Synthesis of Heparin Oligosaccharides

Mild and General Protocol for Selective Deacetylation of Acetyl/Benzoyl-Protected Carbohydrates

Herein, we report a mild and general protocol for chemoselective deacetylation of mixed acetyl- and benzoyl-protected carbohydrates under mild acidic conditions. The protocol allows quick access to partially protected carbohydrates, which serve as versatile synthetic intermediates during the total synthesis of various mono- and oligosaccharide targets. The applicability of the developed protocol was successfully demonstrated on a range of carbohydrate substrates of various configurations and substitution patterns featuring functionalized aliphatic and aromatic aglycones. The protocol has shown excellent compatibility with the widely used O-anomeric protecting groups, prespacer aglycones, and thioglycoside glycosyl donors.

Dimethyl sulfate and diisopropyl sulfate as practical and versatile O-sulfation reagents

O-Sulfation is a vital post-translational modification in bioactive molecules, yet there are significant challenges with their synthesis. Dialkyl sulfates, such as dimethyl sulfate and diisopropyl sulfate are commonly used as alkylation agents in alkaline conditions, and result in the formation of sulfate byproducts. We report herein a general and robust approach to O-sulfation by harnessing the tunable reactivity of dimethyl sulfate or diisopropyl sulfate under tetrabutylammonium bisulfate activation. The versatility of this O-sulfation protocol is interrogated with a diverse range of alcohols, phenols and N-OH compounds, including carbohydrates, amino acids and natural products. The enhanced electrophilicity of the sulfur atom in dialkyl sulfates, facilitated by the interaction with bisulfate anion (HSO4-), accounts for this pioneering chemical reactivity. We envision that our method will be useful for application in the comprehension of biological functions and discovery of drugs.

Synthesis of Anticoagulant Pentasaccharide Fondaparinux via 3,5-Dimethyl-4-(2'-phenylethynylphenyl)phenyl Glycosides

Here, we disclosed a convenient procedure for the preparation of EPP [3,5-dimethyl-4-(2'-phenylethynylphenyl)phenyl] glycosides and their application to an effective synthesis of fondaparinux, the clinically approved anticoagulant heparin pentasaccharide. The use of EPP glycosides in the one-pot orthogonal glycosylation for the synthesis of heparin-like tetrasaccharides has also been achieved.

Synthesis, characterization, and heparin-binding study of a self-assembled p-cymene-Ru(II) metallocycle based on a 4-amino-1,8-naphthalimide Tröger's base supramolecular scaffold

We report the very first example of a self-assembled p-cymene-Ru(II) metallocycle based on a green emitting 4-amino-1,8-naphthalimide Tröger's base (TBNap) supramolecular scaffold. A new cleft-shaped TBNap-derived di-4-picolyl donor was synthesized and reacted in a 2 : 2 stoichiometry ratio with a dinuclear Ru(II) acceptor (Ru-A) to generate a [2 + 2] self-assembled metallocycle (TBNap-Ru-MC) in good yield. Both TBNap and TBNap-Ru-MC showed positive solvatochromism in different solvents with varying polarities. In addition, the binding propensity of cationic TBNap-Ru-MC toward the heparin polyanion was determined using fluorescence titration studies. The initial fluorescence emission of TBNap-Ru-MC was quenched upon the gradual addition of the heparin polyanion, and the Stern-Volmer quenching constant (K_SV) was calculated to be 3.97 × 10⁵ M^-1.

Design and Synthesis of Neutralizable Fondaparinux

Fondaparinux, a clinically approved anticoagulant pentasaccharide for the treatment of thrombotic diseases, displays better efficacy and biosafety than other heparin-based anticoagulant drugs. However, there is no suitable antidote available for fondaparinux to efficiently manage its potential bleeding risks, thereby precluding its widespread use. Herein, we describe a convergent and stereocontrolled approach to efficiently synthesize an aminopentyl-functionalized pentasaccharide, which is further used to prepare fondaparinux-based biotin conjugates and clusters. Biological activity evaluation demonstrates that the anticoagulant activity of the fondaparinux-based biotin conjugate and trimer is, respectively, neutralized by avidin and protamine as effective antidotes. This work suggests that our synthetic biotin conjugate and trimer have potential for the development of neutralizable and safe anticoagulant drugs.

Synthesis of the Three Most Expensive l-Hexose Thioglycosides from d-Glucose

The biologically important l-hexoses, which are less widespread than d-hexoses, cannot be obtained from natural sources or can only be extracted very costly. Due to the complexity of their synthesis, their commercially available derivatives (which are sold mostly in free form) are also very expensive, which is further exacerbated by the current rapid rise in prices. In the present work, starting from the cheapest d-hexose, d-glucose, using inexpensive and readily available chemicals, a reaction pathway was developed in which the three most expensive l-hexoses (l-idose, l-altrose, and l-talose) were successfully prepared in orthogonally protected thioglycoside form, ready for glycosylation. The l-ido and l-talo derivatives were synthesized by C-5 epimerization of the corresponding 5,6-unsaturated thioglycosides. From the l-ido derivatives, the orthogonally protected thioglycosides of l-altrose were then prepared by C-4 epimerization. Different approaches to the preparation of the key intermediates, 5,6-unsaturated thioglycoside derivatives, were systematically investigated in the presence of various protecting groups (ether and ester) and using commercially available reagents.

Design and Synthesis of 6-O-Phosphorylated Heparan Sulfate Oligosaccharides to Inhibit Amyloid β Aggregation

Dysregulation of amyloidogenic proteins and their abnormal processing and deposition in tissues cause systemic and localized amyloidosis. Formation of amyloid β (Aβ) fibrils that deposit as amyloid plaques in Alzheimer's disease (AD) brains is an earliest pathological hallmark. The polysulfated heparan sulfate (HS)/heparin (HP) is one of the non-protein components of Aβ deposits that not only modulates Aβ aggregation, but also acts as a receptor for Aβ fibrils to mediate their cytotoxicity. Interfering with the interaction between HS/HP and Aβ could be a therapeutic strategy to arrest amyloidosis. Here we have synthesized the 6-O-phosphorylated HS/HP oligosaccharides and reported their competitive effects on the inhibition of HP-mediated Aβ fibril formation in vitro using a thioflavin T fluorescence assay and a tapping mode atomic force microscopy.

Beyond GalNAc! Drug delivery systems comprising complex oligosaccharides for targeted use of nucleic acid therapeutics

Nucleic Acid Therapeutics (NATs) are establishing a leading role for the management and treatment of genetic diseases following FDA approval of nusinersen, patisiran, and givosiran in the last 5 years, the breakthrough of milasen, with more approvals undoubtedly on the way. Givosiran takes advantage of the known interaction between the hepatocyte specific asialoglycoprotein receptor (ASGPR) and N-acetyl galactosamine (GalNAc) ligands to deliver a therapeutic effect, underscoring the value of targeting moieties. In this review, we explore the history of GalNAc as a ligand, and the paradigm it has set for the delivery of NATs through precise targeting to the liver, overcoming common hindrances faced with this type of therapy. We describe various complex oligosaccharides (OSs) and ask what others could be used to target receptors for NAT delivery and the opportunities awaiting exploration of this chemical space.

Synthesis of Four Orthogonally Protected Rare l-Hexose Thioglycosides from d-Mannose by C-5 and C-4 Epimerization

l-Hexoses are important components of biologically relevant compounds and precursors of some therapeuticals. However, they typically cannot be obtained from natural sources and due to the complexity of their synthesis, their commercially available derivatives are also very expensive. Starting from one of the cheapest d-hexoses, d-mannose, using inexpensive and readily available chemicals, we developed a reaction pathway to obtain two orthogonally protected l-hexose thioglycoside derivatives, l-gulose and l-galactose, through the corresponding 5,6-unsaturated thioglycosides by C-5 epimerization. From these derivatives, the orthogonally protected thioglycosides of further two l-hexoses (l-allose and l-glucose) were synthesized by C-4 epimerization. The preparation of the key intermediates, the 5,6-unsaturated derivatives, was systematically studied using various protecting groups. By the method developed, we are able to produce highly functionalized l-gulose derivatives in 9 steps (total yields: 21-23%) and l-galactose derivatives in 12 steps (total yields: 6-8%) starting from d-mannose.

Strategies in Synthesis of Heparin/Heparan Sulfate Oligosaccharides: 2000-Present

Heparin and heparan sulfate are members of the glycosaminoglycan family that are involved in a multitude of biological processes. The great interests in the anticoagulant properties of heparin have stimulated major advances in synthetic strategies toward clinically effective analogues, as demonstrated importantly by the approval of the fully synthetic pentasaccharide fragment, termed fondaparinux (Arixtra®), of the heparin macromolecule for treatment of deep-vein thrombosis. Given the highly complex nature of heparin and heparan sulfate, the chemical synthesis of their components is a challenging endeavor. In the past decade, multiple approaches have been developed to improve the overall synthetic efficiency. New strategies have emerged that can generate libraries of oligosaccharide components of heparin and heparan sulfate. This article discusses recent developments in the assembly of heparin and heparan sulfate oligosaccharides and the associated challenges in their synthesis.

Combining Computational Chemistry and Crystallography for a Better Understanding of the Structure of Cellulose

The approaches in this article seek to enhance understanding of cellulose at the molecular level, independent of the source and the particular crystalline form of cellulose. Four main areas of structure research are reviewed. Initially, the molecular shape is inferred from the crystal structures of many small molecules that have β-(1→4) linkages. Then, conformational analyses with potential energy calculations of cellobiose are covered, followed by the use of Atoms-In-Molecules theory to learn about interactions in experimental and theoretical structures. The last section covers models of cellulose nanoparticles. Controversies addressed include the stability of twofold screw-axis conformations, the influence of different computational methods, the predictability of crystalline conformations by studies of isolated molecules, and the twisting of model cellulose crystals.

Progress and challenges in the synthesis of sequence controlled polysaccharides

The sequence, length and substitution of a polysaccharide influence its physical and biological properties. Thus, sequence controlled polysaccharides are important targets to establish structure-properties correlations. Polymerization techniques and enzymatic methods have been optimized to obtain samples with well-defined substitution patterns and narrow molecular weight distribution. Chemical synthesis has granted access to polysaccharides with full control over the length. Here, we review the progress towards the synthesis of well-defined polysaccharides. For each class of polysaccharides, we discuss the available synthetic approaches and their current limitations.

Synthesis of L-hexoses: an Update

Over the years, carbohydrates have increasingly become an important class of compounds contributing significantly to the target specific drug discovery and vaccine development. Several oligosaccharides contain L-hexoses that are biologically relevant as therapeutic and diagnostic tools. Since, L-hexoses and deoxy L-hexoses are not readily available in large amount and pure form, attention is drawn towards development of cost effective and high yielding synthetic routes for their procurement. In this review we give an update on the recent developments in strategies for synthesis of L-hexoses and deoxy L-hexoses.

Solving the Structural Puzzles of Amipurimycin and Miharamycins Enabled by Stereodivergent Total Synthesis

The efforts toward the synthesis of amipurimycin and miharamycin A/B, two peptidyl nucleoside antibiotics bearing a unique nine carbon C3-branched pyranosyl amino acid core, are accounted. Highlighted is our stereodivergent total synthesis of all the possible diastereoisomers of amipurimycin, which has enabled us to solve the structural puzzles of amipurimycin and miharamycin A/B after ∼50 years of their discovery.

Synthesis and immunomodulatory activity of the sulfated tetrasaccharide motif of type B ulvanobiuronic acid 3-sulfate

Ulvan is a sulfated polysaccharide from green algae with potent antitumor, antiviral, and immunomodulatory activities. However, no chemical synthesis of ulvan saccharides has been reported to date. In this paper, we performed the first efficient synthesis of the unique sulfated tetrasaccharide motif of type B ulvanobiuronic acid 3-sulfate. Based on the gold(i)-catalyzed glycosylation with glycosyl ynenoates as donors, efficient construction of the challenging α-(1 → 4)-glycosidic bonds between iduronic acid and rhamnose building blocks was achieved to afford the tetrasaccharide skeleton in a stereospecific manner. The synthetic sulfated tetrasaccharide was found to significantly improve the phagocytic activity of macrophage RAW264.7 cells.

A General Approach to O-Sulfation by a Sulfur(VI) Fluoride Exchange Reaction

O-sulfation is an important chemical code widely existing in bioactive molecules, but the scalable and facile synthesis of complex bioactive molecules carrying O-sulfates remains challenging. Reported here is a general approach to O-sulfation by the sulfur(VI) fluoride exchange (SuFEx) reaction between aryl fluorosulfates and silylated hydroxy groups. Efficient sulfate diester formation was achieved through systematic optimization of the electronic properties of aryl fluorosulfates. The versatility of this O-sulfation strategy was demonstrated in the scalable syntheses of a variety of complex molecules carrying sulfate diesters at various positions, including monosaccharides, disaccharides, an amino acid, and a steroid. Selective hydrolytic and hydrogenolytic removal of the aryl masking groups from sulfate diesters yielded the corresponding O-sulfate products in excellent yields. This strategy provides a powerful tool for the synthesis of O-sulfate bioactive compounds.

Chemical Methods for N- and O-Sulfation of Small Molecules, Amino Acids and Peptides

Sulfation of the amino acid residues of proteins is a significant post-translational modification, the functions of which are yet to be fully understood. Current sulfation methods are limited mainly to O-tyrosine (sY), which requires negatively charged species around the desired amino acid residue and a specific sulfotransferase enzyme. Alternatively, for solid-phase peptide synthesis, a de novo protected sY is required. Therefore, synthetic routes that go beyond O-sulfation are required. We have developed a novel route to N-sulfamation and can dial-in/out O-sulfation (without S-sulfurothiolation), mimicking the initiation step of the ping-pong sulfation mechanism identified in structural biology. This rapid, low-temperature and non-racemising method is applicable to a range of amines, amides, amino acids, and peptide sequences.

Synthesis of Heparan Sulfate- and Dermatan Sulfate-Related Oligosaccharides via Iterative Chemoselective Glycosylation Exploiting Conformationally Disarmed [2.2.2] l-Iduronic Lactone Thioglycosides

Heparan sulfate (HS) and dermatan sulfate (DS) are l-iduronic acid containing glycosaminoglycans (GAGs) which are implicated in a number of biological processes and conditions including cancer and viral infection. Chemical synthesis of HS and DS is required to generate structurally defined oligosaccharides for a biological study. Herein, we present a new synthetic approach to HS and DS oligosaccharides using chemoselective glycosylation which relies on a disarmed [2.2.2] l-ido lactone motif. The strategy provides a general approach for iterative-reducing end chain extension, using only shelf-stable thioglycoside building blocks, exploiting a conformational switch to control reactivity, and thus requires no anomeric manipulation steps between glycosylations.

The Miharamycins and Amipurimycin: their Structural Revision and the Total Synthesis of the Latter

The structural puzzle of amipurimycin, a peptidyl nucleoside antibiotic, is solved by total synthesis and X-ray diffraction analysis, with the originally proposed configurations at C3' and C8' inverted and those at C6', C2'', and C3'' corrected. A similar structural revision of the relevant miharamycins is proposed via chemical transformations and then validated by X-ray diffraction analysis. The miharamycins bear an unusual trans-fused dioxabicyclo[4.3.0]nonane sugar scaffold, which was previously assigned as being in the cis configuration.

Selective Electrochemical Capture and Release of Heparin Based on Amine-Functionalized Carbon/Titanium Dioxide Nanotube Arrays

Heparin (HEP) is a sulfated glycosaminoglycan that is a clinical anticoagulant agent. Commercially derived from porcine intestinal mucosa, HEP is challenging to separate from this complex biological mixture for additional purification. This study aimed to raise the purity of isolated HEP using electrochemical potential to increase its selective capture and release. We demonstrate an electrochemical platform featuring an anode composed of amine-functionalized carbon/titanium dioxide nanotube arrays on titanium foil (Ti/C-TNTAs-NH₂) and a cathode made of expanded graphite. Our results show that Ti and Ti/C-TNTAs control plates do not adsorb HEP, even while applying an external potential to the cell. However, when the Ti/C-TNTAs electrode is modified by 3 aminopropyltriethoxysilane, the terminal NH₂ groups provide a high density of positive charges that serve as binding sites, enabling the adsorption of HEP. This attraction is further strengthened by applying an external potential to the anode. Subsequent release of the HEP molecules and regeneration of the Ti/C-TNTAs-NH₂ electrode are easily accomplished by applying an anodic potential to the plate, as well as by increasing the concentration of NaCl in solution. This electrochemical system demonstrates the good selectivity of HEP, even within a mixture of other probable interfering species (e.g., bovine serum albumin and chondroitin sulfate). Additionally, it maintains 90.11% of its initial electrosorption efficiency after ten repeated HEP adsorption/desorption cycles, indicating this system's promising stability and reusability for HEP purification.

Programmable one-pot synthesis of heparin pentasaccharides enabling access to regiodefined sulfate derivatives

Heparin (H) and heparan sulfate (HS) belong to the glycosaminoglycan (GAG) family of oligosaccharides, and their sequences and sulfation patterns are known to regulate the functions of various proteins in biological processes. Among these, the 6-O-sulfation of HS/H contributes most significantly to the structural diversity and binding interactions. However, the synthesis of HS with defined sulfation patterns remains a major challenge. Herein, we report a highly efficient and programmable one-pot method for the synthesis of protected heparin pentasaccharides using thioglycoside building blocks with optimized relative reactivities to allow the selective deprotection and preparation of regiodefined sulfate derivatives.

The Role of Single-Molecule Force Spectroscopy in Unraveling Typical and Autoimmune Heparin-induced Thrombocytopenia

For the last two decades, heparins have been widely used as anticoagulants. Besides numerous advantages, up to 5% patients with heparin administration suffer from a major adverse drug effect known as heparin-induced thrombocytopenia (HIT). This typical HIT can result in deep vein thrombosis, pulmonary embolism, occlusion of a limb artery, acute myocardial infarct, stroke, and a systemic reaction or skin necrosis. The basis of HIT may lead to clinical insights. Recent studies using single-molecule force spectroscopy (SMFS)-based atomic force microscopy revealed detailed binding mechanisms of the interactions between platelet factor 4 (PF4) and heparins of different lengths in typical HIT. Especially, SMFS results allowed identifying a new mechanism of the autoimmune HIT caused by a subset of human-derived antibodies in patients without heparin exposure. The findings proved that not only heparin but also a subset of antibodies induce thrombocytopenia. In this review, the role of SMFS in unraveling a major adverse drug effect and insights into molecular mechanisms inducing thrombocytopenia by both heparins and antibodies will be discussed.

Heparin/DNA aptamer co-assembled multifunctional catecholamine coating for EPC capture and improved hemocompatibility of vascular devices

Good hemocompatibility and rapid endothelialization are two key factors in the success of stent interventional therapy. In this study, aptamers with the ability to capture endothelial progenitors and anticoagulant molecular heparin were successfully immobilized on the surface of dopamine/polyethylenimine (PDA/PEI) copolymer coating via electrostatic interaction. The results of X-ray spectroscopy (XPS), water contact angle (WCA), and immunofluorescence staining tests confirmed the successful introduction of heparin and aptamers. Platelet adhesion and whole blood experiments demonstrated that the hemocompatibility of the co-modified surface was improved. Dynamic endothelial progenitor cell (EPC) capture experiments showed that the modified surfaces could effectively capture the endothelial progenitor in dynamic conditions. More importantly, ex vivo experiments revealed that the modified surfaces could regulate the distribution of CD34/vWF-positive cells on stent surfaces, and this was beneficial for the endothelialization of vascular stents. These results suggested that heparin and aptamer co-modified stents could capture EPCs and promote endothelialization. This surface co-modification strategy has great potential for enhancing stent development.

Single-molecule force spectroscopy applied to heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT), occurring up to approximately 1% to 5% of patients receiving the antithrombotic drug heparins, has a complex pathogenesis involving multiple partners ranging from small molecules to cells/platelets. Recently, insights into the mechanism of HIT have been achieved by using single-molecule force spectroscopy (SMFS), a methodology that allows direct measurements of interactions among HIT partners. Here, the potential of SMFS in unraveling the mechanism of the initial steps in the pathogenesis of HIT at single-molecule resolution is highlighted. The new findings ranging from the molecular binding strengths and kinetics to the determination of the boundary between risk and non-risk heparin drugs or platelet-surface and platelet-platelet interactions will be reviewed. These novel results together have contributed to elucidate the mechanisms underlying HIT and demonstrate how SMFS can be applied to develop safer drugs with a reduced risk profile.

Highly Efficient Synthesis of Multiantennary Bisected N-glycans Based on Imidates

The occurrence of N-glycans with a bisecting GlcNAc modification on glycoproteins has many implications in developmental and immune biology. However, these particular N-glycans are difficult to obtain either from nature or through synthesis. We have developed a flexible and general method for synthesizing bisected N-glycans of the complex type by employing modular TFAc-protected donors for all antennae. The TFAc-protected N-glycans are suitable for the late introduction of a bisecting GlcNAc. This integrated strategy permits for the first time the use of a single approach for multiantennary N-glycans as well as their bisected derivatives via imidates, with unprecedented yields even in a one-pot double glycosylation. With this new method, rare N-glycans of the bisected type can be obtained readily, thereby providing defined tools to decipher the biological roles of bisecting GlcNAc modifications.

The stereoselectivities of tributyltin hydride-mediated reductions of 5-bromo-D-glucuronides to L-iduronides are dependent on the anomeric substituent: syntheses and DFT calculations

One of the shortest synthetic routes to L-iduronic acid derivatives is via free radical reduction of the C-5 bromide of the corresponding protected D-glucuronic acid derivative. The epimerization of such C-5 bromides to the L-ido derivatives via reaction with tributyltin hydride was investigated. It was found that the stereoselectivity of the reaction was dependent on the anomeric substituent. If the substituent was fluoride the L-ido product was obtained exclusively in 65-72% yield whereas the O-methyl or O-acetyl derivatives led to isomeric mixtures of both the L-ido and D-gluco products in different ratios depending on the reaction conditions. DFT calculations were performed to determine the stereoelectronic factors that favour formation of the L-ido isomer from the fluoride and suggest the selectivity is due to a transition state gauche effect and an Sn-F interaction.

Formal Synthesis of Anticoagulant Drug Fondaparinux Sodium

The practical formal synthesis of the anticoagulant drug fondaparinux sodium 1 was accomplished using an optimized modular synthetic strategy. The important pentasaccharide 2, a precursor for the synthesis of fondaparinux sodium, was synthesized on a 10 g scale in 14 collective steps with 3.5% overall yield from well-functionalized monosaccharide building blocks. The strategy involved a convergent [3 + 2] coupling approach, with excellent stereoselectivity in every step of glycosylation from the monosaccharide building blocks. Efficient routes to the syntheses of these fully functionalized building blocks were developed, minimizing oligosaccharide stage functional-group modifications. The syntheses of all building blocks avoided rigorous reaction conditions and the use of expensive reagents. In addition, common intermediates and a series of one-pot reactions were employed to enhance synthetic efficiency, improving the yield considerably. In the monosaccharide-to-oligosaccharide assembly reactions, cheaper activators (e.g., NIS/TfOH, TESOTf, and TfOH) were used to facilitate highly efficient glycosylations. Furthermore, crystallization of several monosaccharide and oligosaccharide intermediates significantly simplified purification procedures, which would be greatly beneficial to the scalable synthesis of fondaparinux sodium.

Synthetic Approaches to L-Iduronic Acid and L-Idose: Key Building Blocks for the Preparation of Glycosaminoglycan Oligosaccharides

L-Iduronic acid (IdoA) is an important monosaccharide component of glycosaminoglycans (GAGs) such as heparin, heparan sulfate and dermatan sulfate. GAGs are complex, highly sulfated polysaccharides that mediate a multitude of physiological and pathological processes via their interactions with a range of diverse proteins. The main challenge in the synthesis of GAG oligosaccharides is the efficient gram-scale preparation of IdoA building blocks since neither IdoA nor L-idose is commercially available or readily accessible from natural sources. In this review, the different synthetic approaches for the preparation of IdoA and its derivatives, including L-idose, are presented and discussed. Derivatives of the latter are often used in GAG synthesis and are elaborated to IdoA via selective oxidation at C-6 after incorporation into a GAG chain. Particular focus will be given to the preparation of IdoA synthons most commonly used for GAG oligosaccharide synthesis, and on the progress made since the last systematic review in this area.

Quantitative description of thermodynamic and kinetic properties of the platelet factor 4/heparin bonds

Heparin is the most important antithrombotic drug in hospitals. It binds to the endogenous tetrameric protein platelet factor 4 (PF4) forming PF4/heparin complexes which may cause a severe immune-mediated adverse drug reaction, so-called heparin-induced thrombocytopenia (HIT). Although new heparin drugs have been synthesized to reduce such a risk, detailed bond dynamics of the PF4/heparin complexes have not been clearly understood. In this study, single molecule force spectroscopy (SMFS) is utilized to characterize the interaction of PF4 with heparins of defined length (5-, 6-, 8-, 12-, and 16-mers). Analysis of the force-distance curves shows that PF4/heparin binding strength rises with increasing heparin length. In addition, two binding pathways in the PF4/short heparins (≤8-mers) and three binding pathways in the PF4/long heparins (≥8-mers) are identified. We provide a model for the PF4/heparin complexes in which short heparins bind to one PF4 tetramer, while long heparins bind to two PF4 tetramers. We propose that the interaction between long heparins and PF4s is not only due to charge differences as generally assumed, but also due to hydrophobic interaction between two PF4s which are brought close to each other by long heparin. This complicated interaction induces PF4/heparin complexes more stable than other ligand-receptor interactions. Our results also reveal that the boundary between antigenic and non-antigenic heparins is between 8- and 12-mers. These observations are particularly important to understand processes in which PF4-heparin interactions are involved and to develop new heparin-derived drugs.

Crystal packing in three related disaccharides: precursors to heparan sulfate oligosaccharides

The three title compounds form part of a set of important precursor dissacharides which lead to novel therapeutics, in particular for Alzheimer's disease. All three crystallize as poorly diffracting crystals with one independent mol-ecule in the asymmetric unit. Two of them are isostructural: 4-meth-oxy-phenyl 4-O-[6-O-acetyl-2-azido-3-O-benzyl-2-de-oxy-4-O-(9-fluor-en-yl-methyl-oxycarbon-yl)-α-d-gluco-pyranos-yl]-2-O-benzoyl-3-O-benzyl-6-O-chloro-acetyl-α-l-ido-pyran-oside, C59H56ClN3O16, (I), the ido-relative of a reported gluco-disaccharide [Gainsford et al., 2013 ▶). Acta Cryst. C69, 679-682] and 4-meth-oxy-phenyl 4-O-[6-O-acetyl-2-azido-3-O-benzyl-2-de-oxy-4-O-(9-fluorenyl-methyl-oxycarbon-yl)-α-d-gluco-pyranos-yl]-2-O-benzoyl-3-O-benzyl-6-O-meth-oxy-acetyl-α-l-ido-pyran-oside, C60H59N3O17, (II). Both exhibit similar conformational disorder of pendant groups. The third compound 4-meth-oxy-phenyl 4-O-[6-O-acetyl-2-azido-3,4-di-O-benzyl-2-de-oxy-α-d-gluco-pyranos-yl]-2-O-benzoyl-3-O-benzyl-6-O-meth-oxy-oacetyl-β-d-gluco-pyran-oside, C52H55N3O15, (III), illustrates that a slightly larger set of weak inter-molecular inter-actions can result in a less disordered mol-ecular arrangement. The mol-ecules are bound by weak C-H⋯O(ether) hydrogen bonds in (I) and (II), augmented by C-H⋯π inter-actions in (III). The absolute configurations were determined, although at varying levels of significance from the limited observed data.

Facile chemoenzymatic synthesis of biotinylated heparosan hexasaccharide

A biotinylated heparosan hexasaccharide was synthesized using a one-pot multi-enzyme strategy, in situ activation and transfer of N-trifluoroacetylglucosamine (GlcNTFA) to a heparin backbone significantly improved the synthetic efficiency. The biotinylated hexasaccharide could serve as a flexible core to diversify its conversion into heparan sulfate isoforms with potential biological applications and therapeutics.

Synthesis of glycosaminoglycan mimetics through sulfation of polyphenols

In nearly all cases of biological activity of sulfated GAGs, the sulfate group(s) are critical for interacting with target proteins. A growing paradigm is that appropriate small, sulfated, nonsaccharide GAG mimetics can be designed to either mimic or interfere with the biological functions of natural GAG sequences resulting in the discovery of either antagonist or agonist agents. A number of times these sulfated NSGMs can be computationally designed based on the parent GAG-protein interaction. The small sulfated NSGMs may possess considerable aromatic character so as to engineer hydrophobic, hydrogen-bonding, Coulombic or cation-pi forces in their interactions with target protein(s) resulting in higher specificity of action relative to parent GAGs. The sulfated NSGMs can be easily synthesized in one step from appropriate natural polyphenols through chemical sulfation under microwave-based conditions. We describe step-by-step procedures to perform microwave-based sulfation of several small polyphenol scaffolds so as to prepare homogenous NSGMs containing one to more than 10 sulfate groups per molecule in high yields.