Studies on PNPP Hydrolysis Catalyzed by Divalent Metal Ion Macrocyclic Schiff Base Complexes in Micellar Solution

Two transitional metal ion macrocyclic Schiff base complexes, NiL and CuL were synthesized and characterized, and the metallomicelles made up of the nickel(II) and copper(II) complexes and surfactants(LSS, Brij35, CTAB), as mimic hydrolytic metalloenzyme, were used in catalytic hydrolysis of carboxylic ester (PNPP). The analysis of specific absorption spectrums of the hydrolytic reaction systems indicates that key intermediates, made up of PNPP and Ni(II) or Cu(II) complexes, have formed in the reaction processes of the PNPP catalytic hydrolysis. In this, based on the analytic result of specific absorption spectrum, the mechanism of PNPP catalytic hydrolysis has been proposed; a kinetic mathematical model, applied to the calculation of the kinetic parameter of PNPP catalytic hydrolysis has been established on the foundation of the mechanism proposed; the acid effect of reaction system, structure effect of the complexes, effect of temperature and effects of micelle on the rate of PNPP hydrolysis catalyzed by the complexes also have been discussed.     

Serine and Threonine Schiff Base Esters React with β-Anomeric Peracetates in the Presence of BF3·Et2O to Produce β-Glycosides

Improved procedures are reported for the glycosylation of L-serine and L-threonine utilizing activated Schiff base glycosyl acceptors, which are less expensive and more efficient alternatives to published methods. L-serine or L-threonine benzyl ester hydrochloride salts were reacted with the diarylketimine bis-(4-methoxyphenyl)-methanimine in CH₃CN at rt to form the more nucleophilic Schiff bases 3a and 3b in excellent yield. These Schiff bases exhibited ring-chain tautomerism in CDCl₃ as shown by ¹H NMR. Schiff bases 3a and 3b, acting as glycosyl acceptors, reacted at rt with simple sugar peracetate donors with BF₃·OEt₂ promotion to provide the corresponding L-serine and L-threonine O-linked glycosides in excellent yields and purities. The dipeptide ester Schiff base Ar₂C = N-Ser-Val-OCH₃ 3e also reacted to provide β-glycosides in excellent yields, and without epimerization. With microwave irradiation the reactions were complete in 2 to 5 min. To investigate this reaction further, classical AgOTf-promoted Koenigs-Knorr reaction of D-glucopyranosyl, lactosyl, and maltosyl bromides were examined, providing the β-glycosides with yields ranging from 35% to 68%. The difference in reactivity between α- and β-carbohydrate peracetate donors was remarkable. The less configurationally stable D-xylopyranosyl tetra-acetate (a pentose) showed no selectivity (αvsβ-configuration) toward the Schiff bases.     

The Synthesis of a New Class of Potential Inhibitors for Glycoside Hydrolases†

Some attempts toward the synthesis of novel inhibitors of glycosyl transferases are described. More successfully, the synthesis of an activated cyclopropacyclohexene and an amide and an amine of a cyclopropa‐fused pyranose are described. None of these three novel compounds proved to be a significant inhibitor of a retaining α‐glucosidase from barley.     

Effect of Anomeric Linkage on the Sialylation of Glycosides by Cells

The synthesis of sialylated glycosides using saccharide primers and cells was investigated. α · and β · Saccharide primers were chemically synthesized and introduced into B16 melanoma cells to prime oligosaccharide synthesis. Incorporation of α‐ and β‐dodecyl lactosides into B16 cells resulted in the sialylation of the galactose residue to give GM3‐type oligosaccharides. The β‐dodecyl galactoside primer was sialylated but the α‐dodecyl galactoside primer was not. Both the α‐ and β‐dodecyl glucoside primers were not elongated. In the glycosylation of primers by cells, this research confirmed that sialyl transferases tolerate acceptor modifications and are permissive to primer elongation regardless of the α‐ or β‐linkage to the aglycon unit. However, the presence of the terminal galactose residue that is β‐linked to the adjacent saccharide or aglycon unit is essential for sialylation by cellular enzymes to occur.     

Recent developments and applications of screen-printed electrodes in environmental assays—A review

Screen-printed electrodes (SPEs), which are used as economical electrochemical substrates, have gone through significant improvements over the past few decades with respect to both their format and their printing materials. Because of their advantageous material properties, such as disposability, simplicity, and rapid responses, SPEs have been successfully utilised for the rapid in situ analysis of environmental pollutants. This critical review describes the basic fabrication principles, the configuration designs of SPEs and the hybrid analytical techniques based on SPEs. We mainly overview the electrochemical applications of SPEs in environmental analysis over the past 3 years, including the determination of organic compounds, heavy metals and gas pollutants.     

β-榄香烯含S,Se糖苷衍生物的设计合成

以β-榄香烯(1)为先导化合物, 经由其13位氯代物(2), 依据生物电子等排原理将具有相似共价半径的杂原子S和Se分别引入到β-榄香烯的骨架中, 得到一对相应的类似物3和6; 进而通过多种方法与系列糖供体对接, 立体选择性地合成了相应的乙酰化1,2-反式糖苷类衍生物11a~11c和12a~12c, 经水解脱去保护基团, 得到目标产物β-榄香烯含S糖苷13a~13c及其类似物β-榄香烯含Se糖苷14a~14c. 目标化合物的结构经IR, 1H NMR, 13C NMR, 77Se NMR, HRMS等方法确证.