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The sulfolipid sulfoquinovosyl diacylglycerol (SQDG), produced by plants, algae, and cyanobacteria, constitutes a major sulfur reserve in the biosphere. Microbial breakdown of SQDG is critical for the biological utilization of its sulfur. This commences through release of the parent sugar, sulfoquinovose (SQ), catalyzed by sulfoquinovosidases (SQases). These vanguard enzymes are encoded in gene clusters that code for diverse SQ catabolic pathways. To identify, visualize and isolate glycoside hydrolase CAZY‐family 31 (GH31) SQases in complex biological environments, we introduce SQ cyclophellitol‐aziridine activity‐based probes (ABPs). These ABPs label the active site nucleophile of this enzyme family, consistent with specific recognition of the SQ cyclophellitol‐aziridine in the active site, as evidenced in the 3D structure of Bacillus megaterium SQase. A fluorescent Cy5‐probe enables visualization of SQases in crude cell lysates from bacteria harbouring different SQ breakdown pathways, whilst a biotin‐probe enables SQase capture and identification by proteomics. The Cy5‐probe facilitates monitoring of active SQase levels during different stages of bacterial growth which show great contrast to more traditional mRNA analysis obtained by RT‐qPCR. Given the importance of SQases in global sulfur cycling and in human microbiota, these SQase ABPs provide a new tool with which to study SQase occurrence, activity and stability. [ABSTRACT FROM AUTHOR]

The transfer of an adenosine diphosphate (ADP) ribose moiety to a nucleophilic side chain by consumption of nicotinamide adenine dinucleotide is referred to as ADP‐ribosylation, which allows for the spatiotemporal regulation of vital processes such as apoptosis and DNA repair. Recent mass‐spectrometry based analyses of the "ADP‐ribosylome" have identified histidine as ADP‐ribose acceptor site. In order to study this modification, a fully synthetic strategy towards α‐configured N(τ)‐ and N(π)‐ADP‐ribosylated histidine‐containing peptides has been developed. Ribofuranosylated histidine building blocks were obtained via Mukaiyama‐type glycosylation and the building blocks were integrated into an ADP‐ribosylome derived peptide sequence using fluorenylmethyloxycarbonyl (Fmoc)‐based solid‐phase peptide synthesis. On‐resin installation of the ADP moiety was achieved using phosphoramidite chemistry, and global deprotection provided the desired ADP‐ribosylated oligopeptides. The stability under various chemical conditions and resistance against (ADP‐ribosyl) hydrolase‐mediated degradation has been investigated to reveal that the constructs are stable under various chemical conditions and non‐degradable by any of the known ADP‐ribosylhydrolases. [ABSTRACT FROM AUTHOR]

We herein report the first total synthesis of the Streptococcus pneumoniae serotype 1 (Sp1) oligosaccharide, a unique zwitterionic capsular polysaccharide carrying labile O‐acetyl esters. The target oligosaccharides, featuring rare α‐2,4‐diamino‐2,4,6‐trideoxy galactose (AAT) and α‐galacturonic acids, were assembled up to the 9‐mer level, in a highly stereoselective manner using trisaccharide building blocks. The lability of the O‐acetyl esters imposed a careful deprotection scheme to prevent migration and hydrolysis. The migration was investigated in detail at various pD values using NMR spectroscopy, to show that migration and hydrolysis of the C‐3‐O‐acetyl esters readily takes place under neutral conditions. Structural investigation showed the oligomers to adopt a right‐handed helical structure with the acetyl esters exposed on the periphery of the helix in close proximity of the neighboring AAT residues, thereby imposing conformational restrictions on the AATα1‐4GalA(3OAc) glycosidic linkages, supporting the helical shape of the polysaccharide, that has been proposed to be critical for its unique biological activity. [ABSTRACT FROM AUTHOR]

The assembly of complex bacterial glycans presenting rare structural motifs and cis‐glycosidic linkages is significantly obstructed by the lack of knowledge of the reactivity of the constituting building blocks and the stereoselectivity of the reactions in which they partake. We here report a strategy to map the reactivity of carbohydrate building blocks and apply it to understand the reactivity of the bacterial sugar, caryophyllose, a rare C12‐monosaccharide, containing a characteristic tetrasubstituted stereocenter. We mapped reactivity–stereoselectivity relationships for caryophyllose donor and acceptor glycosides by a systematic series of glycosylations in combination with the detection and characterization of different reactive intermediates using experimental and computational techniques. The insights garnered from these studies enabled the rational design of building blocks with the required properties to assemble mycobacterial lipooligosaccharide fragments of M. marinum. [ABSTRACT FROM AUTHOR]

Galactosaminogalactan (GAG) is a prominent cell wall component of the opportunistic fungal pathogen Aspergillus fumigatus. GAG is a heteropolysaccharide composed of α‐1,4‐linked galactose, galactosamine and N‐acetylgalactosamine residues. To enable biochemical studies, a library of GAG‐fragments was constructed featuring specimens containing α‐galactose‐, α‐galactosamine and α‐N‐acetyl galactosamine linkages. Key features of the synthetic strategy include the use of di‐tert‐butylsilylidene directed α‐galactosylation methodology and regioselective benzoylation reactions using benzoyl‐hydroxybenzotriazole (Bz‐OBt). Structural analysis of the Gal, GalN and GalNAc oligomers by a combination of NMR and MD approaches revealed that the oligomers adopt an elongated, almost straight, structure, stabilized by inter‐residue H‐bonds, one of which is a non‐conventional C−H⋅⋅⋅O hydrogen bond between H5 of the residue (i+1) and O3 of the residue (i). The structures position the C‐2 substituents almost perpendicular to the oligosaccharide main chain axis, pointing to the bulk solvent and available for interactions with antibodies or other binding partners. [ABSTRACT FROM AUTHOR]