Synthesis of N-(fluoren-9-ylmethoxycarbonyl)glycopyranosylamine uronic acids

Para-Methoxybenzylidene Acetal-Protected D-Glucosamine Derivatives as pH-Responsive Gelators and Their Applications for Drug Delivery

Carbohydrate-based low molecular weight gelators (LMWGs) are compounds with the capability to self-assemble into complex molecular networks within a solvent, leading to solvent immobilization. This process of gel formation depends on noncovalent interactions, including Van der Waals, hydrogen bonding, and π-π stacking. Due to their potential applications in environmental remediation, drug delivery, and tissue engineering, these molecules have emerged as an important area of research. In particular, various 4,6-O-benzylidene acetal-protected D-glucosamine derivatives have shown promising gelation abilities. In this study, a series of C-2-carbamate derivatives containing a para-methoxy benzylidene acetal functional group were synthesized and characterized. These compounds exhibited good gelation properties in several organic solvents and aqueous mixtures. Upon removal of the acetal functional group under acidic conditions, a number of deprotected free sugar derivatives were also synthesized. Analysis of these free sugar derivatives revealed two compounds were hydrogelators while their precursors did not form hydrogels. For those protected carbamates that are hydrogelators, removal of the 4,6-protection will result in a more water-soluble compound that produces a transition from gel to solution. Given the ability of these compounds to form gels from solution or solution from gels in situ in response to acidic environments, these compounds may have practical applications as stimuli-responsive gelators in an aqueous medium. In turn, one hydrogelator was studied for the encapsulation and release of naproxen and chloroquine. The hydrogel exhibited sustained drug release over a period of several days, with the release of chloroquine being faster at lower pH due to the acid lability of the gelator molecule. The synthesis, characterization, gelation properties, and studies on drug diffusion are discussed.

Cu(I)-Catalyzed Click Chemistry in Glycoscience and Their Diverse Applications

Copper(I)-catalyzed 1,3-dipolar cycloaddition between organic azides and terminal alkynes, commonly known as CuAAC or click chemistry, has been identified as one of the most successful, versatile, reliable, and modular strategies for the rapid and regioselective construction of 1,4-disubstituted 1,2,3-triazoles as diversely functionalized molecules. Carbohydrates, an integral part of living cells, have several fascinating features, including their structural diversity, biocompatibility, bioavailability, hydrophilicity, and superior ADME properties with minimal toxicity, which support increased demand to explore them as versatile scaffolds for easy access to diverse glycohybrids and well-defined glycoconjugates for complete chemical, biochemical, and pharmacological investigations. This review highlights the successful development of CuAAC or click chemistry in emerging areas of glycoscience, including the synthesis of triazole appended carbohydrate-containing molecular architectures (mainly glycohybrids, glycoconjugates, glycopolymers, glycopeptides, glycoproteins, glycolipids, glycoclusters, and glycodendrimers through regioselective triazole forming modular and bio-orthogonal coupling protocols). It discusses the widespread applications of these glycoproducts as enzyme inhibitors in drug discovery and development, sensing, gelation, chelation, glycosylation, and catalysis. This review also covers the impact of click chemistry and provides future perspectives on its role in various emerging disciplines of science and technology.

An Overview on Glyco-Macrocycles: Potential New Lead and their Future in Medicinal Chemistry

Macrocycles cover a small segment of molecules with a vast range of biological activity in the chemotherapeutic world. Primarily, the natural sources derived from macrocyclic drug candidates with a wide range of biological activities are known. Further evolutions of the medicinal chemistry towards macrocycle-based chemotherapeutics involve the functionalization of the natural product by hemisynthesis. More recently, macrocycles based on carbohydrates have evolved a considerable interest among the medicinal chemists worldwide. Carbohydrates provide an ideal scaffold to generate chiral macrocycles with well-defined pharmacophores in a decorated fashion to achieve the desired biological activity. We have given an overview on carbohydrate-derived macrocycle involving their synthesis in drug design and discovery and potential role in medicinal chemistry.

Biosynthetic and synthetic access to amino sugars

Amino sugars are important constituents of a number of biomacromolecules and products of microbial secondary metabolism, including antibiotics. For most of them, the amino group is located at the positions C1, C2 or C3 of the hexose or pentose ring. In biological systems, amino sugars are formed due to the catalytic activity of specific aminotransferases or amidotransferases by introducing an amino functionality derived from L-glutamate or L-glutamine to the keto forms of sugar phosphates or sugar nucleotides. The synthetic introduction of amino functionalities in a regio- and stereoselective manner onto sugar scaffolds represents a substantial challenge. Most of the modern methods of for the preparation of 1-, 2- and 3-amino sugars are those starting from "an active ester" of carbohydrate derivatives, glycals, alcohols, carbonyl compounds and amino acids. A substantial progress in the development of region- and stereoselective methods of amino sugar synthesis has been made in the recent years, due to the application of metal-based catalysts and tethered approaches. A comprehensive review on the current state of knowledge on biosynthesis and chemical synthesis of amino sugars is presented.

Cu-Catalyzed Click Reaction in Carbohydrate Chemistry

Cu(I)-catalyzed azide-alkyne 1,3-dipolar cycloaddition (CuAAC), popularly known as the "click reaction", serves as the most potent and highly dependable tool for facile construction of simple to complex architectures at the molecular level. Click-knitted threads of two exclusively different molecular entities have created some really interesting structures for more than 15 years with a broad spectrum of applicability, including in the fascinating fields of synthetic chemistry, medicinal science, biochemistry, pharmacology, material science, and catalysis. The unique properties of the carbohydrate moiety and the advantages of highly chemo- and regioselective click chemistry, such as mild reaction conditions, efficient performance with a wide range of solvents, and compatibility with different functionalities, together produce miraculous neoglycoconjugates and neoglycopolymers with various synthetic, biological, and pharmaceutical applications. In this review we highlight the successful advancement of Cu(I)-catalyzed click chemistry in glycoscience and its applications as well as future scope in different streams of applied sciences.

Nitrogen-containing macrocycles having a carbohydrate scaffold

Nitrogen-containing macrocyclic compounds (amines, amides, and N-heterocyclic derivatives) are important targets in supramolecular chemistry. This chapter discusses the importance of aza-macrocycles in general and, in particular, those receptors containing sugar unit(s). The combination of a carbohydrate scaffold bearing nitrogen-containing functional groups in macrocyclic molecules opens a convenient route to chiral receptors having potentially useful properties. The carbohydrate-based macrocycles discussed are classified into several general groups: (1) aza-crown ethers containing a carbohydrate subunit, (2) cyclic homooligomers from amino sugars, (3) sugar-based cryptands, (4) cyclic peptides containing amino sugar units (including C2- and C3-symmetrical macrocyclic glycopeptides), (5) nitrogen- containing glycophanes, and (6) 1,2,3-triazoles containing synthetic cyclodextrin analogues. The general strategies employed, as well as specific ones leading to such complex derivatives, are surveyed. Applications of such carbohydrate receptors, pointing to their importance as hosts in supramolecular chemistry, are discussed.

Studies Directed to Understanding the Structure of Chitosan−Metal Complexes: Investigations of Mono- and Disaccharide Models with Platinum(II) Group Metals

X-ray and NMR experiments were performed with simple chitosan models based on glucosamine monosaccharides and disaccharides to understand the binding properties and structures of the complexes formed between this polysaccharide and platinum(II) metals. Subjection of the glucosamine derivatives with [PdCl2(PhCN)2] provided trans-diamine complexes which upon further treatment with excess (NH4)PF6 generated complexes possessing two 5-membered chelate rings involving the C2-amine and the C3-hydroxyl group of the two individual glucosamine units.

Synthesis, Biological Activity, and Preliminary Pharmacokinetic Evaluation of Analogues of a Phosphosulfomannan Angiogenesis Inhibitor (PI-88)

The phosphosulfomannan 1 (PI-88) is a mixture of highly sulfated oligosaccharides that is currently undergoing clinical evaluation in cancer patients. As well as its anticancer properties, 1 displays a number of other interesting biological activities. A series of analogues of 1 were synthesized with a single carbon (pentasaccharide) backbone to facilitate structural characterization and interpretation of biological results. In a fashion similar to 1, all compounds were able to inhibit heparanase and to bind tightly to the proangiogenic growth factors FGF-1, FGF-2, and VEGF. The compounds also inhibited the infection of cells and cell-to-cell spread of herpes simplex virus (HSV-1). Preliminary pharmacokinetic data indicated that the compounds displayed different pharmacokinetic behavior compared with 1. Of particular note was the n-octyl derivative, which was cleared 3 times less rapidly than 1 and may provide increased systemic exposure.

Control of Helix Formation in Vinylogous γ-Peptides by (E)- and (Z)-Double Bonds: A Way to Ion Channels and Monomolecular Nanotubes

[structure: see text] A complete overview on the alternative and competitive helices in vinylogous gamma-peptides is given, which was obtained on the basis of a systematic conformational analysis at various levels of ab initio MO theory (HF/6-31G*, DFT/B3LYP/6-31G*, PCM/HF/6-31G*). Contrary to the parent gamma-peptides, there is a strict control of helix formation by the configuration of the double bond between the C(alpha) and C(beta) atoms of the monomer constituents. (E)-Double bonds favor helices with larger pseudocycles beginning with 14- up to 27-membered hydrogen-bonded rings, whereas the (Z)-configuration of the double bonds supports a distinct preference of helices with smaller seven- and nine-membered pseudocycles showing interactions between nearest-neighbor peptide bonds. The rather stable helices of the (E)-vinylogous peptides with 22-, 24-, and 27-membered hydrogen-bonded pseudocycles have inner diameters large enough to let molecules or ions pass. Thus, they could be interesting model compounds for the design of membrane channels and monomolecular nanotubes. Since (E)- and (Z)-vinylogous gamma-amino acids and their oligomers are synthetically accessible, our study may stimulate structure research in this novel field of foldamers.

δ-Peptides and δ-Amino Acids as Tools for Peptide Structure DesignA Theoretical Study

An overview on all possible helix types in oligomers of delta-amino acids (delta-peptides) and their stabilities is given on the basis of a systematic conformational analysis employing various methods of ab initio MO theory (HF/6-31G*, B3LYP/6-31G*, PCM//HF/6-31G*). A wide variety of novel helical structures with hydrogen-bonded pseudocycles of different size are predicted. Since a delta-amino acid constituent may replace a dipeptide unit in alpha-peptides, there are close relationships between the secondary structures of peptides with delta-amino acid residues and typical secondary structures of alpha-peptides. However, the preference of gauche conformations at the central C(beta)-C(gamma) bonds of delta-amino acids, which correspond to the peptide linkages in alpha-peptides, over staggered ones makes completely novel structure alternatives for helices and turns more probable. The peculiarities of beta-turn formation by sugar amino acids derived from delta-amino acids are compared with the turn formation in delta-amino acid residues and in alpha-peptides. The considerable potential of secondary structure formation in delta-peptides and single delta-amino acid constituents predicted by ab initio MO theory may stimulate experimental work in the field of peptide and foldamer design.