C-glucosylarenes from O-α-d-glucosyl trichloroacetimidates. Structure of bergenin derivatives

Rearrangement of Benzylic Trichloroacetimidates to Benzylic Trichloroacetamides

The rearrangement of allylic trichloroacetimidates is a well-known transformation, but the corresponding rearrangement of benzylic trichloroacetimidates has not been explored as a method for the synthesis of benzylic amines. Conditions that provide the trichloroacetamide product from a benzylic trichloroacetimidate in high yield have been developed. Methods were also investigated to transform the trichloroacetamide product directly into the corresponding amine, carbamate, and urea. A cationic mechanism for the rearrangement is implicated by the available data.

C-Glycopyranosyl Arenes and Hetarenes: Synthetic Methods and Bioactivity Focused on Antidiabetic Potential

This Review summarizes close to 500 primary publications and surveys published since 2000 about the syntheses and diverse bioactivities of C-glycopyranosyl (het)arenes. A classification of the preparative routes to these synthetic targets according to methodologies and compound categories is provided. Several of these compounds, regardless of their natural or synthetic origin, display antidiabetic properties due to enzyme inhibition (glycogen phosphorylase, protein tyrosine phosphatase 1B) or by inhibiting renal sodium-dependent glucose cotransporter 2 (SGLT2). The latter class of synthetic inhibitors, very recently approved as antihyperglycemic drugs, opens new perspectives in the pharmacological treatment of type 2 diabetes. Various compounds with the C-glycopyranosyl (het)arene motif were subjected to biological studies displaying among others antioxidant, antiviral, antibiotic, antiadhesive, cytotoxic, and glycoenzyme inhibitory effects.

Diversity, pharmacology and synthesis of bergenin and its derivatives: potential materials for therapeutic usages

Bergenin, a natural secondary metabolite, has been isolated from different parts of a number of plants. It is one of active ingredients in herbal and Ayurvedic formulations. It exhibits antiviral, antifungal, antitussive, antiplasmodial, antiinflammatory, antihepatotoxic, antiarrhythmic, antitumor, antiulcerogenic, antidiabetic and wound healing properties. It has been analyzed and estimated in different plant extracts, blood and drug samples using chromatographic techniques, and pharmacokinetic studies have been made. Several bergenin derivatives were isolated and/or synthesized and were found to possess pharmacological activities. Total synthesis of bergenin and its derivatives were reported. This review article covers literature on bergenin and its derivatives until 2013. Ethnomedicinal value of bergenin containing plant materials is also highlighted. This comprehensive review provides information on the potentiality of bergenin and its derivatives for therapeutic usages.

Concise total syntheses of aspalathin and nothofagin

Syntheses of the C-glycosyl flavone natural products aspalathin and nothofagin have been accomplished in eight steps from tribenzyl glucal, tribenzylphloroglucinol, and either 4-(benzyloxy)phenylacetylene or 3,4-bis(benzyloxy)phenylacetylene. The key step of the syntheses involves a highly stereoselective Lewis acid promoted coupling of 1,2-di-O-acyl-3,4,6-tribenzylglucose with tribenzylphloroglucinol, which gives rise to the corresponding beta-C-aryl glycoside in 30-65% yields.

Benzyne arylation of oxathiane glycosyl donors

The arylation of bicyclic oxathiane glycosyl donors has been achieved using benzyne generated in situ from 1-aminobenzotriazole (1-ABT) and lead tetraacetate. Following sulfur arylation, glycosylation of acetate ions proceeded with high levels of stereoselectivity to afford α-glycosyl acetates in a ‘one-pot’ reaction, even in the presence of alternative acceptor alcohols.

Aryl C-glycosylation of phenols with glycosyl trifluoroacetimidates

Aryl C-glycosylation of a variety of phenols with glycosyl trifluoroacetimidates in the presence of TMSOTf was examined, leading to the corresponding ortho-hydroxyaryl C-glycosides in variable yields.

An Efficient Stereoselective Dihydroxylation of Glycals using a Bimetallic System, RuCl3/CeCl3/NaIO4

A catalytic dihydroxylation reaction on glycals has been developed using a bimetallic oxidizing system to furnish sugar 1,2-diols in a highly stereoselective manner.

Synthesis of Tricolorin F

A hetero-trisaccharide resin glycoside of jalapinolic acid known as tricolorin F has been synthesized. The approach involved the preparation of intermediate 5 and a subsequent coupling reaction with imidate 6 to produce disaccharide 7, which after deacetylation generated intermediate 8. A further coupling between this glycosyl acceptor and the quinovose glycosyl donor 9 resulted in the formation of the tricoloric acid C derivative 10. Basic hydrolysis afforded the intermediate 11, which was subsequently lactonized under Yamaguchi conditions to produce protected macrolactone 12. Removal of acetonide and benzyl protecting groups afforded pure tricolorin F (1).

Synthesis of C-aryl and C-alkyl glycosides using glycosyl phosphates

[reaction: see text] Mannosyl and glucosyl phosphate donors were successfully used in constructing C-aryl linkages common to many natural products via a Lewis acid induced Fries-like rearrangement. The rearrangement was stereo- and regiospecific, yielding only one C-glycoside product. C-Alkyl glycoside carbohydrate mimetics were generated by using silicon-derived C-nucleophiles and glycosyl phosphates.

The structure of bergenin

X-ray analysis of the 3,4,8,10,11-penta-acetate (3) of bergenin has confirmed the earlier structural assignments.

Synthesis of C-glycosylarenes by way of internal reactions of benzylated and benzoylated carbohydrate derivatives

"Internal" C-glycosylarenes [e.g., (2R,3S,3aS,9bR)-3,3a,5,9b-tetrahydro-3-methoxy- and -3,7-dimethoxy-2-methoxymethyl-2H-furo[3,2-c][2]benzopyran] were prepared by intramolecular reactions of 2-O-benzyl derivatives of methyl 3,5-di-O-methyl-D-xylofuranoside (2) and their conversion into authentic C-glycosylated aromatic systems was investigated. The auxiliary benzylic linkage could not be cleaved by hydrogenolysis; isochroman derivatives (e.g., (3S)-3,4-dihydro-3-[(1R,2R)-2-hydroxy-1,3-dimethoxypropyl]-5-metho xy-1H- 2-benzopyran) were obtained under these conditions. However, oxidation of the primary benzylic position with ruthenium tetraoxide gave the corresponding lactone (a dihydroisocoumarin derivative, e.g., (2R,3S,3aS,9bR)-2,3,3a,9b-tetrahydro-3,7-dimethoxy-2-methoxy - methyl-5H-furo[3,2-c][2]benzopyran-5-one) which could be opened by saponification, thereby leading to a stereochemically unique C-glycosylbenzoic acid derivative. The same type of lactone was obtained directly from a derivative of 2 bearing a sufficiently reactive benzoyl group at O-2 (3,5-dimethoxybenzoyl); this process provides a useful approach to a heterocyclic system present in a variety of natural products. In related studies, the 2-O-phenyl substituent was found to be much less reactive than the 2-O-benzyl group in intramolecular Friedel-Crafts reactions of 2-O-substituted glycofuranosides. The first examples of successful internal C-arylation in the pyranoid series were achieved from 2-O-(3-methoxybenzyl)-D- mannopyranosides; the resulting "internal C-glycosides" [( 2R,3S,4S,4aS,10bS)-2,3,4,4a,6,10b- hexahydro-3,4,8-trimethoxy-2-methoxymethylpyrano[3,2-c][2]benzopyr an and 3,4-bis(benzyloxy)-2-benzyloxymethyl-8-methoxy analog] contain a heterocyclic skeleton closely related to that of the natural product bergenin.