One-Pot Synthesis of Structurally Diverse Iminosugar-Based Hybrid Molecules

An alternative route for tricyclic quinazolinone-iminosugars and their glucosidase inhibitory activities

A series of novel tricyclic quinazolinone-iminosugars 5 and their derivatives 7 were obtained from the tosylated sugars by three steps. Firstly, the reaction of the isopropylidene protected sugar tosylate 1 and o-aminobenzylamine 2 generated the precursor tricyclic quinazolin-iminosuar 3, which was then oxidized by KMnO4 to produce the corresponding quinazolinone 4. Finally, removal of the isopropylidene group yielded the target tricyclic quinazolinone iminosugars 5. In addition, quinazolinone-iminosugars 4ac, 4bc and 4cc who contain bromine in the aromatic region underwent Suzuki reaction with phenylboronic acid, followed with the removal of the isopropylidene group to afford the derivatives 7. This strategy will help to construct such fused multicyclic quinazolinone-iminosugars efficiently. Some compounds show certain inhibition against α-glucosidase (saccharomyce cerevisiae).

Recent progress in the synthesis of natural product inspired bioactive glycohybrids

Carbohydrates are a basic structural component that are indispensable to all cellular processes. In addition to being employed as chiral starting materials in the synthesis of a variety of natural products, carbohydrates are recognized as naturally occurring molecules having an enormous variety of functional, stereochemical, and structural properties. The understanding and biological roles of carbohydrate derived molecules can be greatly improved by selectively synthesizing functional carbohydrates through incorporating them with privileged scaffolds. For a deeper understanding of their roles and the development of functional materials based on sugar, it is crucial to develop new techniques for efficiently synthesizing, functionalizing, and modifying carbohydrates. Glycohybrids have a wide range of structural and functional characteristics along with protein-carbohydrate interactions that are crucial to mammalian biology and a number of disease states. This review, consisting the literature from January 2017 to July 2023 and provide an overview of recent developments in the chemical synthesis of glycohybrids based on natural product scaffolds of coumarin, quinolone, naphthalene diimide, indole, isatin, naphthoquinone, imidazole and pyrimidine. The biological activity of active glycohybrids are discussed in this review.

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

Intramolecular Palladium-Catalyzed Carboamination for the Stereoselective Synthesis of Five-Membered Iminosugar C-Glycosides

We report here a new method for the stereoselective synthesis of five-membered iminosugar C-glycosides using an intramolecular palladium-catalyzed carboamination. We have prepared efficiently two sugar-derived aminoalkenes, which were submitted to the carboamination conditions in the presence of different aryl bromides. A small library of protected iminosugars carrying a 1-C-arylmethyl substituent was obtained, and some of them were fully deprotected to yield original iminosugar C-glycosides. This methodology provides one of the shortest pathways to this family of molecules.

Design and synthesis of novel benzimidazole-iminosugars linked a substituted phenyl group and their inhibitory activities against β-glucosidase

A series of novel benzimidazole-iminosugars linked a (substuituted) phenyl group on benzene ring of benzimidazole 5(a-p) and 6(a-p) have been rationally designed and conveniently synthesized through Suzuki coupling reaction in high yields. All compounds have been evaluated for their inhibitory activities against β-glucosidase (almond). Six compounds 5d, 6d, 6e, 6i, 6n, and 6p showed more significant inhibitory activities with IC₅₀ values in the range of 0.03-0.08 μM, almost 10-fold improved than that of the parent analogue 4, and much higher than that of the positive control castanospermine. The additional phenyl ring and the electron donating groups on it would be beneficial for the activity. Compounds 6d, 6n, and 4 had been chosen to be tested for their inhibition types against β-glucosidase. Interestingly, three compounds have different inhibition types although they had very similar structure. Their K_i values were calculated to be 0.02 ± 0.01 μM, 0.02 ± 0.01 μM, and 0.66 ± 0.14 μM, respectively. The equilibrium dissociation constant (K_D) for 6d, 6n, and 4 and β-glucosidase was 0.04 μM, 0.03 μM and 0.45 μM by the ITC-based assay, respectively. Molecular docking work suggests that such benzimidazole-iminosugars derivatives might bind to the active site of β-glucosidase mainly through hydrogen bonds, the additional phenyl ring towards the solvent-exposed region played an important effect on their inhibitory activity against β-glucosidase.

Efficient one-pot synthesis of the unexpected fused multicyclic iminosugars by an aza-Diels–Alder mechanism

A simple and efficient one-pot protocol has been developed by an aza-Diels–Alder mechanism for the stereoselective synthesis of novel fused multicyclic iminosugars with structural diversity.

Cyclisations and Strategies for Stereoselective Synthesis of Piperidine Iminosugars

This personal account focuses on synthesis of polyhydroxylated piperidines, a subset of compounds within the iminosugar family. Cyclisations to form the piperidine ring include reductive amination, substitution via amines, iminium ions and cyclic nitrones, transamidification (N-acyl transfer), addition to alkenes, ring contraction and expansion, photoinduced electron transfer, multicomponent Ugi reaction and ring closing metathesis. Enantiomerically pure piperidines are obtained from chiral pool precursors (e. g. sugars, amino acids, Garner's aldehyde) or asymmetric reactions (e. g. epoxidation, dihydroxylation, aminohydroxylation, aldol, biotransformation). Our laboratory have contributed cascades based on reductive amination from glycosyl azide precursors as well as Huisgen azide-alkene cycloaddition. The latter's combination with allylic azide rearrangement has given substituted piperidines, including those with quaternary centres adjacent to nitrogen.

Crystal structure of methyl 2-(6,11-dioxo-2,3,6,11-tetrahydro-1H-benzo[f]pyrrolo[2,1-a]isoindole-5-carbonyl)benzoate, C24H17NO5

C24H17NO5, triclinic, P1̄ (no. 2), a = 8.5858(2) Å, b = 9.2397(4) Å, c = 13.7831(8) Å, α = 97.11(3)°, β = 103.23(3)°, γ = 113.33(3)°, V = 948.8(2) Å3, Z = 2, R gt(F) = 0.0545, wR ref(F 2) = 0.1669, T = 296(2) K.

Switching Electrophile Intermediates to Nucleophiles: Michael and Oxa-Diels-Alder Reactions to Afford Polyoxy-Functionalized Piperidine Derivatives with Tetrasubstituted Carbon

Michael, Michael-annulation, and oxa-Diels-Alder reactions of carbohydrate derivatives that afford polyoxy-functionalized piperidine derivatives bearing tetrasubstituted carbon at the 3-position of the piperidine ring are reported. Iminium ions generated from carbohydrate derivatives with amines were converted to enamines in situ, which acted as nucleophiles. As a result, substituents were introduced at the 3-position or both 2- and 3-positions of the piperidines bearing polyoxy groups. This strategy will be useful in drug discovery efforts.

Synthesis of tricyclic quinazolinone-iminosugars as potential glycosidase inhibitors via a Mitsunobu reaction

A series of novel tricyclic quinazolinone-iminosugars 1 (a-c) were synthesized from the benzyl protected sugars through three steps. Firstly, the benzyl protected sugar (aldehyde) 5 reacted with o-aminobenzamide by the iodine-induced oxidative condensation to afford the corresponding aldo-quizanolinone 6. Secondly, through the intramolecular cyclization of the unprotected OH and the amide NH in 6, the tricyclic compounds 7 and 8 were constructed by the key Mitsunobu reaction. Finally, removal of the benzyl group gave the target tricyclic quinazolinone-iminosugars 1. The protocol was effective for the preparation of the tricyclic iminosugars in satisfactory yield. Interestingly, an unusual C-2 epimerization was observed with d-mannose and d-ribose compounds under the conditions of the Mitsunobu reaction that generated the products having the trans configuration at the C-2 and C-3 positions. Unfortunately, such tricyclic quinazolinone-iminosugars showed no inhibitory effects on the tested five glycosidases.

Stereoselective synthesis of sugar mimetics from simple monosaccharides

A number of bicyclic imino- and carba-sugars (examples are presented in the Scheme) can be obtained from simple monosaccharides (hexoses or pentoses) by various methods.