Synthesis of phospholipids containing perfluorooctyl group and their interfacial properties

Highly fluorinated single-chained and/or double-chained phospholipids containing the perfluorooctyl group as the terminal segment of hydrophobic chains and a phosphocholine moiety as the hydrophilic headgroup were synthesized in order to investigate the effect of fluorinated segments on the stability of phospholipid monolayers formed at the air-water interface. Judging from the equilibrium spreading pressures (π_es) of their monolayers at the air-water interface, all of the fluorinated phospholipids formed more stable monolayers than the corresponding non-fluorinated counterparts. In addition, the fluorinated double-chained phosphatidylcholine containing C-C triple bond (monoyne group) formed stable and fluid vesicle membranes in water, although the single-chained phospholipids did not form vesicle membranes but micellar solutions under the present conditions.     

W(CO)5-amine catalyzed exo- and endo-selective cyclizations of omega-alkynyl silyl enol ethers: a highly useful method for the construction of polycyclic compounds

[reaction: see text] A highly useful method for the construction of polycyclic compounds based on the amine-controlled exo- and endo-selective cyclizations of omega-alkynyl silyl enol ethers catalyzed by W(CO)5L is reported. When bis-alkynyl silyl enol ethers were treated with a catalytic amount of W(CO)6, DABCO, and water under photoirradiation, synthetically useful tricyclic ketones were obtained in good yield.     

Aldehyde-selective addition of alkynylchromium compounds prepared by reduction of alkynyl halides with chromium(II) reagent

Alkynyl halides are reduced by chromium(II) chloride in DMF to give unisolable alkynylchromium compounds which add selectively to an aldehyde moiety without affecting the coexisting ketone group of the substrate.     

Highly fluorinated C18 fatty acids: synthesis and interfacial properties

A fluorinated oleic acid 1-Z containing a perfluorooctyl group and its analogues (E-isomer 1-E, alkyne type 2 and saturated type 3) were synthesized in good yields. In these syntheses, it was found that a key compound 5 could be converted to each of 1-Z, 1-E and 2. Furthermore, equilibrium spreading pressures of their monolayers at the air-water interface were measured in order to demonstrate how the degree of unsaturation in the hydrophobic chain, the geometric isomerization, and the presence of F-atoms influence the monolayer stability. Irrespective of the structural alteration in the hydrophobic chains, the fluorinated fatty acids formed more stable monolayers with high spreading pressures as compared to their hydrocarbon counterparts.     

New artificial host compounds containing galactose end groups for binding chiral organic amine guests: chiral discrimination and their complex structures

New linear host (1) and cyclic hosts (2 and 3), which have galactopyranose skeletons as chiral origins and oxyethylenes skeletons as binding sites, were designed based on the structural features extracted from the fructo-oligosaccharide derivatives, having a large chiral discrimination ability, and were then synthesized. These hosts showed chiral discrimination toward chiral organic ammonium salts. For example, the chiral discrimination ability (the ratio of association constants: K(R)/K(S)) of host 1, which has the highest value among them, was K(R)/K(S) = 3 for Trp-O-(i)Pr(+) and K(R)/K(S) = 0.7 for 1-(1-naphthyl)ethylammonium (NEA(+)) at 298 K in CHCl(3). It was clarified that host 1 changed the conformation from a linear structure to the pseudo-ring structure by complexation with cations such as alkali metallic ions and chiral organic ammonium ions. The (1)H NMR induced shifts of host 1 by adding the NEA(+) guests showed that the host-guest complex structures are clearly different, depending upon the chirality of the guest; in the complex with (R)-NEA(+), the naphthyl group of the guest is located above the oxyethylene skeleton of the host and in the complex with (S)-NEA(+), and the naphthyl group is located between the edges of the pseudo-ring of the host. The clearly different structure of the complex of host 1 with NEA(+) may be caused by the dynamic molecular recognition, thus the induced-fitting mechanism.     

Periodate oxidation analysis of carbohydrates: Part 12. Rapid Determination of Aldehydes in the Oxidation Products of Oligoglycosides by the Dithioacetal Method

A rapid and convenient analysis for glycosidic linkages in oligoglycosides was developed by improving the ditbioacetal method. A sample (0.1–1 μmol) was oxidized with an aqueous or aqueous methanolic 0.05 M solution of sodium metaperiodate for 3 h at 50°C. An equivalent amount of silver nitrate was added and the mixture was evaporated to dryness. The residue was treated with a 2:1 (v/v) mixture of ethanethiol and trifluoroacetic acid for 10 min at 25°C, and subsequently trimethylsilylated with hexamethyldisilazane and trimethylchlorosilane for 30 min at 50°C. Gas chromatography of the product allowed the simultaneous determination of the conjugated aldehydes in the oxidation product with high reproducibility. The glycosidic linkages in various oligoglycosides were examined by this procedure.     

Inhibitory effect of validamine, valienamine and valiolamine on activities of carbohydrases in rat small intestinal brush border membranes

Three pseudo-aminosugars, validamine, valienamine and valiolamine, produced by Streptomyces hygroscopicus subsp. limoneus showed potent inhibitory action on rat small intestinal carbohydrase activities such as sucrase, maltase, glucoamylase, isomaltase and trehalase activities, but negligible action on lactase activity and pancreatic alpha-amylase activity. Where inhibition was seen, kinetic analysis showed fully competitive inhibition of the carbohydrase activities by all three inhibitors. Valiolamine has more potent carbohydrase inhibitory activity than validamine or valienamine, and the apparent Ki values of valiolamine for sucrase, maltase, glucoamylase, isomaltase and trehalase activities were 3.2 x 10(-7), 2.9 x 10(-6), 1.2 x 10(-6), 9.1 x 10(-7) and 4.9 x 10(-5) M, respectively, which are 10(-5) to 10(-3) times smaller than the apparent Km values.     

Studies on cardiotonic agents. III. Synthesis of 1-[1-(6,7-dimethoxy-4-quinazolinyl)-4-piperidinyl]-3-substituted 2-imidazolidinone and 2-imidazolidinethione derivatives

A series of 1-[1-(6,7-dimethoxy-4-quinazolinyl)-4-piperidinyl]-3-substituted 2-imidazolidinone and 2-imidazolidinethione derivatives was synthesized and examined for cardiotonic activity in anesthetized dogs. Alkylation of the 2-imidazolidinone (1) afforded the N-alkylated products, while alkylation of the 2-imidazolidinethione (12) afforded the S-alkylated derivatives accompanied with a small quantity of the N-alkylated products. The N-alkylated derivatives showed generally potent activity, and the S-alkylated ones exhibited weak activity. Insertion of an alkyl group between the piperidine and the imidazolidinone moiety generally resulted in a fall in activity.     

Convergent synthesis of the E'FGH ring fragment of ciguatoxin 1B via an acetylene cobalt complex strategy

A convergent synthesis of the E'FGH ring fragment 28 of ciguatoxin 1B, a principal toxin causing widespread seafood poisonings "ciguatera", has been accomplished through (i) coupling between the E' ring-acetylide 9 and the H ring-aldehyde 20, (ii) stereoselective F ring cyclization via an acetylene cobalt complex, (iii) conversion to a carbonyl function under high-pressure hydrogenation, and (iv) reductive hydroxyketone cyclization to construct the G ring. In the (1)H NMR analysis of 28 at room temperature, a considerable broadening phenomenon was observed due to the slow conformational changes of the FG ring, as reported for natural ciguatoxin 1B. When measured in pyridine at -20 degrees C, the spectra of 28 exhibited a 3.5:1 mixture of two conformational isomers (UP and DOWN conformers).     

Generation of reactive species by one-electron reduction of Fischer-type carbene complexes of group 6 metals and their use for carbon-carbon bond formation

Carbon-carbon bond-forming reactions mediated by one-electron reduction of Fischer-type carbene complexes of Group 6 metals were investigated. In the case of aryl- or silylcarbene complexes of tungsten, the anion radical species generated by one-electron reduction smoothly underwent addition reaction to ethyl acrylate. One-electron reduction of alpha,beta-unsaturated carbene complexes afforded biscarbene complexes by dimerization of the corresponding anion radical species at the position gamma to the metal center. In contrast, one-electron reduction of chromium phenyl- or alkylcarbene complexes gave, via carbonyl insertion, alpha-methoxyacylchromate complexes, which further underwent conjugate addition to various electron-poor olefins to give the corresponding alpha-methoxyketones.