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Biomass Chemistry
Published in Jay J. Cheng, Biomass to Renewable Energy Processes, 2017
So far, the structures of monosaccharides have been depicted in a chain form. However, in solution, monosaccharides form ring structures that are in equilibrium with the open chain forms. In general, aldehydes and ketones react with alcohols to form hemiacetals and hemiketals. Since monosaccharides contain several hydroxyl groups and one aldehyde or ketone group within the same molecule, they form cyclic hemiacetals and hemiketals. Most monosaccharides form five member rings called furanoses or six member rings called pyranoses. Smaller (<4) and larger (>6) hemiacetals and hemiketals are thermodynamically unstable.
Biomolecules and Complex Biological Entities
Published in Simona Badilescu, Muthukumaran Packirisamy, BioMEMS, 2016
Simona Badilescu, Muthukumaran Packirisamy
Because the five-membered ring structure resembles the organic molecule furan, derivatives with this structure are termed furanoses. Those with six-membered rings resemble the organic molecule pyran and are termed pyranoses. In the case of pyranose rings, the two favored structures are the chair conformation and the boat conformation. Straight and ring structures of glucose are given in Figure 3.38 for reference.
Carbohydrates and Nucleic Acids
Published in Michael B. Smith, A Q&A Approach to Organic Chemistry, 2020
A furanose is a saccharide in a five-membered ring that consists of four carbon atoms and one oxygen atom. Formally, a furanose is a derivative of tetrahydrofuran, a five-membered ring ether. What is an aldohexose? A ketohexose? An aldopyranose? A ketofuranose?
Chemical pretreatment of corncob for the selective dissolution of hemicellulose and lignin: influence of pretreatment on the chemical, morphological and thermal features
Published in Biofuels, 2023
Alejandro Ramírez-Estrada, Violeta Y. Mena-Cervantes, Ignacio Elizalde-Martínez, Gabriel Pineda-Flores, Raúl Hernández-Altamirano
Figure 12 shows the IR spectrum of soluble-acid compounds (Soluble-AC-IR). This spectrum shows a broad absorption band at 3600–3000 cm−1 (O − H stretching vibration in carbohydrates); absorption bands at 3000–2800 cm−1 (C − H stretching vibration); 1721 cm−1 (C = O stretching vibration of the carboxyl group in acetyl group); 1640 cm−1 (C = C stretching vibrations), absorption bands in the range 1500–1200 cm−1 (vibrations of C − H, −OH, C–O bonds); a strong overlapped-adsorption at 1034 cm−1 (vibration C − O bonds and C − O−C stretching vibration); 943 cm−1 (C − O stretching vibration of pyranose ring), and at 897 cm−1 (vibration of the β-glycoside bond in oligosaccharides). The absorption bands in the ranges 3600–3000 cm−1 and 1200–800 cm−1 confirm the presence of sugars pyranose and furanose structures; these absorption bands are characteristics of sugars and oligosaccharides [55]. Likewise, the absorption band observed at 1721.50 cm−1 denotes the presence of acetyl acids linked to the backbone of oligosaccharides [56].
Crystalline fructose production: a conceptual design with experimental data and operating cost analysis
Published in Chemical Engineering Communications, 2022
C. E. Crestani, A. T. C. R Silva, A. Bernardo, C. B. B. Costa, M. Giulietti
In solutions with ethanol mass fraction in the solvent of 0.9 (Experiments 7, 8, and 9), yields are lower than expected too, although the solutions at this mass fraction are less viscous than in the set of the first three experiments. Flood et al. (Flood et al. 1996) showed that fructose interconverts naturally in solution into five tautomeric forms by mutarotation, but only β-D-fructopyranose crystallizes. According to those authors, in aqueous solutions, β-D-fructopyranose is the most representative tautomer, with more than 70% at 303.15 K, for example. In aqueous-ethanolic solutions, the most representative tautomer is β-D-fructofuranose. Besides that, the rate of mutarotation in solutions with ethanol mass fraction in the solvent of 0.9 is fivefold slower than in aqueous solutions. Therefore, the tautomeric composition of fructose in aqueous-ethanolic solutions affects the crystallization process, due to the slow rate of mutarotation of furanose forms to β-D-fructopyranose (the only form that crystallizes) and it may be the cause of the yields being lower than expected in Experiments 7, 8, and 9.
Strategies for introducing sulfur atom in a sugar ring: synthesis of 5-thioaldopyranoses and their NMR data
Published in Journal of Sulfur Chemistry, 2019
In continuation with synthetic efforts towards synthesizing 5-thio-l-fucopyranose, Hashimoto et al. had developed a shorter synthetic route to 5-thio-l-fucose from d-arabinose via one-carbon elongation to a d-arabino-pentodialdo-l,4-furanose 140 [103,104] (Scheme 19). d-Arabinose diethyl dithioacetal 136 [107] was benzoylated selectively to yield its 5-O-benzoate 137 in good amounts. 5-O-benzoyl-d-arabinofuranose 137 was converted into 5-O-benzoyl-l,2-O-isopropylidene-α-d-arabinofuranose 138 by acetonation with mercuric chloride in dry acetone. Allylation and subsequent debenzoylation afforded 3-allyl ether 139 quantitatively. Pentodialdose 140 was obtained by Swern oxidation [108] of 139 in excellent yield. The key precursor 143 was obtained in four steps. Initially, stereoselective methylation of the dialdose 140 with methyl lithium afforded two diastereoisomers (d-altro 141 and l-galacto 142) favoring the desired d-altrofuranose 141 in a 10:1 ratio with an overall yield (77%). d-altrofuranose 141 was tosylated and the allyl ether bond underwent selective cleavage with Wilkinson's catalyst [109] followed by deprotection with mercuric chloride and mercuric oxide [110] and subsequent acetylation led to compound 143. The sulfur atom in the sugar ring was successfully introduced with an inversion of the configuration at C5 using potassium thioacetate to furnish the 5-thio-l-fucofuranoside derivative 144. Compound 144 was then subjected to hydrolysis of the isopropylidene acetal group and subsequent deprotection of acetyl groups with aqueous ammonia in methanol in the presence of dl-dithiothreitol (DTT) [111] produced 5-thio-α-l-fucopyranose 134. The 5-thio-α-l-fucopyranose thus obtained was characterized as a solid peracetate 135.