Order of Reactivity of OH/NH Groups of Glucosamine Hydrochloride and N-Acetyl Glucosamine Toward Benzylation Using NaH/BnBr in DMF

The order of reactivity of OH and NH groups of glucosamine hydrochloride (GlcNH₂^.HCl) and N-acetyl glucosamine (GlcNAc) toward benzylation with NaH/BnBr in DMF was investigated. For GlcNH₂^.HCl, benzyl groups were introduced in the order of N-Bn > N-Bn₂ > 1-O-Bn > 6-O-Bn > 4-O-Bn > 3-O-Bn; for GlcNAc, benzyl groups were introduced in the order of 1-O-Bn > 6-O-Bn > 4-O-Bn > 3-O-Bn > N-Bn. A range of partially benzylated 2-N,N′-dibenzyl glucopyranosides and GlcNAc derivatives were obtained in a single step.     

A homotopy analysis method for limit cycle of the van der Pol oscillator with delayed amplitude limiting

In this work, a powerful analytical method, called Liao’s homotopy analysis method is used to study the limit cycle of a two-dimensional nonlinear dynamical system, namely the van der Pol oscillator with delayed amplitude limiting. It is shown that the solutions are valid for a wide range of variation of the system parameters. Comparison of the obtained solutions with those achieved by numerical solutions and by other perturbation techniques shows that the utilized method is effective and convenient to solve this type of problems with the desired order of approximation.     

Preyssler-type heteropoly acid:A new,mild and efficient catalyst for protection of carbonyl compounds

Preyssler-type heteropoly acid is introduced as a new,mild and efficient catalyst for protection of a variety of carbonyl compounds with 1,3-propane dithiol.     

Double Heck Cross‐Coupling Reactions of Dibrominated Pyridines

Double Heck cross‐coupling reactions of 2,3‐ and 3,5‐dibromopyridine with various alkenes afforded the corresponding novel di(alkenyl)pyridines. The Heck reaction of 2,5‐dibromopyridine unexpectedly afforded 5,5′‐di(alkenyl)‐2,2′‐bipyridines by palladium‐catalyzed dimerization to give 5,5′‐dibromo‐2,2′‐bipyridine and subsequent twofold Heck reaction.     

Influences of Different Enzymatic Treatment on Denim Garment

In current study, the effects of different enzymatic treatment including acid cellulases, neutral cellulases, and combination of laccases with cellulases on denim garment were investigated. The color changes of different samples were compared by colorimetric indices for the garment surface and back and also white pocket. Abrasion resistance, tensile strength, and crease recovery angle of the samples were measured within the standard methods. Also, surfaces of the treated samples were observed by SEM. The results showed that the combination of laccases with cellulases help to improve the lightness and decrease staining on both back of garment and on white pocket.     

On ordinary generalized geometric–arithmetic index

The ordinary generalized geometric–arithmetic index of graphs is introduced and some properties especially lower and upper bounds in terms of other graph invariants and topological indices are obtained.     

Palladium(II)‐catalyzed catalytic aminocarbonylation and alkoxycarbonylation of terminal alkynes: regioselectivity controlled by the nucleophiles

The aminocarbonylation and alkoxycarbonylation reactions of terminal alkynes took place smoothly and efficiently using a catalyst system Pd(OAc)₂–dppb–p‐TsOH? CH₃CN? CO under relatively mild experimental conditions. The catalytic system was tested and optimized using two different nucleophiles: alcohols and amines. Phenylacetylene (1a) was considered as an alkyne along with diisobutylamine (2b₁) and methanol (2c₁) as nucleophiles. The results showed significant differences in the conversion of 1a and in the selectivity towards the gem or trans unsaturated esters or amides with these nucleophiles. The effects of the type of palladium catalysts, the type of ligands, the amount of dppb and the solvents were carefully studied. With diisobutylamine (2b₁), excellent regioselectivity towards the 2‐acrylamides (gem isomer, 3ab₁) was almost always observed, while trans‐α,β‐unsaturated esters 4ac₁ was the predominant product with methanol (2c₁) as a nucleophile. This remarkable sensitivity in the selectivity of the reaction indicates two different possible mechanistic pathways for these carbonylation reactions. Copyright © 2009 John Wiley & Sons, Ltd.     

A novel antimicrobial flavonoidic glycoside from the leaves of Alstonia macrophylla Wall ex A. DC (Apocynaceae)

<正>A new flavonoidic glycoside,tricin-4'-O-β-L-arabinoside(1) was isolated from the leaves of Alstonia macrophylla along with two known flavonoids,vitexin and myricetin-3′-rhamnoside-3-O-galactoside.Their structures were established by chemical and spectral evidences.The known compounds were reported for the first time from this plant.Moreover compound 1 was tested for antifungal and antibacterial activities.