The relationship between the conformational degree of freedom of template-containing threads and slippage in the formation of [2]rotaxane building blocks.

A straightforward slippage strategy has been used for the synthesis of three [2]rotaxane building blocks that all contain an ammonium template for the dibenzo-24-crown-8 macrocycle and an N-hydroxysuccinimide end. The kinetic rate of the slipping-on process proved to be highly dependent on both the length and flexibility of the thread.

Synthesis of triazolium-based mono- and tris-branched [1]rotaxanes using a molecular transporter of dibenzo-24-crown-8.

We report a diverted route to [1]rotaxane and tris-branched [1]rotaxane that are devoid of any efficient template and which could not be obtained by classical straightforward strategies. The described chemical route relies on the utilization of a "macrocycle transporter", which is able first to bind a macrocycle, second to link temporarily a triazolium-containing molecular axle, and third to deliver the macrocycle around the new docked axle through molecular machinery in a [1]rotaxane structure. The extended encircled thread is eventually cleaved by an amine or a triamine to afford the triazolium-containing [1]rotaxanes, releasing at the same time, the macrocycle transporter as a recyclable species.

A model for double asymmetric induction in the stereocontrolled reduction of glycosyl alpha-ketoesters with oxazaborolidines.

Experimental diastereoselectivities for the stereocontrolled reduction of glycosyl alpha-ketoesters into the corresponding alpha-hydroxyesters have recently been reported with unexpected results. The process is catalyzed by a chiral oxazaborolidine derivative (the so-called CBS catalyst) and represents the key step in the synthesis of glycosyl alpha-amino acids synthons, a class of compounds that allow preparation of natural glycopeptides analogues exhibiting potential therapeutic relevance. Good to very good diastereomeric excesses have been obtained for a series of reactions with different glucidic derivatives, but surprisingly, the major product obtained does not correspond to that predicted by using Corey's model. In the present work, we carry out a theoretical investigation of these reactions at the density functional level. Separated effects from the catalyst and from the glucidic derivative have been computed to rationalize the observed diastereoselectivities and the double asymmetric induction.

Structure of epitopes recognized by the antibodies to alpha(181-192) peptides of neuronal nicotinic acetylcholine receptors: extrapolation to the structure of acetylcholine-binding domain.

Using the alpha(181-192) peptides of neuronal nicotinic acetylcholine receptor (nAChR) and Ala-substituted peptide analogues, amino acid residues critical for specific monoclonal antibody (mAb) binding were identified. By means of 2D nuclear magnetic resonance (2D-NMR) analysis followed by molecular modeling, it was found that mAb binding resulted in stabilization of the free alpha3(181-192) peptide flexible conformation yielding an extended structure with residues 6-11 of the peptide being in direct contact with the Ab. Since the Ab binds the native AChR as well, it is suggested that the corresponding fragment of AChR alpha3 subunit is exposed to solution and also appears in extended conformation.