Gram-scale carbasugar synthesis via intramolecular seleno-Michael/aldol reaction

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.

Chemoselective Nozaki-Hiyama-Takai-Kishi and Grignard reaction: short synthesis of some carbahexopyranoses

A common, divergent, efficient, stereoselective and short approach for the total syntheses of some carbahexopyranoses namely, MK7607, (-)-gabosine A, (-)-conduritol E, (-)-conduritol F, 6a-carba-β-d-fructopyranose and other carbasugars using chemoselective Grignard or Nozaki-Hiyama-Takai-Kishi (NHTK) reactions and RCM. Herein, the Grignard and NHTK reactions are able to differentiate the reactivity difference between lactol or lactolacetate and aldehyde of 2 & 6 under given conditions to give the desired skeleton chemoselectivity.

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.

Heparan Sulfate, Mucopolysaccharidosis IIIB and Sulfur Metabolism Disorders

Mucopolysaccharidosis, type IIIB (MPS IIIB) is a rare disease caused by mutations in the N-alpha-acetylglucosaminidase (NAGLU) gene resulting in decreased or absent enzyme activity. On the cellular level, the disorder is characterized by the massive lysosomal storage of heparan sulfate (HS)—one species of glycosaminoglycans. HS is a sulfur-rich macromolecule, and its accumulation should affect the turnover of total sulfur in cells; according to the studies presented here, it, indeed, does. The lysosomal degradation of HS in cells produces monosaccharides and inorganic sulfate (SO₄²⁻). Sulfate is a product of L-cysteine metabolism, and any disruption of its levels affects the entire L-cysteine catabolism pathway, which was first reported in 2019. It is known that L-cysteine level is elevated in cells with the Naglu^−/− gene mutation and in selected tissues of individuals with MPS IIIB. The level of glutathione and the Naglu^−/− cells’ antioxidant potential are significantly reduced, as well as the activity of 3-mercaptopyruvate sulfurtransferase (MPST, EC 2.8.1.2) and the level of sulfane sulfur-containing compounds. The direct reason is not yet known. This paper attempts to identify some of cause-and-effect correlations that may lead to this condition and identifies research directions that should be explored.

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

Carbasugars are a group of carbohydrate derivatives in which the ring oxygen is replaced by a methylene group, producing a molecule with a nearly identical structure but highly different behavior. Over time, this definition has been extended to include other unsaturated cyclohexenols and carba-, di-, and polysaccharides. Such molecules can be found in bacterial strains and the human body, acting as neurotransmitters (e.g., inositol trisphosphate). In science, there are a wide range of research areas that are affected by, and involve, carbasugars, such as studies on enzyme inhibition, lectin-binding, and even HIV and cancer treatment. In this review article, different methods for synthesizing carbasugars, their derivatives, and similar cyclohexanes presenting comparable characteristics are summarized and evaluated, utilizing diverse starting materials and synthetic procedures.