Current Synthetic Approaches to the Synthesis of Carbasugars from Non-Carbohydrate Sources

Exploring the Chemistry and Applications of Thio-, Seleno-, and Tellurosugars

Given the crucial roles of carbohydrates in energy supply, biochemical processes, signaling events and the pathogenesis of several diseases, the development of carbohydrate analogues, called glycomimetics, is a key research area in Glycobiology, Pharmacology, and Medicinal Chemistry. Among the many structural transformations explored, the replacement of endo- and exocyclic oxygen atoms by carbon (carbasugars) or heteroatoms, such as nitrogen (aza- and iminosugars), phosphorous (phosphasugars), sulfur (thiosugars), selenium (selenosugars) or tellurium (tellurosugars) have garnered significant attention. These isosteric substitutions can modulate the carbohydrate bioavailability, stability, and bioactivity, while introducing new properties, such as redox activity, interactions with pathological lectins and enzymes, or cytotoxic effects. In this manuscript we have focused on three major families of glycomimetics: thio-, seleno-, and tellurosugars. We provide a comprehensive review of the most relevant synthetic pathways leading to substitutions primarily at the endocyclic and glycosidic positions. The scope includes metal-catalyzed reactions, organocatalysis, electro- and photochemical transformations, free-radical processes, and automated syntheses. Additionally, mechanistic insights, stereoselectivity, and biological properties are also discussed. The structural diversity and promising bioactivities of these glycomimetics underscore their significance in this research area.

An Update: Enzymatic Synthesis for Industrial Applications

Supported by rapid technological advancements, biocatalytic applications have matured into sustainable, scalable, and cost-competitive alternatives to established chemical catalysis. This review presents the most recent examples of enzyme-based solutions for the manufacturing of molecules with extended carbon-carbon frameworks and multiple stereogenic centers at commercial scale, including peptide building blocks, (rare) sugars, synthetic (oligo)nucleotides, and terpenoids, such as (-)-Ambrox®. Novel enzyme classes are highlighted along with their potential applications-the synthesis of DNA/RNA, the depolymerization of synthetic plastics, or fully enzymatic protection/deprotection schemes-pointing toward the diversification and broader industrial utilization of biocatalysis-based processes.

Diverse Library of 5a-Substituted Carba-Glucosamines

Carba-sugars─carbohydrate mimics in which the ring oxygen is replaced by a methylene group─are carbohydrate analogues of natural or synthetic origin that can have important biological functions. Especially, carba-aminosugars and glycosides containing carba-aminosugars are potent antibiotics. Furthermore, they have been shown to induce the self-cleavage reaction of the glmS riboswitch and thereby inhibit the ability of bacteria to synthesize glucosamine-6-phosphate, which is required to build up the bacterial cell wall. We report the synthesis of a library of 20 carba-glucosamine derivatives with various substituents at the carba-position including amines, alkyl, alkoxy, and aryloxy derivatives, fluorine derivatives, glycosylated derivatives, and a cyclopropane derivative. The compounds were obtained in an efficient way starting from late-stage synthetic intermediates of an earlier-developed synthesis of carba-substituted carba-glucosamines. All carba-glucosamine mimics were tested for their antibacterial properties against Bacillus subtilis, and some of them displayed promising activities in a filter disk assay.

General strategy for the synthesis of unsaturated carbasugars via a diastereoselective seleno-Michael/aldol reaction

Carbasugars are a diverse group of carbohydrate mimetics in which the ring oxygen is replaced by a methylene group. We have developed a simple and efficient carbasugar synthesis from d-aldopentoses via temporary protection of the hydroxyl moieties with TMS groups followed by consecutive intramolecular tandem Michael/aldol cyclisation. It is important to note that only the n-butylselenolate nucleophile is compatible with per-O-TMS-protected substrates. The desired products were obtained in five steps, with total yields reaching up to 40% with excellent diastereoselectivity of up to 19 : 1.

Synergy of R-(-)carvone and cyclohexenone-based carbasugar precursors with antibiotics to enhance antibiotic potency and inhibit biofilm formation

The widespread use of antibiotics in recent decades has been a major factor in the emergence of antibiotic resistances. Antibiotic-resistant pathogens pose increasing challenges to healthcare systems in both developing and developed countries. To counteract this, the development of new antibiotics or adjuvants to combat existing resistance to antibiotics is crucial. Glycomimetics, for example carbasugars, offer high potential as adjuvants, as they can inhibit metabolic pathways or biofilm formation due to their similarity to natural substrates. Here, we demonstrate the synthesis of carbasugar precursors (CSPs) and their application as biofilm inhibitors for E. coli and MRSA, as well as their synergistic effect in combination with antibiotics to circumvent biofilm-induced antibiotic resistances. This results in a biofilm reduction of up to 70% for the CSP rac-7 and a reduction in bacterial viability of MRSA by approximately 45% when combined with the otherwise ineffective antibiotic mixture of penicillin and streptomycin.