淀粉聚乙二醇葡糖苷的合成

用玉米淀粉与聚乙二醇在酸催化下反应合成了聚乙二醇葡糖苷,考察了反应温度、醇糖摩尔比、催化剂用量、反应时间和反应压力等因素对反应的影响,结果表明在较合适的工艺条件下,6.6 kPa,130℃,120 m in,n(催化剂)n∶(糖元)n∶(聚乙二醇)=0.03∶1∶1,淀粉转化率可达95%。     

大豆异黄酮糖苷水解研究进展

该文在介绍大豆异黄酮的组成、化学结构、特性及生理功能基础上,详细介绍水解法制备大豆异黄酮苷元原理、工艺流程、大豆异黄酮苷元分离纯化及检测方法。     

Acetylated Xylan Degradation by Glycoside Hydrolase Family 10 and 11 Xylanases from the White-rot Fungus Phanerochaete chrysosporium

Endo-type xylanases are key enzymes in microbial xylanolytic systems, and xylanases belonging to glycoside hydrolase (GH) families 10 or 11 are the major enzymes degrading xylan in nature. These enzymes have typically been characterized using xylan prepared by alkaline extraction, which removes acetyl sidechains from the substrate, and thus the effect of acetyl groups on xylan degradation remains unclear. Here, we compare the ability of GH10 and 11 xylanases, PcXyn10A and PcXyn11B, from the white-rot basidiomycete Phanerochaete chrysosporium to degrade acetylated and deacetylated xylan from various plants. Product quantification revealed that PcXyn10A effectively degraded both acetylated xylan extracted from Arabidopsis thaliana and the deacetylated xylan obtained by alkaline treatment, generating xylooligosaccharides. In contrast, PcXyn11B showed limited activity towards acetyl xylan, but showed significantly increased activity after deacetylation of the xylan. Polysaccharide analysis using carbohydrate gel electrophoresis showed that PcXyn11B generated a broad range of products from native acetylated xylans extracted from birch wood and rice straw, including large residual xylooligosaccharides, while non-acetylated xylan from Japanese cedar was readily degraded into xylooligosaccharides. These results suggest that the degradability of native xylan by GH11 xylanases is highly dependent on the extent of acetyl group substitution. Analysis of 31 fungal genomes in the Carbohydrate-Active enZymes database indicated that the presence of GH11 xylanases is correlated to that of carbohydrate esterase (CE) family 1 acetyl xylan esterases (AXEs), while this is not the case for GH10 xylanases. These findings may imply co-evolution of GH11 xylanases and CE1 AXEs.     

糖及糖苷功能配合物的研究进展

主要综述了糖及糖苷功能配合物的研究现状 ,并探讨了其生物功能、合成及表征     

思茅引种催吐萝芙木的化学成分研究

从加纳引种思茅的催吐萝芙木(Rauvolfia vomitoriaAfzel)根的乙醇提取物分别在pH=2和pH=9时,用氯仿萃取,从中得到了14个化合物,经波谱分析鉴定为:α-onocerin(1)、methyl 3,4,5-trimethoxycinnamate(2)、betulinic acid(3)、3β,22E,22S-stigmasta-5,22-dien-3-O-β-D-glucopyranoside(4)、loganic acid(5)、7,2′-O-diacetylloganic acid(6)、mitoridine(7)、10,11-dimethoxy-α-yohimbine(8)、isoreserpiline(9)、19-epiajmalicine(10)、10,11-dimethoxy-19-epiajmalicine(11)、reserpine(12)、poke-weed cerebroside(13)、β-sitoterol(14)。其中化合物1、2、3、4、6、13为首次从该属植物中分离得到。     

The Structure of Stable Cellulolytic Consortia Isolated from Natural Lignocellulosic Substrates

Recycling plant matter is one of the challenges facing humanity today and depends on efficient lignocellulose degradation. Although many bacterial strains from natural substrates demonstrate cellulolytic activities, the CAZymes (Carbohydrate-Active enZYmes) responsible for these activities are very diverse and usually distributed among different bacteria in one habitat. Thus, using microbial consortia can be a solution to rapid and effective decomposition of plant biomass. Four cellulolytic consortia were isolated from enrichment cultures from composting natural lignocellulosic substrates—oat straw, pine sawdust, and birch leaf litter. Enrichment cultures facilitated growth of similar, but not identical cellulose-decomposing bacteria from different substrates. Major components in all consortia were from Proteobacteria, Actinobacteriota and Bacteroidota, but some were specific for different substrates—Verrucomicrobiota and Myxococcota from straw, Planctomycetota from sawdust and Firmicutes from leaf litter. While most members of the consortia were involved in the lignocellulose degradation, some demonstrated additional metabolic activities. Consortia did not differ in the composition of CAZymes genes, but rather in axillary functions, such as ABC-transporters and two-component systems, usually taxon-specific and associated with CAZymes. Our findings show that enrichment cultures can provide reproducible cellulolytic consortia from various lignocellulosic substrates, the stability of which is ensured by tight microbial relations between its components.     

Natural and low-caloric rebaudioside A as a substitute for dietary sugars: A comprehensive review

For health and safety concerns, traditional high-calorie sweeteners and artificial sweeteners are gradually replaced in food industries by natural and low-calorie sweeteners. As a natural and high-quality sugar substitute, steviol glycosides (SvGls) are continually scrutinized regarding their safety and application. Recently, the cultivation of organic stevia has been increasing in many parts of Europe and Asia, and it is obvious that there is a vast market for sugar substitutes in the future. Rebaudioside A, the main component of SvGls, is gradually accepted by consumers due to its safe, zero calories, clear, and sweet taste with no significant undesirable characteristics. Hence, it can be used in various foods or dietary supplements as a sweetener. In addition, rebaudioside A has been demonstrated to have many physiological functions, such as antihypertension, anti-diabetes, and anticaries. But so far, there are few comprehensive reviews of rebaudioside A. In this review article, we discuss the physicochemical properties, metabolic process, safety, regulatory, health benefits, and biosynthetic pathway of rebaudioside A and summarize the modification methods and state-of-the-art production and purification techniques of rebaudioside A. Furthermore, the current problems hindering the future production and application of rebaudioside A are analyzed, and suggestions are provided.     

Hydrothermal conversion of fructose to lactic acid and derivatives: Synergies of metal and acid/base catalysts

With increasing strict regulation on single-use plastics, lactic acid (LA) and alkyl lactates, as essential monomers for bio-degradable polylactic acid (PLA) plastic products, have gained worldwide attention in both academia and industry. While LA is still dominantly produced through fermentation processes from start, chemical synthesis from cellulosic biomass remains a grand challenge, owing to poor selectivity in activating C-H and C-C bonds in sugar molecules. To our best knowledge, recent publications have been focused on hydrothermal conversion of glucose to LA, while this review summarizes the highlights on direct thermal conversion of fructose as starting material to LA and derivatives. In particular, the synergies of metal/metal cations and acid/base catalysts will be critically revised on retro-aldol and dehydration reactions. This work will provide insights into rational design of active and selective catalysts for the production of carboxylic acids from biomass feedstocks.     

Ligand-Directed Chemistry on Glycoside Hydrolases – A Proof of Concept Study

Selective covalent labelling of enzymes using small molecule probes has advanced the scopes of protein profiling. The covalent bond formation to a specific target is the key step of activity-based protein profiling (ABPP), a method which has become an indispensable tool for measuring enzyme activity in complex matrices. With respect to carbohydrate processing enzymes, strategies for ABPP so far involve labelling the active site of the enzyme, which results in permanent loss of activity. Here, we report in a proof of concept study the use of ligand-directed chemistry (LDC) for labelling glycoside hydrolases near – but not in – the active site. During the labelling process, the competitive inhibitor is cleaved from the probe, departs the active site and the enzyme maintains its catalytic activity. To this end, we designed a building block synthetic concept for small molecule probes containing iminosugar-based reversible inhibitors for labelling of two model β-glucosidases. The results indicate that the LDC approach can be adaptable for covalent proximity labelling of glycoside hydrolases.