Efficient and stereoselective syntheses of DAB-1 and d-fagomine via chiral 1,3-oxazine

The concise, stereocontrolled syntheses of DAB-1 and d-fagomine were achieved utilizing chiral oxazine. The key features in these strategies are the stereoselective intramolecular oxazine formation catalyzed by palladium(0), and pyrrolidine and piperidine formation by catalytic hydrogenation of oxazine.     

Total synthesis of methyl l-daunosaminide hydrochloride via chiral 1,3-oxazine

Total synthesis of methyl l-daunosaminide hydrochloride was achieved from readily available l-tyrosine. Key steps in this strategy were palladium(0) catalyzed stereoselective intramolecular oxazine formation and catalytic hydrogenation of oxazine intermediate. This paper reported ¹H and ¹³C NMR data of α- and β-anomer of methyl l-daunosaminide hydrochloride.     

Synthesis of 4-hydroxy-5-methyl-2-[2-(4-oxo-4<Emphasis Type="Italic">H</Emphasis>-chromen-3-yl)ethenyl]-6<Emphasis Type="Italic">H</Emphasis>-1,3-oxazin-6-ones and their reaction with hydrazine

4-Hydroxy-6H-1,3-oxazin-6-ones containing a 3-vinylchromone fragment in the 2-position were synthesized. The direction of their reactions with hydrazine hydrate was found to depend on the solvent nature. The reaction in protic solvents (methanol, acetic acid) resulted in recyclization of both oxazine ring to 1,2,4-triazole and pyranone ring to pyrazole. Aprotic acetonitrile favored attack of hydrazine exclusively on the oxazine ring, while the 3-vinylchromone fragment remained intact.     

Synthesis of naphtho[1,2-<Emphasis Type="Italic">e</Emphasis>]-pyrazolo[5,1-<Emphasis Type="Italic">b</Emphasis>][1,3]oxazines

The previously unknown heterocyclic system naphtho[1,2-e]pyrazolo[5,1-b][1,3]oxazine was synthesized by the condensation of 1-dimethylaminomethyl-2-naphthols with bromopyrazoles. It is proposed that the highly reactive o-methylenequinone of the naphthalene series is formed as an intermediate.     

Synthesis and reactivity of 4-hydroxy-5-methyl-2-(2-oxo-2<Emphasis Type="Italic">H</Emphasis>-chromen-3-yl)-6<Emphasis Type="Italic">H</Emphasis>-1,3-oxazin-6-ones

4-Hydroxy-6H-1,3-oxazin-6-ones with a coumarin fragment in position 2 of the oxazine ring were synthesized. Their hydrolysis, alcoholysis, and hydrazinolysis afforded a number of new coumarin derivatives containing malonamic acid and 1,2,4-triazole residues. The low stability of the title compounds toward oxygencentered nucleophiles was interpreted by quantum chemical calculations.     

<Emphasis Type="Italic">Ab Initio</Emphasis> conformational analysis of tetrahydro-1,3-oxazine

Nonempirical RHF/STO-3G and 6-31G(d) studies on conformational behavior of tetrahydro-1,3- oxazine showed that interconversion between the axial (global minimum) and equatorial chair conformers can follow five independent pathways. The potential energy surface contains seven minima corresponding to chair and twist conformers, as well as seven transition states having sofa, half-chair, and symmetrical and unsym- metrical boat conformations. Additional potential barriers to interconversion, resulting from pyramidal inversion of the nitrogen atom, were also revealed.     

PHOTOCHEMISTRY ON SURFACES: TRIPLET-TRIPLET ENERGY TRANSFER ON MICROCRYSTALLINE CELLULOSE STUDIED BY DIFFUSE REFLECTANCE TRANSIENT ABSORPTION and EMISSION SPECTROSCOPY*

Triplet-triplet energy transfer has been studied between benzophenone and an oxazine dye (2,7-bis(diethyl-amino)-phenazoxonium chloride) co-adsorbed on the surface of microcrystalline cellulose. Ground state absorption and fluorescence measurements provide evidence for dimer formation of the oxazine dye when adsorbed on cellulose in contrast to the behaviour in ethanol solution where no dimerization is observed. The equilibrium constant for dimerization, which is found to be (1.0 × 0.1) × 10⁶ mol^?1 g (2560 × 250 dm³ mol^?1) for oxazine alone on cellulose decreases in the presence of co-adsorbed benzophenone. Fluorescence is detected from excited monomeric but not from excited dimeric oxazine. The absorption spectrum of the triplet state of oxazine adsorbed on cellulose was obtained and its extinction coefficient evaluated relative to that of triplet benzophenone which was used as a sensitizer. The lifetime of adsorbed triplet oxazine is 4.3 ms which is 300 times longer than that in acetonitrile solution. The efficiency of energy transfer from triplet benzophenone to oxazine on cellulose was studied using both time resolved sensitized absorption and phosphorescence intensity measurements as a function of oxazine concentration. Lifetime measurements show that the energy transfer process involves static quenching since the benzophenone lifetime is independent of oxazine loading at the surface. A mechanism is proposed to explain the results in which one oxazine molecule is suggested as being able to quench phosphorescence from a “pool” consisting of 2 to 3 benzophenone molecules.     

吡啶并[1,4]噁嗪衍生物的合成新方法--酰胺溴代吡啶的分子内偶联

描述了一个方便制备吡啶并1，4-噁嗪衍生物的合成新方法，该法通过分子内偶联构建了噁嗪环系统。     

Colorimetric detection of cyanide with a chromogenic oxazine

[reaction: see text] We have designed a chromogenic oxazine for the colorimetric detection of cyanide. Indeed, the [1,3]oxazine ring of our compound opens to form a 4-nitrophenylazophenolate chromophore in response to cyanide. This quantitative chromogenic transformation permits the detection of micromolar concentrations of cyanide in water. Furthermore, our chromogenic oxazine is insensitive to the presence of large concentrations of fluoride, chloride, bromide, or iodide anions, which are generally the principal interferents in the colorimetric detection of cyanide.     

Thermoresponsive Poly(2‐oxazine)s

The monomers 2‐methyl‐2‐oxazine (MeOZI), 2‐ethyl‐2‐oxazine (EtOZI), and 2‐n‐propyl‐2‐oxazine (nPropOZI) were synthesized and polymerized via the living cationic ring‐opening polymerization (CROP) under microwave‐assisted conditions. pEtOZI and pnPropOZI were found to be thermoresponsive, exhibiting LCST behavior in water and their cloud point temperatures (T_CP) are lower than for poly(2‐oxazoline)s with similar side chains. However, comparison of poly(2‐oxazine) and poly(2‐oxazoline)s isomers reveals that poly(2‐oxazine)s are more water soluble, indicating that the side chain has a stronger impact on polymer solubility than the main chain. In conclusion, variations of both the side chains and the main chains of the poly(cyclic imino ether)s resulted in a series of distinct homopolymers with tunable T_CP.     

A highly sensitive and selective chemosensor for cyanide

A highly sensitive and selective cyanide chemosensor based on fused indoline and benzooxazine fragment was reported with fast response. The detection of cyanide was performed via the nucleophilic attack of cyanide anion on the oxazine. (1)H NMR and MS studies confirmed the cleavage of C-O bond of oxazine and binding of cyanide to the spiro center of oxazine. The specific reaction results in high selectivity for cyanide ion. Addition of cyanide anion to the oxazine in MeCN/H(2)O solution results in a loss in absorbance at 343 nm and an increase in new absorbance at 411 nm, thus resulting in obvious color changes. Cyanide can be detected down to 1 microM levels in a fast response of less than 30s with no interference of other anionic species. The cyanide detection method should have potential application in a variety of settings requiring rapid and accurate analysis of cyanide anion for drinking and fresh water.     

A one-pot asymmetric organocatalytic tandem reaction for the synthesis of oxazine derivatives

An easy one-pot tandem reaction catalyzed by a chiral secondary amine for the synthesis of optically active oxazine derivatives has been performed and the corresponding substituted benzo[d]pyrido[2,1-b][1,3]oxazine derivatives were afforded in generally high yields (up to 99%) and excellent enantioselectivities (up to >99%).     

The effect of chromophore-chromophore interaction on the spectral luminescent properties of oxazine dye dimers

Spectral and luminescent properties were studied for chemical dimers and molecular aggregates of Nile Red oxazine dye in solutions. Chemical bonding of two oxazine dye molecules leads to the formation of a dimer whose spectral behavior is in close agreement with the exciton model constructed for “physical” molecular aggregates. Chemical dimers luminesce, whereas dimers formed because of van der Waals interactions do not.     

Functional derivatives of thiophene

2-Aryl-4-oxothieno[2,3-d]oxazine derivatives were synthesized. Opening of the oxazine ring to give 2-benzamidothiophene-3-carboxylic acid hydrazide derivatives is observed when these compounds are treated with hydrazine hydrate.See [1] for Communication 17.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 45–46, January, 1980.     

Development of the 1,2-oxaza-Cope rearrangement

A method for a concise assembly of oxazine rings based on a Lewis acid-promoted hetero-Cope rearrangement is described. The hetero-Cope rearrangement features the first examples of the [3,3]-sigmatropic transpositions involving the nitroso group. A variety of functionalized substrates have been subjected to the reaction. The described method has a strong potential for the synthesis of marine natural products containing oxazine rings.     

Plasmonic Activation of a Fluorescent Carbazole–Oxazine Switch

The covalent attachment of a carbazole fluorophore to an oxazine photochrome permits the reversible activation of fluorescence under optical control. Ultraviolet irradiation with a pulsed laser opens the oxazine ring to shift bathochromically the absorption of the carbazole component. Concomitant visible illumination excites selectively the carbazole fluorophore of the photochemical product to produce fluorescence. The photogenerated and fluorescent species reverts spontaneously on a submicrosecond timescale to the initial nonemissive state of the carbazole–oxazine dyad. The photochemical and photophysical properties engineered into this particular molecular switch allow the convenient monitoring of plasmonic effects on photochemical reactions with fluorescence measurements. In close proximity to silver nanoparticles, visible illumination with a continuous‐wave laser also results in fluorescence activation. The metallic nanostructures enable the two‐photon excitation of the oxazine component to induce the photochromic transformation and then facilitate the one‐photon excitation of the photochemical product to generate fluorescence. Thus, these operating principles offer the opportunity to avoid altogether the need of pulsed ultraviolet irradiation to trigger the photochromic transformation and, instead, allow fluorescence activation with a single visible source operating at low illumination power.     

Application of Pd(0)-catalyzed intramolecular oxazine formation to the efficient total synthesis of (-)-anisomycin

The enantioselective total synthesis of (-)-anisomycin, a potent antibiotic agent, has been achieved. The key steps are a Pd(0)-catalyzed stereoselective intramolecular oxazine formation from d-tyrosine and pyrrolidine formation by catalytic hydrogenation of the oxazine.     

Coupling to the pyrimido[4,5-b][1,4]oxazine ring system: Synthesis of potential antifolates

The ability of 2-amino-4-hydroxy-7H-pyrimido[4,5-b][1,4]oxazine derivatives to inhibit dihydrofolate reductase led to a search for means of synthesizing new side chain substituted analogs of this marginally stable pyrimidooxazine system. A study of the synthesis and use of 6-functionalized pyrimido[4,5-b][1,4]oxazines for coupling side chains was begun and has now revealed methods for coupling p-aminobenzoic acid with 2-amino-4-hydroxy-6-carboxy-7H-pyrimido[4,5-b][1,4]oxazine and hydrolyzed 2-amino-4-hydroxy-6-carbe-thoxymethylene-6,7-dihdyro-5H-pyrimido[4,5-b][1,4]oxazine. The products are of interest for evaluation as potential antifolates.     

4-溴-5-甲基靛红的Baeyer-Villiger氧化反应

Baeyer-Viliger反应是由酮制备酯的重要方法^[1].氧化剂通常有两类:(1)有机过酸;(2)过硫酸钾/硫酸(Caro酸).由于靛红结构特殊,我们分别以单过邻苯二甲酸^[2]和过硫酸钾/硫酸^[3]为氧化剂氧化4-溴-5-甲基靛红(1).     

Dimer formation of organic fluorophores reports on biomolecular dynamics under denaturing conditions

Stacking interactions between organic fluorophores can cause formation of non-fluorescent H-dimers. Dimer formation and dissociation of two fluorophores site-specifically incorporated in a biomolecule result in fluorescence intermittency that can report on conformational dynamics. We characterize intramolecular dimerization of two oxazine fluorophores MR121 attached to an unstructured polypeptide. Formation of stable non-fluorescent complexes with nano- to microsecond lifetimes is a prerequisite for analysing the intermittent fluorescence emission by fluorescence correlation spectroscopy and extracting relaxation time constants on nano- to millisecond time scales. Destabilization of the generally very stable homodimers by chemical denaturation reduces the lifetime of H-dimers. We demonstrate that H-dimer formation of an oxazine fluorophore reports on end-to-end contact rates in unstructured glycine-serine polypeptides under denaturing conditions.