One‐pot synthesis of a new high vinyl content hybrid silica monolith dedicated to nanoliquid chromatography

A new vinyltrimethoxysilane‐based hybrid silica monolith was developed and used as a reversed‐phase capillary column. The synthesis of this rich vinyl hybrid macroporous monolith, by cocondensation of vinyltrimethoxysilane with tetramethoxysilane, was investigated using an unconventional (formamide, nitric acid) porogen/catalyst system. A macroporous hybrid silica monolith with 80% in mass of vinyltrimethoxysilane in the feeding silane solution was obtained and compared to a more conventional low vinyl content hybrid monolith with only of 20% vinyltrimethoxysilane. Monoliths were characterized by scanning electron microscopy, ²⁹Si nuclear magnetic resonance spectroscopy and N₂ adsorption–desorption. About 80% of the vinyl precursor was incorporated in the final materials, leading to 15.9 and 61.5% of Si atoms bonded to vinyl groups for 20% vinyltrimethoxysilane and 80% vinyltrimethoxysilane, respectively. The 80% vinyltrimethoxysilane monolith presents a lower surface area than 20% vinyltrimethoxysilane (159 versus 551 m²/g), which is nevertheless compensated by a higher vinyl surface density. Chromatographic properties were evaluated in reversed‐phase mode. Plots of ln(k) versus percentage of organic modifier were used to assess the reversed‐phase mechanism. Its high content of organic groups leads to high retention properties. Column efficiencies of 170 000 plates/m were measured for this 80% vinyltrimethoxysilane hybrid silica monolith. Long capillary monolithic columns (90 cm) were successfully synthesized (N = 120 000).     

Highly modular synthesis of C1-symmetric aminosulfoximines and their use as ligands in copper-catalyzed asymmetric Mukaiyama-aldol reactions

The development of C1-symmetric aminosulfoximines, their highly modular synthesis, and their application in enantioselective copper-catalyzed Mukaiyama-type aldol reactions between pyruvates and enolsilanes is described. In this context, the influence of the ligand architecture as well as the optimization of the reaction conditions are discussed. In detail, the dependence of the catalyst efficiency on the solvent, the metal source and the temperature are reported, and an interesting additive effect is highlighted. Furthermore, the substrate scope will be presented. With the optimized catalyst system, a number of aldol products with quaternary stereogenic centers have been obtained in high yields and with enantiomeric excesses up to 99 %.     

Intramolecular (4+3) Cycloadditions of Pyrroles and Application to the Synthesis of the Core of Class II Galbulimima Alkaloids

The first intramolecular (4+3) cycloaddition of pyrroles with epoxy enolsilanes as the electrophiles was developed and used to generate optically‐enriched cycloadducts containing the nortropane substructure in good yields. Using this pyrrole cycloaddition as the key step, we achieved the asymmetric synthesis of a nortropane compound bearing the BCDEF ring structure common to the Class II galbulimima alkaloids.     

Chemoselective Activation of Diethyl Phosphonates: Modular Synthesis of Biologically Relevant Phosphonylated Scaffolds

Phosphonates have garnered considerable attention for years owing to both their singular biological properties and their synthetic potential. State‐of‐the‐art methods for the preparation of mixed phosphonates, phosphonamidates, phosphonothioates, and phosphinates rely on harsh and poorly selective reaction conditions. We report herein a mild method for the modular preparation of phosphonylated derivatives, several of which exhibit interesting biological activities, that is based on chemoselective activation with triflic anhydride. This procedure enables flexible and even iterative substitution with a broad range of O, S, N, and C nucleophiles.     

Glycyl-d-threonine dihydrate

Glycyl-d-threonine dihydrate, C₆H₁₂N₂O₄ · 2H₂O, is orthorhombic, with space groupP2₁2₁2₁,a = 9.6211(3),b = 10.0313(2),c = 10.6642(4) Å,Z = 4. Crystals were grown from a solution of the racemic mixture glycyl-d,l-threonine. The structure was refined toR = 0.025 for 2140 reflections of the typehkl and¯hkl; the absolute configuration of the sample crystal was determined from the anomalous scattering of CuK radiation by C, N, and O. The N-H and O-H bond distances and, especially, bond angles seem to be strongly influenced by the positions of the hydrogen-bond acceptors.Contribution No. 6122 from the Arthur Amos Noyes Laboratory of Chemical Physics.     

Cobalt Complexes Supported by Phosphinoquinoline Ligands for the Catalyzed Hydrosilylation of Carbonyl Compounds

P,N phosphinoquinoline based ligands differing by the nature of the phosphorus substituent (ⁱPr, Ph) were employed to synthesize a series of cobalt(II) complexes ( [LCoBr₂] , [L₂CoBr](PF₆) and [L’₂CoBr](PF₆) ). The latter were obtained in high yield and characterized among others by X-ray analysis and elemental analysis. Complex [L₂CoBr](PF₆) showed a very good catalytic activity for the hydrosilylation of various ketones. The catalysis proceeds at a low catalytic loading (1 mol %) with only 1 equivalent of Ph₂SiH₂ in mild conditions and was efficient with aliphatic or aromatic ketones giving moderate to excellent yields of the corresponding silylated ether.     

De novo synthesis of glycosaminoglycans by equine multipotent mesenchymal stromal cells in vitro – Studied by stable isotopic labeling and matrix-assisted laser desorption ionization mass spectrometry

Glycosaminoglycans (GAGs) play an important role in extracellular matrix (ECM) homeostasis and are crucial for maintaining the specific biomechanical and functional properties of musculoskeletal tissues. Aiming at regenerating these tissues, multipotent mesenchymal stromal cells (MSCs) are frequently used, their targeted differentiation and ECM synthesis being a part of their complex mechanism of action. To achieve a better understanding of these processes and to improve the targeted use of the cells for the development of regenerative therapies, reliable quantification of GAGs synthesized by MSCs represents an important step. The aim of this study was to develop a novel technique to specifically assess the de novo synthesis of GAGs, particularly chondroitin sulfate (CS), by MSCs.

Adipose tissue-derived equine MSCs were cultured in vitro for 2, 7, 14, and partially 28 d. Harvested cell populations were enzymatically digested with chondroitinase ABC from Proteus vulgaris and afterwards subjected to CS analysis by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS).

The herein chosen detection method of MALDI-TOF MS combined with enzymatic digestion represents a reliable technique to monitor the culture time-dependent GAG biosynthesis of MSCs cultured in vitro. Furthermore, the addition of ¹³C-labeled glucose as cell culture medium supplement is a useful approach to obtain information regarding cellular GAG and in particular CS synthesis.     

Absorbing boundary conditions for the one-dimensional Schrödinger equation with an exterior repulsive potential

Mathematical constructions and comparisons of accurate absorbing boundary conditions for the one-dimensional Schrödinger equation with a general variable repulsive potential are developed. Stable semi-discretization schemes are built for the associated initial boundary value problems. Finally, some numerical simulations give a comparison of the various absorbing boundary conditions and show that they yield accurate computations.     

Synthesis of fluorinated analogues of the immunosuppressive drug FTY720

Four fluorinated derivatives of the immunosuppressive drug FTY720 were synthesized by a convergent strategy, using the Sonogashira coupling as the key reaction to assemble the two major fragments.     

Frontal free‐radical photopolymerization of thick samples: Applications to LED‐induced fiber‐reinforced polymers

Free‐radical photopolymerization is scarcely used for the manufacturing of fiber‐reinforced polymers. The main issue relies on the penetration depth of light which affects the conversion degree when photopolymerizing thick samples. Consequently, this could lead to inhomogeneous polymer properties. The ability of acylphosphine oxides to photobleach under near UV irradiation makes them of great interest for the curing of thick samples. Therefore, the influence of (2,4,6‐trimethylbenzoyl) phosphine oxide on the curing of composites under LED is investigated. Although that a frontal photopolymerization process can be evidenced, it was found that full photobleaching is hardly obtained at high concentration of photoinitiator. Six layers laminates made of unidirectional fiber glass and unsaturated polyester resin were prepared. The existence of an optimal range of concentration for which the conversion of the resin is the most homogeneous throughout its thickness was pointed out, a fact that is confirmed by dynamic mechanical analysis. Interestingly, this effect is reflected in the shrinkage of the resin as shown by direct measurements or deflection experiments. Mechanical analysis was undertaken whose results correlate well with the aforementioned study, demonstrating the occurrence of a balance between the concentration of photoinitiator and the mechanical properties of the samples. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 898–906