Glycosylation of cardiosteroids

The review considers methods of glycosylating cardiosteroids with the aim of obtaining compounds possessing a specific action on the cardiac muscle.Institute of the Chemistry of Plant Substances, Academy of Sciences of the UzbekSSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 547–563, September–October, 1984.     

A new panaxadiol from the acid hydrolysate of Panax ginseng

A new panaxadiol(compound 1) was obtained from the acid hydrolysate of the total ginsenosides of Panax ginseng C.A.Meyer (Araliaceae).On the basis of spectroscopic data and single-crystal X-ray diffraction data,its chemical structure was elucidated to be dammar-(E)-20(22)-ene-3β,12β,25-triol.     

Glycosylation and metastases

The change of cellular glycosylation is one of the key events in malignant transformation and neoplastic progression, and tumor‐related glycosylation alterations are promising targets in both tumor diagnosis and therapy. Both malignant transformation and neoplastic progression are the consequence of gene expression alterations and alterations in protein expression. Micro environmental factors such as extracellular matrix (ECM) also play an important role in their growth and metastasis. Tumor‐associated glycans are important biomarker candidates for cancer diagnosis and prognosis, and analytical methods for their detection were developed recently. Glycoproteomics that use mass spectrometry for identification of cancer antigens and structural analysis of glycans play a key role in the investigation of changes of glycosylation during malignant transformation and tumor development and metastasis. Deep understanding of glycan remodeling in cancer and the role of glycosyltransferases that are involved in this process will require a detailed profiling of glycosylation patterns of tumor cells, and corresponding analytical methods for their detection were developed.     

Statistical Analysis of Glycosylation Reactions

Chemical synthesis is one of the practical approaches to access carbohydrate-based natural products and their derivatives with high quality and in a large quantity. However, stereoselectivity during the glycosylation reaction is the main challenge because the reaction can generate both α- and β-glycosides. The main focus of the present article is the concept of recent mechanistic studies that have applied statistical analysis and quantitation for defining stereoselective changes during the reaction process. Based on experimental evidence, a detailed discussion associated with the mechanism and degree of influence affecting the stereoselective outcome of glycosylation is included.     

Efficient synthesis of panaxadiol derivatives using continuous-flow microreactor and evaluation of anti-tumor activity

An efficient method has been developed for the synthesis of a series of(20R)-panaxadiol derivatives(4a–w) using a continuous-flow microreactor.The antitumor activities of the newly synthesized compounds were evaluated in vitro in two human prostate adenocarcinoma tumor cell lines(i.e.,PC-3and LNCa P cells),and their cytotoxicities were evaluated using a standard MTT assay.Compounds 4c,4h,4p,4q and 4s exhibited higher antitumor activities toward PC-3 cell line than panaxadiol,which was used as a reference standard.     

Transition-Metal-Mediated Glycosylation with Thioglycosides

Thioglycosides are among the most common glycosyl donors that find broad application in the synthesis of glycans and glycoconjugates. However, the requirement for toxic and/or large access of activators needed for common glycosylations with thioglycosides remains a notable drawback. Due to the increased awareness of the chemical waste impact on the environment, synthetic studies have been driven by the goal of finding non-toxic reagents. The main focus of this review is to highlight recent methods for thioglycoside activation that rely on transition metal catalysis.     

Glycosylation of betulin acetates with glycals

Betulin 2-deoxy-α-d-, 2-deoxy-α-l-, and 2,6-dideoxy-α-l-arabino-hexopyranosides were synthesized by acid-catalyzed glycosylation (cationite in the H⁺ form, LiBr) of betulin 3- and 28-monoacetates with glycal acetates. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 531–534, March, 1998.     

光促进的糖基化反应研究进展

糖类化合物与蛋白质、核酸均为基本的生命物质.糖不仅是生物体内的能量来源与结构物质，而且在许多生化过程（分子间识别、细胞间信息传递、免疫应答反应、细胞的分化和凋亡等）中也发挥着极为重要的作用.相较于核酸和蛋白质，糖类由于其种类的多样性和结构的复杂性，难有统一、高效的合成方法.伴随着光化学反应在有机合成中的应用，光促进的糖基化反应也吸引了越来越多科研工作者的注意.主要根据光促进糖基化反应使用的光源（紫外光、可见光）、催化剂（金属催化剂、非金属催化剂）的类型对近年来光促进糖基化反应的发展和应用进行分类总结和展望.     

Azidosphingosine Glycosylation in Glycosphingolipid Synthesis

Abstract

The 3-O-protected azide derivatives of C₁₈-sphingcsine s me 1A-1C reacted with O-acyl protected trichloroacetimidates of D-glucose, D-galactose, and laczose to afford the corresresponding β-glycosides in high yields. Ortho-ester formation in the case of O-acetyl compound could he avoided by increasing the amount of bcrcn trifluoride diethyl ether catalyst. Deprotection. and azido group reduction provided the psychosines of D-gluccse, D-galactose, and lactose (5, 10, and 15), which are versatile intermediates for the attachment of different fatty acii residues. With hexadecanoyl chloride, for instance, the corresponding glycosphingolipids 6, 11, and 16, respectively, were obtained.     

Glycosylation of cyclosieversiosides A and H

Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan. Tashkent Pharmaceutical Institute. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 621–622, July–August, 1993.     

Enzymatic Glycosylation of Branched Symmetrical Non-Carbohydrate Polyols

Abstract

Three glycosidases, α-mannosidase from Jack beans, β-galactosidase from Aspergillus oryzae and β-N-acetylhexosaminidase from Aspergillus oryzae were evaluated for their ability to catalyze the glycosylation of non-saccharidic polyols. A series of monoglycosylated derivatives of tris(2-aminoethyl)cyanuric acid, pentaerythritol and bis(hydroxymethyl)benzene were obtained in pure form and characterized by NMR-spectroscopy.     

Studies on the Glycosylation of N-Acetylneuraminic Acid

Abstract

Glycal derivatives of N-acetylneuraminic acid were prepared and their N-iodosuccinimide-mediated glycosylation shown to proceed only with most reactive alcohols, Their reduced enol ether reactivity is attributed to the α unsaturated ester reature. Thus several reduced glycal derivatives were synthesized. These couid be glycosyiatec with simple alcohols as well as otner saccnarides as aglycones in averaae to modest yields with the trans-diaxiai additions compounas prevailing. A number or selective and specific prepparation led to both the anomeric phenylthioglycosides or N dcety Ineuraminic acid. These could be used in phenylmercurl triflate-promoted glycosylations to afford several derivatives.     

Recent Advances in Transition Metal-Catalyzed Glycosylation

Having access to mild and operationally simple techniques for attaining carbohydrate targets will be necessary to facilitate advancement in biological, medicinal, and pharmacological research. Even with the abundance of elegant reports for generating glycosidic linkages, stereoselective construction of α- and β-oligosaccharides and glycoconjugates is by no means trivial. In an era where expanded awareness of the impact we are having on the environment drives the state-of-the-art, synthetic chemists are tasked with developing cleaner and more efficient reactions for achieving their transformations. This movement imparts the value that prevention of waste is always superior to its treatment or cleanup. This review will highlight recent advancement in this regard by examining strategies that employ transition metal catalysis in the synthesis of oligosaccharides and glycoconjugates. These methods are mild and effective for constructing glycosidic bonds with reduced levels of waste through utilization of sub-stoichiometric amounts of transition metals to promote the glycosylation.     

Optimal Synthetic Glycosylation of a Therapeutic Antibody

Glycosylation patterns in antibodies critically determine biological and physical properties but their precise control is a significant challenge in biology and biotechnology. We describe herein the optimization of an endoglycosidase‐catalyzed glycosylation of the best‐selling biotherapeutic Herceptin, an anti‐HER2 antibody. Precise MS analysis of the intact four‐chain Ab heteromultimer reveals nonspecific, non‐enzymatic reactions (glycation), which are not detected under standard denaturing conditions. This competing reaction, which has hitherto been underestimated as a source of side products, can now be minimized. Optimization allowed access to the purest natural form of Herceptin to date (≥90 %). Moreover, through the use of a small library of sugars containing non‐natural functional groups, Ab variants containing defined numbers of selectively addressable chemical tags (reaction handles at Sia C1) in specific positions (for attachment of cargo molecules or “glycorandomization”) were readily generated.