Synthesis and antiviral activities of spacer-linked 1-thioglucuronide analogues of glycyrrhizin

• Christian Stanetty,
• Andrea Wolkerstorfer,
• Hassan Amer,
• Andreas Hofinger,
• Ulrich Jordis,
• Dirk Claßen-Houben and
• Paul Kosma

Beilstein J. Org. Chem. 2012, 8, 705–711, doi:10.3762/bjoc.8.79

• cells, wherein the 3-(2-thioethyl)-N-acetylamino- and 3-(2-thioethyl)-thio-linked glucuronide derivatives were effective inhibitors with IC50 values as low as 54 µM. Keywords: antiviral activity; carbenoxolone; glycyrrhizin; influenza A virus; thioglycoside; triterpene; Introduction The triterpene

• corresponding glucuronyl 1-thiol 3 in 89% yield [17][18]. Reaction of 3 with an excess of 1,2-dibromoethane (3–4 equiv) in DMF in the presence of sodium hydride, with the strict exclusion of oxygen, afforded the 2-bromoethyl 1-thioglycoside 4 in 80% yield. Under these conditions formation of the bis

• -substitution product 5 (3%) and the disulfide oxidation product of 1-thiol 3 was observed in only very minor quanities. The corresponding 2-iodoethyl derivative 6 was prepared by a Finkelstein reaction from the bromoethyl 1-thioglycoside 4 in 95% yield (Scheme 1). The previously reported 3β-amino derivative of

2-Allylphenyl glycosides as complementary building blocks for oligosaccharide and glycoconjugate synthesis

• Hemali D. Premathilake and
• Alexei V. Demchenko

Beilstein J. Org. Chem. 2012, 8, 597–605, doi:10.3762/bjoc.8.66

• acceptor 25 afforded the respective disaccharide 26 in 78–97% yield (Table 2, entries 7–10). These series of results indicates a completely orthogonal character of AP and the thioglycosides. To expand this observation, disaccharide 26 was coupled with thioglycoside acceptor 21 in the presence of TMSOTf

• leading to trisaccharide 30 in 90% (Scheme 3). Since 30 is equipped with the SPh anomeric leaving group, it is available for further chain elongation directly. In a similar fashion, thioglycoside disaccharide 16 was coupled with AP acceptors 25 and 13 in the presence of MeOTf to afford trisaccharides 31

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

• glycosylations via glycosyl triflate intermediates. In this paper, we report the generation, accumulation, and characterization by low-temperature NMR analyses, of the corresponding glycosyl triflates. Electrochemical glycosylation of the thioglycoside donor with 2,3-oxazolidinone protecting group gave both 1,2

• of thioglycoside 1a (4 mA, 1 h) exhibited a single set of peaks for glycosyl triflate 2a in the 1H NMR spectrum at −80 °C (Figure 1). In contrast to the previous reports by Kerns and Ye, the corresponding β-triflate was not observed under these conditions [11][19]. The small coupling constant of the

Convergent synthesis of the tetrasaccharide repeating unit of the O-antigen of Shigella boydii type 9

• Abhishek Santra and
• Anup Kumar Misra

Beilstein J. Org. Chem. 2011, 7, 1182–1188, doi:10.3762/bjoc.7.137

• conversion of O-acetyl group to O-benzyl group [22], (iv) activation of glycosyl trichloroacetimidate and thioglycoside donors by perchloric acid supported on silica (HClO4–SiO2) [23][24][25][26], and late stage TEMPO mediated selective oxidation [27][28][29] of the primary hydroxy group to the carboxylic

• tetrasaccharide 1 was achieved by the stereoselective coupling of a D-maltose derived disaccharide derivative 2 and a disaccharide thioglycoside derivative 7 followed by functional group manipulations of the resulting tetrasaccharide derivative 8. For this purpose, suitably functionalized reaction intermediates 2

• (br s, H-1C), 4.95 (d, J = 3.6 Hz, H-1D) in the 1H NMR and signals at δ 92.8 (C-1D), 81.0 (C-1C) in the 13C NMR spectrum). Compound 6 was transformed into disaccharide thioglycoside donor 7 in 91% yield under a one-pot deacetylation–benzylation reaction condition [22] (Scheme 2). In this case, the

Synthesis of glycoconjugate fragments of mycobacterial phosphatidylinositol mannosides and lipomannan

• Benjamin Cao,
• Jonathan M. White and
• Spencer J. Williams

Beilstein J. Org. Chem. 2011, 7, 369–377, doi:10.3762/bjoc.7.47

• provided diacetate 19 in 60% yield. Compound 19 was converted into the trichloroacetimidate 16 following the approach of Kong and coworkers [38] or to the thioglycoside 17 by treatment with p-thiocresol and BF3·Et2O in toluene. Assembly of mannosides 1–4 Synthesis of the protected disaccharide 20 was

• achieved by glycosylation of 14 with the thioglycoside donor 21 [41] using NIS/TfOH in 84% yield (Scheme 4). The protected trisaccharide 25 was prepared by an approach similar to that reported for the corresponding octyl trisaccharide [22][23]. Thus glycosylation of 14 with the silylated donor 22 using NIS

• /TfOH afforded the silylated disaccharide 23 (99%). Compound 23 was desilylated using HF·pyridine and the primary alcohol 24 was glycosylated using thioglycoside 21 to give the trimannoside 25. Evidence for the exclusive formation of the α-anomer in all mannosylations in this work was obtained through

Synthesis of 6-PEtN-α-D-GalpNAc-(1–>6)-β-D-Galp-(1–>4)-β-D-GlcpNAc-(1–>3)-β-D-Galp-(1–>4)-β-D-Glcp, a Haemophilus influenzae lipopolysacharide structure, and biotin and protein conjugates thereof

• Andreas Sundgren,
• Martina Lahmann and
• Stefan Oscarson

Beilstein J. Org. Chem. 2010, 6, 704–708, doi:10.3762/bjoc.6.80

• -containing lactose derivative a suitably protected lacto-N-neotetraose tetrasaccharide structure was constructed through subsequential couplings with two thioglycoside donors, a glucosamine residue followed by a galactose derivative, using NIS/AgOTf as promoter. Removal of a silyl protecting group at the

• designed and synthesised (Scheme 1). Reductive ring opening, with BH3/Bu2BOTf [12], of the benzylidene acetal in the known ethyl thioglycoside 1 [13] gave the 6-hydroxy derivative 2 (85%), which was then silylated to afford donor 3 (90%). Regioselective silylation of the 2-azido-galactose ethyl

• thioglycoside 4 [14] yielded the 6-O-silylated compound 5 (92%), benzylation of which gave donor 6 (85%). A benzyl group in the 4-position was preferred to an ester group to avoid the risk of acyl migration during subsequent reactions; desilylation, glycosidation and phosphorylation. 3II,4II-Diols of lactose

Bis(oxazolines) based on glycopyranosides – steric, configurational and conformational influences on stereoselectivity

• Tobias Minuth and
• Mike M. K. Boysen

Beilstein J. Org. Chem. 2010, 6, No. 23, doi:10.3762/bjoc.6.23

• step however, on switching to L-selectride for the stereoselective reduction [26], the allosamine derived thioglycoside 10 was obtained in good overall yield. For an alternative route, 7 was transformed into the 3-O-triflate 9 and then subjected to nucleophilic displacement with sodium nitrite in the

• (amide) 15. For the preparation of 3-deoxygenated ligands, we planned a defunctionalisation of the key intermediate 7. Surprisingly, a thorough search of the literature revealed only one example of the 3-deoxygenation of a glucosamine-derived thioglycoside, reported by Herdewijn et al. in 2006 [31

Benzyne arylation of oxathiane glycosyl donors

• Martin A. Fascione and
• W. Bruce Turnbull

Beilstein J. Org. Chem. 2010, 6, No. 19, doi:10.3762/bjoc.6.19

• inbuilt α-directing group (Scheme 1b) [13]. The principal objective of our approach was to develop a thioglycoside donor that could mimic the key trans-decalin intermediate 2 by using the sulfur-containing auxiliary as both the anomeric leaving group and α-directing participating group. An efficient

• synthesis of the key bicyclic intermediate was achieved starting from a simple thioglycoside 4 where the essential β-sulfur linkage was already installed, followed by a regio and stereoselective cyclisation onto the O-2 position to afford oxathiane glycosyl donor framework 5. The oxathiane ketal donor 5 is

• then already pre-organised to give a 1,2-cis directing group upon activation, and afford 1,2-cis-glycosides 7 on alcohol addition. Following the synthesis of the oxathiane ketal glycosyl donors 5, activation of the β-thioglycoside linkage was necessary to form the key trans-decalin sulfonium ion 6, and

Chemical synthesis using enzymatically generated building units for construction of the human milk pentasaccharides sialyllacto-N-tetraose and sialyllacto-N-neotetraose epimer

• Dirk Schmidt and
• Joachim Thiem

Beilstein J. Org. Chem. 2010, 6, No. 18, doi:10.3762/bjoc.6.18

• derivatives. Keywords: block synthesis; human milk oligosaccharides; sialyllacto-N-neotetraose epimer; sialyllacto-N-tetraose; trisaccharide thioglycoside donors; Introduction From an inspection of contemporary syntheses of biologically and medicinally relevant oligosaccharides, it is evident that the

Convergent syntheses of Le^X analogues

• An Wang,
• Jenifer Hendel and
• France-Isabelle Auzanneau

Beilstein J. Org. Chem. 2010, 6, No. 17, doi:10.3762/bjoc.6.17

• situ by adding water to the reaction mixture. The resulting triacetate was chloroacetylated at O-3 and the resulting fully protected thioglycoside 23 was converted to the corresponding hemiacetal that was, in turn, treated with trichloroacetonitrile and DBU to give the α-trichloroacetimidate galactosyl