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At least 127 records · Page 7Linked to original sources
PubMed2002

Structure and dynamics of condensed DNA probed by 1,1'-(4,4,8,8-tetramethyl-4,8-diazaundecamethylene)bis[4-[[3- methylbenz-1,3-oxazol-2-yl]methylidine]-1,4-dihydroquinolinium] tetraiodide fluorescence.

Information on the structure and dynamics of condensed forms of DNA is important in understanding both natural situations such as DNA packaging and artificial systems such as gene delivery complexes. We have established the fluorescence of bisintercalator 1,1'-(4,4,8,8-tetramethyl-4,8-diazaundecamethylene)bis[4-[[3-methylbenz-1,3-oxazol-2-yl]methylidine]-1,4-dihydroquinolinium] tetraiodide (YOYO-1) as a novel probe for DNA condensation. When the level of DNA-bound YOYO-1 is sufficiently large, condensation by either polyethylenimine (PEI) or the cationic detergent cetyltrimethylammonium bromide (CTAB) leads to electronic interaction among YOYO-1 molecules bound on the same DNA molecule. This interaction results in an excitonic blue shift of the absorption spectra of YOYO-1 and dramatic decrease in the fluorescence quantum yield. These observations constitute a signature of the condensation of DNA. We further examined the comparative properties of DNA condensed by PEI, CTAB, or Co(NH(3))(6)(3+) through the steady-state and dynamic fluorescence of YOYO-1. Condensation by either PEI or CTAB was associated with a blue shift in the absorption spectra of YOYO-1, although the magnitude of the shift was larger in the case of PEI when compared to that of CTAB. In contrast, condensation by Co(NH(3))(6)(3+) was not associated with a measurable shift in the absorption spectra. These results were interpreted as signifying the varying level of compactness of the DNA condensates. Quenching of fluorescence by acrylamide showed that condensation by all three agents led to an increase in the level of solvent exposure of the base pairs. Observation of the decay of fluorescence intensity and anisotropy of DNA-bound YOYO-1 showed that while condensation by either PEI or CTAB froze the segmental mobility of the helix, condensation by Co(NH(3))(6)(3+) enhanced the flexibility of DNA. The relevance of our findings to functions such as efficiency of gene delivery is discussed.

Benzoxazoles↗
PubMed1996

The chemistry of pseudomonic acid. 17. Dual-action C-1 oxazole derivatives of pseudomonic acid having an extended spectrum of antibacterial activity.

A series of C-1 oxazole isosteres of pseudomonic acid A (mupirocin) bearing a nitroheterocycle have been synthesized, and significant differences in both spectrum of activity and potency were found between these derivatives and mupirocin. Additionally, the antibacterial potency of two members of this class of compounds against mupirocin-resistant staphylococci could not be accounted for solely by inhibition of the target enzyme isoleucyl-tRNA synthetase (IRS), indicating an additional mode of action. The most potent compound, the nitrofuran 3f (SB 205952), was the most electron affinic derivative prepared and was transformed by NAD(P)H-dependent bacterial reductases at a rate similar to that for nitrofurantoin. The second mode of action of this compound may therefore arise from its reduction to a species with cellular targets other than IRS. In in vivo studies, 3f was shown to be a very effective agent by both the subcutaneous and oral routes of administration.

Anti-Bacterial Agents↗
PubMed2002

Asymmetric Diels-Alder, Michael, and aldol reactions using a planar chiral 1,3-oxazol-2(3H)-one derived from (R)-(+)-4-hydroxy-[2.2]paracyclophane.

(+)-(R)-[2.2]Paracyclophane[4,5-d]-1,3-oxazol-2(3H)-one exhibiting planar chirality has been used as a chiral auxiliary in asymmetric Diels-Alder, Michael, and aldol reactions of alpha,beta-unsaturated carboxy and enolate imides, respectively. The endo-exo- and face-diastereoselectivity is good and is controlled by the spatial relationship between the prochiral center and the C9-C10 ethylene bridge of the [2.2]paracyclophane moiety. The chiral auxiliary is easily removed and quantitatively recovered.

Journal Article↗
PubMed2004

Novel synthesis of bicycles with fused pyrrole, indole, oxazole, and imidazole rings.

Reactions of benzotriazol-1-yl(1H-pyrrol-2-yl)methanone 10 and benzotriazol-1-yl(1H-indol-2-yl)methanone 11 with diverse ketones, isocyanates, and isothiocyanates in the presence of base afforded pyrrolo[1,2-c]oxazol-1-ones 1, oxazolo[3,4-a]indol-1-ones 2, pyrrolo[1,2-c]imidazoles 3, and imidazo[1,5-a]indoles 4 by a simple one-step procedure.

Journal Article↗
PubMed1996

Oxidation of Oxazolines and Thiazolines to Oxazoles and Thiazoles. Application of the Kharasch-Sosnovsky Reaction.

Using a modification of the Kharasch-Sosnovsky reaction, the oxidation of oxazolines and thiazolines bearing a variety of 2-alkyl substituents (chiral and achiral) were smoothly oxidized to their corresponding oxazoles and thiazoles, respectively. The key feature involved in the successful implementation of this important oxidation was the use of a mixture of Cu(I) and Cu(II) salts to enhance the oxidation of the intermediate captodative radical, 24. The main limitation of this method was shown when the oxidation failed with oxazolines/thiazolines lacking the carboalkoxy group at C-4.

Journal Article↗
PubMed1996

Chiral Auxiliary-Bearing Isocyanides as Synthons: Synthesis of Strongly Fluorescent (+)-5-(3,4-Dimethoxyphenyl)-4-[[N- [(4S)-2-oxo-4-(phenylmethyl)-2-oxazolidinyl]]carbonyl]oxazole and Its Enantiomer.

Both (4S-(+)-3-(isocyanoacetyl)-4-(phenylmethyl)-2-oxazolidinone (R)-1 and its enantiomer (S)-1 have been synthesized as potentially useful synthons in asymmetric synthesis. Optically active (+)-5-(3,4-dimethoxyphenyl)-4-[[N-[(4S)-2-oxo-4-(phenylmethyl)-2-oxazolidinyl]]carbonyl] oxazole (S)-2 and its enantiomer (R)-2 obtained by treating 3,4-dimethoxybenzoyl chloride with (S)-1 and (R)-1, respectively, in the presence of the nonionic superbase P(MeNCH(2)CH(2))(3)N, have high fluorescence quantum yields. The molecular structure of (S)-2 obtained by X-ray means is also presented.

Journal Article↗
PubMed2000

Synthetic studies of the formation of oxazoles and isoxazoles from N-acetoacetyl derivatives: scope and limitations

[reaction: see text] The preparation of two types of heterocycles, oxazoles and isoxazoles, were achieved in good yields in a rapid and simple way by using N-acetoacetyl derivatives. Steric and electronic effects caused by the nature of the substituents at C1, C2, and C3 were studied. The best results were obtained with a chiral oxazolidinone moiety on C1 derived from (1R,2S)-(-)-norephedrine.

Journal Article↗
PubMed2004

Gold catalysis: mild conditions for the synthesis of oxazoles from N-propargylcarboxamides and mechanistic aspects.

2,5-Disubstituted oxazoles are synthesized from the corresponding propargylcarboxamides under mild reaction conditions via homogeneous catalysis by AuCl(3). While monitoring the conversion via (1)H NMR spectroscopy, an intermediate 5-methylene-4,5-dihydrooxazole can be observed and accumulated up to 95%, being the first direct and catalytic preparative access to such alkylidene oxazolines. The intermediate was fully characterized and can be trapped at -25 degrees C for several weeks. Deuteration experiments show a stereospecific mode of the two first steps of the reaction.

Journal Article↗
PubMed2006

Suzuki coupling of oxazoles.

A protocol for the functionalization of the oxazole 2- and 4-positions using the Suzuki coupling reaction is described. 2-Aryl-4-trifloyloxazoles undergo rapid, microwave-assisted coupling with a range of aryl and heteroaryl boronic acids in good to excellent yields. The methodology is similarly effective using 4-aryl-2-chlorooxazoles as the coupling partner and has been extended to the synthesis of a novel class of homo- and heterodimeric 4,4-linked dioxazoles. [reaction: see text]

Journal Article↗
PubMed2004

Stereoselective generation of vicinal stereogenic quaternary centers by photocycloaddition of 5-methoxy oxazoles to alpha-keto esters: synthesis of erythro beta-hydroxy dimethyl aspartates.

The photocycloaddition of methyl pyruvate and methyl phenylglyoxylate, respectively, to 5-methoxy oxazoles bearing additional substituents at C-2 and C-4 leads to bicyclic oxetanes 2 and 3 with high to moderate (exo) diastereoselectivity that can be easily ring-opened to give bis-quaternary aspartic acid diester derivatives 4 and 5.

Journal Article↗
PubMed2006

Matching-pursuit split-operator Fourier-transform simulations of excited-state intramolecular proton transfer in 2-(2'-hydroxyphenyl)-oxazole.

The excited-state intramolecular proton-transfer dynamics associated with the keto-enolic tautomerization reaction in 2-(2(')-hydroxyphenyl)-oxazole is simulated according to a numerically exact quantum-dynamics propagation method and a full-dimensional excited-state potential energy surface, based on an ab initio reaction surface Hamiltonian. The reported simulations involve the propagation of 35-dimensional wave packets according to the recently developed matching-pursuit/split-operator-Fourier-transform (MP/SOFT) method by Wu and Batista. The underlying propagation scheme recursively applies the time-evolution operator as defined by the Trotter expansion to second order accuracy in dynamically adaptive coherent-state expansions. Computations of time-dependent survival amplitudes, photoabsorption cross sections, and time-dependent reactant(product) populations are compared to the corresponding calculations based on semiclassical approaches, including the Herman-Kluk semiclassical initial value representation method. The reported results demonstrate the capabilities of the MP/SOFT method as a valuble computational tool to study ultrafast reaction dynamics in polyatomic systems as well as to validate semiclassical simulations of complex (nonintegrable) quantum dynamics in multidimensional model systems.

Journal Article↗
PubMed1996

Fluorescence detection of specific sequence of nucleic acids by oxazole yellow-linked oligonucleotides. Homogeneous quantitative monitoring of in vitro transcription.

We have developed a fluorescent DNA probe, oxazole yellow (YO)-linked oligonucleotide complementary to a target DNA/RNA, which can enhance the fluorescence on hybridizing with a target nucleotide. We demonstrated the applicability of the YO-linked oligonucleotide probe to real-time monitoring of the in vitro transcription process of a plasmid DNA constructed containing the 5'-terminus non-coded region of hepatitis C virus RNA. In the process of in vitro transcription in the presence of YO-linked complementary oligonucleotide, the fluorescence of the reaction mixture showed a time-dependent linear increase corresponding to the generated target RNA product.

Benzoxazoles↗
PubMed1996

Synthesis and anticonvulsant activity of some 1,2,3,3a-tetrahydropyrrolo[2,1-b]-benzothiazol-, -thiazol- or -oxazol-1-ones in rodents.

To identify more potent anticonvulsant agents and to gain insights into the structural properties determining the potency of a new class of anticonvulsants, some 3a-substituted tetrahydropyrrolo[2,1-b]benzothiazol-1-ones (1a-d) and the thiazole and oxazole analogues (2a-c and 3a-c, respectively) have been synthesized and tested for anticonvulsant activity against isoniazid-induced seizures in rodents. The most active compound, 2a, with a median effective dose (ED50, i.p.) of 24.3 mg kg-1 and 15.9 mg kg-1 in mice and in rats, respectively, was more extensively investigated and found to strengthen the effects of diazepam. No clear correlation was observed between the anticonvulsant activity and molecular lipophilicity descriptors of compounds 1-3. Structural similarity between the antiepileptic drug phenobarbital and compounds 1-3 was evidenced by molecular modelling studies and used to derive preliminary structure-activity relationships. The results demonstrate that 2a is an attractive candidate as an anticonvulsant agent worthy of further study and may help the design of other anticonvulsant drugs.

Animals↗
PubMed1980

Antiinflammatory activity and other pharmacological properties of 11 beta, 21-dihydroxy-2'-methyl-5' beta H-pregna-1,4 dieno[17,16-d] oxazole 3,20-dione-21-acetate (Deflazacort).

The pharmacology of 11 alpha, 21-dihydroxy-2'-methyl-5' beta H-pregna-1,4-dieno[17,16-d]oxazole-3,20-dione-21-acetate (deflazacort) was studied by oral and parenteral administration in acute, short- and long-term experiments in rats. Deflazacort has antiinflammatory activity in various laboratory models, such as carrageenin and nystatin oedema, cotton pellet granuloma, adjuvant arthritis and on liver glycogen storage. The antiinflammatory potency of deflazacort is greater than that of prednisolone, but lower than that of dexamethasone. Absorption from the gut and duration of action appear to be highly satisfactory, as deduced from pharmacological and biochemical measurements. Glucose tolerance curves seem less affected by deflazacort than by prednisolone, while cardiovascular and central nervous system findings do not show unexpected responses.

Animals↗