Synthesis of cyclic phosphonate analogues of (lyso)phosphatidic acid using a ring-closing metathesis reaction

We describe a versatile and efficient method for the preparation of acyloxy-substituted six-membered cyclic phosphonates using the ring-closing metathesis. After closure, the key cyclic phosphonate intermediate was dihydroxylated and converted to a new class of conformationally constrained PA and LPA analogues. The oleoyloxy-substituted cyclic phosphonate 4 had unique receptor-selective properties as a ligand, showing partial activation of the LPA2 GPCR and weak antagonism of the LPA1 GPCR.     

Lewis acid-promoted rearrangement of 2,3-epoxy alcohol derivatives: stereochemical control and selective formation of two types of chiral quaternary carbon centers from the single carbon skeleton

The Lewis acid-promoted rearrangement of 2,2,3,3-tetrasubstituted 2,3-epoxy alcohols with several kinds of protecting groups was investigated. When SnCl4 is used as a Lewis acid, the reaction proceeds in a regio- and stereo-controlled manner to afford two types of carbonyl compounds selectively from a single 2,3-epoxy alcohol only by changing the protecting group of the alcohol. The method was then applied to the formation of two types of acyclic and cyclic quaternary carbon centers from the single compound in optically active forms.     

On some algebraic properties of CM-types of CM-fields and their reflexes

Text

The purpose of this paper is to show that the reflex fields of a given CM-field K are equipped with a certain combinatorial structure that has not been exploited yet.The first theorem is on the abelian extension generated by the moduli and the b-torsion points of abelian varieties of CM-type, for any natural number b. It is a generalization of the result by Wei on the abelian extension obtained by the moduli and all the torsion points. The second theorem gives a character identity of the Artin L-function of a CM-field K and the reflex fields of K. The character identity pointed out by Shimura (1977) in [10] follows from this.The third theorem states that some Pfister form is isomorphic to the orthogonal sum of defined on the reflex fields _⊕Φ∈ΛK^∗(Φ). This result suggests that the theory of complex multiplication on abelian varieties has a relationship with the multiplicative forms in higher dimension.

Video

For a video summary of this paper, please click here or visit http://www.youtube.com/watch?v=IIwksVYV5YE.     

Circular dichroism of copoly(γ-stearyl-L-glutamate–γ-methyl-L-glutamate)

Copoly(γ-stearly-L -glutamate-γ-methyl-L -glutamate)s with various compositions were synthesized by the ester exchange reaction of poly(γ-methyl-L -glutamate). Circular dichroism studies were carried out for solution and solid film as a function of the degree of stearylation and temperature. The slight and gradual temperature dependence of molecular ellipticity was observed for solution of all the copolyglutamates studied here and for the solid film of the copolyglutamate with the degree of stearylation of 16%, indicative of no reversal in the helix sense. However the remarkable change in negative molecular ellipticity with temperature was detected for the solid film of the copolyglutamate with a low degree of stearylation, e.g., 52%, whereas the drastic change in molecular ellipticity from a negative to positive value appeared for that with a higher degree of stearylation. This is discussed in terms of the reversal in the helix sense from a right- to left-handed α helix with the increase of temperature occurring at the melting temperature of the ordered side chain region.     

Folding Dynamics of 10‐Residue β‐Hairpin Peptide Chignolin

Short peptides that fold into β‐hairpins are ideal model systems for investigating the mechanism of protein folding because their folding process shows dynamics typical of proteins. We performed folding, unfolding, and refolding molecular dynamics simulations (total of 2.7 μs) of the 10‐residue β‐hairpin peptide chignolin, which is the smallest β‐hairpin structure known to be stable in solution. Our results revealed the folding mechanism of chignolin, which comprises three steps. First, the folding begins with hydrophobic assembly. It brings the main chain together; subsequently, a nascent turn structure is formed. The second step is the conversion of the nascent turn into a tight turn structure along with interconversion of the hydrophobic packing and interstrand hydrogen bonds. Finally, the formation of the hydrogen‐bond network and the complete hydrophobic core as well as the arrangement of side‐chain–side‐chain interactions occur at approximately the same time. This three‐step mechanism appropriately interprets the folding process as involving a combination of previous inconsistent explanations of the folding mechanism of the β‐hairpin, that the first event of the folding is formation of hydrogen bonds and the second is that of the hydrophobic core, or vice versa.     

Preparation of PAMAM- and PPI-metal (silver, platinum, and palladium) nanocomposites and their catalytic activities for reduction of 4-nitrophenol

Dendrimer-metal (silver, platinum, and palladium) nanocomposites are prepared in aqueous solutions containing poly(amidoamine) (PAMAM) dendrimers with surface amino groups (generations 3, 4, and 5) or poly(propyleneimine) (PPI) dendrimers with surface amino groups (generations 2, 3, and 4). The particle sizes of the metal nanoparticles obtained are almost independent of the generation as well as the concentration of the dendrimer for both the PAMAM and the PPI dendrimers; the average sizes of silver, platinum, and palladium nanoparticles are 5.6-7.5, 1.2-1.6, and 1.6-2.0 nm, respectively. It is suggested that the dendrimer-metal nanocomposites are formed by adsorbing the dendrimers on the metal nanoparticles. Studies of the reduction reaction of 4-nitrophenol by these nanocomposites show that the rate constants are very similar between PAMAM and PPI dendrimer-silver nanocomposites, whereas the rate constants for the PPI dendrimer-platinum and -palladium nanocomposites are greater than those for the corresponding PAMAM dendrimer nanocomposites. In addition, it is found that the rate constants for the reduction of 4-nitrophenol involving all the dendrimer-metal nanocomposites decrease with an increase in the dendrimer concentrations, and the catalytic activity of dendrimer-palladium nanocomposites is highest.     

Membrane Potential Photoresponse of Crowned Malachite Green Derivatives Affording Perfect Photoswitching of Metal Ion Complexation

Photoirradiation effect on potential response to metal ion concentrations and photoinduced potential change were investigated with poly(vinyl chloride) membranes based on a Malachite Green derivative carrying a bis(monoaza-15-crown-5) moiety, by comparing other Malachite Green derivatives. The Malachite Green carrying a bis(crown ether) moiety caused a potential response to potassium ion concentration changes under dark condition. In the membrane potential response, a clear-cut photoinduced switching of potential response was realized by the membrane of Malachite Green carrying a bis(crown ether) moiety, which exhibited no potential response to potassium ion concentrations (0 mV/decade) on UV irradiation. On the other hand, a Malachite Green carrying a monocyclic benzocrown ether moiety showed a considerable dependence of the membrane potential on the metal ion concentrations under both dark and UV irradiation conditions.This revised version was published online in July 2005 with a corrected issue number.     

A method for detecting O-glycanase in biological samples using a combination of MALDI-TOF mass spectrometry and time-resolved fluorimetry

O-Glycans (mucin type oligosaccharides) are ubiquitously found in various glycoproteins such as mucin-type glycoproteins on the surface of various digestive organs. In the present paper, we propose a method for detecting O-glycanase which catalyzes the hydrolysis of the O-glycan linkage between oligosaccharides and serine/threonine residues of mucin-type glycoprotein. As the substrate for O-glycanases, we chose glycopeptides containing O-glycans derived from bovine fetuin. The present method is divided into two parts. At the initial stage, the presence of O-glycanase was confirmed by observing characteristic ions due to O-glycans and peptides released from the glycopeptide by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. In the second step, europium labeled O-glycosylated peptide permits more detailed analysis such as enzyme kinetics. We demonstrated the usefulness of the present method using O-glycanase (Streptococcus pneumoniae) as model enzyme. The present approach can easily confirm the presence of O-glycanase by detecting both deglycosylated peptides and O-glycans, even if contaminating peptides or glycosidases are present in crude biological samples.     

Conversion from arenes having a benzene ring to those having a picolinic acid by simple growing cell reactions using Escherichia coli that expressed the six bacterial genes involved in biphenyl catabolism

The comprehensive bioconversion of aromatic compounds with a benzene ring to a picolinic acid was achieved with a recombinant Escherichia coli strain that expressed the six genes involved in biphenyl catabolism, these being the bphA1(2072)A2A3A4 genes encoding the evolved biphenyl dioxygenase, the bphB gene encoding dihydrodiol dehydrogenase, and the bphC gene encoding catechol 2,3-dioxygenase.