Late-stage O-glycosylation has rapidly evolved into a paradigm-shifting strategy for the total synthesis of architecturally complex and pharmacologically privileged natural products. Unlike early-stage glycosylation, which is often constrained by protecting-group manipulations and linear synthetic planning, late-stage installation of glycosidic units offers unprecedented flexibility, enabling chemists to directly fine-tune biological performance at advanced synthetic stages. By strategically appending glycosyl residues onto fully elaborated aglycone scaffolds, this approach allows for rational modulation of solubility, metabolic stability, cell permeability, and target selectivity-properties that dictate clinical success yet are notoriously difficult to optimize through conventional synthetic modifications. This chapter highlights the conceptual evolution and methodological breakthroughs underpinning site- and stereoselective late-stage O-glycosylation. Recent innovations in transition-metal catalysis, organocatalytic activation, enzyme-mediated glycosyl transfer, and protecting-group-free tactics have expanded the synthetic toolbox, permitting precise glycosidic bond construction in densely functionalized settings. Case studies spanning anticancer anthracyclines, immunosuppressive macrolides, and antimicrobial glycopeptides illustrate how strategic glycosylation can reshape structure-activity relationships (SAR), improve therapeutic indices, and unlock access to glycoengineered analogues with superior drug-like profiles. Beyond synthetic utility, late-stage O-glycosylation provides a powerful lens through which chemical biology and medicinal chemistry converge. By transforming natural product frameworks into customizable molecular platforms, this strategy not only bridges the divide between synthetic innovation and translational drug discovery but also sets the stage for next generation glycomimetic therapeutics. Looking forward, integration of late-stage glycosylation with automated synthesis, chemoenzymatic platforms, and machine-learning-driven reaction design is poised to accelerate the discovery of tailor-made glycosylated drugs, cementing its role as a cornerstone of 21st-century molecular medicine.
Glycosyl esters constitute a versatile class of molecules with significant roles in medicinal chemistry, natural product synthesis, and materials science. However, achieving their efficient synthesis continues to be a challenge, largely due to difficulties in controlling stereoselectivity and accommodating diverse functional groups. This chapter surveys recent developments in the stereoselective synthesis of glycosyl esters derived from various glycosyl donors. The discussion is organized around key activation strategies, Lewis acid catalysis, organocatalysis, and metal-free methods, highlighting their mechanistic foundations, catalytic efficiencies, and substrate scopes. This chapter aims to serve as a resource for researchers seeking to develop efficient, selective, and environmentally responsible routes to glycosyl esters.
Stereoselective glycosylation remains one of the most powerful strategies for constructing biologically active molecules, yet precise control over anomeric selectivity continues to be a formidable challenge. Recently, visible-light-driven, photocatalyst-free protocols for generating glycosyl radicals have emerged as a reliable and sustainable alternative to stereoselective glycoside synthesis. The introduction of a wide variety of radical precursors has significantly broadened the scope of this chemistry, enabling access to structurally diverse and biologically relevant glycosidic architectures. These methods proceed under mild conditions, display excellent tolerance toward sensitive functional groups, and are inherently aligned with green chemistry principles. In this chapter, we discuss recent progress in photocatalyst-free glycosyl radical generation, with particular attention to innovative radical precursors and their applications in the construction of glycosides.
The stereoselective synthesis of 1,2-cis glycosidic linkages remains a vital challenge in carbohydrate chemistry owing to the lack of reliable anomeric directing effects. Intramolecular aglycon delivery (IAD) has emerged as an effective strategy to address this problem by employing temporary tethers that guide the glycosyl acceptor toward the anomeric center with high stereocontrol. As the methodology evolved, IAD has been advanced through the introduction of diverse acetal and ketal linkages, including dimethyl, dimethylsilyl, benzylidene, and iodoalkylidene tethers, enabling the efficient synthesis of challenging linkages such as β-mannopyranosides, β-L-rhamnosides, and α-glucosides. Further progress has been facilitated by the development of common alcohol protecting-group as tether, particularly p-methoxybenzyl (PMB) and 2-naphthylmethyl (NAP) groups, which have improved both the versatility and operational simplicity of IAD. A key advantage of this methodology lies in its ability to deliver exclusive 1,2-cis selectivity without generating anomeric mixtures, while also being amenable to iterative assembly of complex glycans. This chapter outlines the development, scope, and mechanistic insight of IAD, highlighting its limitations as well as its potential applications in the stereoselective synthesis of bioactive O-glycosides and structurally complex glycans.
As fundamental structural and functional units of biological systems, carbohydrates are recognized as indispensable to diverse physiological processes. Recent advances in the synthesis of well-defined glycopolymers enabled the development of biomimetic analogues that mimic natural glycans through cluster effects. These compounds have demonstrated critical significance in elucidating carbohydrate-mediated physiological mechanisms, identifying pathogenic pathways, and developing novel therapeutic strategies. Carbohydrate-protein interactions mediated by receptors such as ASGPR, DC-SIGN, M6PR, HA/NA, FimH, MR (CD206), Galectins, GLUTs, and BCR constitute the molecular basis for glycopolymer functionality and applications. Substantial explorations have been conducted in antimicrobial/antiviral applications and advanced drug delivery systems including gene therapy, antibody-protein conjugation, and small molecule encapsulation. These collective endeavors aim to expand the therapeutic frontiers of glycopolymers while offering transformative insights for next-generation pharmaceutical development.
Cancer causes dysregulation of apoptosis, a genetically controlled mechanism necessary for growth and homeostasis, which permits unchecked cell division and resistance to cell death. The Warburg effect, metabolic flexibility, and glucose reliance of malignant cells are highlighted in this chapter's analysis of the molecular interactions among insulin/IGF-1 signaling, carbohydrate metabolism, and tumor biology. We examine the data relating increased tumor survival, proliferation, and metastasis to hyperglycemia, hyperinsulinemia, and inflammatory cytokines. In the context of primary, secondary, and tertiary cancer prevention across a variety of tumor types, including colorectal, prostate, breast, and head and neck cancers, the epidemiological and experimental literature on dietary carbohydrates-from simple sugars to complex fibers-is assessed. There is discussion of mechanistic processes involving altered metabolism, hormonal regulation, and acidity of the microenvironment. While recognizing discrepancies and data gaps that need more study, the chapter emphasizes dietary modification-specifically, limiting carbohydrates and increasing fiber intake-as a promising adjunct in cancer prevention and survivorship.
Carbohydrates are one of the most significant macronutrients in the human diet. They are necessary for energy metabolism and health. However, the prevalence and progression of cardiovascular diseases (CVD) have been associated with the intake of excessive refined sugars and carbohydrates. This paper provides an overview of the complex relationship between carbohydrates and CVD. Highlights include how simple sugars, starches, and fibers can affect the cardiovascular system. Excessive consumption of high glycemic index, and refined carbohydrates can lead to insulin resistance, dyslipidemia and chronic inflammation which all increase the risk of atherosclerosis and other cardiovascular diseases. On the contrary, fiber-rich carbohydrates from fruits, vegetables, and whole grains have been shown to have favorable effects on blood pressure, vascular function, and lipids, and contributes to a lower risk of CVD. The review also examines the role of functional foods, low glycemic index diets, and carbohydrate restriction, and other current dietary modifications for the prevention and treatment of CVD. Additionally, personalized diet therapy, as a potential new strategy for reducing carbohydrate-related CVD risk and new therapeutic possibilities where pharmacological agents have been developed to target these metabolic pathways.
Carbonic anhydrases (CAs) are a family of metalloenzymes that catalyze the reversible conversion of carbon dioxide into bicarbonate and proton, a key reaction involved in numerous physiological and pathological processes. Over the past few decades, CAs have attracted considerable attention as therapeutic targets for conditions such as glaucoma, epilepsy, and cancer. The development of highly potent and selective inhibitors has consequently become a major focus, leading to the identification of novel drug candidates. Among the various strategies explored, the design of carbohydrate-based carbonic anhydrase inhibitors (CAIs) has proven to be particularly versatile for achieving selective CA targeting. The introduction of glycosyl groups as hydrophilic moieties into different CAI frameworks has resulted in the discovery of diverse sugar-based CAIs with significant inhibitory activity. This chapter provides an overview of carbohydrate-based CAIs reported to date.
Sucrose, an inexpensive starting material available in virtually unlimited quantities, affords entry into a variety of novel and useful carbohydrate compounds. Selective protection of the secondary hydroxyl groups gives rise to a group of O-benzyl-protected intermediates that are useful in the synthesis of chiral phosphines and amino compounds of interest in the study of biological systems. The benzyl-protected fine chemicals are also key components in the synthesis of crown, thia-crown, and aza-crown compounds. Sophisticated molecular cages and molecular switches can be prepared from fine-tuned intermediates derived from selectively protected sucrose derivatives.
The article leads the reader through an up-to-date presentation of the concepts, developments, and main applications of computational modeling to study protein-carbohydrate interactions. It follows with the presentation of some current issues and perspectives arising from the expected evolution of generic methodological developments in deep learning, immersive analytics, and virtual reality for molecular visualization and data management. Such methodological developments for macromolecular interactions would greatly benefit a wide range of scientific endeavors in the field of carbohydrate chemistry and biochemistry, including the following interrelated efforts dealing with highly crowded media, with examples concerning glycoside transferases, the extracellular matrix, and the exploration of interactions between complex carbohydrates and intrinsically disordered proteins.
Lectins are predominantly oligomeric proteins with several binding sites per molecule. Glycoconjugates are their natural ligands, which often possess multiple binding epitopes. Thus, lectin-glycoconjugate interactions are mostly multivalent in nature. The mechanism of multivalent binding is fundamentally different from those described for monovalent interactions in textbooks and research papers. Over the years, binding studies that make use of different lectins and a variety of multivalent glycoconjugate ligands were conducted in order to understand the underlying principles of multivalency. Starting with seemingly simple synthetic multivalent analogs, systematic studies were carried out using natural glycoconjugate ligands with increasing valency and complexity. Those ligands included multivalent glycoproteins, polyvalent polysaccharides, including glycosaminoglycans, as well as supra-valent mucins and proteoglycans. Models and mechanisms of multivalent binding derived from quantitative data are summarized in the present updated review.
The biological signaling properties of lectins, which are carbohydrate-binding proteins, are due to their ability to bind and cross-link multivalent glycoprotein receptors on the surface of normal and transformed cells. While the cross-linking properties of lectins with multivalent carbohydrates and glycoproteins are relatively well understood, the mechanisms of binding of lectins to multivalent glycoconjugates are less well understood. Recently, the thermodynamics of binding of lectins to synthetic clustered glycosides, a multivalent globular glycoprotein, and to linear glycoproteins (mucins) have been described. The results are consistent with a dynamic binding mechanism in which lectins bind and jump from carbohydrate to carbohydrate epitope in these molecules. Importantly, the mechanism of binding of lectins to mucins is similar to that for a variety of protein ligands binding to DNA. Recent analysis also shows that high-affinity lectin-mucin cross-linking interactions are driven by favorable entropy of binding that is associated with the bind and jump mechanism. The results suggest that the binding of ligands to biopolymers, in general, may involve a common mechanism that involves enhanced entropic effects which facilitate binding and subsequent complex formation including enzymology.
Fructosamine has long been considered as a key intermediate of the Maillard reaction, which to a large extent is responsible for specific aroma, taste, and color formation in thermally processed or dehydrated foods. Since the 1980s, however, as a product of the Amadori rearrangement reaction between glucose and biologically significant amines such as proteins, fructosamine has experienced a boom in biomedical research, mainly due to its relevance to pathologies in diabetes and aging. In this chapter, we assess the scope of the knowledge on and applications of fructosamine-related molecules in chemistry, food, and health sciences, as reflected mostly in publications within the past decade. Methods of fructosamine synthesis and analysis, its chemical, and biological properties, and degradation reactions, together with fructosamine-modifying and -recognizing proteins are surveyed.
The proper conformation and orientation of membrane protein integration in cells is an important biological event. Interestingly, a new factor named MPIase (membrane protein integrase) was proven essential in this process in Escherichia coli, besides proteinaceous factors, such as Sec translocons and an insertase YidC. A combination of spectroscopic analyses and synthetic work has revealed that MPIase is a glycolipid despite its enzyme-like activity. MPIase has a long glycan chain comprised of repeating trisaccharide units, a pyrophosphate linker, and a diacylglycerol anchor. In order to determine the mechanism of its activity, we synthesized a trisaccharyl pyrophospholipid termed mini-MPIase-3, a minimal unit of MPIase, and its derivatives. A significant activity of mini-MPIase-3 indicated that it involves an essential structure for membrane protein integration. We also analyzed intermolecular interactions of MPIase or its synthetic analogs with a model substrate protein using physicochemical methods. The structure-activity relationship studies demonstrated that the glycan part of MPIase prevents the aggregation of substrate proteins, and the 6-O-acetyl group on glucosamine and the phosphate of MPIase play important roles for interactions with substrate proteins. MPIase serves at an initial step in the Sec-independent integration, whereas YidC, proton motive force, and/or SecYEG cooperatively function(s) with MPIase at the following step in vivo. Furthermore, depletion of the biosynthetic enzyme demonstrated that MPIase is crucial for membrane protein integration and cell growth. Thus, we elucidated new biological functions of glycolipids using a combination of synthetic chemistry, biochemistry, physicochemical measurements, and molecular-biological approaches.
The synthesis of sialic acid-containing molecules has posed a formidable challenge to carbohydrate chemists for over 50 years. Our research group has intensively searched for robust chemistry to enable the construction of a broad spectrum of sialic acid-containing molecules to advance the understanding and application of their biological functions. Herein, we describe our research findings on the development of sialic acid donors for α-selective glycosidation and the chemical synthesis of sialic acid- containing molecules, with a special focus on gangliosides and their fluorescent probes.
Professor Hidetoshi Yamada, who demonstrated his creativity in various respects, passed away in November 2019. His research targets were highly diverse, including sweet saponins, ellagitannins, novel cyclodextrins, and conformationally distorted donors for stereoselective glycosylations. In memory of his creativity, this chapter highlights his prominent achievements in carbohydrate chemistry.
This chapter describes the 21-year history of research conducted by Professor Hidetoshi Yamada. Sugars often exist in a six-membered ring structure, and the equatorial-rich chair conformation is stable. In contrast, its pyranose ring in a biological glycosylation is easily deformed and changed by various factors. Therefore, controlling the steric conformation of the pyranose ring is a great starting point to influence the stereoselectivity of the glycosylation reaction. His research developed stereoselective glycosylation reactions by deforming the sugar ring from the most stable equatorial-rich chair conformation. Initially, the research began to restrict the pyranose ring into the axial-rich chair form. The evolution to the locked skew-boat system allowed highly selective glycosylation by bulky silyl-protected or o-xylylene-bridged glycosyl donors. Development of the 1,1’-(ethane-1,2-diyl)dibenzene-2,2’-bis(methylene) bridging group created that which is known as the supple conformation system, which when combined with an α-selective glycosylation, led to the remarkable synthesis of the smallest cyclodextrins on record. Professor Yamada's consistent research in these areas willfully contributed to the development of carbohydrate chemistry.
The concept of “therapeutic in vivo synthetic chemistry” refers to chemical synthesis in living systems using new-to-nature reactions for the treatment or diagnosis of diseases. This review summarizes our development of therapeutic in vivo synthetic chemistry using glycan-modified human serum albumin (glycoHSA) and utilizing the selective glycan-targeting and metal protective effects of metal catalysts. The four artificial metalloenzymes with glycoHSA provided good cancer treatment results based on on-site drug synthesis and selective cell-tagging strategies. Thus, we propose that therapeutic in vivo synthetic chemistry using glycoHSA as a new modality of therapy or diagnosis is applicable to a wide range of diseases.
In nucleophilic reactions using sugars as electrophiles, i.e., glycosyl donors, their conformation affects the generation rate or stability of the glycosyl cation intermediates and determines at which side of the SN2-SN1 borderline and at what rate the reaction occurs. In addition, changes in the conformation create the steric or stereoelectronic effects of the substituents, which also change the reaction rate and stereoselectivity. Bulky silyl protecting groups, uronic acid esters, and transannular structures have been utilized to change the conformation. Consequently, reactions with unique reactivities and stereoselectivities have been developed. In this chapter, a discussion of the reaction mechanisms relating stereoselectivity to conformation is provided.
Work by the author and colleagues has been focused on the development of pseudo-glycans (pseudo-glycoconjugates), in which the O-glycosidic linkage of the natural-type glycan structure is replaced by a C-glycosidic linkage. These analogs are not degraded by cellular glycoside hydrolases and are thus expected to be useful molecular tools that may maintain the original biological activity for a long period in the cell. However, their biological potential is not yet well understood because only a few pseudo glycans have so far been synthesized. This article aims to provide a bird's-eye view of our recent studies on the creation of C-glycoside analogs of ganglioside GM3 based on the CHF-sialoside linkage, and summarizes the chemical insights acquired during our stereoselective synthesis of the C-sialoside bond, ultimately leading to pseudo-GM3. Conformational analysis of the synthesized CHF-sialoside disaccharides confirmed that the anticipated conformational control by F-atom introduction was successful, and furthermore, enhanced the biological activity. In order to improve access to C-glycoside analogs based on pseudo-GM3, it is still important to streamline the synthesis process. With this in mind, we designed and developed a direct C-glycosylation method using atom-transfer radical coupling, and employed it in syntheses of pseudo-isomaltose and pseudo-KRN7000.
