One-pot synthesis of per-O-acetylated thioglycosides from unprotected reducing sugars

A sequential per-O-acetylation and thioglycosidation of unprotected reducing sugars using a stoichiometric quantity of acetic anhydride and alkyl- or arylthiols is reported. These reactions, which are catalyzed by BF3.OEt2, together constitute an efficient one-pot method for the synthesis of acetylated thioglycosides.     

Insights in starch acetylation in sub- and supercritical CO2

An in-depth study on the acetylation of starch with acetic anhydride (Ac₂O) and sodium acetate (NaOAc) as the catalyst in pressurized carbon dioxide (scCO₂) in a broad pressure range (8–25 MPa) and a temperature of 90 °C is provided. Highest degrees of substitution (DS) of 0.29 (1 h reaction time) and 0.62 (24 h reaction time) were found near the critical point of the mixture (15 MPa). The phase behavior of the system CO₂, starch and acetic anhydride (Ac₂O) was studied in a high pressure view cell. The critical points were a clear function of the temperature and increased from the range of 9.4–10 MPa to 14.5–14.8 MPa when going from 50 to 90 °C (Ac₂O mole fraction at the critical point in the range of 0.08–0.09). Acetylation experiments with a range of starch particles sizes showed a clear relation between the DS and the particle size.     

Reaction kinetics and mechanism of acid-catalyzed anomerization of 1-O-acetyl-2,3,5-tri-O-benzoyl-l-ribofuranose

The mechanism of the acid-catalyzed anomerization of 1-O-acetyl-2,3,5-O-benzoyl-α- and -β-l-ribofuranoses in different acetic acid-acetic anhydride mixtures was investigated. The progress of the reactions was followed by NMR spectroscopy and the rate constants for the reactions were determined by the use of a kinetic model. The site of anomeric activation was clarified by the use of ¹³C-labeled acetic acid and acetic anhydride, respectively, proving that the anomerization takes place by exocyclic C-O cleavage, thus ruling out anomerization via acyclic intermediates. The role of the acetyl cation as the catalytically active species was further verified.     

FeCl3 mediated arylidenation of carbohydrates

Glycosides and thioglycosides based on monosaccharides in reaction with benzaldehyde dimethylacetal or p-methoxybenzaldehyde dimethyl acetal undergo FeCl₃-catalyzed (20 mol %) regioselective 4,6-O-arylidenation producing the corresponding acetals in high yields. FeCl₃ also mediates acetalation of glycosides and thioglycosides of cellobiose, maltose, and lactose affording the corresponding 4′,6′-O-benzylidene acetals, which were isolated after their acetylation in situ with acetic anhydride and pyridine. The combined yields (two steps) of these final products are also high (61–84%). The procedure is applicable to a wide variety of functional groups including –OBn.     

Derivatization procedures for reducing oligosaccharides,part 2: Chemical transformation of 1-deoxy-1-(4-trifluoroacetamidophenyl)aminoalditols

Three chemical transformations of oligosaccharide 1-deoxy-1-(4-trifluoroacetamidophenyl)aminoalditols are described. 1) Oxidation with hydrogen peroxide to give the corresponding reducing oligosaccharides. 2) Oxidation with cerium ammonium nitrate to give the corresponding 1-amino-1-deoxyalditols. 3) Treatment with acetic anhydride to give the correspondingN-acetylated derivatives, which are more stable towards oxidation.     

Synthesis and antihyperlipidemic activity of acetylated derivative of ulvan from Ulva pertusa

In this study, acetylated ulvan (AU) was prepared with acetic anhydride in N,N-dimethylacetamide, and the antihyperlipidemic activity of natural ulvan and its acetylated ulvan derivative (AU) in mice was determined. Obvious differences in antihyperlipidemic activity between natural ulvan and its derivative were observed, moreover, AU showed stronger antihyperlipidemic activity on triglyceride (TG) and low density lipoprotein cholesterol (LDL-C).     

Acetylation and characterization of spruce (Picea abies) galactoglucomannans

Acetylated galactoglucomannans (GGMs) are the main hemicellulose type in most softwood species and can be utilized as, for example, bioactive polymers, hydrocolloids, papermaking chemicals, or coating polymers. Acetylation of spruce GGM using acetic anhydride with pyridine as catalyst under different conditions was conducted to obtain different degrees of acetylation on a laboratory scale, whereas, as a classic method, it can be potentially transferred to the industrial scale. The effects of the amount of catalyst and acetic anhydride, reaction time, temperature and pretreatment by acetic acid were investigated. A fully acetylated product was obtained by refluxing GGM for two hours. The structures of the acetylated GGMs were determined by SEC-MALLS/RI, ¹H and ¹³C NMR and FTIR spectroscopy. NMR studies also indicated migration of acetyl groups from O-2 or O-3 to O-6 after a heating treatment in a water bath. The thermal stability of the products was investigated by DSC-TGA.     

Corrected order in the simultaneous debenzylation-acetolysis of methyl 2,3,4,6-tetra-O-benzyl-alpha-D-glucopyranoside

The benzyl groups of methyl 2,3,4,6-tetra-O-benzyl-alpha-d-glucopyranoside were cleaved in the order of 6-O-Bn>3-O-Bn>4-O-Bn>2-O-Bn under acid-mediated conditions in acetic anhydride. The order is a correction of that previously reported.     

氨基酸的消旋研究

在纯乙酸溶剂中,以乙酸酐酰化消旋酪氨酸,消旋温度为90℃,L-酪氨酸和乙酸酐的摩尔比为12,每消旋1gL-酪氨酸时,溶剂乙酸的用量为5mL,效果较好。同样的方法应用于L-脯氨酸,L-苏氨酸,L-缬氨酸,L-赖氨酸,L-半胱氨酸等氨基酸,消旋率均可达到100%。     

Synthesis, the crystal structure, and high-resolution NMR spectroscopy of methyl 4-O-acetyl-3-azido-2,3,6-trideoxy-6-iodo-alpha-D-arabino-hexopyranoside

Selective tosylation followed by acetylation of methyl 3-azido-2,3-dideoxy-alpha-D-arabino-hexopyranoside (1) in pyridine at room temperature affords a mixture of methyl 4-O-acetyl-3-azido-2,3-dideoxy-6-di-O-p-tolylsulfonyl-alpha-D-arabino-hexopyranoside (4) and methyl 3-azido-2,3-dideoxy-4,6-di-O-p-tolylsulfonyl-alpha-D-arabino-hexopyranoside (3). Compound 4 undergoes nucleophilic displacement with sodium iodide in acetic anhydride to give methyl 4-O-acetyl-3-azido-2,3,6-trideoxy-6-iodo-alpha-D-arabino-hexopyranoside (7), whose crystal structure and (1H) and (13)C NMR data are reported. This compound adopts the 4C(1) conformation.