Stereoelectronic effects in ring-chain tautomerism of 1,3-diarylnaphth[1,2-e][1,3]oxazines and 3-alkyl-1-arylnaphth[1,2-e][1,3]oxazines

The disubstitution effects of X and Y in 1-(Y-phenyl)-3-(X-phenyl)-2,3-dihydro-1H-naphth[1,2-e][1,3]oxazines on the ring-chain tautomerism, the delocalization of the nitrogen lone pair (anomeric effect), and the (13)C NMR chemical shifts were analyzed by using multiple linear regression analysis. Study of the three-component equilibrium B<==>A<==>C revealed that the chain<==>trans (A<==>B) equilibrium constants are significantly influenced by the inductive effect (sigma(F)) of substituent Y on the 1-phenyl ring. In contrast, no significant substituent dependence on Y was observed for the chain<==>cis (A<==>C) equilibrium. There was an analogous dependence for the epimerization (C<==>B) constants of 1-(Y-phenyl)-3-alkyl-2,3-dihydro-1H-naphth[1,2-e][1,3]oxazines. With these model compounds, significant overlapping energies of the nitrogen lone pair was observed by NBO analysis in the trans forms B (to sigma*(C1-C1'), sigma*(C1-C10b), and sigma*(C3-O4)) and in the cis forms C (to sigma*(C1-H), sigma*(C1-C10b), and sigma*(C3-O4)). The effects of disubstitution revealed some characteristic differences between the cis and trans isomers. However, the results do not suggest that the anomeric effect predominates in the preponderance of the trans over the cis isomer. When the (13)C chemical shift changes induced by substituents X and Y (SCS) were subjected to multiple linear regression analysis, negative rho(F)(Y) and rho(F)(X) values were observed at C-1 and C-3 for both the cis and trans isomers. In contrast, the positive rho(R)(Y) values at C-1 and the negative rho(R)(X) values at C-3 observed indicated the contribution of resonance structures f (rho(R) > 0) and g (rho(R) < 0), respectively. The classical double bond-no-bond resonance structures proved useful in explaining the substituent sensitivities of the donation energies and the behavior of the SCS values.     

Synthesis of new 1,3-disubstituted-2,3-dihydro-1H-naphth[1,2e][1,3]oxazines

1,3-Disubstituted-2,3-dihydro-1H-naphth[1,2-e][1,3]oxazines were prepared through the ring-closure reactions of the aminobenzylnaphthols with substituted aryl- and heteroarylaldehydes.     

Synthesis of novel pyrido[2,3-e][1,3]oxazines

The preparation of novel pyrido[2,3-e][1,3]oxazines starting from 3-hydroxy-pyridine-2-carbonitrile, N-aralkoxy-3-hydroxy-pyridine-2-carboxamides and 3-hydroxy-pyridine-2-carboxylic acid hydrazides is described.     

Synthesis of some pyrazolo[4,3-e][1,2]- and thiazolo[4,5-e][1,2]thiazine 1,1-dioxide derivatives

The synthesis of various 2-methylpyrazolo[4,3-e]- and thiazolo[4,5-e][1,2]thiazine 1,1-dioxide derivatives is described.     

Synthesis,characterization and antimicrobial activity evaluation of new 2,4-Thiazolidinediones bearing imidazo[2,1-b][1,3,4]thiadiazole moiety

The synthesis and antimicrobial activity of 2,4-thiazolidinedione derivatives 5a–g and 6a–g are described. The structures of the newly synthesized compounds were confirmed by IR, NMR, mass and elemental analyses. All compounds were evaluated for their preliminary in vitro antibacterial and antifungal activity. The results revealed that most of the compounds showed high or moderate biological activity against tested microorganisms.     

Synthesis of novel imidazo[1,2-a][3,1]benzothiazines 4, imidazo[1,2-a]-[1,2,4]benzotriazines 5, and 4H-imidazo[2,3-c]pyrido[2,3-e][1,4]oxazines 6

Starting from the readily available 2-aminobenzhydrols ( 7 ), 3-amino-1,2,4-benzotriazine ( 11 ) and 2-amino-3-pyridinol ( 12 ), novel derivatives of 5-phenyl-5H-imidazo[1,2-a][3,1]benzothiazine-2-carboxylic acid, ethyl ester ( 4 ), imidazo[2,1-c][1,2,4]benzotriazine-2-carboxylic acid, ethyl ester ( 5 ) and 4H-imidazo[2,3-c]pyrido-[2,3-e][1,4]oxazine ( 6 ) were prepared.     

Synthesis of a new pyrrolo[1,3]diazepine: 4H-pyrrolo[1,2-a]thieno[2,3-e][1,3]diazepine

The 4H-pyrrolo[1,2-a]thieno[2,3-e][1,3]diazepine (20) was synthesized by the one-pot intramolecular cyclization of the appropriate nitroaldehyde 13 . This key intermediate 13 was obtained by two pathways from methyl 3-bromomethylthiophene-2-carboxylate (6).     

Synthesis,in vitro antibacterial and antifungal evaluation of novel 1,3,4-oxadiazole thioether derivatives bearing the 6-fluoroquinazolinylpiperidinyl moiety

A series of structurally novel 1,3,4-oxadiazole thioether derivatives(6a-6z) containing a 6-fluoroquinazolinylpiperidinyl moiety were designed and synthesized using pharmacophore hybrid approach,and their structures were fully characterized by ^1H NMR,¹³C NMR and HRMS spectra.Among them,the structure of compound 6 d was further corroborated via single-crystal X-ray diffraction analysis.In vitro antibacterial bioassays showed that compounds 6 a,6 g,6 u and 6 v possessed EC₅₀ values of 30.4,30.6,27.5 and 26.0 μg/mL against phytopathogenic bacterium Xanthomonas oryzae pv.oryzae,respectively,which were significantly superior to that of commercially-available bactericide Bismerthiazol(85.1 μg/mL).Moreover,in vitro antifungal bioassays indicated that seven compounds demonstrated broad-spectrum fungicidal acitivties against six types of phytopathogenic fungi at 50 μg/mL.The present work showed the potential of 1,3,4-oxadiazole thioether derivatives carrying a 6-fluoroquinazolinylpiperidinyl moiety as effective antimicrobial agents for crop protection,deserving further investigations in the future.     

Synthesis of certain 3,5,7-disubstituted pyrazolo[3,4-e][1,3]oxazines. Derivatives of a new heterocyclic ring system

The synthesis of several 3,5,7-trisubstituted pyrazolo[3,4-e][1,3]oxazines by ring annulation of the appropriately substituted pyrazoles is described.     

Synthesis and antifungal activity of trichodermin derivatives

<正>A series of derivatives were synthesized from trichodermin(1) which was an antifungal metabolite produced by Trichoderma taxi sp.nov.Their structures were confirmed by ~1H NMR,MS spectrum.Their antifungal activities were evaluated in vitro.The preliminary structure activity relationships(SAR) results indicated that the double bond,epoxide moiety and ester group were main pharmacophore elements,the stereochemistry of C4 position played a key role as well,and the compounds 1e-1g displayed stronger antifungal activity against Magnaporthe grisea than 1.     

Design, synthesis and antifungal activity of novel triazole derivatives

Twenty-three 1 -(1H-1,2,4-triazole-1 -y1)-2-(2,4-difluorophenyl)-3-(iV-cycloproyl-N-substituted-amino)-2-propanols were designed and synthesized on the basis of the active site of lanosterol 14α-demethylase. In vitro antifungal activities showed that some of the title compounds had higher antifungal activity and broader antifungal spectrum than fluconazole.     

Synthesis and in vitro anticancer activity of some novel cyclohepta[b]thiophene-3-carboxamides bearing pyrazole moiety

2-Aminothiophene 3 was achieved through the one-pot multicomponent reaction of cycloheptanone, cyanoacetamide, elemental sulfur, and morpholine in ethanol. Diazotization of 2-aminothiophene 3 with NaNO₂/HCl gave the corresponding diazonium salt 4 , that combined with the appropriate active methylene components; 5a , 5b , 7 , 11 , 13 , 16 , 18 , 21 , 9 , 19 , 22a , and 22b in pyridine (AcONa/EtOH) to form the corresponding hydrazones 6a , 6b , 8 , 10 , 14 , 15 , 17 , 20 , 23 , 24 , 25a , and 25b , respectively. Heating of compound 8 with malononitrile 9 in ethanol gave the thiazole 10 . Treatment of compound 10 , 25a , and 25b with hydrazine hydrate achieve the pyrazoles 12 , 27a , and 27b , respectively. Hydrazinolysis of compound 14 with hydrazine hydrate, followed by condensation of the obtained hydrazide 15 with acetylacetone 19 gave the pyrazole 20 . The recently orchestrated thiophenes were assessed for their cytotoxic action. The result revealed that compound 12 indicated comparable and better action towards HePG2, HCT-116, MCF-7, and PC3 cancer cell lines than Doxorubicin.     

Synthesis,anticancer activity and molecular docking studies of novel pyrido[1,2-a]pyrimidin-4-one derivatives

A series of novel triazolothione, thiadiazole, triazole, and oxadiazole-functionalized pyrido[1,2-a]pyrimidin-4-ones 6a–6l and 7a–7f were prepared, starting from pyridine derivatives 1a and 1b. All the compounds 6a–6l and 7a–7f were screened against four human cancer cell lines (HeLa, COLO205, Hep G2, and MCF 7), among which compounds 6d, 6h, 6j, 7b, and 7e showed promising anticancer activity. Molecular docking studies showed good binding energy and exhibited interactions and better lower free energy values, indicating more thermodynamically favored interaction.     

Synthesis and Antimicrobial Activity of 3-Substituted 8-Propenylbenzo[e][1,3]oxazines

Russian Journal of Applied Chemistry - A series of 1,3-benzoxazine derivatives were prepared by ternary Mannich condensation of 2-propenylphenol, formaldehyde, and primary amines (aniline,...     

Synthesis and stereochemistry of indano[1,2‐d][1,3]oxazines and thiazines,new ring systems

A set of structurally varied indano[1,2‐d][1,3]oxazines and thiazines, which are new ring systems, were prepared by ring‐closure reactions of amino alcohols 4–6. The reactions of cis‐ and trans‐1‐amino‐ and cis‐ 1‐benzylamino‐2‐hydroxymethylindane (4–6) with 1 equivalent of an aromatic aldehyde in methanol at room temperature resulted in three‐component equilibria (15a‐g), or a Schiff base (16), or a ring‐closure product alone (17a‐c), respectively, depending on the substitution or configuration of the starting amino alcohol. The ring‐chain tautomeric equilibria can be described by an equation of Hammett type.     

Electrophilic acetylation and bromination reactions of benzo[b]naphtho[2,3-e][1,4]dioxin

The reactivity of benzo[b]naphtho[2,3-e][1,4]dioxin in the electrophilic aromatic substitution reactions has been studied. Friedel-Crafts acetylation resulted in the formation of three out of the possible five monoacetylated products, with the acetyl group located in positions 8 (major), 7 and 6 (minor) of the heterocycle. In the bromination reaction a higher selectivity was observed with the 6-bromo derivative found as the only monobrominated product and the 6,11-dibromo derivative found as the only polybrominated product. A ratio of unreacted heterocycle:6-bromo:6,11-dibromo derivatives in the bromination reaction has been found to depend strongly on the reaction conditions and on the heterocycle:bromine ratio.