Synthesis of Glycomimetics by Diastereoselective Passerini Reaction

Cyrene: a very reactive bio-based chiral ketone in diastereoselective Passerini reactions

Cyrene, a green bioderived solvent from waste cellulose, was applied to the synthesis of novel α-acyloxyamide derivatives through a Passerini-3CR with carboxylic acids and isocyanides with good yields and diastereoselectivities under mild conditions. Cyrene showed exceptionally high reactivity and the degree of diastereoselection was dependent mostly on the isocyanide. DFT calculations as well as the experimental findings indicated that both kinetic and thermodynamic effects might explain the results.

Sugars in Multicomponent Reactions: A Toolbox for Diversity-Oriented Synthesis

Multicomponent reactions (MCRs) cover strategically employed chemical transformations that incorporate three or more reactants in one pot leading to a functionalized final product. Thus, it is an ideal tool to achieve high levels of complexity, diversity, yields of desired products, atom economy, and reduced reaction times. Sugars belong to the class of naturally occurring compounds with fascinating applications in the field of drug discovery due to the presence of various hydroxy groups and well-defined stereochemistry. However, their potential in MCRs has been realized only recently. This account describes recent advances in the synthesis of sugar-derived heterocycles synthesized by MCRs. We hope to encourage the synthetic and medicinal chemistry community to apply this powerful MCR chemistry to generate novel glycoconjugate challenges.

1 Introduction

2 Synthesis of Various Functionalized Sugar Compounds

2.1 Passerini and Ugi Multicomponent Reactions

2.2 Petasis Reaction

2.3 Hantzsch Reaction

2.4 Domino Ferrier–Povarov Reaction

2.5 Marckwald Reaction

2.6 Groebke–Blackburn–Bienaymé (GBB) Reaction

2.7 Prins–Ritter Reaction

2.8 Debus–Radziszewski Imidazole Synthesis Reaction

2.9 Mannich Reaction

2.10 A3-Coupling Reaction

2.11 [3+2]-Cycloaddition Reactions

2.12 Miscellaneous Reactions

3 Conclusion

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2017-2018

This review is the tenth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization mass spectrometry (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2018. Also included are papers that describe methods appropriate to glycan and glycoprotein analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, new methods, matrices, derivatization, MALDI imaging, fragmentation and the use of arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Most of the applications are presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. The reported work shows increasing use of combined new techniques such as ion mobility and highlights the impact that MALDI imaging is having across a range of diciplines. MALDI is still an ideal technique for carbohydrate analysis and advancements in the technique and the range of applications continue steady progress.

Synthesis of Homo- and Heteromultivalent Fucosylated and Sialylated Oligosaccharide Conjugates via Preactivated N-Methyloxyamine Precision Macromolecules and Their Binding to Polyomavirus Capsid Proteins

Glycoconjugates are a versatile class of bioactive molecules that have found application as vaccines and antivirals and in cancer therapy. Their synthesis typically involves elaborate functionalization and use of protecting groups on the carbohydrate component in order to ensure efficient and selective conjugation. Alternatively, non-functionalized, non-protected carbohydrates isolated from biological sources or derived through biotechnological methods can be directly conjugated via N-methyloxyamine groups. In this study, we introduce such N-methyloxyamine groups into a variety of multivalent scaffolds─from small to oligomeric to polymeric scaffolds─making use of solid-phase polymer synthesis to assemble monodisperse sequence-defined macromolecules. These scaffolds are then successfully functionalized with different types of human milk oligosaccharides deriving a library of homo- and heteromultivalent glycoconjugates. Glycomacromolecules presenting oligosaccharide side chains with either α2,3- or α2,6-linked terminal sialic acid are used in a binding study with two types of polyomavirus capsid proteins showing that the multivalent presentation through the N-methyloxyamine-derived scaffolds increases the number of contacts with the protein. Overall, a straightforward route to derive glycoconjugates from complex oligosaccharides with high variability yet control in the multivalent scaffold is presented, and applicability of the derived structures is demonstrated.

Miscellaneous Passerini Reaction for α-Acyloxy Carboxamide: Synthesis and Process Optimization Study

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An accelerating effect of “Phase Transfer Catalyst” as additive was exposed for the Passerini three-component reactions and the influence on the reaction rate was studied concerning direct involvement of reactant molecules. The most flexible reaction for the rapid formation of diverse “α-acyloxycarboxamides” using passerini reaction involved multicomponent reactions using miscellaneous 2-(prop-2-ynyloxy)benzaldehyde with various aromatic acid and slightly non-polar fragment i.e. 2-isocyano-2,3,3-trimethylbutane and the representative molecule was characterized with resepct to DEPT135 NMR technique.

The 100 facets of the Passerini reaction

This perspective aims at celebrating the 100th anniversary of the discovery of the Passerini three component reaction. After being nearly neglected for many years, now this reaction has become quite popular, thanks to the achievements of the last 30 years, which have revealed several chances of exploitation in organic synthesis. Though not being comprehensive, this review means to show the various ways that have been used in order to expand the utility of the Passerini reaction. Post-MCR transformations to give heterocycles or peptidomimetics, variants through single component replacement, stereochemical issues, and applications in total syntheses will be especially covered.

Synthesis of chimera oligopeptide including furanoid β-sugar amino acid derivatives with free OHs: mild but successful removal of the 1,2-O-isopropylidene from the building block

Complementary to hydrophobic five membered ring β-amino acids (e.g. ACPC), β-sugar amino acids (β-SAAs) have found increasing application as hydrophilic building blocks of foldamers and α/β chimeric peptides. Fmoc-protected β-SAAs [e.g. Fmoc-RibAFU(ip)-OH] are indeed useful Lego elements, ready to use for SPPS. The removal of 1,2-OH isopropylidene protecting group increasing the hydrophilicity of such SAA is presented here. We first used N3-RibAFU(ip)-OH model compound to optimize mild deprotection conditions. The formation of the 1,2-OH free product N3-RibAFU-OH and its methyl glycoside methyl ester, N3-RibAFU(Me)-OMe were monitored by RP-HPLC and found that either 50% TFA or 8 eqv. Amberlite IR-120 H+ resin in MeOH are optimal reagents for the effective deprotection. These conditions were then successfully applied for the synthesis of chimeric oligopeptide: -GG-X-GG- [X=RibAFU(ip)]. We found the established conditions to be effective and-at the same time-sufficiently mild to remove 1,2-O-isopropylidene protection and thus, it is proposed to be used in the synthesis of oligo- and polypeptides of complex sequence combination.

Synthesis of d-glycopyranosyl depsipeptides using Passerini reaction

A protocol based on Passerini multi-component reaction has been developed for facile, efficient and atom economical synthesis of a small library of twenty potential bioactive (2R)-2-(d-glycopyranosyl)-2-acyloxyacetamides using perbenzylated d-glycopyranosyl aldehydes, substituted isocyanides and different aliphatic/aromatic carboxylic acids. All twenty synthesized d-glycopyranosyl α-acyloxy amides, commonly known as depsipeptides were unambiguously identified on the basis of their spectral (IR, ¹H, ¹³C NMR, COSY, HSQC, NOESY and HRMS) data analysis.

Modern Catalysts in A3- Coupling Reactions

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Propargylamines are an important constituent of diverse, biologically active and industrially valuable compounds. These useful, convenient and effective compounds can be synthesized via the A3-coupling reactions between an aldehyde, amine, and alkyne in the presence of a catalyst. In the past years, most of the catalysts containing transition metals were applied in these reactions, but today, various heterogeneous catalysts, especially nanocatalysts are used. The purpose of this review was to introduce some modern catalysts for the A3-coupling reaction.

Ag2O-catalysed nucleophilic isocyanation: selective formation of less-stable benzylic isonitriles

Both primary and secondary benzylic isonitriles were exclusively produced by the Ag₂O-catalysed reaction of benzylic phosphates and trimethylsilyl cyanide without formation of the thermodynamically favoured regioisomers, benzylic nitriles.

Stereodivergent access to all four stereoisomers of chiral tetrahydrobenzo[f][1,4]oxazepines, through highly diastereoselective multicomponent Ugi–Joullié reaction

Starting from easily accessible chiral enantiopure 1,2-amino alcohols and salicylaldehydes, a concise route to cyclic imines has been developed. These chiral cyclic imines undergo a highly diastereoselective Ugi–Joullié reaction to give trans tetrahydrobenzo[f][1,4]oxazepines with the introduction of up to 4 diversity inputs. The cis isomer may also be attained, thanks to a thermodynamically controlled base catalysed epimerization. Free secondary amines have been obtained using an unprecedented “removable” carboxylic acid.

Starting from easily accessible enantiopure 1,2-aminoalcohols and salicylaldehydes, a concise and diastereodivergent route to tetrahydrobenzo[f][1,4]oxazepines has been developed.

C-Linked Glycomimetic Libraries Accessed by the Passerini Reaction

Carbohydrates and their conjugates are the most abundant natural products, with diverse and highly important biological roles. Synthetic glycoconjugates are versatile tools used to probe biological systems and interfere with them. In an endeavor to provide an efficient route to glycomimetics comprising structurally diverse carbohydrate units, we describe herein a robust, stereoselective, multicomponent approach. Isopropylidene-protected carbohydrate-derived aldehydes and ketones were utilized in the Passerini reaction, giving different glycosylated structures in high yields and diastereoselectivities up to 90:10 diastereomeric ratio (d.r). Access to highly valuable building blocks based on α-hydroxy C-glycosyl acids or more complex systems was elaborated by simple post-condensation methodologies.

Structure and Reactivity of Glycosyl Isocyanides

3D structural information was obtained from mono-, di- and trisaccharide formamide and isocyanide derivatives by analysis of their X-ray crystal structure and NMR spectroscopy. The isocyanide anomeric effect was observed. Data mining of the Cambridge Structural Database (CSD) was performed and statistically confirmed our findings. Application of the glycoside isocyanides in the synthesis of novel glycoconjugates as drug-like scaffolds by MCR chemistry underscores the usefulness of the novel building blocks.