High Anomeric Selectivity Research Articles

Sm(OTf)3 as a highly efficient catalyst for the synthesis of 2,3-unsaturated O- and S-pyranosides from glycals and the temperature-dependent formation of 4-O-acetyl-6-deoxy-2,3-unsaturated S-pyranosides and 4-O-acetyl-6-deoxy-3-alkylthio glycals

By using Sm(OTf)3 as the catalyst, synthesis of 2,3-unsaturated-glycosides has been performed. A series of 2,3-unsaturated glycosides were obtained from 3,4,6-tri-O-acetyl–d-glucal or 3,4-di-O-acetyl-l-rhamnal under mild reaction conditions in good yield and high anomeric selectivity. It was found that under certain conditions, reaction of 3,4-di-O-acetyl-l-rhamnal with thiol leads to temperature-dependent formation of C-1-S and C-3-S product. A temperature-dependent profile of the yield of these two products is given.

Y(OTf)3 as a highly efficient catalyst in Ferrier Rearrangement for the synthesis of O- and S-2,3-unsaturated glycopyranosides

By using Y(OTf)3 as the catalyst, a series of 2,3-unsaturated-glucosides have been synthesized from 3,4,6-tri-O-acetyl-d-glucal, 3,4-di-O-acetyl-l-rhamnal, and 3,4,6-tri-O-benzyl-d-glucal under mild reaction conditions in good yields with high anomeric selectivities. It was found that, in this reaction, 3,4,6-tri-O-benzyl-d-glucal behaved differently from the other two glucals when it was reacted with phenol, O-benzyl glucoside instead of O-phenyl glucoside formed as the sole product. An explanation is given for this phenomenon.

FeCl3·6H2O/C: An Efficient and Recyclable Catalyst for the Synthesis of 2,3-Unsaturated O- and S-Glycosides

A novel method for synthesizing 2,3-unsaturated glycosides has been developed using a handy and eco-friendly immobilized catalyst, FeCl3·6H2O/C. A series of 2,3-unsaturated O- and S-glycosides were obtained for bioassay from corresponding 3,4,6-tri-O-acetyl-D-glucal and D-galactal in good to excellent yields (56%–99%) and high anomeric selectivity (α/β = 7:1 to >19:1). Furthermore, the catalyst was efficient on gram-scale reactions and recyclable for at least three times.

Copper(II) Triflate as a Mild and Efficient Catalyst for Ferrier Glycosylation: Synthesis of 2,3-Unsaturated O-Glycosides

Various acceptors including carbohydrates, amino acids, natural products, and hydroxylamine derivatives were coupled with 3,4,6-tri-O-acetyl- d -glucal in the presence of Cu(OTf)2 as catalyst. The protocol offers facile and efficient Ferrier glycosylation for the synthesis of 2,3-unsaturaed O-glycosides in good yields and high anomeric selectivity.

RuCl3·3H2O as catalyst for Ferrier rearrangement: an efficient procedure for the preparation of pseudoglycosides

By using RuCl3·3H2O as catalyst, an improved method for the synthesis of 2,3-unsaturated-glycosides has been established. A series of 2, 3-unsaturated-glucosides were obtained from 2,4,6-tri-O-acetyl-d-glucal or 3,4-di-O-acetyl-6-deoxy-l-glucal in good yield and high anomeric selectivity.

An efficient procedure for the synthesis of 2,3-unsaturated-O-glycosides: TiCl3(OTf) as the catalyst for type I Ferrier rearrangement

An efficient type I Ferrier rearrangement reaction system for the synthesis of 2,3-unsaturated-O-glycosides has been established by using TiCl3(OTf) as the catalyst. A series of 2,3-unsaturated-O-glucosides were prepared from 3,4,6-tri-O-acetyl-d-glucal in good yield and high anomeric selectivity.

CF3SO3H–SiO2 as catalyst for Ferrier rearrangement: an efficient procedure for the synthesis of pseudoglycosides

An efficient method for the conversion of 2,4,6-tri-O-acetyl-d-glucal to 2,3-unsaturated glycosides by using triflic acid on SiO2 as catalyst has been established. A series of 2,3-unsaturated glucosides were synthesized in good yield and high anomeric selectivity under transition metal-free conditions.

ChemInform Abstract: Iron(III) Triflate, a New Efficient Catalyst for Type I Ferrier Rearrangement.

AbstractA series of unsaturated‐O‐glucosides are obtained from acetyl‐D‐glucal (I) in good yields and high anomeric selectivity.

Efficiency of organic solvents on the ability of α2,3-sialyltransferase from Photobacterium sp. JT-ISH-224 to control a hydrolysis side reaction

Enzymatic synthesis of oligosaccharides using specific sialyltransferases enables single-step glycosylation with high positional and anomeric structural selectivity. The α2,3-sialyltransferase cloned from the marine bacterium Photobacterium sp. JT-ISH-224 has unique and broad acceptor specificity, but this enzyme possesses not only sialyltransferase activity but also sialidase activity. To synthesize sialoside derivative effectively, only sialyltransferase activity is required. We report here that addition of organic solvents was effective to control the sialidase activity and a resulting product was not hydrolyzed. The enzyme was even active in the presence of acetonitrile, ethanol, methanol, or acetone. To determine the suitable concentrations of these organic solvents, only sialyltransferase activity could be allowed, and as a result, the stable synthesis of sialoside could be achieved.

Silicon Fluorides for Acid‐Base Catalysis in Glycosidations

AbstractAdduct formation between alcohols as glycosyl acceptors and phenylsilicon trifluoride (PhSiF3) as catalyst permits acid‐base‐atalyzed glycosidations with O‐glycosyl trichloroacetimidates as glycosyl donors. In this way, from various glycosyl donors and acceptors 1,2‐trans‐ and some 1,2‐cis‐glycosides could be obtained with high anomeric selectivity. A preference for an intramolecular bimolecular nucleophilic substitution (SN2‐type) reaction course with concomitant donor and acceptor activation is supported by the results.

Iron(III) triflate, a new efficient catalyst for Type I Ferrier Rearrangement

By using iron(III) triflate as catalyst, an improved method for the synthesis of 2,3-unsaturated-O-glycosides has been established. A series of 2,3-unsaturated-O-glucosides were obtained from 2,4,6-tri-O-acetyl-d-glucal in good yield and high anomeric selectivity.

Synthesis of Vildagliptin-β-<i>O</i>-Glucuronide

A linear 7-step synthesis of vildagliptin-β-O-glucuronide (2) starting from commercially available D-glucurono-6, 3-lactone (3) was herein achieved with 11.3% overall yield. Efficient preparation of compound 6 in pure α form was obtained, which was proved critical to achieve high anomeric selectivity in β-O-glycosylation later. The direct β-O-glycosylation of vildagliptin (1) containing both a tertiary alcohol and a secondary amine was studied and achieved in good yield. The deprotection step to afford product was delicately executed to avoid hydrolysis of nitrile group. The target compound 2 was obtained after purification by reversed-phase C18 chromatography.

NaHSO 4 supported on silica gel: an alternative catalyst for Ferrier rearrangement of glycals

NaHSO 4 supported on silica gel catalyses the Ferrier rearrangement reaction of 3,4,6- tri- O-acetyl- d-glucal with alcohols and thiols to give the corresponding 2,3-unsaturated glycosides in high anomeric selectivity and good to excellent yield in short reaction time.

Glycoside Bond Formation via Acid–Base Catalysis

Acid-base catalyzed glycosyl donor and then glycosyl acceptor activation with phenylboron difluoride or diphenylboron fluoride permits hydrogen bond mediated intramolecular S(N)2-type glycosidation in generally high anomeric selectivity.

A New Process for Antineoplastic Agent Clofarabine

Clofarabine is a promising DNA polymerase inhibitor currently in clinical trials for a variety of liquid and solid tumor indications. The efforts for development of a new manufacturing process for clofarabine are presented. This new process allows for the reliable and efficient production of drug substance in high anomeric excess and high overall purity, without using chromatography. The high anomeric selectivity is achieved by reacting 2-chloroadenine with 1-bromo-2-deoxy-2-fluoro-3,5di-O-benzoyl-rD-ribofuranose (4) and potassium tert-butoxide in a mixture of three solvents. Following crystallization, anomeric ratios exceeding 50 (‚/r) are achieved. Deprotection and additional crystallization afford a clofarabine drug substance containing less than 0.1% of the r-anomer.

Synthesis of 2,3-unsaturated glycopyranosides by Ferrier rearrangement in FeCl3 based ionic liquid

A novel and stereocontrolled glycosidation of 3,4,6-tri-O-acetyl-d-glucal with various alcohols to give the corresponding 2,3-unsaturated glycopyranosides using [bmim]Cl–1.5FeCl3 based ionic liquid is presented. This ionic liquid has proved to be an efficient reaction medium, playing a dual role of a catalyst as well as of a solvent. Salient features of this simple methodology include non-hazardous reaction conditions, good yields in short reaction times and high anomeric selectivity.

LiBF 4-mediated C-glycosylation of glycals with allyltrimethylsilane: a facile synthesis of allyl C-glycosylic compounds

The treatment of glycals with allyltrimethylsilane in the presence of lithium tetrafluoroborate in acetonitrile gave the corresponding allyl 2,3-unsaturated C-glycosylic compounds in excellent yields with high anomeric selectivity.