Novel one-pot total syntheses of deoxyvasicinone, mackinazolinone, isaindigotone, and their derivatives promoted by microwave irradiation

[reaction: see text]. Total syntheses of deoxyvasicinone (1), mackinazolinone (2), and 8-hydroxydeoxyvasicinone (3) via novel microwave-assisted domino reactions, as well as a novel three-component one-pot total synthesis of isaindigotone (5) promoted by microwave irradiation, are reported. The efficient reaction process enabled us to rapidly access related natural product derivatives and to identify a new class of cytotoxic agents.     

Potential allergenicity of novel proteins in murine models

Bioengineered crops represent an important advancement for farmers who want to avoid losses caused by insect infestations or adverse environmental conditions. However, the use of modern biotechnology has raised questions regarding the safety of bioengineered foods because of the potential allergenicity of proteins expressed by the newly introduced genes. Standard approaches for safety assessment of these foods are still evolving. Animal models have been suggested as a tool that could help evaluate the potential allergenicity of such compounds. Several investigators are developing animal models to evaluate novel proteins, but none of these have yet been validated. This article reviews the published murine models, rat and mouse in particular, and the different methods used to evaluate parameters related to allergy. It also addresses the factors involved in the development of a model. Finally, it raises some questions that should be considered by the international community so that financial and intellectual efforts can be addressed in a unified manner.     

C2-symmetric diphosphinite ligands derived from carbohydrates. The strong influence of remote stereocenters on asymmetric rhodium-catalyzed hydrogenation

Modular ligands of C(2) symmetry (13a-e, 14a,b,d, and ent-9), systematically modified at positions 2 and 5, were easily prepared from d-glucosamine, D-glucitol, and tartaric acid, respectively. The application of these ligands in the rhodium-catalyzed hydrogenation of methyl acetamidoacrylate, methyl acetamidocinnamate, and dimethyl itaconate shows that both the configuration and the substituents at positions 2 and 5 of the tetrahydrofuran backbone have a strong influence on the enantioselectivty of the processes.     

Complete control of the chemoselectivity in catalytic carbene transfer reactions from ethyl diazoacetate: an N-heterocyclic carbene-Cu system that suppresses diazo coupling

The complex IPrCuCl (1) catalyzes the transfer of the :CHCO2Et group from ethyl diazoacetate (EDA) to unsaturated and saturated substrates (olefins, amine, alcohols) with very high yields. In the absence of substrate, the complex 1 does not react with EDA to give the diazo coupling products (fumarate and maleate), a rare example in the field of metal-catalyzed diazocompounds decomposition.     

Towards an understanding of the heat capacity of liquids. A simple two-state model for molecular association

A model for the temperature dependence of the isobaric heat capacity of associated pure liquids C(p,m)(o)(T) is proposed. Taking the ideal gas as a reference state, the residual heat capacity is divided into nonspecific C(p) (res,ns) and associational C(p) (res,ass) contributions. Statistical mechanics is used to obtain C(p)(res,ass) by means of a two-state model. All the experimentally observed C(p,m)(o)(T) types of curves in the literature are qualitatively described from the combination of the ideal gas heat capacity C(p)(id)(T) and C(p)(res,ass)(T). The existence of C(p,m)(o)(T) curves with a maximum is predicted and experimentally observed, for the first time, through the measurement of C(p,m)(o)(T) for highly sterically hindered alcohols. A detailed quantitative analysis of C(p,m)(o)(T) for several series of substances (n-alkanes, linear and branched alcohols, and thiols) is made. All the basic features of C(p,m)(o)(T) at atmospheric and high pressures are successfully described, the model parameters being physically meaningful. In particular, the molecular association energies and the C(p)(res,ns) values from the proposed model are found to be in agreement with those obtained through quantum mechanical ab initio calculations and the Flory model, respectively. It is concluded that C(p,m)(o)(T) is governed by the association energy between molecules, their self-association capability and molecular size.     

Reductive cyclizations of hydroxysulfinyl ketones: enantioselective access to tetrahydropyran and tetrahydrofuran derivatives

The stereocontrolled formation of cis-2,5-disubstituted tetrahydrofurans and cis-2,6-disubstituted tetrahydropyrans is achieved from enantiopure ketosulfinyl esters by reduction, Weinreb's amide, and ketone formation, followed by the reductive cyclization (Et3SiH/TMSOTf) of the resulting hydroxysulfinyl ketones. The sulfoxide-bearing heterocycles were transformed into two natural products, (-)-centrolobine (1) and both enantiomers of cis-(6-methyltetrahydropyran-2-yl)acetic acid (2).     

The role of the counteranion in the cation-pi interaction

Chemical double mutant cycles have been used to quantify cation-pi interactions in chloroform as a function of the nature of the counteranion. The cation-pi interaction is -2.5 +/- 0.4 kJ mol(-1) and independent of the anion, even though the overall stability of the complexes varies by an order of magnitude due to competition of the anion for alternative binding sites.     

Synthesis of the polycyclic ring systems of artocarpol A and D

The first synthesis of the polycyclic ring systems of artocarpol A and D has been accomplished. These natural products were isolated recently from the root bark of Artocarpus rigida, and artocarpol A has been shown to have potent antiinflammatory properties. The synthesis of an artocarpol D analogue was achieved on condensation of 11H-dibenzo[b,f]oxepin-10-one with senecialdehyde. The reaction of this oxepinone with citral afforded a 2H-pyran that on subsequent irradiation afforded an analogue of artocarpol A. [reaction: see text]     

Carbohydrate-derived spiroketals: stereoselective synthesis of di-D-fructose dianhydrides via intramolecular aglycon delivery

[reaction: see text] A one-pot synthesis of C(2)-symmetric di-d-fructose dianhydrides having the 1,6,9,13-tetraoxadispiro [4.2.4.2]tetradecane skeleton has been accomplished via intramolecular aglycon delivery from (6 --> 6) xylylene-tethered fructofuranose precursors. The stereochemical outcome of the glycosylation-spiroketalization process is governed by the geometrical constraints imposed by the rigid tetracyclic structure of the final compound.