An improved procedure for the preparation of 2-isoxazolines

Utilisation of Enols of Mono- and Dicarbonyls Compounds in 1,3-Dipolar Cycloaddition Reactions

2-Isoxazolines were obtained from substituted enols or their ester or ether derivatives in 1,3-dipolar cycloaddition reactions with aliphatic or aromatic nitrile oxides.

Chemoenzymatic Synthesis of Primary Alcohols with a 2-Isoxazoline Moiety

Racemic 2-isoxazoline-5-carboxylate esters were reduced under mild conditions to form the corresponding primary alcohols. These alcohols were enzymically resolved by acylation with succinic anhydride in the presence of Amano AK lipase.

Iminosugar C-Nitromethyl Glycoside: Stereoselective Synthesis of Isoxazoline and Isoxazole-Fused Bicyclic Iminosugars

A simple and efficient method for the stereoselective synthesis of isoxazoline/isoxazole-fused iminosugar derivatives has been developed using intramolecular nitrile oxide cycloaddition (INOC) as a key step. Iminosugar C-nitromethyl glycosides, derived from simple carbohydrates, served as excellent nitrile oxide precursors in 1,3-dipolar cycloaddition reactions. N-Alkenyl iminosugar C-nitromethyl glycosides afforded novel isoxazoline-fused indolizidine-, pyrrolizidine-, and quinolizidine-based iminosugars in excellent yields with a high degree of stereoselectivity, whereas N-alkynyl iminosugar C-nitromethyl glycosides furnished the corresponding isoxazole containing tricyclic iminosugars in very good yields.

Synthesis and in Vitro and in Vivo Evaluation of MMP-12 Selective Optical Probes

In designing new tracers consisting of a small peptide conjugated to a reporter of comparable size, particular attention needs to be paid to the selection of the reporter group, which can dictate both the in vitro and the in vivo performances of the whole conjugate. In the case of fluorescent tracers, this is particularly true given the large numbers of available dye moieties differing in their structures and properties. Here, we have investigated the in vitro and in vivo properties of a novel series of MMP-12 selective probes composed of cyanine dyes varying in their structure, net charge, and hydrophilic character, tethered through a linker to a potent and specific MMP-12 phosphinic pseudopeptide inhibitor. The impact of linker length has been also explored. The crystallographic structure of one tracer in complex with MMP-12 has been obtained, providing the first crystal structure of a Cy5.5-derived probe and confirming that the binding of the targeting moiety is unaffected. MMP-12 remains the tracers' privileged target, as attested by their affinity selectivity profile evaluated in solution toward a panel of 12 metalloproteases. In vivo assessment of four selected probes has highlighted not only the impact of the dye structure but also that of the linker length on the probes' blood clearance rates and their biodistributions. These experiments have also provided valuable data on the stability of the dye moieties in vivo. This has permitted the identification of one probe, which combines favorable binding to MMP-12 in solution and on cells with optimized in vivo performance including blood clearance rate suitable for short-time imaging. Through this series of tracers, we have identified various critical factors modulating the tracers' in vivo behavior, which is both useful for the development and optimization of MMP-12 selective radiolabeled tracers and informative for the design of fluorescent probes in general.

2′-Deoxyuridines with a 5-Heteroaromatic Substituent: Synthesis and Biological Evaluation

A series of novel 2′-deoxyuridines with a thienyl substituent in the 5-position were synthesized as potential anti-HSV-1 agents. The brominated derivatives (1d, 1e and 3b) were obtained via halogenation reactions of the protected 5-(thien-2-yl)-2′-deoxyuridine and 5-(thien-3-yl)-2′-deoxyuridine, respectively. The palladium-catalysed cross-coupling reaction with stannylated thiophene was used for the synthesis of ( E)-5-(2-thienylvinyl)-2′-deoxyuridine and 5-(5,2′-dithien-2-yl)-2′-deoxyuridine. These compounds show moderate to good activity against herpes simplex virus type 1 (HSV-1) in the order of decreasing activity 1d>4>1e>3b∼5. Finally, two substituted 5-isoxazol derivatives of 2′-deoxyuridine (6a and 6b) were obtained via a 1,3-dipolar cycloaddition of the protected 5-ethynyl-2′-deoxyuridine. These new compounds demonstrated poor affinity for the virus-specific enzyme thymidine kinase.

Metal-free DBU promoted regioselective synthesis of isoxazoles and isoxazolines

A new simple and efficient metal-free 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) promoted regioselective synthesis of 3,5-disubstituted isoxazoles and isoxazolines from aldoximes has been described.

Substrate-dependent divergent outcomes from catalytic reactions of silyl-protected enol diazoacetates with nitrile oxides: azabicyclo[3.1.0]hexanes or 5-arylaminofuran-2(3H)-ones

Dirhodium(II)-catalyzed reactions of silyl-protected enol diazoacetates with nitrile oxides exhibit high nitrile oxide substituent dependence in the production rearrangement products via dipolar cycloaddition and either the Neber rearrangement or the Lossen rearrangement.

Synthesis of benzisoxazoles by the [3 + 2] cycloaddition of in situ generated nitrile oxides and arynes

A variety of substituted benzisoxazoles has been prepared by the [3 + 2] cycloaddition of nitrile oxides and arynes. Both components, being highly reactive intermediates, have been generated in situ by fluoride anion from readily prepared aryne precursors and chlorooximes. The reaction scope is quite general, affording a novel, direct route to functionalized benzisoxazoles under mild reaction conditions.

Highly Efficient Retro-cycloaddition Reaction of Isoxazolino[4,5:1,2][60]- and -[70]fullerenes

Isoxazolino[4,5:1,2][60]- and -[70]fullerenes undergo an efficient retro-cycloaddition reaction to pristine fullerene by thermal treatment in the presence of an excess of a dienophile and Cu(II) catalysis, which can be selectively used in the presence of malonate or pyrrolidine cycloadducts. Trapping experiments using N-phenylmaleimide as dipolarophile have shown that the reaction mechanism occurs by thermal removal of the nitrile oxide 1,3-dipole, in a process which is favored by the presence of Cu(II) as the catalyst. The ESI-MS study supports the observed retro-cycloaddition process for both C60 and C70 derivatives. In contrast to previous electrochemical retro-cycloaddition processes observed in fulleropyrrolidines, isoxazolinofullerenes were stable under oxidative conditions.

Advances in cycloaddition polymerizations

Cycloaddition reactions have been employed in polymer synthesis since the mid-nineteen sixties. This critical review will highlight recent notable advances in this field. For example, [2 + 2] cycloaddition reactions have been utilized in numerous polymerizations to enable the construction of strained polymer systems such as poly(2-azetidinone)s that can, in turn, afford polyfunctional beta-amino acid derived polymers. Polymers have also been synthesized successfully via (3 + 2) cycloaddition methods utilizing both thermal and high-pressure conditions. 'Click chemistry'--a process involving the reaction of azides with olefins, has also been adopted to generate linear and hyperbranched polymer architectures in a very efficient manner. [4 + 2] Cycloadditions have also been utilized under thermal and high-pressure conditions to produce rigid polymers such as polyimides and polyphenylenes. These cycloaddition polymerization methods afford polymers with potential for use in high performance polymers applications such as high temperature resistant coatings and polymeric organic light emitting diodes.

Chemical and biochemical transformations of 5-ethoxycarbonyl-5-phenyl-2-isoxazolines

The salts, 2-methyl-5,5-disubstituted 4,5-dihydroisoxazolium methylsulfates comprising various substituents at the C-3 carbon atom were subjected to transformations. The structure of applied compounds permitted to monitor the effect of this factor on the transformation course of the 2-isoxazoline ring. The nucleophilic addition of cyanide anion to the selected salts enabled the obtaining of a next heterocyclic system of changed physicochemical and biological properties in comparison to the starting 2-isoxazolines. The diastereoselective hydrolysis of the cyanide group in 2-isoxazolidines by the bacteria strain Rhodococcus rhodochrous PCM 909 leads to the obtaining of a racemic mixture of the trans-hydroxyacid. The introduction of new functional groups into the heterocyclic ring made these compounds attractive objects for further chemical and microbial transformations and to study their biological activity.

One-pot synthesis of functionalized 4,5-dihydroisoxazole derivatives via nitrile oxides and biological evaluation with plant cells

1,3 Dipolar cycloadditions of nitrile oxides generated in situ in the presence of a variety of olefins provided 4,5-dihydroisoxazoles. The whole procedure could be performed in a practical and efficient one-pot operation. The products are of excellent purity (95%) and are isolated in 60-83% yields. Some of them enhanced the accumulation of indole alkaloids in periwinkle cell cultures.