxyl-substituted pyran moiety on the carthamin (CTM) and anthocyanin (ATC) constituents in SPRE hardly contributed to its reactive activity due to their adsorption processes. Therefore, CTM and ATC exhibited imperfect parallel adsorption on the Fe (100) plane according to the molecular dynamics simulation, while anthoxanthin (ATA) and catechinic acid (CCA) constituents exhibited a flat orientation on the iron surface.

Molecular Diversity via Tetrasubstituted Alkenes Containing a Barbiturate Motif: Synthesis and Biological Activity.

The synthesis of a molecularly diverse library of tetrasubstituted alkenes containing a barbiturate motif is described. Base-induced condensation of N1-substituted pyrimidine-2,4,6(1H,3H,5H)-triones with 5-(bis(methylthio)methylene)-2,2-dimethyl-1,3-dioxane-4,6-dione gave 3-substituted 5-(methylthio)-2H-pyrano[2,3-d]pyrimidine-2,4,7(1H,3H)-triones (‘pyranopyrimidinones’), regioselectively. A sequence of reactions involving ring-opening of the pyran moiety, displacement of the methylthio group with an amine, re-formation of the pyran ring, and after its final cleavage with an amine, gave tetrasubstituted alkenes (3-amino-3-(2,4,6-trioxotetrahydropyrimidin-5(2H)-ylidene)propanamides) with a diversity of substituents. Cleavage of the pyranopyrimidinones with an aniline was facilitated in 2,2,2-trifluoroethanol under microwave irradiation. Compounds were tested against Escherichia coli, Staphylococcus aureus, the yeast Schizosaccharomyces pombe, and the pathogenic fungus Candida albicans. No compounds exhibited activity against E. coli, whilst one compound was weakly active against S. aureus. Three compounds were strongly active against S. pombe, but none was active against C. albicans.

Tautomerism in Flindersine - A DFT Treatment

Flindersine is a natural product of plant kingdom. Its structure contains a lactam group which could undergo 1,3-type proton tautomerism. It also has an embedded pyran moiety which might show valence tautomerism. Presently, those tautomers are investigated within the restrictions of density functional theory at the level of B3LYP/6-311++G(d,p). Certain quantum chemical output has been collected compared and discussed. Also the possibility of valence tautomerism has been searched by proposing two transition state paths.

Cytotoxic Activity of Some Spirooxindole-4H-pyran Derivatives

Aims: Isatin is a honored scaffold and one of the most favorable class of heterocyclic systems that possesses many interesting biological activities and well-tolerated in humans. Here a series of fifteen spirooxindole-4H-pyran derivatives containing both isatin and pyran moieties (ICa-ICo) will be examine for their anti-cancer activity.
 Study Design: Cytotoxic evaluation of some spirooxindole-4H-pyran derivatives in two cancerous cell lines. 
 Place and Duration of Study: Pharmaceutical Science Research Center and Shiraz Institute for Cancer Research, Medical School in Shiraz University of Medical Sciences, Shiraz, Iran, between June 2018 and July 2019.
 Methodology: MTT assay was used to evaluate the cytotoxic activities of these compounds. The anticancer properties of the tested compounds were determined using A549 and MCF-7 cell lines.
 Results: Among the tested compounds ICc, ICd and ICf showed the best cytotoxic activities against both cancerous cell lines. Compounds ICh and ICj showed desirable cytotoxic activities against A549 cell line. Compound ICb showed desirable cytotoxic activities against MCF-7 cell line.
 Conclusion: We conclude that the isatin-linked pyran analog can serve as a prototype molecule for further development of a new class of anticancer agents.

Conventional and Microwave‐Assisted Synthesis and Biological Activity Study of Novel Heterocycles Containing Pyran Moiety

Under both conventional and microwave methods, 2‐amino‐4H‐pyran‐3‐carbonitrile derivative 1 was synthesized and reacted with different reagents. Thus, 2‐amino‐4H‐pyran‐3‐carbonitrile derivative was treated with chloroacetyl chloride, phenyl isocyanate, cyanoacetic acid, benzoyl chloride, triethyl orthoformate, acetic anhydride/H2SO4, arylidene malononitrile, urea, and/or p‐aminosulphaguanidine producing chloroacetamide, 3‐phenylurea, cyanoacetamide, N‐benzoylpyran, ethylformimidate, pyranopyrimidin‐4‐one, pyranopyridine, pyranopyrimidin‐2‐one, and pyranopyrimidin‐2‐imine derivatives, respectively. Meanwhile, compound 1 was reacted with ethyl bromoacetate, phenacyl bromide, phthalic anhydride, different aromatic amines, and/or acetic acid/H2SO4 to produce 5‐aminopyrano[2,3‐b]pyrrole‐6‐carboxylate, dihydropyrano[2,3‐b]pyrrole‐6‐yl‐(phenyl)methanone, 1,3‐dioxoisoindolinyl pyran, 1,4‐dihydropyridine, and 2‐hydroxy‐1,4‐dihydropyridine derivatives, respectively. On the other hand, when compound 1 was allowed to react with maleic anhydride and/or hydrazine hydrate, pyran‐4‐oxobut‐2‐enoic acid and 3‐aminopyranopyrazole derivatives were obtained, respectively. Reaction of pyran‐4‐oxobut‐2‐enoic acid with malononitrile under different conditions gave 2‐(furan‐2‐yl)‐4H‐pyran and 2‐(4H‐pyran‐2‐yl)‐1H‐pyrrole derivatives, while condensation of 3‐aminopyranopyrazole with benzaldehyde gave 1,4‐dihydropyrano[2,3‐c]pyrazol‐3‐yl‐1‐phenylmethanimine derivative. The newly synthesized compounds were characterized by the spectroscopic tools IR, 1H‐NMR, 13C‐NMR, MS, and elemental analysis. Some of these compounds have been screened in vitro for antimicrobial activity against different strains of bacteria and fungi and also were tested against two cancer cell lines: mammary gland breast cancer (MCF‐7) and colon cancer (HCT‐118).

Synthesis and Anticancer Evaluation of Some Novel Quinazolin‐4(3H)‐one Derivatives

A new series of quinazolinone derivatives bearing pyridine, pyrimidine, pyrazole, or pyran moieties were synthesized for the purpose of anticancer cell line evaluation. Synthesis of these derivatives was achieved by the reaction of the ketone 2 with the appropriate aldehydes in the presence of either ethylcyanoacetate or malononitrile and ammonium acetate in one‐pot reaction. Chalcones 6 reacted also with hydrazine hydrate to give the corresponding pyrazolines 7 and reacted with urea or thiourea to give the 2‐oxopyrimidines or the 2‐thioxopyrimidines 8, respectively. Evaluation of some representative examples of the newly synthesized compounds against cancer cell lines showed promising activity as anticancer agents.

α-Glucosidase inhibitory caged xanthones from the resin ofGarcinia hanburyi

A yellow resin (gamboge) from Garcinia hanburyi has been widely used as folk medicine due to its antibacterial and antitumor activities. We isolated four α-glucosidase inhibitory compounds from the methanol extract of gamboge. The compounds (1-4) were identified as gambogoic acid (1), moreollic acid (2), gambogic acid (3), and 10-methoxygambogenic acid (4), respectively through spectroscopic data including 2D-NMR and HREIMS. All compounds were examined in the enzyme inhibition assay against α-glucosidase to identify their inhibitory potencies and kinetic behavior. All compounds (1-4) showed enzyme inhibition against α-glucosidase, but the activity was significantly affected by the methoxy group on C-10 of ring A and pentenyl pyran moiety of ring D. For example, compound 1 (IC50 =41.4 μM) bearing pyran ring eight times effective that 4 (IC50 =350.6 μM) having geranyl group itself. Most active compound was found out to be gambogoic acid (1) which was analyzed most abundant metabolite in gamboge by LC-ESI-MS/MS. In kinetic study, compounds 1 and 2 were proved as noncompetitive inhibitors.

Expanding the Rubterolone Family: Intrinsic Reactivity and Directed Diversification of PKS-derived Pyrans.

We characterized two key biosynthetic intermediates of the intriguing rubterolone family (tropolone alkaloids) that contain a highly reactive pyran moiety (in equilibrium with the hydrolyzed 1,5-dione form) and undergo spontaneous pyridine formation in the presence of primary amines. We exploited the intrinsic reactivity of the pyran moiety and isolated several new rubterolone derivatives, two of which contain a unique thiazolidine moiety. Three rubterolone derivatives were chemically modified with fluorescence and biotin tags using peptide coupling and click reaction. Overall, eight derivatives were fully characterized by HRMS/MS and 1D and 2D NMR spectroscopy and their antimicrobial, cytotoxic, anti-inflammatory and antiparasitic activities evaluated.