A new ruthenium-catalyzed cyclopropanation of alkenes using propargylic acetates as a precursor of vinylcarbenoids

[RuCl₂(CO)₃]₂ catalyzes intermolecular cyclopropanation of various alkenes with propargylic acetates to give vinylcycloropanes in good yields. The key intermediate of this reaction is a vinylcarbene complex generated by nucleophilic attack of the carbonyl oxygen of the acetate to an internal carbon of alkyne activated by the ruthenium complex.     

Novel antiviral fucoidan from sporophyll of Undaria pinnatifida (Mekabu)

Structural characterization and antiviral activities of fucoidan from sporophyll of Undaria pinnatifida (Mekabu) was examined. The fucoidan was composed of fucose and galactose with an approximately ratio of 1.0:1.1. Degree of substitution of sulfate was 0.72 and its apparent molecular weight was 9,000. Methylation analyses showed that fucoidan had various sugar linkages, and revealed that the fucoidan might have complicated structure. This fucoidan showed potent antiviral activities against herpes simplex virus type 1 (HSV-1), HSV-2, and human cytomegalovirus.     

1H-NMR study on the tautomer ratios between the hydrazone imine and diazenylenamine forms in 3-(arylhydrazono)-methyl-2-oxo-1,2-dihydroquinoxalines

The o-substituted 3-(arylhydrazono)methyl-2-oxo-1,2-dihydroquinoxalines 1a-c and 2a , c were synthesized to investigate the tautomeric behavior between the hydrazone imine A and diazenylenamine B forms in a series of mixed dimethyl sulfoxide/trifluoroacetic acid media. The chemical shifts of the hydrazone NH, N₄-H, hydrazone CH, and diazenyl CH protons for o-, m-, and p-substituted 3-(arylhydrazono)methyl-2-oxo-1,2-dihydroquinoxalines 1 and 2 synthesized so far are summarized in Tables 3 and 4, respectively, which are found to be useful for the specification of the proton signals due to the hydrazone imine form A (hydrazone NH, hydrazone CH) and diazenylenamine form B (N₄-H, diazenyl CH).     

Ruthenium-catalyzed cyclopropanation of alkenes using propargylic carboxylates as precursors of vinylcarbenoids

Intermolecular cyclopropanation reactions of various alkenes with propargylic carboxylates 1 are catalyzed by [RuCl2(CO)3]2 to give vinylcyclopropanes 2 in good yields. The key intermediate of the reaction is a vinylcarbene complex generated in situ by nucleophilic attack of a carbonyl oxygen of the carboxylates to an internal carbon of the alkyne activated by the ruthenium complex. A variety of transition-metal compounds other than the Ru compound can also be employed in this system. Similar cyclopropanation proceeds with conjugated dienes as well to give trans-vic-divinylcyclopropane derivatives and cycloheptadiene derivatives 5, the latter being thermally derived from the initially formed cis-vic-isomers via Cope-type rearrangement. The present reaction is chemically equivalent to the transition metal-catalyzed cyclopropanation reaction using alpha-diazoketones as carbenoid precursors.     

Strong binding between acidic guests and fluorescein modified -γ-Cyclodextrin via hydrogen bonding

-Cyclodextrin with appended fluorescein (1) has been prepared as a sensor and a charge-changeable receptor for detecting organic compounds including terpenoids, carboxylic acids and bile acids. Compound1 has cationic, neutral and anionic forms depending on the pH of the solutions. The anionic form of1 at about neutral pH exhibits the highest sensing ability for carboxylic acids and bile acids, while at alkaline pH it detects hardly any of the guests examined. The high sensitivity and selectivity of the anionic form of1 at around neutral pH for acidic guests seems to be caused by the hydrogen bond between the phenoxide anion moiety of fluorescein and acidic guests. The neutral form of1 exhibits little sensing ability for all the guests, but the cationic form shows comparatively higher sensing ability for the guests examined.     

Rhodium-catalyzed cyclopropanation using ene-yne-imino ether compounds as precursors of (2-pyrrolyl)carbenoids

[reaction: see text] The reaction of alkenes with conjugated ene-yne-imino ether or ene-yne-aldimine in the presence of a catalytic amount of [Rh(OAc)(2)](2) gives (2-pyrrolyl)cyclopropanes in good yields. The key intermediate of this cyclopropanation is a (2-pyrrolyl)carbenoid generated by the nucleophilic attack of imine nitrogen atom at an internal alkyne carbon activated by rhodium complex. The intramolecular reaction also proceeds to afford a polycyclic pyrrole.     

Preparation of high‐temperature polyurethane by alloying with reactive polyamide

A series of novel poly(urethane amide) films were prepared by the reaction of a polyurethane (PU) prepolymer and a soluble polyamide (PA) containing aliphatic hydroxyl groups in the backbone. The PU prepolymer was prepared by the reaction of polyester polyol and 2,4‐tolylenediisocyanate and then was end‐capped with phenol. Soluble PA was prepared by the reaction of 1‐(m‐aminophenyl)‐2‐(p‐aminophenyl)ethanol and terephthaloyl chloride. The PU prepolymer and PA were blended, and the clear, transparent solutions were cast on glass substrates; this was followed by thermal treatments at various temperatures to produce reactions between the isocyanate group of the PU prepolymer and the hydroxyl group of PA. The opaque poly(urethane amide) films showed various properties, from those of plastics to those of elastomers, depending on the ratio of the PU and PA components. Dynamic mechanical analysis showed two glass‐transition temperatures (T_g's), a lower T_g due to the PU component and a higher T_g due to the PA component, suggesting that the two polymer components were phase‐separated. The rubbery plateau region of the storage modulus for the elastic films was maintained up to about 250 °C, which is considerably higher than for conventional PUs. Tensile measurements of the elastic films of 90/10 PU/PA showed that the elongation was as high as 347%. This indicated that the alloying of PU with PA containing aliphatic hydroxyl groups in the backbone improved the high‐temperature properties of PU and, therefore, enhanced the use temperature of PU. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3497–3503, 2002     

Positive working resists sensitive to visible light,I: poly(tert-butyl and 2-phenylpropyl-2 methacrylates) sensitized with diphenyliodonium salt — p-aminobenzylidene dye system

Visible-light-sensitive positive type resists have been developed. The chemistry to form images is based on the cleavage of side chain ester bonds of poly(methacrylates) catalyzed by an acid which is generated on sensitized photodecomposition of a diphenyliodonium (DPI) salt. Homopolymers and copolymers of tert-butyl methacrylate (BMA) and 2-phenylpropyl-2 methacrylate (PPMA) were used as acid labile polymers. Exposure of thin films of the poly(methacrylates) containing DPI salt and p-dimethylaminobenzylidene derivatives to an Ar laser beam emitting 488 nm light and subsequent heat treatment resulted in solubility alteration of the polymers, which became soluble in a protic solvent system. Considerable reduction of film thickness was observed after heating an image-wise exposed thin film of PPMA polymers. The minimum exposure energies of 488 nm light for the positive image formation were 60 mJ/cm² and 40 mJ/cm² for BMA and PPMA homopolymers, respectively.     

Looking glass inhibitors: L-DMDP, a more potent and specific inhibitor of alpha-glucosidases than the enantiomeric natural product DMDP

L-DMDP, prepared from D-gulonolactone, is a highly specific inhibitor of a number of plant and mammalian alpha-glucosidases [between 2 and 4 orders of magnitude more potent than the enantiomeric natural product DMDP] but is not an inhibitor of bacterial and yeast alpha-glucosidases. Additionally N-butyl-DMDP is a potent inhibitor of ceramide-specific glucosyltransferase but N-butyl-L-DMDP shows no inhibition.