Exploring divalent conjugates of 5-N-acetyl-neuraminic acid as inhibitors of coxsackievirus A24 variant (CVA24v) transduction

Coxsackievirus A24 variant (CVA24v) is responsible for several outbreaks and two pandemics of the highly contagious eye infection acute hemorrhagic conjunctivitis (AHC).

Designing and Development of FRET-Based Nanosensor for Real Time Analysis of N-Acetyl-5-Neuraminic Acid in Living Cells

N-acetyl-5-neuraminic acid (NeuAc) plays crucial role in improving the growth, brain development, brain health maintenance, and immunity enhancement of infants. Commercially, it is used in the production of antiviral drugs, infant milk formulas, cosmetics, dietary supplements, and pharmaceutical products. Because of the rapidly increasing demand, metabolic engineering approach has attracted increasing attention for NeuAc biosynthesis. However, knowledge of metabolite flux in biosynthetic pathways is one of the major challenges in the practice of metabolic engineering. So, an understanding of the flux of NeuAc is needed to determine its cellular level at real time. The analysis of the flux can only be performed using a tool that has the capacity to measure metabolite level in cells without affecting other metabolic processes. A Fluorescence Resonance Energy Transfer (FRET)-based genetically-encoded nanosensor has been generated in this study to monitor the level of NeuAc in prokaryotic and eukaryotic cells. Sialic acid periplasmic binding protein (SiaP) from Haemophilus influenzae was exploited as a sensory element for the generation of nanosensor. The enhanced cyan fluorescent protein (ECFP) and Venus were used as Fluroscence Resonance Energy Transfer (FRET) pair. The nanosensor, which was termed fluorescent indicator protein for sialic acid (FLIP-SA), was successfully transformed into, and expressed in Escherichia coli BL21 (DE3) cells. The expressed protein of the nanosensor was isolated and purified. The purified nanosensor protein was characterized to assess the affinity, specificity, and stability in the pH range. The developed nanosensor exhibited FRET change after addition to NeuAc. The developed nanosensor was highly specific, exhibited pH stability, and detected NeuAc levels in the nanomolar to milimolar range. FLIP-SA was successfully introduced in bacterial and yeast cells and reported the real-time intracellular levels of NeuAc non-invasively. The FLIP-SA is an excellent tool for the metabolic flux analysis of the NeuAc biosynthetic pathway and, thus, may help unravel the regulatory mechanism of the metabolic pathway of NeuAc. Furthermore, FLIP-SA can be used for the high-throughput screening of E. coli mutant libraries for varied NeuAc production levels.

Facile Anomer-oriented Syntheses of 4-Methylumbelliferyl Sialic Acid Glycosides

<p>As part of a program to find new sialidases and determine their enzymatic specificity and catalytic activity, a library of 4-methylumbelliferyl sialic acid glycosides derivatised at the C-5 position were prepared from <i>N</i>-acetylneuraminic acid. Both α- and β-4-methylumbelliferyl sialic acid glycosides were prepared in high yields and excellent stereoselectivity. Alpha anomers were accessed via reagent control by utilising additive CH₃CN and TBAI, whereas the beta anomers were synthesised through a diastereoselective addition reaction of iodine and the aglycone to the corresponding glycal followed by reduction of the resulting 3-iodo compounds. Both anomer-oriented synthetic pathways allow for gram-scale stereoselective syntheses of the desired C-5 modified neuraminic acid derivatives for use as tools to quantify the enzymatic activity and substrate specificity of known<b> </b>sialidases, and potential detection and investigation of<b> </b>novel sialidases.</p>

Facile Anomer-oriented Syntheses of 4-Methylumbelliferyl Sialic Acid Glycosides

<p>As part of a program to find new sialidases and determine their enzymatic specificity and catalytic activity, a library of 4-methylumbelliferyl sialic acid glycosides derivatised at the C-5 position were prepared from <i>N</i>-acetylneuraminic acid. Both α- and β-4-methylumbelliferyl sialic acid glycosides were prepared in high yields and excellent stereoselectivity. Alpha anomers were accessed via reagent control by utilising additive CH₃CN and TBAI, whereas the beta anomers were synthesised through a diastereoselective addition reaction of iodine and the aglycone to the corresponding glycal followed by reduction of the resulting 3-iodo compounds. Both anomer-oriented synthetic pathways allow for gram-scale stereoselective syntheses of the desired C-5 modified neuraminic acid derivatives for use as tools to quantify the enzymatic activity and substrate specificity of known<b> </b>sialidases, and potential detection and investigation of<b> </b>novel sialidases.</p>

Synthesis of 4-O-Alkylated N-Acetylneuraminic Acid Derivatives

<p><i>N</i>-acetyl neuraminic acid<i> </i>(Neu5Ac) is a densely functionalized nine-carbon monosaccharide. It ubiquitously decorates the surface of mammalian cells were it is found in terminal positions of glycolipids and glycoproteins. This important saccharide and natural analogs play important roles in a number of processes in health and disease. Despite this few Neu5Ac based therapeutics have been developed. To further study and understand the chemistry and biology of Neu5Ac efficient protocols for synthesis of the parent natural compounds as well as synthetic analogs are required. In the manuscript, we report investigation of alkylation reactions to produce selectively modified Neu5Ac with focus on position 4. The study provides insights in the reaction and we establish robust protocols that allow selective modification of Neu5Ac for use as tool compounds and starting points for drug discovery.</p>

Synthesis of 4-O-Alkylated N-Acetylneuraminic Acid Derivatives

<p><i>N</i>-acetyl neuraminic acid<i> </i>(Neu5Ac) is a densely functionalized nine-carbon monosaccharide. It ubiquitously decorates the surface of mammalian cells were it is found in terminal positions of glycolipids and glycoproteins. This important saccharide and natural analogs play important roles in a number of processes in health and disease. Despite this few Neu5Ac based therapeutics have been developed. To further study and understand the chemistry and biology of Neu5Ac efficient protocols for synthesis of the parent natural compounds as well as synthetic analogs are required. In the manuscript, we report investigation of alkylation reactions to produce selectively modified Neu5Ac with focus on position 4. The study provides insights in the reaction and we establish robust protocols that allow selective modification of Neu5Ac for use as tool compounds and starting points for drug discovery.</p>