Progress and challenges in the synthesis of sequence controlled polysaccharides

• Giulio Fittolani,
• Theodore Tyrikos-Ergas,
• Denisa Vargová,
• Manishkumar A. Chaube and
• Martina Delbianco

Beilstein J. Org. Chem. 2021, 17, 1981–2025, doi:10.3762/bjoc.17.129

• oligosaccharides having multiple α-glycosidic linkages by AGA [171]. Additional strategies include the dehydrative glycosylation of glucosyl hemiacetal [172] or the halide-catalyzed in situ anomerization of glucosyl iodide donors that yielded α(1–6)-hexaglucans [173]. The halide-catalyzed in situ anomerization

Metal-free glycosylation with glycosyl fluorides in liquid SO₂

• Krista Gulbe,
• Jevgeņija Lugiņina,
• Edijs Jansons,
• Artis Kinens and
• Māris Turks

Beilstein J. Org. Chem. 2021, 17, 964–976, doi:10.3762/bjoc.17.78

• the anomerization of the glycosylated products towards their thermodynamic equilibrium is promoted by the species formed during the glycosylation reaction [76]. Thus, when anomerically pure thiomannoside β-3c was subjected to the glycosylation conditions (100 °C, 16 h) in liquid SO2 without any

• additives, no anomerization was observed and the tested substrate β-3c was almost fully recovered. In contrast, when the same thiomannoside β-3c was added to the glycosylation mixture containing 1-dodecanethiol (2m) and mannosyl fluoride α-1a or bromide α-1c (Table 6), anomerization occurred approaching the

• saturated SO2 solutions.a Anomerization of thiomannoside β-3c under glycosylation conditions. Supporting Information Supporting Information File 144: Experimental procedures; experimental data for synthesized compounds; competitive glycosylation of O- and S-nucleophiles; problematic glycosyl acceptors

Regioselectivity of glycosylation reactions of galactose acceptors: an experimental and theoretical study

• Enrique A. Del Vigo,
• Carlos A. Stortz and
• Carla Marino

Beilstein J. Org. Chem. 2019, 15, 2982–2989, doi:10.3762/bjoc.15.294

• order to allow for anomerization to occur (Scheme 1) [20]. In our hands, treatment of methyl glycosides 7 and 8 with two equivalents of protecting reagents resulted in the formation of a mixture of di- and trisubstituted derivatives, and thus the regioselectivity could not be controlled. All Galp

Anomeric modification of carbohydrates using the Mitsunobu reaction

• Julia Hain,
• Patrick Rollin,
• Werner Klaffke and
• Thisbe K. Lindhorst

Beilstein J. Org. Chem. 2018, 14, 1619–1636, doi:10.3762/bjoc.14.138

• equilibrium of both, α- and β-anomers (Scheme 2, right dashed box). However, full anomerization is often not observed as the rate and the extent of mutarotation depends on various parameters such as anchimeric effects of neighboring groups and the reaction conditions. Hence it has been frequently observed in

• Mitsunobu reactions with carbohydrate hemiacetals, that sugar anomerization is either absent or slower than the formation of the O-glycosyloxyphosphonium salt, which can play the intermediate during the reaction (Scheme 2, pathway A) [21]. Another possible explanation for limited anomerization lies in the

• :47 ratio after work-up due to slight anomerization. As 42 can be easily converted into the target molecule, the authors concluded, that in spite of the poor stereoselectivity, the Mitsunobu reaction constitutes a key step in a successful access to β-mannosyl phosphates such as 43. Reactions with

AuBr₃-catalyzed azidation of per-O-acetylated and per-O-benzoylated sugars

• Jayashree Rajput,
• Srinivas Hotha and
• Madhuri Vangala

Beilstein J. Org. Chem. 2018, 14, 682–687, doi:10.3762/bjoc.14.56

• slow anomerization [52]. In 2011, Chen’s group reported that 5 mol % FeCl3 can catalyze the reaction of trimethylsilyl azide with per-O-acetylated β-monosaccharides to afford glycosyl azides in 3–7 h, whereas per-O-acetylated β-di- and trisaccharides required 22–28 h for complete conversion [53

O-Alkylated heavy atom carbohydrate probes for protein X-ray crystallography: Studies towards the synthesis of methyl 2-O-methyl-L-selenofucopyranoside

• Roman Sommer,
• Dirk Hauck,
• Annabelle Varrot,
• Anne Imberty,
• Markus Künzler and
• Alexander Titz

Beilstein J. Org. Chem. 2016, 12, 2828–2833, doi:10.3762/bjoc.12.282

• anomerization improved the ratio towards the α-anomer (13α/13β = 5:1 after 24 h). This α/β-ratio of 5:1 is likely to be the equilibrium of this reaction since it was determined after 2 h and remained constant (see Supporting Information File 1). Finally, the desired methyl 2-O-methyl selenofucoside (3) could be

Mycothiol synthesis by an anomerization reaction through endocyclic cleavage

• Shino Manabe and
• Yukishige Ito

Beilstein J. Org. Chem. 2016, 12, 328–333, doi:10.3762/bjoc.12.35

• anomerization reaction from an easily prepared β-aminoglycoside through endocyclic cleavage. Keywords: anomerization; aminoglycoside; endocyclic cleavage reaction; inositol; mycothiol; Introduction Tuberculosis is an infectious disease and has had a high death rate over the past few decades [1][2][3][4]. The

• pyranosides with N-acetyl 2,3-trans-carbamate groups exhibited complete anomerization from β-glycoside to α-glycoside in the presence of a weak Lewis acid through an endocyclic cleavage reaction [29][30][31][32][33]. We showed evidence of the endocyclic cleavage reaction by trapping linear cations through

• reduction, and intramolecular Friedel–Crafts reaction [29][30] (Scheme 2). In particular, the reaction of pyranosides bearing acetyl substituents on the carbamate groups showed complete anomerization [32]. We expected that anomerization via endocyclic cleavage would be useful for mycothiol synthesis

Concise total synthesis of two marine natural nucleosides: trachycladines A and B

• Haixin Ding,
• Wei Li,
• Zhizhong Ruan,
• Ruchun Yang,
• Zhijie Mao,
• Qiang Xiao and
• Jun Wu

Beilstein J. Org. Chem. 2014, 10, 1681–1685, doi:10.3762/bjoc.10.176

• correlations of H-1, H-3, 5-CH3 and 2-β-methyl. Then, the remaining 3-(O-2,4-dichlorobenzyl) group was removed under hydrogenation with 20% Pd(OH)2/C as a catalyst to give 12 in 91% yield. As the anomerization of the 1-O-α-methyl glycoside may occur under acidic conditions, the structural characterization may

Synthesis of 4” manipulated Lewis X trisaccharide analogues

• Christopher J. Moore and
• France-Isabelle Auzanneau

Beilstein J. Org. Chem. 2012, 8, 1134–1143, doi:10.3762/bjoc.8.126

• used conditions very similar to those used by Risbood et al. to prepare peracetylated trichloroethyl galactopyranoside from peracetylated galactose. Indeed, in agreement with their work [57], the ratio of α-anomer isolated here suggests a late anomerization of the β-glycoside during our extended

Electrochemical generation of 2,3-oxazolidinone glycosyl triflates as an intermediate for stereoselective glycosylation

• Toshiki Nokami,
• Akito Shibuya,
• Yoshihiro Saigusa,
• Shino Manabe,
• Yukishige Ito and
• Jun-ichi Yoshida

Beilstein J. Org. Chem. 2012, 8, 456–460, doi:10.3762/bjoc.8.52

• temperatures. However, α-selectivity was observed in the absence of base at elevated reaction temperatures. In situ generated triflic acid promotes the isomerization of β-products to α-products. Keywords: amino sugar; anomerization; electrochemical oxidation; glycosylation; thioglycoside; Introduction

• group, simply by changing the reaction conditions. In order to confirm that the anomerization of 8β to 8α could take place under the reaction conditions, we examined the acid-mediated isomerization of the β-isomer of disaccharide 8β to the α-isomer 8α (Scheme 2). Triflic acid (TfOH) must be generated in

• at elevated temperatures after anomerization of the β-products, as both Oscarson and our group have previously reported [18][22][23][24]. Namely, α- and β-glycosides were obtained from 2,3-oxazolidinone donors by changing the reaction conditions. Further investigations to reveal the scope and