Circularly Polarized Luminescence and Circular Dichroism of Bichromophoric Difluoroboron-β-diketonates: Inversion and Enhanced Chirality Based on Spatial Arrangements and Self-Assembly

We synthesized two bichromophoric difluoroboron-β-diketonates (DFB) connected in para and meta positions by using cyclohexane diamine as a chiral bridge ( para and meta (R/S)-CyDFB ). TD-DFT calculations revealed that the variation in connectivity of the DFB units leads to different spatial arrangements and a chirality inversion of the bichromophoric DFB. Higher g_abs values were obtained in (R/S)-CyDFB connected in para as compared to meta position. Aggregation of para (R/S)-CyDFB in mixture of solvents increase the g_lum values as compared to its monomeric form. Ultrasonication and heating induced the formation of highly ordered nano-helical wires of para (R/S)-CyDFB that increased the g_lum values to 0.015. On the other hand, meta (R/S)-CyDFB failed to form highly ordered self-assembled wires due to hindered H-binding sites. These observations indicate that the chiroptical properties of DFB bi-chromophore system can be modulated with self-assembly and spatial arrangement of the chromophores.     

Glycosyl‐Substituted Dicarboxylates as Detergents for the Extraction,Overstabilization, and Crystallization of Membrane Proteins

To tackle the problems associated with membrane protein (MP) instability in detergent solutions, we designed a series of glycosyl‐substituted dicarboxylate detergents (DCODs) in which we optimized the polar head to clamp the membrane domain by including, on one side, two carboxyl groups that form salt bridges with basic residues abundant at the membrane–cytoplasm interface of MPs and, on the other side, a sugar to form hydrogen bonds. Upon extraction, the DCODs 8 b , 8 c , and 9 b preserved the ATPase function of BmrA, an ATP‐binding cassette pump, much more efficiently than reference or recently designed detergents. The DCODs 8 a , 8 b , 8 f , 9 a , and 9 b induced thermal shifts of 20 to 29 °C for BmrA and of 13 to 21 °C for the native version of the G‐protein‐coupled adenosine receptor A_2AR. Compounds 8 f and 8 g improved the diffraction resolution of BmrA crystals from 6 to 4 Å. DCODs are therefore considered to be promising and powerful tools for the structural biology of MPs.     

Analysis of native amino acids by liquid chromatography/electrospray ionization mass spectrometry: comparative study between two sources and interfaces

The analytical performances of two triple-quadrupole instruments, which differ in their atmospheric-pressure sources, were evaluated for native amino acid analysis. The Applied Biosystems/Sciex API 300 instrument was equipped with a turboIon Spray source and a curtain gas interface while the Waters/Micromass Quattro Ultima instrument was characterized by its Z-spray source. Liquid chromatography/mass spectrometry analysis of native amino acids requires volatile ion-pairing mobile phase additives (mainly perfluorinated carboxylic acids). The effects of the structure and concentration of the ion-pairing reagents as well as the organic modifier percentage on the electrospray response of amino acids were studied in detail. The most favourable chromatographic conditions depend strongly on the mass spectrometer used. Several instrumental parameters were also studied, including spray voltage, transmission lens voltages, temperature of desolvation and auxiliary gas flow rates. The results show substantial qualitative differences depending on the instrument geometry. The quantitative performances of the two triple-quadrupole mass spectrometers were evaluated in terms of limits of detection and quantification. The effects of the matrix on the analyte ionization were also examined, and the long-term stability of the electrospray performance was studied over 12 h using a mobile phase containing the perfluorinated ion-pairing reagents. The study provides information on the robustness of the MS instrument and its detection sensitivity towards native amino acid analysis. It appears that each instrument has its good and bad points since one provides higher sensitivity while another is more robust.     

Decarboxylative Mannich Reactions with N-Alkyl Imines

The use of N-alkyl imines in decarboxylative Mannich reaction with substituted malonic acids half oxyesters (SMAHOs) has been developed to afford a direct access to secondary β^2,3-aminoesters. The transformation occurs under very practical conditions (DABCO as a catalyst in bulk toluene and open to air) and can be performed with a broad range of each substrate in yields of 36 to 97 %. Importantly, the reaction was found to require the use of acidic additives in combination with the organocatalyst to limit the competitive olefination reaction.     

Diastereodivergent strategies for the synthesis of homochiral aculeatins

We report concise and stereocontrolled syntheses of aculeatins (-)-A, (+)-B, (+)-D, and (+)-6-epi-D. Diastereodivergent 1,3-inductions in Mukaiyama aldol coupling contribute to reduce steps and to increase flexibility with reactants having sterically restricted proximal substituents (i.e., CH2), involving either a good anti or a moderate syn 1,3-induction, depending on the nature of protecting group (P). In addition, the 3,5-syn-diol-ketone resulting from concomitant deprotection of the beta-alkoxy (Tr = trityl) group proves to be remarkably stable whereas the 3,5-anti diastereoisomer cyclizes spontaneously to the corresponding tetrahydropyran hemiketal, thus enabling a useful and facile separation. The second part of our study is devoted to improving the yield and the diastereoselectivity of the final phenolic oxidation reaction leading to aculeatins.     

Asymmetric synthesis of tetrahydropalmatine via tandem 1,2-addition/cyclization

[Reaction: see text]. The enantioselective synthesis of both enantiomers of tetrahydropalmatine (2) (ee = 98%), a natural alkaloid belonging to the tetrahydroprotoberberine family, is described. The key step of this total synthesis is based on our tandem 1,2-addition/ring-closure methodology employing lithiated methylbenzamide and benzaldehyde SAMP or RAMP hydrazones as substrates. An initial route was investigated for the formation of N- and 3-substituted dihydroisoquinolones starting from 2-substituted benzaldehyde SAMP hydrazones, but although high diastereoselectivity was achieved, only disappointing yields were obtained. In our subsequent synthetic strategy, 2,3-dimethoxy-6-methylbenzamide 6 and 3,4-dimethoxybenzaldehyde SAMP or RAMP hydrazone 19 gave the dihydroisoquinolones 20 in high diastereomeric purity (de > or = 96%) and reasonable yield (54-55%), taking into account the complex functionalities established in one step. Cleavage of the N-N bond of the chiral auxiliary and reduction of the carbonyl group of the amide moiety were performed in the same step, and the resulting tetrahydroisoquinolines 22 (ee = 99%) were N-functionalized by treatment with various electrophiles to investigate the ring closure by Pummerer, Friedel-Crafts, and Pomeranz-Fritsch reactions. The Pummerer cyclization led to the formation of (S)-(-)-2 with slight racemization (ee = 89%), whereas the Friedel-Crafts reaction proved to be unsuccessful. Finally, Pomeranz-Fritsch-type cyclization afforded the desired title compound (R)-(+)-2 in excellent enantioselectivity in 9% overall yield over seven steps and after optimization of the last step (S)-(-)-2 in 17% overall yield.     

Peculiar field-dependent magnetic behavior of cyano-bridged coordination polymer Er(H2O)4[W(CN)8

The two-dimensional cyano-bridged coordination polymer Er(H(2)O)(4)[W(CN)(8)] exhibits a magnetic transition at 12 K and an unusual field-dependent transition from short-range to ferromagnetic ordering.     

Tandem CH Activation/Arylation Catalyzed by Low‐Valent Iron Complexes with Bisiminopyridine Ligands

Tandem C?H activation/arylation between unactivated arenes and aryl halides catalyzed by iron complexes that bear redox‐active non‐innocent bisiminopyridine ligands is reported. Similar reactions catalyzed by first‐row transition metals have been shown to involve substrate‐based aryl radicals, whereas our catalytic system likely involves ligand‐centered radicals. Preliminary mechanistic investigations based on spectroscopic and reactivity studies, in conjunction with DFT calculations, led us to propose that the reaction could proceed through an inner‐sphere C?H activation pathway, which is rarely observed in the case of iron complexes. This bielectronic noble‐metal‐like behavior could be sustained by the redox‐active non‐innocent bisiminopyridine ligands.     

A New Furostanol Saponin from the Water-extract of Dioscorea nipponica Mak., the Raw Material of the Traditional Chinese Herbal Medicine Wei Ao Xin

26-O-β-D-Glucopyranosyl-furost-5(6),20(22)-dien-3β,26-diol 1, a new furostanol saponin, was isolated from the water-extract of Dioscorea nipponica Mak., the raw material of a traditional Chinese herbal medicine Wei Ao Xin. The structure of 1 was determined on the basis of its spectral data especially by NMR spectroscopy. The result provides the first example of naturally occurring furostanol saponins with a single saccharide chain at the C-26 position.     

Phosphorus cluster production by laser ablation

Neutral and charged phosphorus clusters of a wide size range have been produced by pulsed laser ablation (PLA) in vacuum at 532, 337, and 193 nm ablating wavelengths and investigated by time-of-flight mass spectrometry. The neutral P_n clusters are even-numbered with local abundance maxima at n=10 and 14, while the cationic and anionic clusters are preferentially odd-numbered with P₇⁺, P₂₁⁺, and P₁₇^- being the most abundant ions. The dominance of the magic clusters is more pronounced at 337-nm ablation that is explained by efficient direct ejection of their building blocks under these conditions. Nanocrystalline phosphorus films have been produced by PLA in ambient helium gas. PACS 52.38.MF; 61.46.+w; 79.20.Ds; 81.07.B; 81.16.Mk