Synthesis, in vitro Α-Glucosidase, and acetylcholinesterase inhibitory activities of novel Indol-Fused Pyrano[2,3-D]Pyrimidine compounds.

In this study, new indol-fused pyrano[2,3-d]pyrimidines were designed and synthesized. These products were obtained in moderate to good yields and their structures were assigned by NMR, MS, and IR analysis. Afterwards, the biological important of the products was highlighted by evaluating in vitro for α-glucosidase inhibitory activity as well as acetylcholinesterase (AChE) inhibitory activity. Eleven products revealed substantial inhibitory activity against α-glucosidase enzyme, among which, two most potent products 11d,e were approximately 93-fold more potent than acarbose as a standard antidiabetic drug. Besides that, product 11k exhibited good AChE inhibition. The substituents on the 5-phenyl ring, attached to the pyran ring, played a critical role in inhibitory activities. The biological potencies have provided an opportunity to further investigations of indol-fused pyrano[2,3-d]pyrimidines as potential anti-diabetic agents.

Activatable Near-Infrared Versatile Fluorescent and Chemiluminescent Dyes Based on the Dicyanomethylene-4H-pyran Scaffold: From Design to Imaging and Theranostics.

Activatable fluorescent and chemiluminescent dyes with near-infrared emission have indispensable roles in the fields of bioimaging, molecular prodrugs, and phototheranostic agents. As one of the most popular fluorophore scaffolds, the dicyanomethylene-4H-pyran scaffold has been applied to fabricate a large number of versatile activatable optical dyes for analytes detection and diseases diagnosis and treatment by virtue of its high photostability, large Stokes shift, considerable two-photon absorption cross-section, and structural modifiability. This review discusses the molecular design strategies, recognition mechanisms, and both in vitro and in vivo bio-applications (especially for diagnosis and therapy of tumors) of activatable dicyanomethylene-4H-pyran dyes. The final section describes the current shortcomings and future development prospects of this topic.

Truncated derivatives of amphidinol 3 reveal the functional role of polyol chain in sterol-recognition and pore formation.

Here we examined the membrane binding and pore formation of amphidinol 3 (AM3) and its truncated synthetic derivatives. Importantly, both of the membrane affinity and pore formation activity were well correlated with the reported antifungal activity. Our data clearly demonstrated that the C1-C30 moiety of AM3 plays essential roles both in sterol recognition and stable pore formation. Based on the current findings, we updated the interacting model between AM3 and sterol, in which the moiety encompassing from C21 to C67 accommodates a sterol molecule with forming hydrogen bonds with the sterol hydroxy group and van der Waals contact between AM3 polyol and sterol skeleton. Although the conformation of the C1-C20 moiety of AM3 is hard to specify due to its flexibility, the region likely contributes to stabilization of pore structure.

Anti-Inflammatory Phomalones from the Deep-Sea-Derived Fungus Trichobotrys effuse FS522.

Four new phomalones A-D (1-4), together with five known analogues (5-9) were isolated from the deep-sea-derived fungus Trichobotrys effuse FS522. Their structures of the new compounds established by analysis of their NMR and HR-ESI-MS spectroscopic data, and the absolute configurations of 2 was determined by electronic circular dichroism (ECD) calculations. compounds 4, 6 and 8 substantially inhibited the production of nitric oxide (NO) with IC50 values of 4.64, 13.90, and 34.07 µM.

Pd-Catalyzed Ligand-Directed Divergent Cycloaddition of Cyclic 1-Azadienes with Oxo-1,4-dipoles.

Ligand-directed divergent synthesis (LDS) is an important synthetic tool for the preparation of structurally diverse organic molecules without tedious steps to modify substrates. Herein, we introduce the realization of 3,4-, 1,2-, and 1,4-cyclization of benzo[d]isothiazole-1,1-dioxide-fused azadienes (BDAs) through LDS, leading to tetrahydro-2H-pyrans, oxazinanes, and tetrahydro-2H-1,5-oxazocines, respectively. Using phosphinooxazoline (PHOX) ligands, we have developed a [4 + 2] cycloaddition between BDAs and substituted 2-alkylidenetrimethylene carbonates, providing access to multi-substituted chiral tetrahydro-2H-pyrans in good yields with excellent enantio-, diastereo-, and regioselectivities.

Chitosan catalyzed synthesis and mechanistic study of steroidal 2H-pyran ring formation.

A simple and convenient method is reported for the preparation of steroidal 2H-pyran 2 by reacting 3ß-acetoxy cholest-5-ene-7-one 1 with N-benzyl-2-cyanoacetamide in presence of chitosan, a green and heterogeneous catalyst. The product 2 was characterized by using NMR (1H and 3C), IR, and mass spectroscopy. The mechanism of 2H-pyran ring formation is described by employing theoretical B3LYP/6-31G (d) density functional method. The reaction undergoes via formation of two intermediates A and B, and each intermediate undergoes through a transition state TS1 and TS2. The molecular properties like relative energy and FMO analysis were used to explain the mechanism of the reaction. The HOMOs and LUMOs were found in support of the present reaction mechanism. The stability of all the calculated structures which includes reactant (1a), intermediates (A and B), product (2a) as well as TS1 and TS2 transition states, was supported by calculating their energy minima and fundamental frequencies.

A novel strategy for the functionalization and design of 4-methylene-4H-pyran merocyanines via enamination and 1,8-conjugate addition.

4-Methylene-4H-pyrans are popular merocyanine dyes, but their functionalization is limited by the Knoevenagel condensation with aromatic aldehydes. In this work, we developed a novel approach for the construction of a new class of pyran fluorophores based on enamination and subsequent nucleophilic substitution of the dimethylamino group via 1,8-conjugate addition/elimination. This methodology includes selective transformations leading to previously unknown symmetrical and asymmetrical structures. The dimethylaminovinyl-substituted pyrans are reactive intermediates and can be considered as a convenient synthetic tool for the construction of new merocyanines with tunable fluorescence (417-628 nm). The main strategies for the modification of the pyran moiety have been determined for the construction and targeted design of fluorophores. Pyrans bearing two enamine moieties demonstrate significant light extinction coefficients (up to 116 000 M-1 cm-1), high quantum yields (up to 69%) and large Stokes shifts (up to 152 nm) because of their strong push-pull nature. Density Functional Theory (DFT) calculations were performed for the explanation of the structural and photophysical features of the prepared merocyanines. The developed approach can be considered as a useful platform for further application of 4-methylene-4H-pyrans as promising fluorophores for sensors and solar cells, and in bioimaging.

Molecular Insights into Bifunctional Ambruticin DH3 for Substrate Specificity and Catalytic Mechanism.

Dehydratase (DH), a domain located at polyketide synthase (PKS) modules, commonly catalyzes the dehydration of ß-hydroxy to an α,ß-unsaturated acyl intermediate. As a unique bifunctional dehydratase, AmbDH3 (the DH domain of module 3 of the ambruticin PKS) is verified to be responsible for both dehydration and the following pyran-forming cyclization. Besides, in vitro studies showed that its catalytic efficiency varies with different chiral substrates. However, the detailed molecular mechanism of AmbDH3 remains unclear. In this work, the structural rationale for the substrate specificity (2R/2S- and 6R/6S-substrates) in AmbDH3 was elucidated and the complete reaction pathways including dehydration and cyclization were presented. Both MD simulations and binding free energy calculations indicated AmbDH3 had a stronger preference for 2R-substrates (2R6R-2, 2R6S-3) than 2S-substrates (2S6R-1), and residue H51 and G61 around the catalytic pocket were emphasized by forming stable hydrogen bonds with 2R-substrates. In addition, AmbDH3's mild tolerance at C6 was explained by comparison of substrate conformation and hydrogen bond network in 6S- and 6R-substrate systems. The QM/MM results supported a consecutive one-base dehydration and cyclization mechanism for 2R6S-3 substrate with the energy barrier of 25.2 kcal mol-1 and 24.5 kcal mol-1 , respectively. Our computational results uncover the substrate recognition and catalytic process of the first bifunctional dehydratase-cyclase AmbDH3, which will shed light on the application of multifunctional DH domains in PKSs for diverse natural product analogs and benefit the chemoenzymatic synthesis of stereoselective pyran-containing products.

Discovery of PPARγ and glucocorticoid receptor dual agonists to promote the adiponectin and leptin biosynthesis in human bone marrow mesenchymal stem cells.

Adiponectin and leptin are major adipocytokines that control crosstalk between adipose tissue and other organ systems. Hypoadiponectinemia and hypoleptinemia are associated with human metabolic diseases. Compounds with adipocytokine biosynthesis-stimulating activities could be developed as therapeutics against diverse metabolic conditions. In phenotypic screening with human bone marrow mesenchymal stem cells (hBM-MSCs), (E)-4-hydroxy-3-(3-(4-hydroxy-3-methoxyphenyl)acryloyl)-6-methyl-2H-pyran-2-one (1) was identified to increase adiponectin biosynthesis during adipogenesis and simultaneously to stimulate leptin production. Using the compound 1 structure, the structure-activity relationship study was performed to discover more potent compounds stimulating both adiponectin and leptin production. (E)-3-(3-(2-fluoropyridin-4-yl)acryloyl)-4-hydroxy-6-methyl-2H-pyran-2-one (11) exhibited the most potent adiponectin (EC50, 2.87 µM) and leptin (EC50, 2.82 µM) biosynthesis-stimulating activities in hBM-MSCs. In a target identification study, compound 11 was characterized as a dual modulator binding to both peroxisome proliferator-activated receptor (PPAR) γ and glucocorticoid receptor (GR). This study provides a novel pharmacophore for PPARγ/GR dual modulators with therapeutic potential against human metabolic diseases.

2-(2-(Dimethylamino)vinyl)-4H-pyran-4-ones as Novel and Convenient Building-Blocks for the Synthesis of Conjugated 4-Pyrone Derivatives.

A straightforward approach for the construction of the new class of conjugated pyrans based on enamination of 2-methyl-4-pyrones with DMF-DMA was developed. 2-(2-(Dimethylamino)vinyl)-4-pyrones are highly reactive substrates that undergo 1,6-conjugate addition/elimination or 1,3-dipolar cycloaddition/elimination followed by substitution of the dimethylamino group without ring opening. This strategy includes selective transformations leading to conjugated and isoxazolyl-substituted 4-pyrone structures. The photophysical properties of the prepared 4-pyrones were determined in view of further design of novel merocyanine fluorophores. A solvatochromism was found for enamino-substituted 4-pyrones accompanied by a strong increase in fluorescence intensity in alcohols. The prepared conjugated structures demonstrated valuable photophysical properties, such as a large Stokes shift (up to 204 nm) and a good quantum yield (up to 28%).

Towards understanding oxygen heterocycle-forming biocatalysts: a selectivity study of the pyran synthase PedPS7.

Intramolecular oxa-Michael addition-catalysing cyclases are widespread in polyketide biosynthetic pathways. Although they have significant potential in biotechnology and chemoenzymatic synthesis of chiral heterocycles, they have only scarcely been studied. Here, we present detailed investigations on the selectivity profile of the pyran synthase PedPS7 showing that it combines broad substrate tolerance with high selectivity for the formation of up to two new stereocentres and relaxed precursor stereoisomer discrimination. Two of the four possible tetrahydropyran stereoisomers are reliably accessible by this enzyme. The results indicate fundamental differences between the individual subtypes of intramolecular oxa-Michael addition-catalysing cyclases.

Unexpected synthesis, delayed emission and solid-state acidochromism of novel 2,7-naphthyridine derivatives obtained from 2-(3,5-diaryl-4H-pyran-4-ylidene)malononitrile.

Two novel 2,7-naphthyridine derivatives are unexpectedly synthesized by the reaction of 2-(3,5-diaryl-4H-pyran-4-ylidene)malononitrile and benzylamine, and are achieved through different ring-closing mechanisms. These two derivatives with twisted molecular conformations display phosphorescence, thermally activated delayed fluorescence, and high contrast solid-state acidochromism due to special chemical structures.

On-DNA Synthesis of Functionalized 4H-Pyran Scaffolds for Focused DNA-Encoded Chemical Libraries.

The functionalized 4H-pyran scaffold has aroused synthetic attention because it is widely found in many interesting pharmacologically relevant compounds. We here disclose its incorporation into DNA-encoded chemical libraries, combining this scaffold with the merits of scaffold architecture in drug design. Under the optimized DNA-compatible conditions, functionalized 4H-pyrans were efficiently formed with a broad substrate scope. Among the 4H-pyrans formed, the axial structure features rotational restriction, and the spirocyclic structure provides rigidity and three-dimensionality. These efforts open the door for the construction of DNA-encoded chemical libraries with more consideration for this structural architecture.

Activity of singly and doubly modified derivatives of C20-epi-salinomycin against Staphylococcus strains.

Natural polyether ionophore salinomycin (Sal) has been widely used in veterinary medicine as an antibiotic effective in the treatment of coccidian protozoa and Gram-positive bacteria. Moreover, chemical modification of the Sal structure has been found to be a promising strategy to generate semisynthetic analogs with biological activity profiles improved relative to those of the native compound. In this context, we synthesized and thoroughly evaluated the antibacterial potential of a library of C1/C20 singly and doubly modified derivatives of C20-epi-salinomycin, that is, analogs of Sal with inversed stereochemistry at the C20 position. Among the synthesized analog structures, the most promising antibacterial active agents were those obtained via regioselective O-acylation of C20-epi-hydroxyl, particularly esters 7, 9, and 11. Such C20 singly modified compounds showed excellent inhibitory activity against planktonic staphylococci, both standard and clinical strains, and revealed potential in preventing the formation of bacterial biofilms. In combination with their non-genotoxic properties, these Sal derivatives represent attractive candidates for further antimicrobial drug development.

Pyranodipyran Derivatives with Tyrosyl DNA Phosphodiesterase 1 Inhibitory Activities and Fluorescent Properties from Aspergillus sp. EGF 15-0-3.

Four new benzodipyran racemates, namely (±)-aspergiletals A-D (3-6), representing a rare pyrano[4,3-h]chromene scaffold were isolated together with eurotiumide G (1) and eurotiumide F (2) from the soft-coral-derived fungus Aspergillus sp. EGF 15-0-3. All the corresponding optically pure enantiomers were successfully separated by a chiral HPLC column. The structures and configurations of all the compounds were elucidated based on the combination of NMR and HRESIMS data, chiral separation, single-crystal X-ray diffraction, quantum chemical 13C NMR, and electronic circular dichroism calculations. Meanwhile, the structure of eurotiumide G was also revised. The TDP1 inhibitor activities and photophysical properties of the obtained compounds were evaluated. In the TDP1 inhibition assay, as a result of synergy between (+)-6 and (-)-6, (±)-6 displayed strong inhibitory activity to TDP1 with IC50 values of 6.50 ± 0.73 µM. All compounds had a large Stokes shift and could be utilized for elucidating the mode of bioactivities by fluorescence imaging.

Copper-Catalyzed Regioselective [3+3] Annulations of Alkynyl Ketimines with α-Cyano Ketones: the Synthesis of Polysubstituted 4H-Pyran Derivatives with a CF3 -Containing Quaternary Center.

Regioselective [3+3] annulation of alkynyl ketimines with α-cyano ketones for the synthesis of polysubstituted 4H-pyran derivatives with a quaternary CF3 -containing center has been realized by using Cu(OAc)2 as the catalyst. The novel strategy tolerates a wide range of α-CF3 alkynyl ketimines and α-cyano ketones with both aryl and alkyl substitutents. A preliminary asymmetric synthesis of chiral product 3 has been attempted by using copper and chiral thiourea as the cocatalyst with excellent yields (86-99 %) and good enantioselectivities (71-78 % ee). Furthermore, product 3 aa could be obtained on a gram-scale reaction with 75 % yield and 99 % ee after recrystallization. Several products were also transformed readily. Control experiments indicate that the reaction involves a process with a base-catalyzed or chiral thiourea-catalyzed Mannich-type reaction followed by a highly regioselective copper-catalyzed ring-closing reaction on the alkynyl moiety in a 6-endo-dig fashion.

Synthesis and Characterization of 5-(2-Fluoro-4-[11C]methoxyphenyl)-2,2-dimethyl-3,4-dihydro-2H-pyrano[2,3-b]pyridine-7-carboxamide as a PET Imaging Ligand for Metabotropic Glutamate Receptor 2.

Metabotropic glutamate receptor 2 (mGluR2) is a therapeutic target for several neuropsychiatric disorders. An mGluR2 function in etiology could be unveiled by positron emission tomography (PET). In this regard, 5-(2-fluoro-4-[11C]methoxyphenyl)-2,2-dimethyl-3,4-dihydro-2H-pyrano[2,3-b]pyridine-7-carboxamide ([11C]13, [11C]mG2N001), a potent negative allosteric modulator (NAM), was developed to support this endeavor. [11C]13 was synthesized via the O-[11C]methylation of phenol 24 with a high molar activity of 212 ± 76 GBq/µmol (n = 5) and excellent radiochemical purity (>99%). PET imaging of [11C]13 in rats demonstrated its superior brain heterogeneity and reduced accumulation with pretreatment of mGluR2 NAMs, VU6001966 (9) and MNI-137 (26), the extent of which revealed a time-dependent drug effect of the blocking agents. In a nonhuman primate, [11C]13 selectively accumulated in mGluR2-rich regions and resulted in high-contrast brain images. Therefore, [11C]13 is a potential candidate for translational PET imaging of the mGluR2 function.

Synthesis and anti-tumor activity evaluation of salinomycin C20-O-alkyl/benzyl oxime derivatives.

Seventeen C20-O-alkyl/benzyl oxime derivatives were synthesized by a concise and effective method. Most of these derivatives showed tens to several hundred nanomolar IC50 values against HT-29 colorectal, HGC-27 gastric and MDA-MB-231 breast cancer cells, whose antiproliferative activity is 15-240 fold better than that of salinomycin. The C20-oxime etherified derivatives can coordinate potassium ions, and further adjust the cytosolic Ca2+ concentrations in HT-29 cells. The significant improvement of the potency should be attributed to the better ion binding and transport ability of the modified derivatives. In addition, the C20-O-alkyl/benzyl oxime derivatives showed much better selectivity indexes (SI) than salinomycin, indicating that they present lower neurotoxic risk.

Mollugin induced oxidative DNA damage via up-regulating ROS that caused cell cycle arrest in hepatoma cells.

Mollugin has been proven to have anti-tumor activity. However, its potential anti-tumor mechanism remains to be fully elaborated. Herein, we investigated the growth inhibition of HepG2 cells, as well as the anti-tumor effect of mollugin and its molecular mechanism on H22-tumor bearing mice. In vitro, mollugin was shown to have a strong inhibitory effect on HepG2 cells in a concentration-dependent manner. Mollugin induced S-phase arrest of HepG2 cells, and increased intracellular reactive oxygen species (ROS) levels. Comet assay demonstrated that mollugin induced DNA damage in HepG2 cells, as well as an increase in the expression of p-H2AX. In addition, mollugin induced changes in cyclin A2 and CDK2. However, the addition of antioxidant glutathione (GSH) was able to reverse the effect of mollugin. In vivo, mollugin significantly inhibited tumor growth and reduced the tendency of tumor volume growth in mice. The tumor cell density was found to be decreased in the administration group, and the content of ROS in the tumor tissue significantly increased. The expression of p-H2AX, cyclin A2 and CDK2 were consistent with in vitro results. Mollugin demonstrated anti-hepatocellular carcinoma activity in vitro and in vivo, and its anti-hepatocellular carcinoma activity was found to be related to DNA damage and cell cycle arrest induced by excessive ROS production in cells.

A DFT/PCM Study on the Affinity of Salinomycin to Bind Monovalent Metal Cations.

The affinity of the polyether ionophore salinomycin to bind IA/IB metal ions was accessed using the Gibbs free energy of the competition reaction between SalNa (taken as a reference) and its rival ions: [M+-solution] + [SalNa] → [SalM] + [Na+-solution] (M = Li, K, Rb, Cs, Cu, Ag, Au). The DFT/PCM computations revealed that the ionic radius, charge density and accepting ability of the competing metal cations, as well as the dielectric properties of the solvent, have an influence upon the selectivity of salinomycin. The optimized structures of the monovalent metal complexes demonstrate the flexibility of the ionophore, allowing the coordination of one or two water ligands in SalM-W1 and SalM-W2, respectively. The metal cations are responsible for the inner coordination sphere geometry, with coordination numbers spread between 2 (Au+), 4 (Li+ and Cu+), 5/6 (Na+, K+, Ag+), 6/7 (Rb+) and 7/8 (Cs+). The metals' affinity to salinomycin in low-polarity media follows the order of Li+ > Cu+ > Na+ > K+ > Au+ > Ag+ > Rb+ > Cs+, whereas some derangement takes place in high-dielectric environment: Li+ ≥ Na+ > K+ > Cu+ > Au+ > Ag+ > Rb+ > Cs+.