A Preparative Synthesis of 1-Amino-3-hydroxypropylphosphonic Acid (Phosphonic Analogue of Homoserine)

A novel procedure for the preparation of the phosphonic analogue of homoserine is described starting from the commercially available 4-acetoxy-azetidin-2-one.     

Redox reactions between organic halo-compounds and ferrous cations in isopropanol

Summary Halo-compounds of which the half-wave reduction potential is equal to or less negative than that of carbon tetrachloride, are reduced by tetrachloroferrate(II) anions. The bimolecular rate constants measured at 250 in isopropanol are 2 × 10^–5 M^–1 s^–1 and 1 × 10^–4 M^–1 s^–1 respectively for CCl₄ and CCl₃CO₂Me.     

Addition of lithium ethyl fluoroacetate to cis and trans α,β-epoxyaldehydes. Access to C2 fluorinated butyrolactones

The aldolisation reaction of lithium ethyl fluoroacetate with cis and trans α,β-epoxyaldehydes in their racemic forms proceeds with good C₃-OH diastereoselectivity and much less at the C₂-F carbon atom. A two-step reaction on the major aldol compounds (iodination, lactonisation) led to racemic functionalised C₂ fluorinated lactones, possessing a C₂/C₃cis relationship between the fluorine and hydroxyl groups.     

Arresting cancer proliferation by small-molecule gene regulation

A small library of pyrrole-imidazole polyamide-DNA alkylator (chlorambucil) conjugates was screened for effects on morphology and growth characteristics of a human colon carcinoma cell line, and a compound was identified that causes cells to arrest in the G2/M stage of the cell cycle. Microarray analysis indicates that the histone H4c gene is significantly downregulated by this polyamide. RT-PCR and Western blotting experiments confirm this result, and siRNA to H4c mRNA yields the same cellular response. Strikingly, reduction of H4 protein by >50% does not lead to widespread changes in global gene expression. Sequence-specific alkylation within the coding region of the H4c gene in cell culture was confirmed by LM-PCR. The compound is active in a wide range of cancer cell lines, and treated cells do not form tumors in nude mice. The compound is also active in vivo, blocking tumor growth in mice, without obvious animal toxicity.     

Synthesis and characterization of dinuclear niobium(IV), niobium(III) and tantalum(III) chloride complexes with strongly basic phosphanes: PCy3 and P(Bu-t)3

Summary The reactions between niobium and tantalum pentachlorides and tri-t-butylphosphane and tricyclohexylphosphane under various reducing conditions (magnesium turnings, amalgamated magnesium or sodium naphthalenide) were investigated. The products are highly dependent on the experimental conditions. Niobium(IV) adducts: Nb₂Cl₈[P(Bu-t)₃]₂ and Nb₂Cl₈(PCy₃)₄ were obtained with magnesium turnings, while reduction to Ta₂Cl₆(PCy₃)₃ occurred under similar conditions with tantalum. Ligand exchanges from NbCl₄(THF)₂ also yielded niobium(IV) adducts Nb₂Cl₈(PR₃)₃. The formation of the first soluble diamagnetic niobium(IV) adducts appears to be favored by the strong basicity of PCy₃ and P(Bu-t)₃. However, these crowded niobium(IV) complexes are unstable both in the solid and in solution with respect to niobium(III). Derivatives in oxidation state 3: M₂Cl₆(PCy₃)₃ (M=Nb or Ta), Ta₂Cl₆[P(Bu-t)₃]₃ and Nb₂Cl₆[P(Bu-t)₃]₂ were formed more efficiently with amalgamated magnesium or with sodium naphthalenide. Activation of dinitrogen under mild conditions (normal pressure, room temperature) was observed during the reduction process with magnesium, for both tantalum and niobium; an unstable adduct, Nb₂Cl₆[P(Bu-t)₃]₃N₂, could be isolated. All products were characterized by elemental analysis, magnetic susceptibility measurements and i.r. spectroscopy; their molecular structure is discussed in terms of the¹H and³¹P n.m.r. data.     

Molecular dynamics assignment of NMR correlation times to specific motions in a "basket-handle porphyrin" heme

Iron (II) basket-handle porphyrins (BHP) are a series of encumbered heme models designed several years ago to mimic the ligand binding site of hemoproteins. Contrary to expectations, kinetic investigations have revealed that the k(on) rates for CO and/or O2 binding were only marginally affected by the assumed central steric hindrance of the iron atom. Thus, it was hypothesized that the internal dynamics of the molecule might be at the origin of the poor steric protection. To address this issue, measurements of nuclear magnetic resonance relaxation rates, fluorescence anisotropy experiments, and molecular dynamics simulations were undertaken. The size of BHP is small enough to allow the simulation in explicit chloroform with an almost complete sampling of the conformational space. The order parameters calculated from the MD trajectory compare well with the NMR experimental data and the predicted rotational correlation time corresponding to the Brownian motion of the molecule is in good agreement with the fluorescence measurements. Moreover, combining the results obtained using the three techniques allows the attribution of each internal NMR correlation time to a particular internal motion, revealing that even such medium-sized molecules are able to display quite complex internal dynamics. In particular, the handle phenyls that were assumed to sandwich the porphyrin have in fact a vanishing probability to be found in the proximity of the iron atom. They are therefore unable to reduce ligand accessibility significantly, which may explain the behavior of the k(on) rates.     

Selective catalytic hydrogenation of the trans,trans isomer from a mixture of 2,4-hexadienes.

trans, trans-2,4-hexadiene is quantitatively converted into cis-3-hexene by photoinduced hydrogenation catalyzed by chromium carbonyl complexes in presence of acetone which allows both acceleration and selectivity.     

Promotion of sugar-lectin recognition through the multiple sugar presentation offered by regioselectively addressable functionalized templates (RAFT): a QCM-D and SPR study

The investigation of recognition events between carbohydrates and proteins, especially the understanding of how spatial factors and binding avidity are correlated, remains a great interest for glycobiology. In this context we have investigated by nanogravimetry (QCM-D) and surface plasmon resonance (SPR), the kinetics and thermodynamics of the interaction between concanavalin A (Con A) and various neoglycopeptide ligands of low molecular weight. Regioselectively addressable functionalized templates (RAFT) have been used as scaffolds for the design of multivalent neoglycopeptides bearing thiol or biotin functions for their anchoring on transducer surfaces. Although these multivalent neoglycopeptide ligands cannot span multiple binding sites within the same Con A protein, they have increased activities relative to their monovalent counterpart. Our results emphasize that the multivalent RAFT ligands function by clustering several lectins, which leads to enhanced affinities.