Methyl 1,2-Orthoesters in Acid-Washed Molecular Sieves Mediated Glycosylations

De Novo Access to BODIPY C-Glycosides as Linker-Free Nonsymmetrical BODIPY-Carbohydrate Conjugates

Recent years have witnessed an increasing interest in the synthesis and study of BODIPY-glycoconjugates. Most of the described synthetic methods toward these derivatives involve postfunctional modifications of the BODIPY core followed by the covalent attachment of the fluorophore and the carbohydrate through a "connector". Conversely, few de novo synthetic approaches to linker-free carbohydrate-BODIPY hybrids have been described. We have developed a reliable modular, de novo, synthetic strategy to linker-free BODIPY-sugar derivatives using the condensation of pyrrole C-glycosides with a pyrrole-carbaldehyde derivative mediated by POCl3. This methodology allows labeling of carbohydrate biomolecules with fluorescent-enough BODIPYs within the biological window, stable in aqueous media, and able to display singlet oxygen generation.

An environmentally benign protocol for the synthesis of sugar 1,2-orthoesters in poly(ethylene glycol) dimethyl ether (DMPE)

An environmentally benign procedure has been developed for the synthesis of sugar orthoesters using anhydrous sodium acetate in poly (ethylene glycol)dimethyl ether (DMPE). Various sugar orthoesers were prepared without using volatile organic solvent and quaternary ammonium salt. The sugar orthoesters were obtained in good to excellent yields.

A Concise Synthesis of a BODIPY-Labeled Tetrasaccharide Related to the Antitumor PI-88

A convergent synthetic route to a tetrasaccharide related to PI-88, which allows the incorporation of a fluorescent BODIPY-label at the reducing-end, has been developed. The strategy, which features the use of 1,2-methyl orthoesters (MeOEs) as glycosyl donors, illustrates the usefulness of suitably-designed BODIPY dyes as glycosyl labels in synthetic strategies towards fluorescently-tagged oligosaccharides.

In Vitro Antimicrobial Activity of Isopimarane-Type Diterpenoids

The antimicrobial evaluation of twelve natural and hemisynthetic isopimarane diterpenes are reported. The compounds were evaluated against a panel of Gram-positive bacteria, including two methicillin-resistant Staphylococcus aureus (MRSA) strains and one vancomycin-resistant Enterococcus (VRE) strain. Only natural compounds 7,15-isopimaradien-19-ol (1) and 19-acetoxy-7,15-isopimaradien-3β-ol (6) showed promising results. Isopimarane (1) was the most active, showing MIC values between 6.76 µM against S. aureus (ATCC 43866) and 216.62 µM against E. faecalis (FFHB 427483) and E. flavescens (ATCC 49996). Compound (6) showed moderated activity against all tested microorganisms (MIC between value 22.54 and 45.07 µM). These compounds were found to be active against the methicillin-sensitive strains of S. aureus (CIP 106760 and FFHB 29593), showing MIC values of 13.55 (1) and 22.54 (6) µM. Both compounds were also active against vancomycin-resistant E. faecalis (ATCC 51299) (MIC values of 54.14 and 45.07 µM, respectively). In addition, the cytotoxicity of nine compounds 7,15-isopimaradien-3β,19-diol (2); mixture: 15-isopimarene-8β-isobutyryloxy-19-ol and 15-isopimarene-8β-butyryloxy-19-ol (3); 3β-acetoxy-7,15-isopimaradiene-19-ol (5); 19-acetoxy-7,15-isopimaradiene-3β-ol (6); 3β,19-diacetoxy-7,15-isopimaradiene (8); 15-isopimarene-8β,19-diol (9); 19-O-β-d-glucopyranoside-7,15-isopimaradiene (10); lagascatriol-16-O-β-d-glucopyranoside (11) and lagascatriol-16-O-α-d-mannopyranoside (12) was evaluated in the human breast cancer cell line MDA-MB-231. Isopimarane (2) was the only compound showing some cytotoxicity. The IC₅₀ value of compound (2) was 15 µM, suggesting a mild antiproliferative activity against these breast cancer cells.

Applications of alkyl orthoesters as valuable substrates in organic transformations, focusing on reaction media

In this review we focus on applications of alkyl orthoesters as valuable and efficient substrates to perform various classes of two-component and multi-component organic reactions. The article has classified them according to two aspects, which are: (i) a focus on the reaction medium (solvent-free conditions, aqueous media, and organic solvents); and (ii) an examination of product structures. Reaction accomplishment under solvent-free conditions is an eco-friendly process with the absence of volatile toxic solvents, which puts it in line with green chemistry goals. Water is an interesting choice in organic transformations due to its inexpensiveness and safety. The authors hope their assessment will help chemists to attain new approaches for utilizing alkyl orthoesters in various organic synthetic methods. The review covers the corresponding literature up to the beginning of 2020.

In this review we focus on applications of alkyl orthoesters as valuable and efficient substrates to perform various classes of two-component and multi-component organic reactions.

BODIPYs as Chemically Stable Fluorescent Tags for Synthetic Glycosylation Strategies towards Fluorescently Labeled Saccharides

A series of fluorescent boron-dipyrromethene (BODIPY, 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) dyes have been designed to participate, as aglycons, in synthetic oligosaccharide protocols. As such, they served a dual purpose: first, by being incorporated at the beginning of the process (at the reducing-end of the growing saccharide moiety), they can function as fluorescent glycosyl tags, facilitating the detection and purification of the desired glycosidic intermediates, and secondly, the presence of these chromophores on the ensuing compounds grants access to fluorescently labeled saccharides. In this context, a sought-after feature of the fluorescent dyes has been their chemical robustness. Accordingly, some BODIPY derivatives described in this work can withstand the reaction conditions commonly employed in the chemical synthesis of saccharides; namely, glycosylation and protecting-group manipulations. Regarding their photophysical properties, the BODIPY-labeled saccharides obtained in this work display remarkable fluorescence efficiency in water, reaching quantum yield values up to 82 %, as well as notable lasing efficiencies and photostabilities.

A Malonyl-Based Scaffold for Conjugatable Multivalent Carbohydrate-BODIPY Presentations

A concise synthetic route from methylmalonate to a tetravalent aliphatic scaffold has been developed. The ensuing tetra-tethered derivative is equipped with two hydroxyl groups, as well as orthogonal alkene and alkyne functionalities. The usefulness of the scaffold has been demonstrated with the preparation of two representative multivalent derivatives: (i) a tetravalent compound containing two D-mannose units, one fluorescent boron-dipyrromethene (BODIPY) dye and a suitably functionalized amino acid and (ii) by way of dimerization and saponification, a water-soluble tetramannan derivative containing two fluorescent BODIPY units. Additionally, photophysical measurements conducted on these derivatives support the viability of the herein designed single and double BODIPY-labeled carbohydrate-based clusters as fluorescent markers.