Recent progress in the synthesis of glycosphingolipids

To accelerate the biological study and application of the diverse functions of glycosphingolipids (GSLs), the production of structurally defined GSLs has been greatly demanded. In this review, we focus on the recent developments in the chemical and chemoenzymatic synthesis of GSLs. In the chemical synthesis section, the syntheses based on glucosyl ceramide cassette, late-stage sialylation, and diversity-oriented strategies for GSLs or ganglioside synthesis are highlighted, which delivered terpioside B, fluorescent sialyl lactotetraosyl ceramide, and analogs of lacto-ganglio-series GSLs, respectively. In the chemoenzymatic synthesis section, the synthesis of ganglioside GM1 by multistep one-pot multienzyme method and the total synthesis of highly complex ganglioside LLG-5 using a water-soluble lactosyl ceramide as a key substrate for enzymatic sialylation are described.

Chemical Synthesis of Gangliosides

Synthetic methodologies for gangliosides have evolved over the past three decades. The strategies for constructing ganglioside skeletons can generally be classified as late-stage ceramide coupling, the glucosyl ceramide cassette strategy, or late-stage sialylation. Using these synthetic strategies, numerous natural gangliosides and their structural analogs, including functional probes, have been synthesized. This chapter describes the synthetic strategies for gangliosides and provides examples of the total synthesis of several gangliosides using each strategy.

Experimental and computational characterization of dynamic biomolecular interaction systems involving glycolipid glycans

On cell surfaces, carbohydrate chains that modify proteins and lipids mediate various biological functions, which are exerted not only through carbohydrate-protein interactions but also through carbohydrate-carbohydrate interactions. These glycans exhibit considerable degrees of conformational variability and often form clusters providing multiple binding sites. The integration of nuclear magnetic resonance spectroscopy and molecular dynamics simulation has made it possible to delineate the dynamical structures of carbohydrate chains. This approach has facilitated the remodeling of oligosaccharide conformational space in the prebound state to improve protein-binding affinity and has been applied to visualize dynamic carbohydrate-carbohydrate interactions that control glycoprotein-glycoprotein complex formation. Functional glycoclusters have been characterized by experimental and computational approaches applied to various model membranes and artificial self-assembling systems. This line of investigation has provided dynamic views of molecular assembling on glycoclusters, giving mechanistic insights into physiological and pathological molecular events on cell surfaces as well as clues for the design and creation of molecular systems exerting improved glycofunctions. Further development and accumulation of such studies will allow detailed understanding and artificial control of the "glycosynapse" foreseen by Dr. Sen-itiroh Hakomori.

Development of lacto-series ganglioside fluorescent probe using late-stage sialylation and behavior analysis with single-molecule imaging

Gangliosides are a family of sialic-acid-containing glycosphingolipids that form dynamic domains (lipid rafts) with proteins in cell plasma membranes (PMs), and are involved in various biological processes. The dynamic behavior...

Conformational and Structural characterization of carbohydrates and their interactions studied by NMR

Carbohydrates, either free or as glycans conjugated with other biomolecules, participate in many essential biological processes. Their apparent simplicity in terms of chemical functionality hides an extraordinary diversity and structural complexity. Deeply deciphering at the atomic level their structures is essential to understand their biological function and activities, but it is still a challenging task in need of complementary approaches and no generalized procedures are available to address the study of such complex, natural glycans. The versatility of Nuclear Magnetic Resonance spectroscopy (NMR) often makes it the preferred choice to study glycans and carbohydrates in solution media. The most basic NMR parameters, namely chemical shifts, coupling constants and nuclear Overhauser effects, allow defining short or repetitive chain sequences and characterize their structures and local geometries either in the free state or when interacting with other biomolecules, rendering additional information on the molecular recognition processes. The increased accessibility to carbohydrate molecules extensively or selectively labeled with 13C boosts the resolution and detail that analyzed glycan structures can reach. In turn, structural information derived from NMR, complemented with molecular modeling and theoretical calculations can also provide dynamic information on the conformational flexibility of carbohydrate structures. Furthermore, using partially oriented media or paramagnetic perturbations, it has been possible to introduce additional long-range observables rendering structural information on longer and branched glycan chains. In this review, we provide examples of these studies and an overview of the recent and most relevant NMR applications in the glycobiology field.

Chemoenzymatic Total Synthesis of GM3 Gangliosides Containing Different Sialic Acid Forms and Various Fatty Acyl Chains

Gangliosides are sialic acid-containing glycosphingolipids that have been found in the cell membranes of all vertebrates. Their important biological functions are contributed by both the glycan and the ceramide lipid components. GM3 is a major ganglioside and a precursor for many other more complex gangliosides. To obtain structurally diverse GM3 gangliosides containing various sialic acid forms and different fatty acyl chains in low cost, an improved process was developed to chemically synthesize lactosyl sphingosine from an inexpensive l-serine derivative. It was then used to obtain GM3 sphingosines from diverse modified sialic acid precursors by an efficient one-pot multienzyme sialylation system containing Pasteurella multocida sialyltransferase 3 (PmST3) with in situ generation of sugar nucleotides. A highly effective chemical acylation and facile C18-cartridge purification process was then used to install fatty acyl chains of varying lengths and different modifications. The chemoenzymatic method represents a powerful total synthetic strategy to access a library of structurally defined GM3 gangliosides to explore their functions.

Advanced Chemical Methods for Stereoselective Sialylation and Their Applications in Sialoglycan Syntheses

Sialic acid is an important component of cell surface glycans, which are responsible for many vital body functions and should therefore be thoroughly studied to understand their biological roles and association with disorders. The difficulty of isolating large quantities of homogenous-state sialoglycans from natural sources has inspired the development of the corresponding chemical synthesis methods affording acceptable purities, yields, and amounts. However, the related syntheses are challenging because of the difficulties in α-glycosylation of sialic acid, which arises from its certain structural features such as the absence of a stereodirecting group at the C3 position and presence of carboxyl group at the anomeric position. Moreover, the structural complexities of sialoglycans with diverse numbers and locations of sialic acid on the glycan chains pose additional barriers. Thus, efficient α-stereoselective routes to sialosides remain highly sought after, although various types of sialyl donors/acceptors have been developed for the straightforward synthesis of α-sialosides. Herein, we review the latest progress in the α-stereoselective synthesis of sialosides and their applications in the preparation of gangliosides and other sialoglycans.