The use of four different N-protected derivatives of 2-amino-2-deoxy-Dglucose
as donors and acceptors in glycosylation reactions were described in this work. It was formed the N-benzyloxycarbonyl (Cbz), N-pnitrobenzyloxycarbonyl (PNZ), N-phthalimido (Phth) and Ntetrachlorophthalimido (TCP) protecting glycosides. These were transformed into trichloroacetimidates as glycosyl donors. With the same N-protecting groups were syntheses also the 4-O-unprotected glycosyl acceptors in a one-pot reaction.
The glycosylation reactions were performed in the presence of BF3·Et3O as the
catalyst. The reactions with the chosen donors and acceptors furnished b(1-4)-
linked disaccharides in good yields.[...]
Table of Contents
1. Abstract
2. Introduction
2.1. Structure of a glycoside
2.2. N-protecting groups
2.3. N-protected glucosamine as a nucleophilic acceptor
2.4. N-protected glucosamine as electrophilic donor
2.5. Disaccharides
3. Objective
4. Results and discussion
4.1. Preparation of 3,4,6-Tri-O-acetyl-N-protected glucosamine derivatives
4.2. Synthesis of glycosyl acceptor
4.3. Synthesis of glycosyl trichloroacetimidates
4.4. Synthesis of disaccharides
5. Summary / Zusammenfassung
6. Experimental section
Research Objectives and Core Topics
The primary objective of this work is to provide an investigation into the synthesis and outcomes of protected disaccharides utilizing various N-protecting groups, with a focus on optimizing reaction conditions for D-glucosamine derivatives. The research explores the stereochemical control and synthetic efficiency required to produce specific β-linked disaccharides while assessing the role of different protecting groups in glycosylation.
- Synthesis and analysis of N-protected glucosamine monomers and acceptors.
- Evaluation of selective benzylation strategies for C6 and C3 positions.
- Comparison of different N-protecting groups (Cbz, PNZ, Phth, TCP) on glycosylation reactivity.
- Methodological optimization of the trichloroacetimidate strategy for donor preparation.
- Synthesis and characterization of β-(1→4)-linked disaccharides.
Excerpt from the Book
2. Introduction
This work will focus on carbohydrates, one of the four major classes of natural products. Besides lipids, proteins and nucleic acids the carbohydrates are the largest and most important group of naturally occurring organic compounds. They are the essential constituent of flora and fauna.
The carbohydrates have structural, protective and energy-storing functions; their roles in protein folding, regulation of hormones and enzyme activities, cell signalling, pathogen binding to host tissue and tumor cell metastasis are just a few selected examples.
Glycosides of amino sugars, a special group of glycoconjugates, are the main interest of this work. In nature 2-amino-2-deoxy glycosides are frequently encountered in glycoproteins and glycolipids. However, isolation of these amino glycosides from natural sources is a difficult task that often yields in a heterogeneous mixture of oligosaccharides.
Today the synthesis of oligosaccharides is a major objective because some oligosaccharides of 2-amino-2-deoxy-D-glucose are compounds of biological importance. The β-linked oligosaccharides are compounds which constitute for example building blocks of chitin, chitosan and glycan of glycoproteins such as human milk oligosaccharides or blood group substances contain many derivates of amino glycosides. Also antigen polysaccharides and lipopolysaccharides are often encountered with a β-D-glucosamine residue.
The variety of linkages that a sugar molecule can possess is greater when compared to the other natural biopolymers (peptide, proteins, etc.). The oligosaccharides part of the glycolipids or glycoproteins has more structural information in one building block than the rest of the lipid or protein. This causes severe problems in the synthesis. In general, all sugar function groups that are not involved in the reaction have to be masked before.
Summary of Chapters
1. Abstract: Provides a high-level overview of the synthesis of N-protected β-(1→4)-linked disaccharides using specific protecting groups and the trichloroacetimidate strategy.
2. Introduction: Discusses the biological importance of carbohydrates and the specific challenges involved in the synthetic assembly of 2-amino-2-deoxy glycosides.
3. Objective: Outlines the research goals, including the focus on comparing synthetic steps for acceptors and donors using various N-protecting groups.
4. Results and discussion: Details the experimental outcomes regarding the preparation of protected derivatives, the synthesis of acceptors and donors, and the subsequent glycosylation reactions.
5. Summary / Zusammenfassung: Recaps the core findings and synthetic methodologies applied throughout the study.
6. Experimental section: Lists the specific chemical procedures, materials, and characterization data used for the synthesized compounds.
Keywords
Carbohydrates, D-Glucosamine, N-protecting groups, Phthalimide, Cbz, PNZ, TCP, Glycosylation, Disaccharides, Trichloroacetimidate, Stereoselectivity, Benzylation, Synthesis, NMR-spectroscopy, Carbohydrate chemistry.
Frequently Asked Questions
What is the core focus of this research?
This work focuses on the chemical synthesis of β-(1→4)-linked disaccharides derived from D-glucosamine, specifically investigating the impact of different N-protecting groups on the glycosylation process.
What are the primary N-protecting groups investigated?
The research examines Benzyloxycarbonyl (Cbz), p-nitrobenzyloxycarbonyl (PNZ), phthalimido (Phth), and tetrachlorophthalimido (TCP) as protective groups for the amino functionality.
What is the main objective of the thesis?
The goal is to provide insight into the synthesis of protected disaccharides and compare the effectiveness of different synthetic pathways for both glycosyl acceptors and donors.
Which scientific method is predominantly used?
The synthesis employs the trichloroacetimidate method for the formation of glycosidic bonds, supported by regioselective benzylation techniques and Lewis acid catalysis.
What does the main body of the work cover?
It covers the systematic synthesis of glucosamine monomers, the optimization of N-protecting groups, the regioselective preparation of 3,6-di-O-benzyl acceptors, and the synthesis of donors leading to disaccharide coupling.
Which keywords define this work?
Key terms include Carbohydrate chemistry, N-protected glucosamine, glycosyl trichloroacetimidate, β-linkage, and protecting group strategies.
How does the phthalimido (Phth) group affect stereochemistry?
The Phth group demonstrated strong neighbouring group participation, consistently ensuring the exclusive formation of the desired β-anomer during glycosylation.
What difficulties were encountered with the PNZ and TCP groups?
Unlike the Cbz and Phth derivatives, the synthesis of 3,6-di-O-benzyl acceptors for PNZ and TCP groups proved more challenging, often resulting in only C6-benzylation.
- Citar trabajo
- Gerit Brüning (Autor), 2007, Synthesis of chitobioses with different N-protecting groups, Múnich, GRIN Verlag, https://www.grin.com/document/113983
