Solution versus solid-state structure of ytterbium heterobimetallic catalysts

The solution structures of the ytterbium heterobimetallic complexes Na(3)[Yb((S)-BINOL)(3)] (1), K(3)[Yb((S)-BINOL)(3)] (2), and Li(3)[Yb((S)-BINOL)(3)] (3), belonging to a family of well-known enantioselective catalysts, are studied by means of NMR and circular dichroism (CD) in the UV and near-IR regions. The experimental NMR paramagnetic shifts were employed to obtain a refined solution structure of 1. NMR analysis demonstrated that 1, 2, and 3 have the same solution geometry but different magnetic susceptibility anisotropy D factors. By comparing XRD and NMR structures of 1, we demonstrate that, upon dissolution, this complex experiences a rearrangement from the crystalline C(3) symmetry into the solution D(3) symmetry. Remarkably, Yb is not bound to water in solution, and Ln-BINOL bonds are labile as demonstrated through EXSY. NIR-CD is confirmed especially sensitive to changes in the ytterbium coordination sphere.     

An Easy Synthetic Route to Hexakis(6-O-benzoyl)-α-cyclodextrin

A four step preparation of hexakis(6-O-benzoyl)-α-cyclodextrin, through selective protection/deprotection approach, is reported.     

Cyclohydrocarbonylation-based strategy toward poly-substituted piperidines

Convenient accesses to enantiomerically pure 2-, 2,3-, 2,6-, 2,3,6-substituted piperidines and 1,4-substituted indolizine are described. At first, indium-mediated aminoallylation and -crotylation of aldehydes with (R)-phenylglycinol or (1R,2S)-1-amino-2-indanol gave homoallylamines with high stereocontrol. Then, these products, submitted to a Rh(I)-catalyzed hydroformylative cyclohydrocarbonylation, afforded perhydrooxazolo[3,2-a]piridines whose oxazolidines are opened with nucleophiles. Finally, the removal of the chiral auxiliaries delivered the enantiomerically pure piperidines.     

Minimum theorems in incremental linear elastic fracture mechanics

The crack propagation problem for linear elastic fracture mechanics has been studied by several authors exploiting its analogy with standard dissipative systems theory (see e.g. (Nemat-Nasser et al., 1980, Nguyen, 2000, Maugin, 1992, Bourdin et al., 2008, Salvadori, 2008). This approach is here further advanced, by noting that Stress Intensity Factors (SIFs) asymptotic expansion (Amestoy et al., 1986, Amestoy and Leblond, 1992) enjoys a Colonnetti’s decomposition (Colonnetti, 1918, Colonnetti, 1950) interpretation. As a consequence, minimum theorems are derived in terms of crack tip “quasi static velocity”. They are reminiscent of Ceradini’s theorem (Ceradini, 1965, Ceradini, 1966) in plasticity.     

Recent advances in the assessment of the ratios of cortisol to cortisone and of some of their metabolites in urine by LC‐MS‐MS

A previously reported method for the assessment of the ratio of tetrahydrocortisol (THF) + allo‐tetrahydrocortisol (A‐THF) to tetrahydrocortisone (THE) by HPLC‐MS‐MS has been significantly improved, in order to increase either ruggedness and reliability. That was achieved by the introduction of an on‐line sample cleanup stage, which made use of a perfusion column as a solid phase microextraction (SPE) cartridge. The set of analytes was expanded, by introducing cortisol and cortisone, whose ratio supply additional diagnostic information. The response factors of both THF and A‐THF has been checked, resulting almost identical, as well as the influence of the matrix on the calibration curves which, although different for water and urine, had similar effect on the ratios of interest. As a consequence, the calibration solutions can be prepared in pure water. The influence of several different storage procedures has also been tested, resulting in no substantial effect on the final result. Finally, the improved method has been used to run real samples from healthy volunteers, with satisfactory results. Copyright © 2008 John Wiley & Sons, Ltd.     

Stereoselective synthesis of trifluoro- and monofluoro-analogues of frontalin and evaluation of their biological activity.

The stereoselective synthesis of both enantiomers of trifluoro frontalin (-)-(1S,5R)- and (+)-(1R,5S)-8, as well as of diastereomeric monofluoro frontalines (-)-(1R,2R,5R)-18 and (-)-(1R,2S,5R)-20, analogues of the bioactive component of the aggregation pheromone of the Scolytidae insect family, has been accomplished starting from (-)-(1R)- and (+)-(1S)-menthyl (S)-toluene-4-sulfinate as a source of chirality and methyl trifluoroacetate or fluoroacetate, respectively, as sources of fluorine. The C-1 stereocenters were installed via stereoselective epoxidation of beta-sulfinyl ketones 2 and 13 with diazomethane. The bicyclic core was obtained by totally stereocontrolled and chemoselective tandem Wacker oxidation/intramolecular ketalization of the intermediate unsatured sulfinyl diols 5, 15, and 19. Axially fluorinated (-)-20 elicited a strong electroantennographic response in laboratory tests on females of Dendroctonus micans, whereas equatorially fluorinated (-)-18 and the trifluoroanalogue (-)-8 showed modest responses. Field trials using (-)-20 were not indicative owing to the locally scarce population of D. micans, but it showed some attractiveness for other Coleoptera families.     

Synthesis and chromatographic properties of an HPLC chiral stationary phase based upon human serum albumin

Summary A new HPLC stationary phase was synthesized by thein situ covalent immobilization of human serum albumin (HSA). The protein was immobilized on a commerically available diol column which had been activated with 1,1-carbonyldiimidazole. Initial chromatographic studies show that this phase can be used for chiral separations of enantiomeric solutes and that these separations may reflectin vitro binding to the HSA. The effects of mobile phase composition and temperature on the stereochemical resolutions are reported.