Highlights from the 55th Bürgenstock conference on stereochemistry 2022

In May 2022, the 55th Bürgenstock Conference on Stereochemistry happened in person once again. This summary provides insight into the scientific themes discussed during the most recent meeting of this historic and multi-disciplinary conference. [Image: see text

Automated assembly of starch and glycogen polysaccharides

Polysaccharides are Nature’s most abundant biomaterials essential for plant cell wall construction and energy storage. Seemingly minor structural differences result in entirely different functions: cellulose, a β (1–4) linked glucose polymer, forms fibrils that can support large trees, while amylose, an α (1–4) linked glucose polymer forms soft hollow fibers used for energy storage. A detailed understanding of polysaccharide structures requires pure materials that cannot be isolated from natural sources. Automated Glycan Assembly provides quick access to trans-linked glycans analogues of cellulose, but the stereoselective installation of multiple cis-glycosidic linkages present in amylose has not been possible to date. Here, we identify thioglycoside building blocks with different protecting group patterns that, in concert with temperature and solvent control, achieve excellent stereoselectivity during the synthesis of linear and branched α-glucan polymers with up to 20 cis-glycosidic linkages. The molecules prepared with the new method will serve as probes to understand the biosynthesis and the structure of α-glucans

Automated access to well-defined ionic oligosaccharides

Ionic polysaccharides are part of many biological events, but lack structural characterisation due to challenging purifications and complex synthesis. Four monosaccharides bearing modifications not found in nature are used for the automated synthesis of a collection of ionic oligosaccharides. Structural analysis reveals how the charge pattern affects glycan conformation

Synthetic approaches to break the chemical shift degeneracy of glycans

NMR spectroscopy is the leading technique for determining glycans’ three-dimensional structure and dynamic in solution as well as a fundamental tool to study protein-glycan interactions. To overcome the severe chemical shift degeneracy of these compounds, synthetic probes carrying NMR-active nuclei (e.g., 13 C or 19 F) or lanthanide tags have been proposed. These elegant strategies permitted to simplify the complex NMR analysis of unlabeled analogues, shining light on glycans’ conformational aspects and interaction with proteins. Here, we highlight some key achievements in the synthesis of specifically labeled glycan probes and their contribution towards the fundamental understanding of glycans

Modulating the surface and photophysical properties of carbon dots to access colloidal photocatalysts for cross-couplings

Photoredox-mediated Ni-catalyzed cross-couplings are powerful transformations to form carbon–heteroatom bonds and are generally photocatalyzed by noble metal complexes. Low-cost and easy-to-prepare carbon dots (CDs) are attractive quasi-homogeneous photocatalyst alternatives, but their applicability is limited by their short photoluminescence (PL) lifetimes. By tuning the surface and PL properties of CDs, we designed colloidal CD nano-photocatalysts for a broad range of Ni-mediated cross-couplings between aryl halides and nucleophiles. In particular, a CD decorated with amino groups permitted coupling to a wide range of aryl halides and thiols under mild, base-free conditions. Mechanistic studies suggested dynamic quenching of the CD excited state by the Ni co-catalyst and identified that pyridinium iodide (pyHI), a previously used additive in metallaphotocatalyzed cross-couplings, can also act as a photocatalyst in such transformations

Desigualdade na distribuição da renda e crescimento econômico: Nova evidência da América Latina

This paper explores the relationship between the inequality of income distribution and the economic growth of 20 Latin American and Caribbean countries during the 1980-2010 period. The study shows that the features of this relationship depend on the income level. In general, inequality is harmful to economic growth. However, when it comes to the upper tail of the richer countries’ income distribution, higher inequality encourages economic growth and the relation becomes positive. Thus, contrary to the economic policy recommendations for the richer countries, our evidence suggests that progressive redistributive policies in favor of poorer layers of population promote economic growth in lower income economies.En este artículo se estudia la relación entre la desigualdad del ingreso y el crecimiento para veinte economías de América Latina y el Caribe, para el período 1980-2010. Los resultados muestran que la relación entre desigualdad e ingreso depende fuertemente del nivel de ingreso que un país presente. En general, la desigualdad afecta de manera negativa al crecimiento. En cambio, para los países más ricos, mayor desigualdad determina mayor crecimiento. Por ende, las recomendaciones de política que surgen de los resultados de este artículo serían aquellas con objetivo de reforzar las políticas redistributivas progresivas en los países de menor ingreso

Automated glycan assembly of ¹⁹F labelled glycan probes enables high‐throughput NMR studies of protein‐glycan interactions

Protein‐glycan interactions mediate important biological processes, including pathogen host invasion and cellular communication. Major challenges to monitoring these low affinity interactions are the required high sensitivity of a biophysical assay and to cover a breath of synthetic well‐defined structures. Here, we showcase an expedite approach that integrates automated glycan assembly (AGA) of 19 F labelled probes and high‐throughput NMR methods, enabling the study of protein‐glycan interactions. Synthetic Lewis type 2 antigens were screened against seven glycan binding proteins (GBPs), including DC‐SIGN and BambL, respectively involved in HIV‐1 and lung infections in immunocompromised patients, confirming the preference for fucosylated glycans (Le x , H type 2, Le y ). Previously unknown glycan‐lectin weak interactions were detected, and thermodynamic data were obtained. Enzymatic reactions were monitored in real‐time, delivering kinetic parameters. These results demonstrate the utility of AGA combined with 19 F NMR for the discovery and characterization of glycan‐protein interactions, opening up new perspectives for 19 F labelled complex glycans

The flexibility of oligosaccharides unveiled through residual dipolar coupling analysis

The intrinsic flexibility of glycans complicates the study of their structures and dynamics, which are often important for their biological function. NMR has provided insights into the conformational, dynamic and recognition features of glycans, but suffers from severe chemical shift degeneracy. We employed labelled glycans to explore the conformational behaviour of a β(1-6)-Glc hexasaccharide model through residual dipolar couplings (RDCs). RDC delivered information on the relative orientation of specific residues along the glycan chain and provided experimental clues for the existence of certain geometries. The use of two different aligning media demonstrated the adaptability of flexible oligosaccharide structures to different environments