C-H Glycosylation of Native Carboxylic Acids: Discovery of Antidiabetic SGLT-2 Inhibitors

Synthesis of 2-glycosyl-quinazolines and 5-glycosyl-pyrazolo[1,2-a]cinnolines by Cp*Ir(III)-catalyzed C-H activation/cyclization

A novel strategy for the synthesis of 2-glycosyl-quinazolines and 5-glycosyl-pyrazolo[1,2-a]cinnolines has been established through an Ir-catalyzed C-H activation/annulation process. This approach features mild reaction conditions, exhibits good tolerance to diverse functional groups, and facilitates the stereoselective construction of heterocyclic C-glycosides. Significantly, this method is amenable to the late-stage modification of structurally intricate natural products, thus holding great potential in the field of organic synthesis and pharmaceutical chemistry.

Convenient Synthesis of β-C-Acyl Glycosides and its Application in the Synthesis of Scleropentaside A, Scleropentaside B and the Derivatives of Dapagliflozin

C-Glycosides are a common feature in numerous bioactive natural compounds and play a crucial role as mimics of O/N-glycosides. Our process for synthesizing β-C-acyl glycosides involves a reductive cross-coupling of protected glycosyl bromides with the corresponding carboxylic acid, followed by base-assisted deprotection and isomerization. This method is compatible with diverse glycosyl donors, including disaccharides. Consequently, we achieved the total synthesis of the natural products scleropentaside A and scleropentaside B with exceptional efficiency. These β-C-acyl glycosides can be readily transformed into novel forms of C-glycosides capable of disrupting signaling pathways linked to various pathological conditions, such as diabetes.

Practical synthesis of C-aryl glycosides via redox-neutral Borono-Catellani reaction

Herein, we describe a practical Borono-Catellani strategy for the efficient synthesis of C-aryl glycosides, with readily available arylboronic esters and glycosyl chlorides as the building blocks. It features mild reaction conditions, excellent diastereoselectivities, and good functional group tolerance. A diverse array of highly decorated C-(hetero)aryl glycosides are obtained in a convergent and redox-neutral manner.

Pd-Catalyzed Stereospecific Glycosyl Cross-Coupling of Reversed Anomeric Stannanes for Modular Synthesis of Nonclassical C-Glycosides

Nonclassical C-glycosides, distinguished by their unique glycosidic bond connection mode, represent a promising avenue for the development of carbohydrate-based drugs. However, the accessibility of nonclassical C-glycosides hinders broader investigations into their structural features and modes of action. Herein, we present the first example of Pd-catalyzed stereospecific glycosylation of nonclassical anomeric stannanes with aryl or vinyl halides. This method furnishes desired nonclassical aryl and vinyl C-glycosides in good to excellent yields, while allowing for exclusive control of nonclassical anomeric configuration. Of significant note is the demonstration of the generality and practicality of this nonclassical C-glycosylation approach across more than 50 examples, encompassing various protected and unprotected saccharides, deoxy sugars, oligopeptides, and complex molecules. Furthermore, biological evaluation indicates that nonclassical C-glycosylation modifications of drug molecules can positively impact their biological activity. Additionally, extensive computational studies are conducted to elucidate the rationale behind differences in reaction reactivity, unveiling a transmetalation transition state containing silver (Ag) within a six-membered ring. Given its remarkable controllability, predictability, and consistently high chemical selectivity and stereospecificity regarding nonclassical anomeric carbon and Z/E configuration, the method outlined in this study offers a unique solution to the longstanding challenge of accessing nonclassical C-glycosides with exclusive stereocontrol.

Visible-light-promoted direct desulfurization of glycosyl thiols to access C-glycosides

C-Glycosides are essential for the study of biological processes and the development of carbohydrate-based drugs. Despite the tremendous hurdles, glycochemists have often fantasized about the efficient, highly stereoselective synthesis of C-glycosides with the shortest steps under mild conditions. Herein, we report a desulfurative radical protocol to synthesize C-alkyl glycosides and coumarin C-glycosides under visible-light induced conditions without the need of an extra photocatalyst, in which stable and readily available glycosyl thiols that could be readily obtained from native sugars are activated in situ by pentafluoropyridine. The benefits of this procedure include high stereoselectivity, broad substrate scope, and easy handling. Mechanistic studies indicate that the in situ produced tetrafluoropyridyl S-glycosides form key electron donor-acceptor (EDA) complexes with Hantzsch ester (for C-alkyl glycosides) or Et3N (for coumarin C-glycosides), which, upon irradiation with visible light, trigger a cascade of glycosyl radical processes to access C-glycosides smoothly.

ZnI2-Mediated cis-Glycosylations of Various Constrained Glycosyl Donors: Recent Advances in cis-Selective Glycosylations

An efficient and versatile glycosylation methodology is crucial for the systematic synthesis of oligosaccharides and glycoconjugates. A direct intermolecular and an indirect intramolecular methodology have been developed, and the former can be applied to the synthesis of medium-to-long-chain glycans like that of nucleotides and peptides. The development of a generally applicable approach for the stereoselective construction of glycosidic bonds remains a major challenge, especially for the synthesis of 1,2-cis glycosides such as β-mannosides, β-L-rhamnosides, and β-D-arabinofuranosides with equatorial glycosidic bonds as well as α-D-glucosides with axial ones. This review introduces the direct formation of cis-glycosides using ZnI2-mediated cis-glycosylations of various constrained glycosyl donors, as well as the recent advances in the development of stereoselective cis-glycosylations.

Concise synthesis of 3-C-glycosyl isocoumarins and 2-glycosyl-4H-chromen-4-ones

A new Ru-catalyzed C-H activation/cyclization reaction for the synthesis of 3-C-glycosyl isocoumarins and 2-glycosyl-4H-chromen-4-ones with carbonyl sulfoxonium ylide glycogen are reported. In this catalytic system, benzoic acid and its derivatives react with carbonyl sulfoxonium ylide glycogen to yield isocoumarin C-glycosides, while 2-hydroxybenzaldehyde substrates react to produce chromone C-glycosides. These reactions were characterized by mild reaction conditions, broad substrate scope, high functional-group compatibility, and high stereoselectivity to yield several high-value isocoumarins and chromone skeleton-containing C-glycosides. The methods were successfully implemented in the context of large-scale reactions and the late-stage modification of complex natural products.

Assembly of Heterocyclic C-Glycosides by Ru-Catalyzed C-H Activation/Cyclization with Carbonyl Sulfoxonium Ylide Glyco-Reagents

New carbonyl sulfoxonium ylide glyco-reagents have been developed, enabling the synthesis of versatile heteroarene C-glycosides through a Ru-catalyzed C-H activation/annulation strategy. These reactions tolerate various saccharide donors and represent a significant advance in the stereoselective synthesis of heterocyclic C-glycosides. Furthermore, the strategy and methods could be applied to large-scale reactions and late-stage modifications of some structurally complex natural products or drugs.

Palladium-catalyzed Suzuki-Miyaura cross-couplings of stable glycal boronates for robust synthesis of C-1 glycals

C-1 Glycals serve as pivotal intermediates in synthesizing diverse C-glycosyl compounds and natural products, necessitating the development of concise, efficient and user-friendly methods to obtain C-1 glycosides is essential. The Suzuki-Miyaura cross-coupling of glycal boronates is notable for its reliability and non-toxic nature, but glycal donor stability remains a challenge. Herein, we achieve a significant breakthrough by developing stable glycal boronates, effectively overcoming the stability issue in glycal-based Suzuki-Miyaura coupling. Leveraging the balanced reactivity and stability of our glycal boronates, we establish a robust palladium-catalyzed glycal-based Suzuki-Miyaura reaction, facilitating the formation of various C(sp2)-C(sp), C(sp2)-C(sp2), and C(sp2)-C(sp3) bonds under mild conditions. Notably, we expand upon this achievement by developing the DNA-compatible glycal-based cross-coupling reaction to synthesize various glycal-DNA conjugates. With its excellent reaction reactivity, stability, generality, and ease of handling, the method holds promise for widespread appication in the preparation of C-glycosyl compounds and natural products.

Redox-neutral zinc-catalyzed cascade [1,4]-H shift/annulation of diaziridines with donor-acceptor aziridines

The coupling of diaziridines with donor-acceptor aziridines (DAAs) has been achieved using Zn-catalysis to furnish imidazopyrazole-4,4-dicarboxylates via [1,4]-hydride shift. The use of Zn-catalysis, [1,4]-hydride shift, natural product modification and a late-stage molecular docking study are important practical features.

Palladium(II)-Catalyzed Heck Coupling: Direct Stereoselective Synthesis of C-Aryl Glycosides from Nonactivated Glycals and Thianthrenium Salts

Here, we report an efficient Pd(II)-catalyzed Heck coupling reaction utilizing modular and readily available thianthrenium salts. The tunability and ease of thianthrenium salts facilitated the integration of glycals with drugs, natural products, and peptides. This method allows the incorporation of diverse glycals into structurally varied aglycon components without directing groups or prefunctionalization and provides a practical method for synthesizing C-aryl glycosides, offering a new avenue for the production of complex glycosides with potential applications.

Palladium-Catalyzed Regioselective C4-H Acyloxylation of Indoles with Carboxylic Acids via a Transient Directing Groups Strategy

The development of an efficient method for the synthesis of C4 oxy-substituted indoles is an appealing yet challenging task. Herein, we report a general palladium-catalyzed TDG approach for the direct C4-H acyloxylation of indoles. The protocol features atom and step economy, excellent regioselectivity, and good tolerance of functional groups. Moreover, the reaction can accommodate a range of carboxylic acids including benzoic acids, phenylacetic acids, and aliphatic acids.

Carboxylate-Directed Pd-Catalyzed β-C(sp3)-H Arylation of N-Methyl Alanine Derivatives for Diversification of Bioactive Peptides

This study presents a Pd(II)-catalyzed method for the β-C(sp3)-H arylation of N-Cbz- or N-Fmoc-protected N-methyl alanines, providing ready access to building blocks for N-methylated peptide synthesis. For this transformation, the native carboxylate was exploited as the directing group, attributing its success to the use of a monoprotected amino-pyridine ligand. Its synthetic utility was demonstrated by facile generation of nine analogues of the naturally occurring N-methylated cyclic peptide cycloaspeptide A.

Divergent total syntheses of ITHQ-type bis-β-carboline alkaloids by regio-selective formal aza-[4 + 2] cycloaddition and late-stage C-H functionalization

We herein report the first total syntheses of several bis-β-carboline alkaloids, picrasidines G, S, R, and T, and natural product-like derivatives in a divergent manner. Picrasidines G, S, and T feature an indolotetrahydroquinolizinium (ITHQ) skeleton, while picrasidine R possesses a 1,4-diketone linker between two β-carboline fragments. The synthesis of ITHQ-type bis-β-carboline alkaloids could be directly achieved by a late-stage regio-selective aza-[4 + 2] cycloaddition of vinyl β-carboline alkaloids, suggesting that this remarkable aza-[4 + 2] cycloaddition might be involved in the biosynthetic pathway. Computational studies revealed that such aza-[4 + 2] cycloaddition is a stepwise process and explained the unique regioselectivity (ΔΔG = 3.77 kcal mol-1). Moreover, the successful application of iridium-catalyzed C-H borylation on β-carboline substrates enabled the site-selective C-8 functionalization for efficient synthesis and structural diversification of this family of natural products. Finally, concise synthesis of picrasidine R by the thiazolium-catalyzed Stetter reaction was also accomplished.