Recent advances in the gold-catalyzed additions to C–C multiple bonds

• He Huang,
• Yu Zhou and
• Hong Liu

Beilstein J. Org. Chem. 2011, 7, 897–936, doi:10.3762/bjoc.7.103

• glycosylations have appeared in recent years. Ph3PAuOTf is reported to be a superior catalyst (yield increases by >20%) compared to conventionally used ZnCl2 for the well-established glycosylation reaction with 1,2-anhydrosugars 66 as donors (Scheme 14) [39]. The gold(I)-catalyzed reaction of 2,3,4,6-tetra-O

• in the presence of propargyl glycosides and propargyl ethers was developed [41]. Recently, Li et al. reported the gold(I)-catalyzed glycosylation with glycosyl ortho-alkynylbenzoates 73 as donors [42]. This glycosylation protocol was used in an efficient synthesis of a cyclic triterpene

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

• : α-Man-1,6-α-Man, α-Man-1,6-α-Man-1,6-α-Man, α-Man-1,2-α-Man-1,6-α-Man and 2,6-di-(α-Man)-α-Man. The synthesis includes the use of non-benzyl protecting groups compatible with the azido group and preparation of the branched trisaccharide structure 2,6-di-(α-Man)-α-Man through a double glycosylation

• 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

• -glycosylation could be achieved to allow the subsequent synthesis of the α-Man-1,2-Man linkage (Scheme 5). Activation of a mixture of alcohol 14 and trichloroacetimidate 16 at 0 °C with 0.1 equiv of BF3·Et2O provided disaccharide 26 in only 21% yield, with a 1,2-glycosyl orthoester as the major product (40

The allylic chalcogen effect in olefin metathesis

• Yuya A. Lin and
• Benjamin G. Davis

Beilstein J. Org. Chem. 2010, 6, 1219–1228, doi:10.3762/bjoc.6.140

• GlcNAc, mannose and N-acetylamine, which could serve as effective mimics of post-translational protein modifications (glycosylation, lysine acetylation). Conclusion Since the early work by Hoye on secondary allylic alcohols [19] and later the studies on allyl sulfides by our group [17], the allyl

Catalysis: transition-state molecular recognition?

• Ian H. Williams

Beilstein J. Org. Chem. 2010, 6, 1026–1034, doi:10.3762/bjoc.6.117

• complex: it attacks the anomeric carbon of the substrate as a nucleophile and displaces the aglycone nucleofuge (Scheme 3). Glu172 is protonated in the reactant complex and plays a dual role of acid/base catalyst: in the glycosylation step it assists formation of the glycosyl-enzyme intermediate by

A bivalent glycopeptide to target two putative carbohydrate binding sites on FimH

• Thisbe K. Lindhorst,
• Kathrin Bruegge,
• Andreas Fuchs and
• Oliver Sperling

Beilstein J. Org. Chem. 2010, 6, 801–809, doi:10.3762/bjoc.6.90

•  2) [28][29]. Glycosylation of the acceptor diol 11 with the trichloroacetimidate 12 [30] led to mannotrioside 13 with the required azidoethyl aglycone. Reduction of the azido group gave amine 15 and subsequent peptide coupling reaction with Gly5Boc with inexpensive coupling reagents led to the

Preparation of aminoethyl glycosides for glycoconjugation

• Robert Šardzík,
• Gavin T. Noble,
• Martin J. Weissenborn,
• Andrew Martin,
• Simon J. Webb and
• Sabine L. Flitsch

Beilstein J. Org. Chem. 2010, 6, 699–703, doi:10.3762/bjoc.6.81

• ; glycoarrays; glycoconjugation; glycosylation; Introduction The chemical conjugation of carbohydrates through the anomeric centre to biomolecules such as peptides, proteins, lipids, metabolites and to array surfaces is an important synthetic challenge [1][2][3][4][5]. A diverse range of linkers and spacers

• 2-chloroethanol under acid catalysis, followed by peracetylation, nucleophilic substitution with azide and finally, reduction of the azido group [13][14]. Alternatively, the carbohydrate was first activated as the trichloroacetimidate or bromide followed by glycosylation with N-Cbz-aminoethanol [15

• ], bromoethanol [16] or azidoethanol [17] and subsequently transformed into the amine. In the interest of finding fast reliable methods, we have investigated two general aminoethylation protocols: First, the direct glycosylation of peracetylated sugars, which can be either purchased or easily prepared from free

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

• group patterns to improve the reactivity [20][21]. Here, however, NIS/AgOTf-promoted glycosylation of acceptor 13 with donor 3 proceeded without difficulties to produce the tetrasaccharide 14 in high yield (77%, Scheme 3). Before the introduction of the azido-galactose residue, the spacer azido function

• the acetamido carbonyl oxygen also partly behaved as a nucleophile and gave a pseudohexasaccharide acetimidate side product according to MALDI-TOF and NMR. Similar side products have earlier been described [25][26][27][28]. Mild acid treatment of the glycosylation mixture prior to purification led to

New amphiphilic glycopolymers by click functionalization of random copolymers – application to the colloidal stabilisation of polymer nanoparticles and their interaction with concanavalin A lectin

• Otman Otman,
• Paul Boullanger,
• Eric Drockenmuller and
• Thierry Hamaide

Beilstein J. Org. Chem. 2010, 6, No. 58, doi:10.3762/bjoc.6.58

• glycosylation yields, the scale-up of these reactions was shown to be difficult. As a spacer, we chose triethylene glycol. The reaction of 1 with 8-azido-3,6-dioxaoctyloctan-1-ol (prepared in several steps from triethylene glycol) [17] was found to be unsatisfactory since the by-products formed in the reaction

Synthesis of glycosylated β³-homo-threonine conjugates for mucin-like glycopeptide antigen analogues

• Florian Karch and
• Anja Hoffmann-Röder

Beilstein J. Org. Chem. 2010, 6, No. 47, doi:10.3762/bjoc.6.47

• increased biological half-life. Keywords: glycopeptide; glycosylamino acids; β3-homo-threonine; MUC1 antigens; solid-phase synthesis; Introduction Glycosylation is the predominant co- and post-translational modification in higher organisms responsible for tailoring and fine-tuning of the activity of

• proteins involved in fundamental biological recognition events of cell adhesion, cell differentiation and cell growth [1][2][3]. As a consequence, synthetic oligosaccharides and their conjugates are recognised as important tools for the expanding field of chemical biology [4]. Aberrant glycosylation of

• , glycosylation of the corresponding dipeptide precursor Fmoc-β3hThr(OH)-Ala-OBn failed completely. Therefore we encountered the strategy of Arndt–Eistert homologation in the synthesis of the target Fmoc-β3hThr(αAc3GalNAc) and Fmoc-β3hThr(β(Ac4Gal(1–3))α(Ac3GalNAc)) conjugates 2a and 4, respectively, as reported

Bioorthogonal metabolic glycoengineering of human larynx carcinoma (HEp-2) cells targeting sialic acid

• Arne Homann,
• Riaz-ul Qamar,
• Sevnur Serim,
• Petra Dersch and
• Jürgen Seibel

Beilstein J. Org. Chem. 2010, 6, No. 24, doi:10.3762/bjoc.6.24

• analogues enter the cell by pinocytosis and are incorporated into the cellular glycosylation machinery by active transporter systems [5]. In other mammals N-glycolylneuraminic acid (Neu5Gc, 2, Scheme 1) corresponds to Neu5Ac 1 found in humans. Although the human gene for the synthesis of Neu5Gc 2 is

• through the membrane of eukaryotic cells [3]. Neu5Hex (3) is a new substrate for metabolic glycoengineering which is proposed to be incorporated into the cell surface glycan structures. It was shown that carbohydrates in growth media contribute to alterations in glycosylation patterns in human cells [8

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

• sulfur arylation, glycosylation of acetate ions proceeded with high levels of stereoselectivity to afford α-glycosyl acetates in a ‘one-pot’ reaction, even in the presence of alternative acceptor alcohols. Keywords: benzyne; 1,2-cis-glycosides; glycosyl acetates; oxathiane glycosyl donors

• reported an elegant chiral auxiliary-based glycosylation protocol for the synthesis of 1,2-cis-α-glycosides [12]. Completely stereoselective glycosylation was achieved when a thiophenyl-containing chiral auxiliary was attached to O-2 of an imidate glycosyl donor 1 (Scheme 1a). Low temperature 1H NMR

• spectroscopy studies confirmed the formation of a quasi-stable trans-decalin intermediate 2, which was able to cause glycosylation to take place from the α-face of the glycosyl donor. We sought to improve this strategy and recently reported a novel class of bicyclic oxathiane ketal donors 5 containing an

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

• subsequent cleavage of the isopropylidene group with 80% acetic acid at 80 °C gave the diol acceptor 6. Since it is known that in galactopyranosyl structures the nucleophilicity of 3-OH considerably exceeds that of the 4-OH-group, further protecting group manipulations were not required. Glycosylation of 4

• -(2,4,6-tri-O-acetyl-β-D-galactopyranosyl)-(1-4)-2,3,6-tri-O-acetyl-β-D-glucopyranoside (7): Glycosylation was carried out as described for the synthesis of compound 13 from compound 4 (95 mg, 83 μmol) as donor and compound 6 (50 mg, 86 μmol) as acceptor. The pentasccharide derivative 7 was obtained as a

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

• successive galactosylation then fucosylation of a glucosamine acceptor [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28]; 2. a stepwise approach in which the sequence of glycosylation of the glucosamine acceptor is reversed, i.e. the fucosylation is followed by the galactosylation [28][29

• addition to the Lex trisaccharide we are also interested in preparing fragments of the dimLex antigen, we examined the glycosylation at O-4 of glucosamine glycosyl acceptors with galactosyl donor 8, which is chloroacetylated rather than acetylated at O-3. Finally, we also investigated the reactivity

• towards glycosylation of the N-acetylated and phthalimido acceptors 5 and 6, respectively, that both carry a 6-azidohexyl aglycon (Figure 2). Synthesis of monosaccharide building blocks. The 6-chlorohexyl acceptor 4 was prepared in four steps from the known [43] chlorohexyl glucoside 10 (Scheme 1). Thus

A review of new developments in the Friedel–Crafts alkylation – From green chemistry to asymmetric catalysis

• Magnus Rueping and
• Boris J. Nachtsheim

Beilstein J. Org. Chem. 2010, 6, No. 6, doi:10.3762/bjoc.6.6

• of carbon- and heteroatom-centered nucleophiles were effectively applied resulting numerous diarylmethanes and 3-substituted indoles. Moreover, this method could be extended to the C-glycosylation of 1-hydroxysugars and the products 28 were obtained in high yields and with remarkable anomeric ratios

• alkylation as an efficient route to substituted fulvenes. (B) Nanostructured MoO3 mediated intramolecular FC alkylation. FC-type glycosylation of 1,2-dimethylindole and trimethoxybenzene. FC alkylation with highly reactive ferrocenyl- and benzyl alcohols. The reaction proceeds even without Lewis acids just

Acid- mediated reactions under microfluidic conditions: A new strategy for practical synthesis of biofunctional natural products

• Katsunori Tanaka and
• Koichi Fukase

Beilstein J. Org. Chem. 2009, 5, No. 40, doi:10.3762/bjoc.5.40

• Katsunori Tanaka Koichi Fukase Department of Chemistry, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka, 560-0043, Japan 10.3762/bjoc.5.40 Abstract Microfluidic conditions were applied to acid-mediated reactions, namely, glycosylation, reductive opening of the

• complex oligosaccharides has yet to be established in terms of (i) selectivity in the glycosyl bond formations, i.e., β-mannosylation and α-sialylation, and (ii) a non-tedious purification process during each step of glycosylation and deprotection. Our interests in elucidating unknown biological functions

• problems, we used a continuous flow microreactor. An application of the microfluidic system to the glycosylation reaction was first reported by Seeberger and co-workers on α-mannosylation [18]. We also have established an efficient microfluidic glycosylation in combination with the affinity separation

Sordarin, an antifungal agent with a unique mode of action

• Huan Liang

Beilstein J. Org. Chem. 2008, 4, No. 31, doi:10.3762/bjoc.4.31

• sordarin and sordaricin Narasaka et al. published a synthesis of racemic sordaricin in 2004 [16], and 2 years later, they described the first enantioselective synthesis of (−)-sordarin [17]. The retrosynthetic plan is outlined in Scheme 7. (−)-Sordarin would result through a β-selective glycosylation

• into 75 by protection of the OH group with TBDPSCl and saponification of the benzoate ester (LiOH). Lewis acid-induced glycosylation [46] of 75 with trichloroacetimidate 76 gave 77. The latter was then subjected to TBAF deprotection, PCC oxidation, and Pd/C hydrogenation, to afford analog 78. Isopentyl

Dimerization of propargyl and homopropargyl 6-azido- 6-deoxy- glycosides upon 1,3-dipolar cycloaddition

• Nikolas Pietrzik,
• Daniel Schmollinger and
• Thomas Ziegler

Beilstein J. Org. Chem. 2008, 4, No. 30, doi:10.3762/bjoc.4.30

• ][22] and 1g [21]. 2-Propynyl 2,3,4,6-tetra-O-acetyl-α-D-glycopyranosides 1c and 1e have not been described previously. They were prepared from D-glucose and D-galactose in 20% and 22% yield, respectively via classical Fischer-Glycosylation in 2-propynol as the solvent under acidic conditions followed

Cimicifoetisides A and B, two cytotoxic cycloartane triterpenoid glycosides from the rhizomes of Cimicifuga foetida, inhibit proliferation of cancer cells

• Li-Rong Sun,
• Chen Qing,
• Yan-Li Zhang,
• Shu-Yu Jia,
• Zhong-Rong Li,
• Shen-Ji Pei,
• Ming-Hua Qiu,
• Michael L. Gross and
• Samuel X. Qiu

Beilstein J. Org. Chem. 2007, 3, No. 3, doi:10.1186/1860-5397-3-3

• the aglycone portion of 1 with those of cimigenol from the literature, [10] after taking the so-called 'glycosylation effect' [11] into account. Consistently, on glycosylation, a 10.7 ppm downfield shift was observed at C-3 accompanied by up-field shifts for the neighboring carbons C-2 (1.4 ppm) and C

Study of thioglycosylation in ionic liquids

• Jianguo Zhang and
• Arthur Ragauskas

Beilstein J. Org. Chem. 2006, 2, No. 12, doi:10.1186/1860-5397-2-12

• Jianguo Zhang Arthur Ragauskas School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Gerogia, 30332, USA 10.1186/1860-5397-2-12 Abstract A novel, green chemistry, glycosylation strategy was developed based upon the use of ionic liquids. Research studies demonstrated that

• thiomethyl glycosides could readily be activated with methyl trifluoromethane sulfonate, using 1-butyl-3-methylimidazolium tetrafluoroborate as a solvent. This green chemistry glycosylation strategy provided disaccharides with typical yields averaging 75%. The ionic liquid solvent could be readily reused for

• five sequential glycosylation reactions with no impact on product yield. Owing to their unique chemical and physical properties, room temperature ionic liquids (ILs) have received significant attention as alternative solvents for a host of different applications. For example, it has been reported that