Application of Tsunoda reagent to the convenient synthesis of drug-like pyrazoles

The versatility of the under-utilised (cyanomethylene)tributylphosphorane (CMBP, Tsunoda reagent) was demonstrated on two occasions in a drug discovery context. Firstly, the high reactivity of the phosphorane allowed the alkylation of a weakly acidic pyrazole when standard Mitsunobu conditions were unsuccessful. Secondly, the clean reaction profile generally obtained using CMBP allowed the direct use of the crude mixture in a subsequent Suzuki cross coupling. This reagent has utility when isolation of the Mitsunobu reaction product (e.g. containing a boronate) is not desirable.     

Excited Brownian motions as limits of excited random walks

We obtain the convergence in law of a sequence of excited (also called cookies) random walks toward an excited Brownian motion. This last process is a continuous semi-martingale whose drift is a function, say ??, of its local time. It was introduced by Norris, Rogers and Williams as a simplified version of Brownian polymers, and then recently further studied by the authors. To get our results we need to renormalize together the sequence of cookies, the time and the space in a convenient way. The proof follows a general approach already taken by Tóth and his coauthors in multiple occasions, which goes through Ray-Knight type results. Namely we first prove, when ?? is bounded and Lipschitz, that the convergence holds at the level of the local time processes. This is done via a careful study of the transition kernel of an auxiliary Markov chain which describes the local time at a given level. Then we prove a tightness result and deduce the convergence at the level of the full processes.     

Influence of the Metal Ion on the Two‐Photon Absorption Properties of Lanthanide Complexes Including Near‐IR Emitters

The synthesis of tris(2‐thenoyltrifluoroacetonate)lanthanide(III) complexes featuring a diethylaminostyryl‐2,2′‐bipyridine coligand was achieved for lanthanum; the near‐infrared (NIR) emitters neodymium, erbium, and ytterbium; and the transition‐metal yttrium. The photophysical properties were thoroughly studied, and it was demonstrated that the conjugated bipyridine ligand acts as a good antenna for the sensitization of the NIR emitters. The two‐photon absorption (TPA) properties of all five complexes were investigated by using both two‐photon excited fluorescence and the Z‐scan method. We demonstrate that the nature of the rare earth ion has almost no influence on the TPA properties centered on the conjugated bipyridyl ligand. Finally, we show that Yb^III is sensitized by a two‐photon antenna effect, and that Nd^III is mostly sensitized by a one‐photon process involving direct excitation of forbidden f–f transitions.     

CO Adsorption on N2‐Precovered NaY Faujasite: A FTIR Analysis of the Resulting Adsorbed Species

To productively complete the information regarding the reversible adsorption of a gas mixture on the micropores of cationic zeolites, the adsorption of the two gases N₂ and CO on NaY faujasite is taken as a model case study. We analyze herein CO adsorption (77 K) on two distinct N₂‐precovered NaY sets (low and medium). We outline the continuous desorption of N₂ adducts during CO admittance to full N₂ desorption for the highest CO loadings. These features contrast with preceding results obtained for N₂ loading on CO‐precovered NaY. By comparing these results with the sole CO admission and combining both studies regarding the co‐adsorption sets, we demonstrate the influence of the basic strength of the two gases regarding the nature of the surface‐adsorbed species formed. We also propose and discuss a hypothesis regarding the formation of adsorbed mixed species having both N₂ and CO as ligands. These new findings strengthen the statistical response of IR signatures as a helpful proposal for analyzing adsorbed species and their assignments. This survey completes the molecular understanding of gas‐mixture adsorption that lacks experimental data to date.     

The Synthesis of a γ-Keto-α-amino Acid,a Key Intermediate in the Synthesis of Monatin,a New Natural Sweetener

An efficient method was developed for the synthesis of the ketoamino acid 2, a key intermediate in the synthesis of the novel sweet compound, monatin 1. Preparation of 2 entails coupling of a suitably protected indole acetate anion to an aspartic acid derivative.     

“Heteroglycals” As New Potential Glycosidase Inhibitors. Synthetic Approaches From D-Arabinose

Within the frame of an ongoing project on glycosidase inhibitors, we have been interested in the synthesis of “heteroglycals”, namely, glycal analogues with sulfur or nitrogen in the ring. Glycals² are well known for their applications in sugar chemistry in particular for glycosyl transfer.³ They are also known as glycosidase inhibitors through a slow chemical reaction with the enzyme. Recently exo-glycals emerged as a new class of glycals⁴ which showed interesting features as glycosidase inhibitors but also as precursors of glycomimetics such as C-glycosides.⁵ We have undertaken investigations on related heteroglycals: such compounds are of interest because they combine a planar geometry at the anomeric center and a possible charge site - both elements known to be important to mimic the transition state of the enzymatic glycoside hydrolysis process.⁶     

Annelated Pyridines as Highly Nucleophilic and Lewis Basic Catalysts for Acylation Reactions

New heterocyclic derivatives of 9‐azajulolidine have been synthesized and characterized with respect to their nucleophilicity and Lewis basicity. The Lewis basicity of these bases as quantified through their theoretically calculated methyl‐cation affinities correlate well with the experimentally measured reaction rates for addition to benzhydryl cations. All newly synthesized pyridines show exceptional catalytic activities in benchmark acylation reactions, which correlate only poorly with Lewis basicity or nucleophilicity parameters. A combination of Lewis basicity with charge and geometric parameters in the framework of a three‐component quantitative structure–activity relationship (QSAR) model is, however, highly predictive.     

Unprecedented Electron‐Poor Octahedral Ta6 Clusters in a Solid‐State Compound: Synthesis,Characterisations and Theoretical Investigations of Cs2BaTa6Br15O3

The crystal structure of Cs₂BaTa₆Br₁₅O₃ has been elucidated by using synchrotron X‐ray powder diffraction and absorption experiments. It is built from edge‐bridged octahedral [(Ta₆${{\rm Br}{{{\rm i}\hfill \atop 9\hfill}}}$ ${{\rm O}{{{\rm i}\hfill \atop 3\hfill}}}$ )${{\rm Br}{{{\rm a}\hfill \atop 6\hfill}}}$ ]^4? cluster units with a singular poor metallic electron (ME) count equal to thirteen. This leads to a paramagnetic behaviour related to one unpaired electron. The arrangement of the Ta₆ clusters is similar to that of Cs₂LaTa₆Br₁₅O₃ exhibiting 14‐MEs per [(Ta₆${{\rm Br}{{{\rm i}\hfill \atop 9\hfill}}}$ ${{\rm O}{{{\rm i}\hfill \atop 3\hfill}}}$ )${{\rm Br}{{{\rm a}\hfill \atop 6\hfill}}}$ ]^5? motif. The poorer electron‐count cluster presents longer metal–metal distances as foreseen according to the electronic structure of edge‐bridged hexanuclear cluster. Density functional theory (DFT) calculations on molecular models were used to rationalise the structural properties of 13‐ and 14‐ME clusters. Periodic DFT calculations demonstrate that the electronic structure of these solid‐state compounds is related to those of the discrete octahedral units. Oxygen–barium interactions seem to prevent the geometry of the octahedral cluster to strongly distort, allowing stabilisation of this unprecedented electron‐poor Ta₆ cluster in the solid state.