Oxidative Activation of C S Bonds with an Electropositive Nitrogen Promoter Enables Orthogonal Glycosylation of Alkyl over Phenyl Thioglycosides

Supporting Information Oxidative Activation of C S Bonds with an Electropositive Nitrogen Promoter Enables Orthogonal Glycosylation of Alkyl over Phenyl Thioglycosides Annabel Kitowski,, Ester Jiménez-Moreno, Míriam Salvadó,, Jordi Mestre, Sergio Castillón, Gonzalo Jiménez-Osés, #, * Omar Boutureira,, * Gonçalo J. L. Bernardes,, * Department of Chemistry, University of Cambridge, Lensfield Road, CB2 1EW Cambridge (UK) Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Avenida Professor Egas Moniz, 1649 028 Lisboa (Portugal) Departament de Química Analítica i Química Orgànica, Universitat Rovira i Virgili, C/ Marcel lí Domingo 1, 43007 Tarragona (Spain) # Departamento de Química, Centro de Investigación en Síntesis Química, Universidad de La Rioja, 26006 Logroño (Spain) Table of Contents 1. General Remarks... S2 2. Experimental Section... S2 2.1. Chemical synthesis... S2 2.2. Kinetic studies by 1 H NMR... S23 2.3. Computational details... S26 2.4. NMR spectra... S41 3. References... S80 S1

1. General Remarks The used reagents were purchased from Alfa Aesar, Carbosynth Limited, Fisher Scientific and Sigma Aldrich and were used without further purification. Dry solvents were obtained by distillation after common procedure and distilled H 2 O was used for the reactions. Purification of the compounds was performed by chromatography using Silica Gel 60 (mesh 230-400) from Material Harvest. Thin layer chromatography (TLC) was carried out on silica gel coated glass or aluminium plates (60 F 254, Merck) and the reactions were visualized with 5% sulfuric acid in ethanol and UV light (λ = 254 nm). Proton ( 1 H NMR) and carbon ( 13 C NMR) nuclear magnetic resonance spectra were recorded on a Bruker 500 MHz DCM Cryoprobe or 400 MHz DPX-400 Dual spectrometer. Fluor ( 19 F NMR) nuclear magnetic resonance spectra were measured with a Bruker 400 MHz Avance III HD Smart Probe spectrometer. All spectra were fully assigned using COSY, HSQC, and HMBC, the chemical shifts were quoted on the δ scale in ppm and the solvent peak (CDCl 3 : 1 H = 7.26 ppm, 13 C = 77.16 ppm) was used as internal standard. Coupling constants J were reported in Hz, using the following splitting abbreviations: s = singlet, d = duplet, t = triplet, dd = duplet from duplet, m = multiplet. High-resolution mass spectroscopy (HRMS) were received from a Thermo Finnigan Orbitrap Classic or from a Waters Xevo G2-S bench top QTOF using positive ion electrospray ionization (ESI) for essential compounds. All reactions in anhydrous conditions were performed using flame-dried flasks, 3 Å molecular sieves (MS) and argon atmosphere. 2. Experimental Section 2.1. Chemical synthesis Ethyl-O-(mesitylensulfonyl)acetohydroxamate 1 Ethyl N-hydroxyacetamidate (1.18 g, 11.4 mmol) was dissolved in DMF (6 ml), triethylamine (1.5 ml) was added and the solution was cooled to 0 ºC. 2-Mesitylensulfonylchloride (2.5 g, 11.4 mmol) was added in small portions and the mixture was vigorously stirred for 30 min. The reaction was diluted with Et 2 O (100 ml) and washed with H 2 O (4 50 ml). The aqueous layers were extracted with Et 2 O and the combined organic layers were dried over MgSO 4 and S2

concentrated. Ethyl-O-(mesitylensulfonyl)acetohydroxamate (2.39 g, 74%) was obtained as white solid and was used in the next step without further purification. O-Mesitylsulfonylhydroxylamine (MSH) 1 Ethyl-O-(mesitylsulfonyl)-acetohydroxamate (2.39 g, 8.39 mmol) was dissolved in dioxane (3 ml) and cooled to 0 ºC. Perchloric acid (70%, 1 ml) was added dropwise and the reaction was stirred for 10 min. The solidified mixture was transferred into 100 ml of ice water and the flask was rinsed with H 2 O and Et 2 O. The aqueous layer was extracted with Et 2 O (3 30 ml), the combined organic layers were washed with saturated solution of sodium chloride (2 50 ml) and dried/neutralized with K 2 CO 3. After filtration, the solution was carefully concentrated to a volume less than 50 ml and poured into 50 ml of ice-cold petroleum ether. After crystallization, the desired product was obtained (885 mg, 49%) as a white crystalline solid. 1 H NMR (400 MHz, CDCl 3 ): δ = 7.00 (s, 2H, H3, H5), 2.59 (s, 6H, 2 o/p-ch 3 ), 2.34 (s, 3H, m-ch 3 ) ppm. 13 C NMR (100 MHz, CDCl 3 ): δ = 141.0, 131.7 (C-Ar), 22.7 (2 CH 3 ), 21.1 (CH 3 ) ppm. Phenyl 2,3,4,6-tetra-O-acetyl-1-thio-β-D-glucopyranose (1) 2 To a solution of 1,2,3,4,6-penta-O-acetyl-D-glucopyranose (5 g, 12.8 mmol) and thiophenol (1.58 ml, 15.4 mmol) in dry CH 2 Cl 2 (25 ml) under argon, BF 3 OEt 2 (7.89 ml, 64 mmol) was added at room temperature and the reaction was stirred for 5 h. The mixture was poured into a saturated aqueous NaHCO 3 solution and the aqueous layers were extracted with CH 2 Cl 2 (3 50 ml). The combined organic layers were combined, dried over MgSO 4 and concentrated. After purification by column chromatography (1:1 petroleum ether/etoac), phenyl 2,3,4,6-tetra- O-acetyl-1-thio-β-D-glucopyranose 1 was obtained (3.99 g, 71%) as a white solid. 1 H NMR (400 MHz, CDCl 3 ): δ = 7.50 7.31 (m, 5H, Ar), 5.22 (t, J = 9.3 Hz, 1H, H3), 5.03 (t, J = 9.8 Hz, 1H, H4), 4.97 (t, J = 9.6 Hz, 1H, H2), 4.70 (d, J = 10.1 Hz, 1H, H1), 4.25 4.14 (m, 2H, H6a,b), 3.72 (m, 1H, H5), 2.08, 2.07, 2.01, 1.98 (4 s, 4 3H, CH 3 -C=O) ppm. 13 C NMR (100 MHz, CDCl 3 ): S3

δ = 170.7, 170.3, 169.5, 169.3 (4 CH 3 C=O), 133.3, 131.8 (C1, C2 /3 ), 129.1, 128.6 (C3, C4, C5 ), 85.9 (C1), 75.9 (C5), 74.1 (C3), 70.1 (C2), 68.3 (C4), 20.9, 20.8, 20.7, 20.6 (4 CH 3 -C=O) ppm. HRMS-ESI + for [M + Na + ] C 20 H 24 NaO 9 S + (m/z): calc. 463.1033; found 463.1026. Phenyl 1,2,3,4,6-tetra-O-benzyl-1-thio-β-D-glucopyranose (2) 2 To a solution of phenyl 2,3,4,6-tetra-O-acetyl-1-thio-β-D-glucopyranose (1.23 g, 2.79 mmol) in dry MeOH (15 ml), a NaOMe solution (30%, 1.54 ml) was added at room temperature and the reaction was stirred for 40 min, until all starting material was consumed as monitored by TLC. After neutralization with Dowex 5W (H + -form) for 10 min, the resin was removed by filtration and the solvent was evaporated. The obtained product phenyl β-d-thioglucopyranoside (728 mg, 2.67 mmol) was redissolved in dry DMF (10 ml) and cooled to 10 ºC. Sodium hydride (60% in mineral oil, 641 mg, 26.7 mmol) was added and the mixture was stirred for 1 h while warming up to room temperature. Benzyl bromide (4.57 g, 26.7 mmol) was added and the reaction was stirred for 17 h. The reaction was cooled to 0 ºC and H 2 O (15 ml) were added slowly. The aqueous layer was extracted with EtOAc (3 20 ml) and the combined organic layers were concentrated. The reaction was redissolved in Et 2 O and washed with saturated NaCl solution (3 20 ml). The organic layer was dried over MgSO 4 and concentrated. After purification by column chromatography (6:1 petroleum ether/etoac), phenyl 1,2,3,4,6-tetra-O-benzyl-1-thio-β-D-glucopyranose 2 was obtained (1.25 g, 71% over two steps) as a white solid. 1 H NMR (400 MHz, CDCl 3 ): δ = 7.59 (dd, J = 6.6, 3.0 Hz, 2H, H-Phenyl), 7.42 7.19 (m, 23H, 20 H-benzyl, 3 H-Phenyl), 4.91 4.89 (m, 2H, O-CH 2 -Phenyl), 4.87 4.81 (m, 2H, O-CH 2 -Phenyl), 4.74 (d, J = 10.3 Hz, 1H,, O-CH 2 -Phenyl), 4.68 (d, J = 9.7 Hz, 1H, H1), 4.64 4.50 (m, 4H,, O-CH 2 -Phenyl), 3.80 (dd, J = 10.9, 2.0 Hz, 1H, H6a), 3.76 3.63 (m, 3H, H3, H4, H6b), 3.55 3.49 (m, 2H, H2, H5) ppm. 13 C NMR (100 MHz, CDCl 3 ): δ= 138.5, 138.4, 138.2, 133.9, 132.1 (4 C1 -Benzyl, C1 -Phenyl), 129.0, 128.6, 128.6, 128.5, 128.4, 128.3, 128.2, 128.1, 128.0, 127.9, 127.8, 127.7, 127.6 (C2 C5 Benzyl, Phenyl), 87.6 (C1), 86.9 (C6), 80.9 (C2), 79.2 (C5), 77.9 (C4), 75.9, 75.57, 75.20, 73.57 (4 O-CH 2 - Phenyl), 69.2 (C3) ppm. HRMS-ESI + for [M + Na + ] C 40 H 40 NaO 5 S + (m/z): calc. 655.2489; found 655.2500. S4

Ethyl 2,3,4,6-tetra-O-acetyl-1-thio-β-D-glucopyranose (3) 2 1,2,3,4,6-Penta-O-acetyl-D-glucopyranose (5 g, 12.8 mmol) and ethanthiol (1.14 ml, 15.4 mmol) were dissolved in dry CH 2 Cl 2 (25 ml) and BF 3 Et 2 O (7.89 ml, 64 mmol) was added slowly. The reaction mixture was stirred for 6 h, before poured into saturated aqueous NaHCO 3 solution and extracted with CH 2 Cl 2. The organic layer was dried over MgSO 4, filtrated and concentrated. Product 3 was obtained after column chromatography (3:1 hexane/etoac) as white solid (4.77 g, 95%). 1 H NMR (500 MHz, CDCl 3 ): δ = 5.22 (t, J = 9.4 Hz, 1H, H3), 5.08 (t, J = 9.8 Hz, 1H, H4), 5.03 (t, J = 10 Hz, H2), 4.49 (d, J = 10.1 Hz, 1H, H1), 4.24 (dd, J = 12.4 Hz, J = 5.0 Hz, 1H, H6), 4.13 (dd, J = 12.3 Hz, J = 2.3 Hz, 1H, H6), 3.70 (ddd, J = 10.1 Hz, J = 5.0 Hz, J = 2.4 Hz, 1H, H5), 2.70 (m, 2H, SCH 2 ), 2.07, 2.05, 2.02, 2.00 (4 s, 12H, 4 CH 3 ), 1.27 (t, J = 7.5 Hz, 1H, SCH 2 CH 3 ) ppm. 13 C NMR (126 MHz, CDCl 3 ): δ = 170.8, 170.3, 169.6 (CH 3 CO), 83.7 (C1), 76.0 (C5), 74.1 (C3), 69.9 (C2), 68.5 (C4), 62.3 (C6), 24.3 (SCH 2 CH 3 ), 20.9, 20.8, 20.7 (CH 3 CO), 14.9 (SCH 2 CH 3 ) ppm. HRMS-ESI + for [M + Na + ] C 16 H 24 NaO 9 S + (m/z): calc. 415.1033; found 415.1035. 2,3,4,6-Tetra-O-acetyl-D-glucopyranose (3a) 8 Ethyl 2,3,4,6-tetra-O-acetyl-1-thio-β-D-glucopyranose 3 (10 mg, 0.025 mmol) was dissolved in dry CH 2 Cl 2 (1.6 ml). MSH (27.4 mg, 0.127 mmol) and K 2 CO 3 (6.9 mg, 0.05 mmol) were added and the reaction was stirred at room temperature for 16 h. The mixture was diluted with CH 2 Cl 2 and washed with saturated aqueous Na 2 CO 3 and NaCl solutions. The crude was purified by column chromatography (from 1:1 petroleum ether/etoac to EtOAc) to afford 3a (7 mg, 80%) as an inseparable α/β mixture as a white solid. 1 H NMR (400 MHz, CDCl 3 ): δ = 5.54 (t, J = 9.8 Hz, 1H, H3), 5.47 (t, J = 3.4 Hz, 1H, H1), 5.26 (t, J = 9.5 Hz, 1H, H3 ), 5.09 (td, J = 9.7 Hz, J = 1.8 Hz, 1H, H4), 4.92 (dd, J = 10.2 Hz, J = 3.6 Hz, 1H, H2), 4.74 (t, J = 8.1 Hz, 1H, H4 ), 4.30 4.21 (m, 1H, H5), 4.18 4.12 (m, 2H, H6a/b), 3.00 2.96 (m, 1H, OH), 2.10, 2.09, 2.04, 2.02 (4 CH 3 O) ppm. 13 C NMR (10 MHz, CDCl 3 ): δ = 170.9, 170.3, 170.2, 169.7 (4 C(OCH 3 )), 90.4 (C1), 71.2 (C2), 69.9 (C3), 68.5 (C4), 62.1 (C6), 61.9 (C5), 20.9, 20.8, 20.7, 20.7 (4 CH 3 O) ppm. HRMS- ESI + for [M + Na + ] C 14 H 20 NaO + 10 (m/z): calc. 371.0949; found 371.0953. S5

Ethyl 2,3,4,6-tetra-O-benzyl-1-thio-β-D-glucopyranose (4) 2 To a solution of ethyl 2,3,4,6-tetra-O-acetyl-1-thio-β-D-glucopyranose 3 (300 mg, 764 µmol) in dry MeOH (4 ml), a NaOMe solution (30%, 420 µl) was added at room temperature and the reaction was stirred for 1 h, until all starting material was consumed as monitored by TLC. After neutralization with Dowex 5W (H + -form) for 10 min, the resin was removed by filtration and the solvent evaporated. The obtained ethyl thioglucopyranoside was used in the next step without further purification. Ethyl thioglucopyranoside (162 mg, 720 µmol) was dissolved in dry DMF (4 ml) and cooled to 10 ºC. Sodium hydride (60% in mineral oil, 241 mg, 7.20 mmol) was added and the mixture was stirred for 1 h while warming up to room temperature. Benzyl bromide (861 µl, 7.20 mmol) was added and the mixture was stirred for 15 h. The reaction was cooled down to 0 ºC and H 2 O (2 ml) was added slowly. The solution was extracted with CH 2 Cl 2 (3 10 ml) and the combined organic layers were washed with saturated NaCl solution (3 20 ml). After column chromatography (10:1 petroleum ether/etoac), ethyl 2,3,4,6-tetra-Obenzyl-1-thio-β-D-glucopyranose 4 was obtained (274 mg, 61% over two steps) as a white solid. 1 H NMR (400 MHz, CDCl 3 ): δ = 7.39 7.27 (m, 18H, H-Benzyl), 7.17 (dd, J = 7.0, 2.6 Hz, 2H, H- Benzyl), 4.92 (d, J = 10.6 Hz, 2H, O-CH 2 -Phenyl), 4.87 4.79 (m, 2H, O-CH 2 -Phenyl), 4.74 (d, J = 10.1 Hz, 1H, O-CH 2 -Phenyl), 4.63 4.52 (m, 3H, O-CH 2 -Phenyl), 4.46 (d, J = 9.7 Hz, 1H, H1), 3.77 3.72 (m, 1H, H4), 3.71 3.65 (m, 2H, H6a/b), 3.61 (t, J = 9.4 Hz, 1H, H3), 3.50 3.41 (m, 2H, H2, H5), 2.84 2.70 (m, 2H, S-CH 2 CH 3 ), 1.33 (t, J = 7.4 Hz, 3H, S-CH 2 CH 3 ) ppm. 13 C NMR (100 MHz, CDCl 3 ): δ = 138.62, 138.50, 138.24, 138.13 ( 4 C1 -Benzyl), 128.5, 128.3, 128.0, 128.1 ( C2 -C5-Benzyl), 86.8 (C6a/b), 85.1 (C1), 78.2 (C3), 75.7 (CH 2 -OBenzyl), 75.6 (CH 2 -OBenzyl), 74.8 (CH 2 -OBenzyl), 73.5 (CH 2 -OBenzyl), 69.4 (C6), 69.1 (C4), 62.3 (S-CH 2 -CH 3 ), 15.2 (S-CH 2 - CH 3 ) ppm. HRMS-ESI + (m/z) for [M + H + ] C 36 H 41 O 5 S + : calc. 585.2669; found 585.2654; for [M + Na + ] C 36 H 40 NaO 5 S + : calc. 607.2489; found 607.2484. 2,3,4,6-Tetra-O-benzyl-D-glucopyranose (4a) 9 S6

Ethyl 2,3,4,6-tetra-O-acetyl-1-thio-β-D-glucopyranose 3 (10 mg, 0.025 mmol) was dissolved in dry CH 2 Cl 2 (1.6 ml). MSH (18.4 mg, 0.086 mmol) and K 2 CO 3 (4.7 mg, 0.034 mmol) were added and the reaction was stirred at room temperature for 16 h. The mixture was diluted with CH 2 Cl 2 and washed with saturated aqueous Na 2 CO 3 and NaCl solutions. The crude was purified by column chromatography (2:1 petroleum ether/etoac) to afford 4a (10.2 mg, 60%) as an inseparable α/β mixture as a white solid. 1 H NMR (500 MHz, CDCl 3 ): δ = 7.39 7.24 (m, 18H, H-Benzyl), 7.14 (ddd, J = 7.7, 5.7, 2.4 Hz, 2H, H-Benzyl), 5.23 (d, J = 3.5 Hz, 1H, H1), 4.97 4.91 (m, 2H, O-CH 2 - Phenyl), 4.86 4.77 (m, 2H, O-CH 2 -Phenyl), 4.62 4.54 (m, 2H, O-CH 2 -Phenyl), 4.49 (d, J = 11.5 Hz, 2H, O-CH 2 -Phenyl), 4.03 (ddd, J = 10.2, 4.0, 2.1 Hz, 1H, H5), 3.96 (t, J = 9.3 Hz, 1H, H3), 3.74 3.69 (m, 1H, H4), 3.68 3.62 (m, 2H, H6a/b), 3.62 3.56 (m, 1H, H2) ppm. 13 C NMR (126 MHz, CDCl 3 ): δ = 138.8, 138.6, 138.3, 138.0 (4 C1 -Benzyl), 128.7, 128.6, 128.5, 128.3, 128.2, 128.1, 128.1, 128.0, 127.8, 127.7 (C2 -C5 -Benzyl), 91.5 (C1), 84.7, 83.3, 81.9, 80.2, 75.9, 75.2, 74.9, 73.7, 73.47, 70.52, 69.0, 68.7. HRMS-ESI + for [M + Na + ] C 34 H 36 NaO + 6 (m/z): calc. 563.2404; found 563.2397. Phenyl 3,4,6-tri-O-acetyl-2-deoxy-2-fluoro-1-thio-α-D-mannopyranose (5a) 3 BF 3 Et 2 O (210 µl, 1.71 mmol) and thiophenol (72 µl, 0.685 mmol) were added to a solution of 1,3,4,6-tetra-O-acetyl-2-deoxy-2-fluoro-α-D-mannopyranoside (198 mg, 0.57 mmol) in dry CH 2 Cl 2 (8.2 ml) at room temperature. The reaction mixture was stirred at the same temperature for 48 h before solid Na 2 CO 3 was added and stirring continued for 10 min. The crude was then diluted with CH 2 Cl 2 and washed with saturated aqueous NaHCO 3 and brine. The combined organic layers were dried over MgSO 4, filtered, and concentrated under reduced pressure. The residue was purified by column chromatography (from petroleum ether to 1:1 EtOAc/petroleum ether) to afford the product (170 mg, 75%) as a colorless syrup. R f (1:1 EtOAc/petroleum ether): 0.35. 1 H NMR (CDCl 3, 400 MHz): δ = 7.54 7.33 (m, 5H, Ar), 5.67 (dd, J = 14.5 Hz, J = 1.4 Hz, H1), 5.46 (appt, J = 10.1 Hz, H4), 5.22 (ddd, J = 28.7 Hz, J = 10 Hz, J = 2.3 Hz, 1H, H3), 5.10 (ddd, J = 50.7 Hz, J = 2.3 Hz, J = 1.4 Hz, 1H, H2), 4.55 4.50 (m, 1H, H5), 4.33 (dd, J = 12.1 Hz, J = 5.3 Hz, 1H, H6a), 4.12 (dd, J = 12.1 Hz, J = 2.3 Hz, 1H, H6b), 2.12, 2.08, 2.06 (s, 9H, 3 CH 3 OAc) ppm. 19 F NMR (CDCl 3, S7

376.5 MHz): δ = 189.7 (ddd, J F,2 = 50.7 Hz, J F,3 = 28.7 Hz, J F,1 = 14.5 Hz, F-2). LRMS-TOF ES + for [M+Na + ] C 18 H 21 FNaO 7 S + (m/z): calc. 423.1; found 423.1 Phenyl 3,4,6-tri-O-acetyl-2-deoxy-2-fluoro-1-thio-β-D-mannopyranose (5b) 4 To a solution of 3,4,6-tri-O-acetyl-2-deoxy-2-fluoro-α-D-mannopyranosyl bromide 7 (98.7 mg, 0.26 mmol) in CHCl 3 (2.6 ml), was added a solution of tetrabutylammonium bromide (15.9 mg, 0.052 mmol) in H 2 O (340 µl) followed by the addition of thiophenol (41 µl, 0.39 mmol). The mixture was cooled in an ice water bath and a solution of KOH (25 mg, 0.51 mmol) in H 2 O (340 µl) was added. After the addition was complete, the mixture was stirred overnight at room temperature. The organic phase was separated, washed with H 2 O, dried over MgSO 4 and concentrated. The residue was purified by column chromatography (from 4:1 to 1:1 hexane/etoac) to afford (76 mg, 73%) as a white solid. R f (1:1 EtOAc/hexane): 0.47 1 H NMR (CDCl 3, 400 MHz): δ = 7.52 (m, 2H, Ar), 7.32 (m, 3H, Ar), 5.37 (appt, J = 10.0 Hz, 1H, H4), 5.06 (dd, J = 49.9 Hz, J = 2.7 Hz, 1H, H2), 4.98 (ddd, J = 26.8 Hz, J = 10.0 Hz, J = 2.7 Hz, 1H, H3), 4.86 (d, J = 26.8 Hz, 1H, H1), 4.27 (dd, J = 12.2 Hz, J = 6.0 Hz, 1H, H6a), 4.16 (dd, J = 12.2 Hz, J = 2.4 Hz, 1H, H6b), 3.69 (ddd, J = 10.0 Hz, J = 6.0 Hz, J = 2.4 Hz, 1H, H5), 2.11, 208, 2.04 (s, 9H, CH 3 OAc) ppm. 13 C NMR(CDCl 3, 400 MHz): δ = 170.8, 170.4, 169.6 (3 C=O, Ac), 133.3 (C, Ar), 132.2, 129.2, 128.3 (3CH, Ac), 89.11 (d, J 2,F = 187.6 Hz, C2), 85.4 (d, J 1,F =18.2 Hz, C1), 76.4 (C5), 72.5 (d, J 3,F = 17.8 Hz, C3), 65.7 (C4), 62.7 (C6), 20.9, 20.8 (3 CH 3 OAc) ppm. 19 F NMR (CDCl 3, 376.5 MHz): δ = 210.6 (dt, J F,2 = 49.9 Hz, J F,1 = J F,3 =26.8 Hz, F-2). HRMS-TOF ES + for [M+Na + ] C 18 H 21 FNaO 8 S + (m/z): calc. 423.0884; found 423.0881. Phenyl 3,4,6-tri-O-acetyl-2-deoxy-2-fluoro-1-thio-α-D-glucopyranose (6a) BF 3 Et 2 O (160 µl, 1.3 mmol) and thiophenol (66 µl, 0.649 mmol) were added to a solution of 1,3,4,6-tetra-O-acetyl-2-deoxy-2-fluoro-α/β-D-glucopyranoside (151.8 mg, 0.433 mmol) in dry CH 2 Cl 2 (5.2 ml) at room temperature. The reaction mixture was stirred at the same temperature for 48 h before solid Na 2 CO 3 was added and stirring continued for 10 min. The crude was then S8

diluted with CH 2 Cl 2 and washed with saturated aqueous NaHCO 3 and brine. The combined organic layers were dried over MgSO 4, filtered, and concentrated under reduced pressure. The residue was purified by column chromatography (from hexane to 1:1 EtOAc/hexane) and recrystallized from EtOH to afford 6a (97 mg, 56%) as white needles. R f (1:1 EtOAc/hexane): 0.47 1 H NMR (CDCl 3, 400 MHz): δ = 7.51 (m, 2H, Ar), 7.32 (m, 3H, Ar), 5.76 (dd, J = 5.9 Hz, J = 1.4 Hz, 1H, H1), 5.46 (dt, J = 12.3 Hz, J = 9.6 Hz, 1H, H3), 5.05 (appt, J = 9.6 Hz, 1H, H4), 4.83 (ddd, J = 50.0 Hz, J = 9.6 Hz, J = 5.9 Hz, 1H, H2), 4.61 (ddd, J = 10.2 Hz, J = 5.2 Hz, J = 2.2 Hz, 1H, H5), 4.30 (dd, J = 12.4 Hz, J = 5.2 Hz, 1H, H6a), 4.07 (dd, J = 12.4 Hz, J = 2.2 Hz, 1H, H6b), 2.09, 2.06, 2.05 (s, 9H, CH 3 OAc) ppm. 13 C NMR(CDCl 3, 400 MHz): δ = 170.7, 170.1, 169.8 (3 C=O, Ac), 132.5 (C, Ar), 132.4, 129.4, 128.3 (3 CH, Ar), 87.0 (d, J 2,F = 190.9 Hz, C2), 86.0 (d, J 1,F = 16.3 Hz, C1), 71.4 (d, J 3,F = 19.2 Hz, C3), 68.4 (C5), 68.2 (d, J 4,F =6.7 Hz, C4), 62.0 (C6), 20.9, 20.8, (3 CH 3 OAc) ppm. 19 F NMR (CDCl 3, 376.5 MHz): δ = 190.0 (dd, J F,2 =50.0 Hz, J F,3 =12.3 Hz, F- 2) ppm. HRMS-TOF ES + for [M+Na + ] C 18 H 21 FNaO 8 S + (m/z): calc. 423.0884; found 423.0884. Phenyl 3,4,6-tri-O-acetyl-2-deoxy-2-fluoro-1-thio-β-D-glucopyranose (6b) To a solution of 3,4,6-tri-O-acetyl-2-deoxy-2-fluoro-α-D-glucopyranosyl bromide 7 (99.0 mg, 0.26 mmol) in CHCl 3 (2.6 ml), was added a solution of tetrabutylammonium bromide (16 mg, 0.052 mmol) in H 2 O (338 µl) followed by the addition of thiophenol (40 µl, 0.39 mmol). The mixture was cooled in an ice water bath and a solution of KOH (26 mg, 0.52 mmol) in H 2 O (338 µl) was added. After the addition was complete, the mixture was stirred overnight at room temperature. The organic phase was separated, washed with H 2 O, dried over MgSO 4 and concentrated. The residue was purified by column chromatography (from 4:1 to 1:1 hexane/etoac) to afford (77.9 mg, 75%) as a white solid. 1 H NMR (CDCl 3, 400 MHz): δ = 7.57 (m, 2H, Ar), 7.34 (m, 3H, Ar), 5.32 (dt, J = 14.1 Hz, J = 9.2 Hz, 1H, H3), 4.95 (t, J = 9.8 Hz, 1H, H4), 4.69 (dd, J = 9.8 Hz, J = 1.5 Hz, 1H, H1), 4.19 (m, 2H, H6), 4.16 (dt, J = 49.5 Hz, J = 9.4 Hz, 1H, H2), 3.74 (ddd, J = 10.1 Hz, J = 4.5 Hz, J = 2.9 Hz, 1H, H5), 2.08, 2.06, 2.02 (s, 9H, 3 CH 3 OAc) ppm. 13 C NMR (CDCl 3, 100 MHz): δ = 170.7, 170.1, 169.7 (3 CO, Ac), 134.4, 130.2, 129.2, 129.0 (4C, Ar), 87.1, (d, J 2,F = 192.0 Hz, C2), 84.3 (d, J 1,F =23.9Hz, C1), 75.9 (C5), 74.0 (d, J 4,F = 20.4 Hz, C4), 68.1 (d, J 3,F = 7.6 Hz, C3), 62.1 (C6), 20.9, 20.8, 20.7 (3 CH 3 OAc) ppm. 19 F NMR (CDCl 3, S9

376.5 MHz): δ = 190.32 (dd, J F,2 = 49.9 Hz, J F,3 = 14.1 Hz, F-2) ppm. HRMS-TOF ES + for [M+Na + ] C 18 H 21 FNaO 8 S + (m/z): calc. 423.0884; found 423.0879. 3,4,6-Tri-O-acetyl-2-deoxy-2-fluoro-1-O-sulfonylmesityl-α-D-mannopyranose (7) Phenyl 3,4,6-tri-O-acetyl-2-deoxy-2-fluoro-1-thio-β-D-mannopyranose 5b (15 mg, 0.0375 mmol) was dissolved in dry CH 2 Cl 2 (2 ml). MSH (40.4 mg, 0.188 mmol) and K 2 CO 3 (10.3 mg, 0.075 mmol) were added and the reaction was stirred at room temperature for 16 h. The reaction mixture was diluted with CH 2 Cl 2 and washed with saturated aqueous Na 2 CO 3 and NaCl solutions. The organic layer was dried over MgSO 4, filtrated and concentrated. The crude was purified by column chromatography (2:1 petroleum ether/etoac) to afford 7 (8.1 mg, 44%) as a yellowish solid. 1 H NMR (500 MHz, CDCl 3 ): δ = 7.01 (s, 2H, H-Mes), 5.91 (dd, J = 6.3 Hz, J = 1.9 Hz, 1H, H1), 5.35 (t, J = 10.1 Hz, 1H, H4), 5.27 5.13 (m, 1H, H3), 4.88 4.72 (m, 1H, H2), 4.07 (dd, J = 12.6 Hz, J = 3.9 Hz, 1H, H6), 3.79 3.69 (m, 1H, H5), 3.64 (dd, J = 12.6 Hz, J = 2.3 Hz, 1H, H6), 2.65 (s, 6H, CH 3 -Mes), 2.33 (s, 3H, CH 3 -Mes), 2.10, 2.06 2.03, 2.03 (3 s, 9H CH 3 CO) ppm. 13 C NMR (126 MHz, CDCl 3 ): δ = 170.6, 169.9, 169.4 (3 CH 3 CO), 144.4, 140.1 (2 C4 -Mes), 132.1, 131.3 (CH-Mes), 96.1 (d, J 1,F = 32.2 Hz, C1), 86.1 (d, J 2,F = 183.1 Hz, C2), 71.3 (C5), 69.3 (d, J 3,F = 25.0 Hz, C3), 64.8 (C4), 60.8 (C6), 22.8, 21.3 (CH 3 -Mes), 20.77, 20.71 (CH 3 CO) ppm. 19 F NMR (376 MHz, CDCl 3 ) δ 202.59 (bs, F-2) ppm. HRMS-ESI + for [M + Na + ] C 21 H 27 FNaO 10 S + (m/z): calc. 513.1207; found 513.1202. 3,4,6-Tri-O-acetyl-2-deoxy-2-fluoro-1-O-sulfonylmesityl-α/β-D-glucopyranose (8a,b) Phenyl 3,4,6-tri-O-acetyl-2-deoxy-2-fluoro-1-thio-β-D-glucopyranose 6b (20 mg, 0.05 mmol) was dissolved in dry CH 2 Cl 2 (2 ml). MSH (53.8 mg, 0.25 mmol) and K 2 CO 3 (13.8 mg, 0.1 mmol) were added and the reaction was stirred at room temperature for 16 h. The reaction mixture was diluted with CH 2 Cl 2 and washed with saturated aqueous Na 2 CO 3 and NaCl solutions. The organic layer S10

was dried over MgSO 4, filtrated and concentrated. The crude was purified by column chromatography (from 3:1 to 2:1 petroleum ether/etoac) to afford 8a,b (18.6 mg, 76%) as an inseparable 7:1 α/β mixture as a yellowish solid. Data for 8a: 1 H NMR (400 MHz, CDCl 3 ): δ = 6.99 (s, 2H, H-Mes), 5.99 (d, J = 3.9 Hz, 1H, H1), 5.52 5.45 (m, 1H, H3), 5.04 (dd, J = 19.9 Hz, J = 9.9 Hz, 1H, H4), 4.67 4.47 (m, 2H, H2), 4.19 (dd, J = 12.6 Hz, J = 4.0 Hz, 1H, H6), 4.06 4.02 (m, 1H, H5), 3.82 (dd, J = 12.6 Hz, J = 2.2 Hz, 1H, H6 ), 2.65 (s, 6H, 2 CH 3 -Mes), 2.31 (s, 3H, CH 3 -Mes), 2.05 (s, 6H, 2 CH 3 O), 2.03 (s, 3H, CH 3 O) ppm. 13 C NMR (100 MHz, CDCl 3 ): δ = 170.6, 169.9, 169.6 (3 CH 3 CO), 144.2 (p-c-mes), 140.3 (C1-Mes), 132.0, 131.1 (C4 -CH 3 Mes), 94.9 (d, J 1,F = 22.0 Hz, C1), 86.0 (d, J 2,F = 199.0 Hz, C2), 70.2 (d, J 3,F = 20.0 Hz, C3), 69.9 (C5), 67.1 (C4) 60.7 (C6), 22.8 (2 CH 3 -Mes), 21.2 (CH 3 -Mes), 20.7, 20.6 (3 CH 3 O) ppm. 19 F NMR (376 MHz, CDCl 3 ) δ 199.38 (ddd, J = 50.3, 14.7, 3.2 Hz, F-2). Data for 8b: 1 H NMR (400 MHz, CDCl 3 ): δ = 6.96 (s, 2H, H-Mes), 5.42 (dd, J = 7.6 Hz, J = 3.2 Hz, 1H, H1), 5.35 5.24 (m, 1H, H3), 5.05 (t, J = 10.0 Hz, 1H, H3), 5.02 4.98 (m, 1H, H4), 4.67 4.47 (m, 2H, H2), 4.08 (dd, J = 12.4 Hz, J = 4.9 Hz, 1H, H6), 3.97 (dd, J = 12.4 Hz, J = 2.4 Hz, 1H, H6 ), 3.76 (ddd, J = 10.1 Hz, J = 4.9 Hz, J = 2.4 Hz, 1H, H5), 2.63 (s, 6H, 2 CH 3 -Mes), 2.32 (s, 3H, CH 3 -Mes), 2.04 (s, 6H, 2 CH 3 O), 2.01 (s, 3H, CH 3 O) ppm. 13 C NMR (100 MHz, CDCl 3 ): δ = 169.9, 169.6, 169.7 (3 CH 3 CO), 144.1 (p-c-mes), 140.1 (C1-Mes), 132.0, 131.1 (C4 -CH 3 Mes), 96.54 (d, J 1,F = 25.1 Hz, C1), 88.1 (d, J 2,F = 194.5 Hz, C2), 72.5 (d, J 3,F = 20.0 Hz, C3), 69.9 (C5), 67.6 (d, J 4,F = 10.0 Hz, C4), 61.4 (C6), 22.8 (2 CH 3 -Mes), 21.2 (CH 3 -Mes), 20.8 20.7, 20.6 (3 CH 3 O) ppm. 19 F NMR (376 MHz, CDCl 3 ) δ 201.26 (dd, J = 48.3, 11.8 Hz, F-2). HRMS-ESI + for [M + Na + ] C 21 H 27 FNaO 10 S + (m/z): calc. 513.1207; found 513.1210. Ethyl 2,3,4,6-tetra-O-benzyl-1-thio-β-D-galactopyranoside (14) 2, 6 To a solution of ethyl 2,3,4,6-tetra-O-acetyl-1-thio-β-D-galactopyranoside (2.50 g, 6.37 mmol) in dry MeOH (30 ml), a NaOMe solution (30%, 3.13 ml) was added at room temperature and the reaction was stirred until the complete consumption of the starting material as monitored by TLC. The mixture was neutralized with Dowex 50W (H + form). The resin was removed by filtration and the reaction was concentrated. Ethyl thiogalactopyranoside was used without further purification. S11

Ethyl thiogalactopyranoside (1.44 g, 6.42 mmol) was dissolved in dry DMF (24 ml) and cooled to 10 ºC. Sodium hydride (60% in mineral oil, 2.15 g, 64.2 mmol) was added and the reaction was stirred for 1 h, while warming up to room temperature. Benzyl bromide (7.63 ml, 64.2 mmol) was added and the mixture was stirred overnight. H 2 O (30 ml) was added carefully at 0 ºC and the aqueous layer was extracted with EtOAc (3 50 ml). The combined organic layers were washed with NaCl solution (3 30 ml) and dried over MgSO 4. After column chromatography (10:1 petroleum ether/etoac), ethyl 2,3,4,6-tetra-O-benzyl-1-thio-β-D-galactopyranoside 14 was obtained (3.8 g, 60% over two steps) as a yellowish oil. 1 H NMR (400 MHz, CDCl 3 ): δ = 7.42 7.27 (m, 20H, H-Benzyl), 4.95 (d, J = 11.7 Hz, 1H, CH 2 Benzyl), 4.88 (d, J = 10.2 Hz, 1H, CH 2 Benzyl), 4.80 (d, J = 10.1 Hz, 1H, CH 2 Benzyl), 4.73 (s, 2H, CH 2 Benzyl), 4.64 4.57 (m, 1H, CH 2 Benzyl), 4.43 (d, J = 9.1 Hz, 3H, CH 2 Benzyl, H1), 3.96 (d, J = 2.8 Hz, 1H, H4), 3.83 (t, J = 9.4 Hz, 1H, H2), 3.58 (dtd, J = 12.2 Hz, J = 7.4 Hz, J = 6.8 Hz, J = 4.5 Hz, 4H, H3, H5, H6a/b), 2.83 2.64 (m, 2H, SCH 2 CH 3 ), 1.30 (t, J = 7.4 Hz, 3H, SCH 2 CH 3 ) ppm. 13 C NMR (100 MHz, CDCl 3 ): δ = 138.9, 138.5, 138.4, 138.0, 128.6, 128.5, 128.3, 128.2, 128.1, 127.9, 127.8, 127.7, 127.6, 127.5, 127.6 (C-Benzyl), 85.5 (C1), 84.3 (C5), 78.6 (C2), 75.9 (CH 2 Benzyl), 74.6 (CH 2 Benzyl, C3), 73.7 (C4, CH 2 Benzyl), 72.8 (CH 2 Benzyl), 68.9 (C6), 24.9 (SCH 2 CH 3 ), 15.2 (SCH 2 CH 3 ) ppm. HRMS-ESI + for [M + Na + ] C 36 H 40 NaO 5 S + (m/z): calc. 607.2489; found 607.2164. 2,3,4,6-Tetra-O-benzyl-D-glucopyranosyl-(1 6)-1,2:3,4-di-O-isopropylidene-Dgalactopyranoside (15) 12 1,2:3,4-Di-O-isopropylidene-α-D-galactopyranose 9 (11.5 mg, 0.044 mmol) was dissolved in dry CH 3 CN (2 ml) and stirred over 3 Å molecular sieves for 30 min. Cu(OTf) 2 (18.4 mg, 0.051 mmol) was added for 10 min, followed by the addition of 4 (20 mg, 0.034 mmol). MSH (36.6 mg, 0.17 mmol) was added and the reaction was stirred at room temperature. TLC monitoring showed a completion of the reaction after 15 min. The reaction mixture was filtered through Celite and the organic layer was washed with saturated solutions of Na 2 CO 3 and NaCl. The crude was purified by column chromatography (5:1 petroleum ether/etoac) to afford 15 (24.5 mg, 71%) as an S12

inseparable 1:5 α/β mixture as a yellowish solid. 1 H NMR (500 MHz, CDCl 3 ): δ = 7.44 7.39 (m, 2H, H-Aryl), 7.37 7.24 (m, 20H, H-Aryl), 7.17 7.10 (m, 3H, H-Aryl), 5.57 (d, J = 5.0 Hz, 1H, H1 Glc ), 5.52 (d, J = 5.0 Hz, H1α Glc ), 5.05 (d, J = 11.1 Hz, 1H, OCH 2 -Benzyl), 4.96 (d, J = 11.0 Hz, 1H, OCH 2 -Benzyl), 4.84 4.70 (m, 4H, OCH 2 -Benzyl), 4.66 4.56 (m, 2H, OCH 2 -Benzyl), 4.53 4.49 (m, 1H, H3 Glc ), 4.46 (dd, J = 7.5 Hz, J = 2.4 Hz, 1H, H1 Gal ), 4.32 (dd, J = 5.0 Hz, J = 2.4 Hz, 1H, H2 Glc ), 4.25 (dd, J = 7.9, 1.9 Hz, 1H, H4 Glc ), 4.16 (dd, J = 10.7, J = 3.7 Hz, 1H, H6 Glc ), 4.09 (ddd, J = 7.5, J = 3.6 Hz, J = 1.8 Hz, 2H, H5), 3.77 3.67 (m, 3H, H4 Gal, H6a/b Gal ), 3.66 3.58 (m, 1H, H5 Gal ), 3.49 3.41 (m, 2H, H2 Gal, H3 Gal ), 1.50, 1.45, 1.32, 1.26 (4 s, 4 CH 3 ) ppm. 13 C NMR (126 MHz, CDCl 3 ): δ = 143.3, 140.7, 138.9, 138.3, 128.8, 128.4, 128.1, 128.0, 127.9, 127.8, 127.7, 127.6 (12 C-Aryl), 109.5 (C(CH 3 ) 2 ), 108.9 (C(CH 3 ) 2 ), 104.4 (C1 Gal ), 96.5 (C1 Glc ), 84.8 (C2 Gal ), 81.6 (C2/3 Gal ), 77.1, 76.5, 75.7, 75.1 (4 CH 2 -Aryl), 74.4 (C2/3 Gal ), 73.5, 71.5 (C4 Glc ), 70.8 (C3 Glc ), 70.5 (C2 Glc ), 69.7 (C5 Glc ), 68.7 (C6 Gal ), 67.4 (C6 Glc ), 29.9, 26.2, 25.2, 24.6 (4 CH 3 ) ppm. HRMS- ESI + for [M + Na + ] C 46 H 54 NaO + 11 (m/z): calc. 805.3558; found 805.3532. 2,3,4,6-Tetra-O-benzyl-D-glucopyranosyl-(1 3)-1-O-methyl-2,4,6-tri-O-benzyl-α-Dmannopyranoside (16) 10 A solution of methyl 2,4,6-tri-O-benzyl-α-D-mannopyranoside 10 (20.4 mg, 0.044 mmol), Cu(OTf) 2 (18.4 mg, 0.051 mmol), and 4 (20 mg, 0.034 mmol) in dry toluene (1.5 ml) was stirred over 3 Å molecular sieves for 10 min. A solution of MSH (36.6mg, 0.17 mmol) in dry toluene (0.5 ml) was added and the reaction was stirred overnight at room temperature. The reaction mixture was filtered through Celite and the organic layer was washed with saturated solutions of Na 2 CO 3 and NaCl. The crude was purified by column chromatography (19:1 toluene/etoac) to afford 16 (13.4 mg, 40%) as a colorless oil. 1 H NMR (500 MHz, CDCl 3 ): δ = 7.36 7.10 (m, 35H), 5.18 (d, J = 3.5 Hz, 1H, H1 ), 5.08 (d, J = 11.5 Hz, 1H, OCH 2 Bn), 4.92 (d, J = 10.9 Hz, 1H, OCH 2 Bn), 4.83 (d, J = 11.0 Hz, 1H, OCH 2 Bn), 4.80 4.75 (m, 2H, OCH 2 Bn, H1), 4.68 (d, J = 11.9 Hz, 1H, OCH 2 Bn), 4.64 4.40 (m, 9H, OCH 2 Bn), 4.13 (dd, J = 9.2, 3.1 Hz, 1H, H3), 4.09 (t, J = 9.4 Hz, 1H, H3 ), 4.06 3.97 (m, 2H, H5, H4), 3.89 (dd, J = 3.1, 2.0 Hz, 1H, H2), 3.78 (ddd, J = 9.5, 4.9, 2.2 Hz, 1H, H5), 3.75 3.67 (m, 2H, H6), 3.61 (t, J = 9.5 Hz, 1H, H4), 3.56 3.51 (m, 3H, H2, S13

H6 ) 3.34 (s, 3H, OCH 3 ) ppm. HRMS-ESI + for [M + Na + ] C 62 H 66 NaO 11 + (m/z): calc. 1009.4503; found 1009.4542. Table S1. Solvent optimization for secondary glycosyl acceptors entry solvent t (h) yield (%) a α/β ratio b,c 1 CH 3 CN 1 0 d 2 Et 2 O 3 9 >20:1 3 CH 2 Cl 2 1 15 >20:1 4 CH 2 Cl 2 o/n 17 >20:1 5 toluene 1 22 >20:1 6 toluene o/n 40 >20:1 a Isolated yield. b Determined by integration of the anomeric proton signals in the 1 H NMR spectrum of the crude reaction mixture. c Only the α- anomer was detected after purification by SiO 2 flash column chromatography. d Hydrolysis product 4a (75%) was obtained. 2,3,4,6-Tetra-O-benzyl-D-glucopyranosyl-(1 4)-1-O-methyl-2,3,6-tri-O-benzyl-α-Dglucopyranoside (17) 11 A solution of methyl 2,3,6-tri-O-benzyl-α-D-glucopyranoside 11 (20.4 mg, 0.044 mmol), Cu(OTf) 2 (18.4 mg, 0.051 mmol), and 4 (20 mg, 0.034 mmol) in dry toluene (1.5 ml) was stirred over 3 Å molecular sieves for 10 min. A solution of MSH (36.6mg, 0.17 mmol) in dry toluene (0.5 ml) was added and the reaction was stirred overnight at room temperature. The reaction mixture was filtered through Celite and the organic layer was washed with saturated solutions of Na 2 CO 3 and NaCl. The crude was purified by column chromatography (19:1 toluene/etoac) to afford 17 (7.3 mg, 22%) as an inseparable 1.2:1 α/β mixture as a colorless oil. 1 H NMR (500 MHz, CDCl 3 ): δ = 1H NMR (500 MHz, Chloroform-d) δ 7.43 7.07 (m, 77H), 5.69 (d, J = 3.7 Hz, 1H, H1 a), 5.09 (m, 2H), 5.02 (d, J = 11.6 Hz, 1H), 4.91 (d, J = 11.0 Hz, 1H), 4.88 4.83 (m, 2H), 4.83 4.73 (m, 11H), 4.73 4.64 (m, 3H), 4.60 (d, J = 3.9 Hz, 1H, H1a), 4.59 (d, J = 3.5 Hz, 1H, H1b), 4.60 4.57 (m, 2H), 4.58 4.51 (m, 5H), 4.51 4.45 (m, 6H), 4.45 4.39 (m, 2H), 4.38 (d, J = 7.7 Hz, 1H, H1 b), 4.08 (t, J = 9.1 Hz, 1H), 4.04 (t, J = 9.0 Hz, 1H), 3.96 (dd, J = 10.0, 9.0 Hz, 1H), S14

3.90 (dd, J = 9.9, 8.8 Hz, 1H), 3.86 3.80 (m, 4H), 3.76 3.72 (m, 2H), 3.67 3.56 (m, 5H), 3.56 3.52 (m, 1H), 3.51 3.44 (m, 4H), 3.37 (s, 4H), 3.36 (s, 3H), 3.29 (ddd, J = 9.9, 4.8, 1.8 Hz, 1H). ppm. HRMS-ESI + for [M + Na + ] C 62 H 66 NaO 11 + (m/z): calc. 1009.4503; found 1009.4387. Cholesteryl 2,3,4,6-tetra-O-benzyl-β-D-glucopyranoside (18) 13 Cholesterol 12 (17.2 mg, 0.044 mmol) was dissolved in dry CH 3 CN (2 ml) and stirred over 3 Å molecular sieves for 30 min. Cu(OTf) 2 (18.4 mg, 0.051 mmol) was added for 10 min, followed by the addition of 4 (20 mg, 0.034 mmol). MSH (36.6 mg, 0.17 mmol) was added and the reaction was stirred at room temperature. TLC monitoring showed a completion of the reaction after 15 min. The reaction mixture was filtered through Celite and the organic layer was washed with saturated solutions of Na 2 CO 3 and NaCl. The crude was purified by column chromatography (5:1 petroleum ether/etoac) to afford 18 (10.2 mg, 35%) as an inseparable 1:3.7 α/β mixture as a yellowish solid. 1 H NMR (500 MHz, CDCl 3 ): δ = 7.37 7.27 (m, 18H, H-Benzyl), 7.19 7.15 (m, 2H, H-Benzyl), 5.34 (dd, J = 4.7 Hz, J = 2.6 Hz, 1H, CH = ), 4.97 (d, J = 10.9 Hz, 1H, CH 2 Benzyl), 4.92 (d, J = 11.0 Hz, 1H, CH 2 Benzyl ), 4.85 4.74 (m, 2H, CH 2 Benzyl), 4.71 (d, J = 10.9 Hz, 1H, CH 2 Benzyl), 4.57 4.51 (m, 2H, CH 2 Benzyl), 4.50 (d, J = 7.8 Hz, 1H, H1), 3.73 (dt, J = 10.7 Hz, J = 2.9 Hz, 1H, H6a), 3.66 3.58 (m, 3H, H3, H5,6b), 3.57 3.52 (m, 1H, H4), 3.48 3.43 (m, 1H, H2), 2.09 1.94 (m, 6H), 1.90 1.76 (m, 1H), 1.56 1.39 (m, 13H), 1.17 1.06 (m, 4H), 1.03 (s, 3H), 0.92 (d, J = 6.5 Hz, 4H), 0.87 0.85 (m, 6H), 0.68 (s, 3H). 13 C NMR (126 MHz, CDCl 3 ): δ = 138.8, 138.7, 138.4, 138.3, 128.6, 128.5, 128.4, 128.3, 128.2, 128.1, 128.0, 127.9, 127.8, 127.7, 127.5 (C-Benzyl), 121.9, 102.3 (C1), 84.9 (C3), 82.4 (C2), 79.8 (C4), 75.5, 73.3, 69.2 (C5), 69.0 (C6), 56.9, 56.3, 50.3, 42.5, 39.6, 39.3, 37.4, 36.9, 36.3, 35.9, 32.1, 29.8, 28.4, 28.1, 24.4, 23.9, 22.9, 22.7, 21.2, 19.5, 18.9, 12.0 ppm. S15

2,3,4,6-Tetra-O-benzyl-glucopyranosyl-(1)-Boc-L-serine methyl ester (19) Boc-L-serine methyl ester 13 (9.65 mg, 0.044 mmol) was dissolved in dry CH 3 CN (2 ml) and stirred over 3 Å molecular sieves for 30 min. Cu(OTf) 2 (18.4 mg, 0.051 mmol) was added for 10 min, followed by the addition of 4 (20 mg, 0.034 mmol). MSH (36.6 mg, 0.17 mmol) was added and the reaction was stirred at room temperature. TLC monitoring showed a completion of the reaction after 15 min. The reaction mixture was filtered through Celite and the organic layer was washed with saturated solutions of Na 2 CO 3 and NaCl. The crude was purified by column chromatography (5:1 petroleum ether/etoac) to afford 19 (12.6 mg, 50%) as an inseparable 1:2.2 α/β mixture as a colorless oil. 1 H NMR (500 MHz, CDCl 3 ): δ = 7.39 7.35 (m, 2H, H-Benzyl), 7.35 7.27 (m, 15H, H-Benzyl), 7.14 (ddd, J = 8.9 Hz, J = 4.8 Hz, J = 2.8 Hz, 2H, H-Benzyl), 5.64 (d, J = 8.7 Hz, NHα), 5.45 (d, J = 8.6 Hz, 1H, NHβ), 4.93 (d, J = 11.3 Hz, 1H, CH 2 Benzyl), 4.86 (d, J = 10.9 Hz, 1H, CH 2 Benzyl), 4.82 4.78 (m, 2H, CH 2 OCNH,), 4.76 (d, J = 3.7 Hz, H1α), 4.69 (dd, J = 11.4 Hz, J = 4.2 Hz, 1H, CH 2 Benzyl), 4.63 4.58 (m, 2H, CH 2 Benzyl), 4.57 4.51 (m, 2H, CH 2 Benzyl)) 4.48 (s, 1H, CHNH α) 4.37 (d, J = 7.8 Hz, 1H, H1), 3.90 (t, J = 9.3 Hz, 1H, H3α), 3.73 (s, 3H, CH 3 ), 3.82 3.42 (m, 5H, H2, H4, H5, H6ab), 1.43 (s, 9H, (CH 3 ) 3 C) ppm. 13 C NMR (126 MHz, CDCl 3 ): δ = 170.9, 138.2, 131.8, 128.6, 128.1, 127.9, 127.7, 127.6 (C-Benzyl), 104.4 (C1β), 98.5 (C1α), 84.5 (C5, C6), 81.9 (C2), 77.3 (C3), 77.0 (C5, C6), 75.7 (CH 2 Benzyl), 75.2 (CH 2 CN), 75.0 (CH 2 Benzyl), 74.9 (CH 2 Benzyl), 74.8 (C4), 69.8 (C4α, C5α), 68.45, 52.7 (CH 3 O), 29.8, 28.5 (CH 3 ) ppm. HRMS-ESI+ for [M + Na + ] C 43 H 51 NaNO + 10 (m/z): calc. 764.3405; found 764.3436. 2,3,4,6-Tetra-O-benzyl-D-galactopyranosyl-(1 6)-1,2:3,4-di-O-isopropylidene-Dgalactopyranoside (20) 1,2:3,4-Di-O-isopropylidene-α-D-galactopyranose 9 (11.5 mg, 0.044 mmol) was dissolved in dry CH 3 CN (2 ml) and stirred over 3 Å molecular sieves for 30 min. Cu(OTf) 2 (18.4 mg, 0.051 mmol) S16

was added for 10 min, followed by the addition of 14 (20 mg, 0.034 mmol). MSH (36.6 mg, 0.17 mmol) was added and the reaction was stirred at room temperature. TLC monitoring showed a completion of the reaction after 15 min. The reaction mixture was filtered through Celite and the organic layer was washed with saturated solutions of Na 2 CO 3 and NaCl. The crude was purified by column chromatography (5:1 petroleum ether/etoac) to afford 20 (17.2 mg, 50%) as an inseparable 1:2.9 α/β mixture as a white solid. 1 H-NMR (500 MHz, CDCl 3 ): δ = 7.46 7.43 (m, 3H, H-Phenyl), 7.39 7.26 (m, 17H, H-Phenyl), 5.55 (d, J = 5.0 Hz, 1H, H1β), 5.51 (d, J = 5.0 Hz, H1α), 5.04 (d, J = 11.0 Hz, 1H, CH 2 Benzyl), 5.00 (d, J = 3.7 Hz, H1 α), 4.93 4.69 (m, 5H, CH 2 Benzyl), 4.62 4.55 (m, 3H, CH 2 Benzyl, H3), 4.44 4.39 (m, 1H, H1 β), 4.32 4.28 (m, 1H, H2), 4.21 (dd, J H4/H3 = 7.9 Hz, J = 1.9 Hz, 1H, H4), 4.12 (dd, J = 10.6 Hz, J = 3.7 Hz, 1H, H6), 4.09 3.95 (m, 1H, H6), 3.82 (dd, J H2 /H1 = 9.8 Hz, J = 7.7 Hz, 1H, H2 ), 3.68 (dd, J = 10.6 Hz, J = 7.5 Hz, 1H, H5), 3.60 3.54, 3.53 3.48 (m, 4H, H3, H4, H5, H6 ), 1.49, 1.43, 1.30 (3 s, 12H, CH 3 ) ppm. 13 C NMR (126 MHz, CDCl 3 ): δ = 128.7, 128.5, 128.4, 128.3, 128.2, 128.0, 127.9, 127.8, 127.6, 127.5, 127.4 (C-Benzyl), 109.5, 108.7 ((CH 3 ) 2 C), 104.8 (C1 ), 96.5 (C1), 74.9, 74.6, 73.4 (CH 2 ), 73.4 (C2 ), 73.2 (C3, C4, C5,C6 ), 71.6 (C4), 70.7 (C3, C2), 69.6 (C6), 68.9 (C5), 26.1, 26.0, 24.7 (CH 3 ) ppm. HRMS-ESI + for [M + Na + ] C 46 H 54 NaO + 11 (m/z): calc. 805.3558; found 805.3633. Control experiment for the activation of thioglycosides with MSH vs. Cu(OTf) 2 Ethyl 2,3,4,6-tetra-O-benzyl-1-thio-β-D-glucose 4 (33.3 mg, 0.057 mmol) and 1,2:3,4-di-Oisopropylidene-α-D-galactopyranose 9 (10 mg, 0.038 mmol) were dissolved in Et 2 O (2.5 ml) and stirred over 3 Å molecular sieves and Cu(OTf) 2 (30.9 mg, 0.086) for 16 h from 20 ºC to room temperature. The reaction was monitored by TLC (5:1 petroleum ether/etoac) and no disaccharide 15 was detected during the whole reaction time. After 16 h, MSH (41 mg, 0.19 mmol) was added and disaccharide 15 was detected instantaneously. S17

MSH addition product Figure S1. TLC (5:1 petroleum ether/etoac) pictures of the control experiment Control experiment for the glycosylation of intermediate (8a,b) with MeOH 3,4,6-Tri-O-acetyl-2-deoxy-2-fluoro-1-O-sulfonylmesityl-α/β-D-glucopyranose 8a,b (7:1 α/β) (10 mg, 0.02 mmol) was dissolved in dry CH 3 CN (0.5 ml) and stirred over 3 Å molecular sieves for 10 min. Anhydrous MeOH (10 µl, 0.24 mmol) was added for 5 min, followed by the addition of Cu(OTf) 2 (10.9 mg, 0.03 mmol). After 16 h stirring at room temperature, the solvent was evaporated and the residue redissolved in EtOAc. The organic layer was washed with water (3x), dried with MgSO 4, filtered, and concentrated. The crude was purified by column chromatography (2:1 petroleum ether/etoac) to afford (6.5 mg, 99%) as an inseparable 1:1 mixture of S1 24 /S2 as a yellowish syrup. 1 H NMR (CDCl 3, 400 MHz): δ = 5.37 (dt, J = 14.5, 9.3 Hz, 1H, H3-S2), 5.32 (dt, J = 14.6, 9.3 Hz, 2H, H3-S1), 5.04 (t, J = 9.8 Hz, 1H, H4-S1), 5.00 (t, J = 9.7 Hz, 2H, H4-S2), 4.53 (dd, J = 7.7, 2.7 Hz, 1H, H1-S2), 4.50 (dd, J = 7.7, 2.7 Hz, 1H, H1-S1), 4.37 4.17 (m, 3H, H2, H6a-S1), 4.14 (dd, J = 12.4, 2.4 Hz, 1H, H6b-S2), 3.78 (d, J = 12.6 Hz, 1H, H6a-S2), 3.72 (ddd, J = 10.2, 4.7, 2.4 Hz, 1H, H5-S1), 3.59 (t, J = 3.8 Hz, 7H, OMe, H6b-S2), 3.54 (ddd, J = 9.9, 4.4, 2.3 Hz, 1H, H5-S2), 2.09 (s, 3H, OAc), 2.09 (s, 3H, OAc), 2.08 (s, 3H, OAc), 2.06 (s, 3H, OAc), 2.03 (s, 3H, OAc) ppm. 13 C NMR (CDCl 3, 126 MHz): δ = 170.8, 170.4, 170.2, 170.2, 169.7, 101.5 (d, J 1,F = 22.8 Hz, C1), 89.7 (d, J 2,F = 190.8 Hz, C2-S2), 89.5 (d, J 2,F = 190.9 Hz, C1-S1), 74.1 (C5- S2), 73.0 (d, J 3,F = 19.8 Hz, C3-S2), 72.8 (d, J 3,F = 20.0 Hz C3-S1), 71.9 (C5-S1), 68.6 (d, J 4,F = 7.3 Hz, C4-S2), 68.3 (d, J 4,F = 7.5 Hz, C4-S1), 61.9 (C6-S1), 61.2 (C6-S2), 57.5 (OMe), 20.9, 20.8, 20.8, 20.7 (5 x CH 3 OAc) ppm. 19 F NMR (CDCl 3, 376.5 MHz): δ = 199.88 (ddd, J 2,F = 50.5, J 3,F = 14.7, J 1,F = 2.6 Hz, F2-S1), 200.05 (ddd, J 2,F = 50.5, J 3,F = 14.5, J 1,F = 2.5 Hz, F2-S2) ppm. S18

HRMS-TOF ES + for S1 [M+Na + ] C 13 H 19 FNaO 8 + (m/z): calc. 345.0956; found 345.0949. HRMS-TOF ES + for S2 [M+Na + ] C 11 H 17 FNaO 8 + (m/z): calc. 303.0850; found 303.0856. Phenyl 2,3,4-tri-O-benzyl-1-thio-β-D-glucose (21) 7 To a solution of phenyl 2,3,4,6-tetra-O-acetyl-1-thio-β-D-glucopyranose 1 (170 mg, 0.389 mmol) in dry MeOH (1.2 ml), a NaOMe solution (30%, 230 µl) was added at room temperature and the reaction was stirred for 1 h, until all starting material was consumed as monitored by TLC (2:1 petroleum ether/etoac). After neutralization with Dowex 5W (H + -form) for 10 min, the resin was removed by filtration and the solvent evaporated. The obtained phenyl thioglucopyranoside was used in the next step without further purification. Phenyl thioglucopyranoside (106 mg, 0.389 mmol) and trityl chloride (109 mg, 0.389 mmol) were dissolved in pyridine (1 ml) and stirred at room temperature. After 16 h, trityl chloride (70 mg, 0.25 mmol) was added. After 22 h, the reaction mixture was poured into water and extracted with CH 2 Cl 2. The organic layers were washed with water, dried over MgSO 4, filtrated and concentrated. The crude phenyl-6-o-tritylthioglucopyranose was dissolved in anhydrous DMF (2 ml) and cooled to 0 C. NaH (60% in mineral oil, 62.6 mg, 1.87 mmol) was added and the mixture was stirred for 30 min. Benzyl bromide (0.22 ml, 1.87 mmol) was added and the reaction was stirred overnight from 0 ºC to room temperature. The reaction mixture was cooled again and H 2 O (2 ml) were added carefully. The reaction was extracted with CH 2 Cl 2 (3 x 10 ml), the combined organic layers were washed with saturated NaCl (3 x 10 ml), and dried over MgSO 4. After filtration and concentration, the crude product was directly used for the next step without further purification. Phenyl tri-o-benzyl-6-otrityl-1-thio-β-d-glucopyranose was dissolved in 4:1 MeOH/CH 2 Cl 2 and p-tsoh (37.1 mg, 0.195 mmol) was added. After 24 h, TLC showed complete consumption of the starting material. The mixture was neutralized with Et 3 N and the solvent evaporated. The final compound was purified by column chromatography (from 6:1 petroleum ether/etoac to EtOAc) to afford 21 (63.1 mg, 51% overall) as a white solid. 1 H NMR (400 MHz, CDCl 3 ): δ = 7.51 (dt, J = 4.4 Hz, J = 2.4 Hz, 2H, Bn/SPh), 7.42 7.27 (m, 18H, Bn/SPh), 4.96 4.81 (m, 4H, 2 CH 2 Ph), 4.77 (d, J = 10.3 Hz, 1H, CH 2 Ph), 4.72 (d, J = 9.8 Hz, 1H, H1), 4.65 (d, J = 11.0 Hz, 1H, CH 2 Ph), 3.88 (dd, J = 12.0 Hz, J = 2.6 Hz, 1H, H6), 3.78 3.64 (m, 2H, H6, H3), 3.58 (t, J = 9.4 Hz, 1H, H4), 3.53 3.45 (m, 1H, S19

H2), 3.39 (ddd, J = 9.6 Hz, J = 4.9 Hz, J = 2.7 Hz, 1H, H5) ppm. 13 C NMR (100 MHz, CDCl 3 ) δ =139.2, 138.4, 138.0, 137.9 (4 C4 in Ph), 132.0, 129.2, 128.7, 128.6, 128.5, 128.4, 128.2, 128.1, 128.0, 127.9 (CH in Ph), 87.4 (C1), 86.7 (C3) 81.2 (C2), 79.4 (C5), 77.8 (C4), 75.9, 75.7, 75.2 (4 PhCH 2 ), 62.5 (C6). HRMS-ESI + (m/z) C 33 H 34 O 5 S: calc. [M + Na + ] = 565.2019; found [M + Na + ] = 565.2019. Phenyl 6-O-(2,3,4,6-tetra-O-benzyl-β-D-glucopyranosyl)-2,3,4-tri-O-benzyl-β-Dthioglucopyranoside (22) 14 Phenyl 2,3,4-tri-O-benzyl-1-thio-β-D-glucose 21 (23.8 mg, 0.044 mmol) was dissolved in dry CH 3 CN (2 ml) and stirred over 3 Å molecular sieves for 30 min. Cu(OTf) 2 (18.4 mg, 0.051 mmol) was added for 10 min, followed by the addition of 4 (20 mg, 0.034 mmol). MSH (36.6 mg, 0.17 mmol) was added and the reaction was stirred at room temperature. TLC monitoring showed a completion of the reaction after 15 min. The reaction mixture was filtered through Celite and the organic layer was washed with saturated solutions of Na 2 CO 3 and NaCl. The crude was purified by column chromatography (3:1 petroleum ether/etoac) to afford 22 (18.1 mg, 50%) as a yellowish solid. 1 H NMR (500 MHz, CDCl 3 ): δ = 7.54 (d, J = 7.5 Hz, 2H), 7.42-7.15 (m, 38H, H-Phenyl,), 5.02 4.42 (m, 20H), 4.40 (d, J = 7.7 Hz, 1H, H1 ), 4.17 (d, J = 11.1 Hz, 1H), 3.76 3.55 (m, 8H), 3.52 3.39 (m, 4H) ppm. 13 C NMR (126 MHz, CDCl 3 ): δ = 139.1, 138.9, 138.8, 138.7, 138.6, 138.6, 138.4, 138.3, 138.2, 135.4, 134.2, 132.3, 131.6, 129.1, 128.7, 128.6, 128.5, 128.4, 128.4, 128.3, 128.2, 128.1, 128.0, 127.9, 127.8, 127.8, 127.6, 127.6, 127.5, 127.4, 104.1 (C1 ), 97.6 (C1), 88.3, 87.5, 86.9, 84.9, 82.5, 81.9, 81.3, 81.0, 80.3, 79.1, 78.2, 75.9, 75.6, 75.2, 75.1, 74.9, 73.7, 69.1, 68.8 ppm. HRMS-ESI + for [M + Na + ] C 67 H 68 NaO 10 S + (m/z): calc. 1087.4425; found 1087.4386. S20

2,3,4,6-Tetra-O-benzyl-β-D-glucopyranosyl-(1 6)-2,3,4-tri-O-benzyl-β-D-glucopyranosyl- 15, 16 (1 6)-1,2:3,4-di-O-isopropylidene-α-D-galactopyranoside (23) 1,2:3,4-Di-O-isopropylidene-α-D-galactopyranose 9 (4.7 mg, 0.014 mmol) and 22 (6.4 mg, 0.006 mmol) were dissolved in dry CH 3 CN (2 ml) and stirred over 3 Å molecular sieves for 10 min. NBS (3.2 mg, 0.018 mmol) was added. After 5 min, Cu(OTf) 2 (1.63 mg, 0.0045 mmol) was added. The reaction was stirred at room temperature for 16 h before being filtered through Celite. The concentrated crude was purified by column chromatography (from 3:1 petroleum ether/etoac to EtOAc) to afford 23 (4 mg, 50%) as an inseparable 1:1 α/β mixture as a yellowish solid. 1 H NMR (500 MHz, CDCl 3 ): δ = 7.36 7.17, 5.54 (d, J = 4.8 Hz, 1H, H1 c ), 5.52 (d, J = 5.0 Hz, 1H, H1 c ), 5.12, 5.05, 4.94, 4.82 4.68, 4.63 4.48, 4.42 (d, J = 7.8 Hz, 1H, H1 b ), 4.40 (d, J = 7.8 Hz, 1H, H1 a ), 4.35 4.34, 4.33 4.32, 4.32 4.26, 4.24, 4.00 3.95, 3.94 3.90, 3.79 3.58, 3.45 3.39, 1.53, 1.37 ppm. 13 C NMR (126 MHz, CDCl 3 ): δ = 138.8, 138.5, 138.3, 138.2, 128.7, 128.5, 128.2, 128.1, 127.9, 127.8, 127.7, 127.6, 127.4, 109.6, 109.3, 108.9, 108.5, 104.4 (C1 b ), 103.9 (C1 a ), 96.4 (C1 c ), 96.3 (C1 c ), 84.8, 84.5, 81.8, 81.5, 75.7, 75.6, 71.3, 70.8, 70.7, 70.6, 70.5, 70.4, 70.3, 68.1, 67.4, 67.3, 66.9, 26.0, 25.9, 24.9, 24.3 ppm. HRMS-ESI + for [M + Na + ] C 73 H 82 NaO + 16 (m/z): calc. 1237.5495; found 1237.5455. 1-S-acetyl-2,3,4,6-tetra-O-benzyl-β-D-glucopyranose (S3) 17 The reaction was performed under dry conditions with 3 Å molecular sieves and argon atmosphere. Ethyl 2,3,4,6-tetra-O-benzyl-1-thio-β-D-glucopyranose 4 (10 mg, 0.017 mmol) was dissolved in dry CH 2 Cl 2 (2 ml) and MSH (11.8 mg, 0.056 mmol) was added at room temperature. After 10 min, a solution of potassium thioacetate (2.97 mg, 0.026 mmol) and 18-crown-6 (5.6 µl, 0.026 mmol) was added to the mixture and the reaction was stirred for 24 h. The reaction was filtered through Celite and the organic layer was washed with saturated Na 2 CO 3 solution (3 3 ml) and saturated S21

NaCl solution (3 ml). The crude was purified by column chromatography (from 3:1 petroleum ether/etoac to EtOAc) to afford S3 (3.56 mg, 35%) as a yellowish solid. 1 H NMR (400 MHz, CDCl 3 ): δ = 7.38 7.27 (m, 17H, H-Phenyl), 7.16 7.11 (m, 3H, H-Phenyl), 5.16 (d, J 1,2 = 10.2 Hz, 1H, H1), 4.87, 4.82 4.78, 4.77, 4.62, 4.58 4.53, 4.48 (8H, CH 2 Benzyl), 3.78 3.51 (m, 5H, H2, H3, H4, H5, H6a,b), 2.37 (s, 3H, CH 3, SAc) ppm. 13 C NMR (100 MHz, CDCl 3 ): δ = 192.9 (C=O), 128.4, 127.91, 127.8, 127.7 (C-Phenyl), 86.82, 81.7, 80.3, 75.7, 75.3, 74.9, 73.5, 70.40, 68.45 (C1/2/3/4/5/6, 4 CH 2 Benzyl), 29.7 (CH 3, SAc) ppm. HRMS-ESI + (m/z) for [M + H + ] C 36 H 41 O 5 S + : calc. 585.2669; found 585.2654; for [M + Na + ] C 36 H 38 NaO 6 S + : calc. 621.2281; found 621.2285. S22

2.2. Kinetic studies by 1 H NMR All reactions were performed directly in the NMR tube. The NMR of the pure starting material was measured directly before the addition of MSH and K 2 CO 3. All reaction were performed at room temperature and the mixtures were slightly shaken between the measurements. For the kinetic calculations the peak of the anomeric proton H1 of the starting material was used as internal reference with the value 1. The reaction progress was measured, calculating the ratio of the anomeric proton H1 of the intermediate to the starting material. Table S2. 1 H NMR kinetic studies Ac 4 Glc-SPh 1 Bn 4 Glc-SPh 2 Ac 4 Glc-SEt 3 Bn 4 Glc-SEt 4 M [g/mol] 440.5 632.8 392.4 584.8 n compound [mmol} 0.010 0.010 0.010 0.010 m compound [mg] 4.40 6.33 3.92 5.85 m K2CO3 [mg] 2.76 2.76 2.76 2.76 n K2CO3 [mmol] 0.020 0.020 0.020 0.020 m MSH [mg] 10.76 10.76 10.76 10.76 n MSH [mmol] 0.050 0.050 0.050 0.050 V CDCl3 [ml] 0.70 0.70 0.70 0.70 S23

Figure S2. Progress of the reaction of thioglycoside 1 with MSH by 1 H NMR (CDCl 3, 400 MHz) Figure S3. Progress of the reaction of thioglycoside 2 with MSH by 1 H NMR (CDCl 3, 400 MHz) S24

Figure S4. Progress of the reaction of thioglycoside 3 with MSH by 1 H NMR (CDCl 3, 400 MHz) Figure S5. Progress of the reaction of thioglycoside 4 with MSH by 1 H NMR (CDCl 3, 400 MHz) S25

2.3. Computational details Full geometry optimizations were carried out with Gaussian 09 18 using the M06-2X hybrid functional 19 and 6-31G(d,p) basis set. Bulk solvent effects in dichloromethane were considered implicitly through the IEF-PCM polarizable continuum model. 20 The possibility of different conformations was taken into account for all structures. All stationary points were characterized by a frequency analysis performed at the same level used in the geometry optimizations from which thermal corrections were obtained at 298.15 K. The quasiharmonic approximation reported by Truhlar et al. was used to replace the harmonic oscillator approximation for the calculation of the vibrational contribution to enthalpy and entropy. 21 Scaled frequencies were not considered. Massweighted intrinsic reaction coordinate (IRC) calculations were carried out by using the Gonzalez and Schlegel scheme 22,24 in order to ensure that the TSs indeed connected the appropriate reactants and products. Gibbs free energies (ΔG) were used for the discussion on the relative stabilities of the considered structures. Free energies calculated using the gas phase standard state concentration (1 atm = 1/24.5 M) were converted to reproduce the standard state concentration in solution (1 M) by adding or subtracting 1.89 kcal mol 1 for bimolecular additions and decompositions, respectively. Cartesian coordinates, electronic energies, entropies, enthalpies, Gibbs free energies, and lowest frequencies of the calculated structures are available below. S26

Figure S6. Guide to compound numbering of calculated structures (only the lowest energy conformers) S27

Figure S7. Guide to compound numbering of calculated structures (only the lowest energy conformer was shown) S28

Table S3. Energies, entropies and lowest frequencies of the lowest energy calculated structures a Structure E elec + ZPE Lowest freq. # of imag E elec (Hartree) H (Hartree) S (cal mol -1 K -1 ) G (Hartree) (Hartree) (cm -1 ) freq. α-me 4 Glc-1- OMs 1584.656706 1584.253451 1584.223910 188.4 1584.307492 28.8 0 α-me 4 Glc-1-253.6 1584.612295 1584.210635 1584.181605 185.9 1584.264630 OMs_TS hyd 1 α-ac 4 Glc-1-OMs 2037.961352 2037.517769 2037.481553 220.9 2037.579041 24.4 0 α-ac 4 Glc-1-159.3 2037.915655 2037.474135 2037.438647 216.0 2037.534840 OMs_TS hyd 1 α-2-f-ac 3 Glc-1- OMs 1909.361489 1908.968843 1908.936303 201.5 1909.026274 29.2 0 α-2-f-ac 3 Glc-1- OMs_TS hyd 1909.30989 1908.919554 1908.887113 204.4 1908.977158 330.9 1 α-2-f-ac 3 Man- 9.3 1909.367614 1908.974693 1908.942390 202.6 1909.031510 1-OMs 0 α-2-f-ac 3 Man- 1-OMs_TS hyd 1909.314639 1908.923641 1908.891570 201.6 1908.980803 259.6 1 a Energy values calculated at the PCM(CH2 Cl 2 )/M06-2X/6-31G(d.p) level. 1 Hartree = 627.51 kcal mol -1. Thermal corrections at 298.15 K. S29

Table S4. NBO Second Order Perturbation Energies (in kcal mol -1 ) Calculated with PCM(CH 2 Cl 2 )/M06-2X/6-31G(d,p) Structure endo-anomeric effect n Oendo σ* C1 Oexo exo-anomeric effect n Oexo σ* C1 Oendo TOTAL anomeric effect endo-gauche effect σ O,F C2 σ* C1 Oexo exo-gauche effect σ C1 Oexo σ* O,F C2 TOTAL gauche effect α-ac 4 Glc-1-OMes 1.7 + 18.3 0.3 + 14.1 34.4 0.2 0.1 0.3 β-ac 4 Glc-1-OMes 5.3 + 0.2 0.7 + 11.1 17.3 0.1 0.1 0.2 α-2-f-ac 3 Glc-1-OMes 1.7 + 18.1 0.3 + 14.2 34.3 0.2 0.2 0.4 β-2-f-ac 3 Glc-1-OMes 5.1 + 0.6 0.2 + 14.6 20.6 0.1 0.1 0.2 α-2-f-ac 3 Man-1-OMes 1.6 + 19.1 0.4 + 14.0 35.1 2.4 1.9 4.3 β-2-f-ac 3 Man-1-OMes 5.9 + 0.3 0.7 + 12.2 19.0 1.3 4.1 5.4 S30

Cartesian coordinates of the lowest energy structures calculated with PCM(CH 2 Cl 2 )/M06-2X/6-31G(d,p) H -3.12560-2.43580-2.20640 Structure α-me4glc-1-oms C -0.83510 0.30220 0.33650 C 0.12460 1.46540 0.53940 C 1.28430 1.41750-0.44750 C 1.94150 0.04800-0.37320 C 0.90090-1.05350-0.59340 O -0.18070-0.92950 0.34160 H -1.56540 0.28540 1.14140 H 0.90860 1.57750-1.46960 H 2.38170-0.07900 0.62470 H 0.51290-0.96130-1.61810 O -1.51640 0.49470-0.92050 S -2.86700-0.36530-1.15540 O -3.41380-0.73640 0.14500 O -3.66870 0.41290-2.07350 H 0.52310 1.32240 1.55350 O -0.58720 2.67470 0.45390 C -2.25950-1.82080-1.96070 H -1.73110-1.51880-2.86450 H -1.60250-2.33550-1.25900 C -0.34370 3.54030 1.55290 H -0.95750 4.42880 1.39930 H -0.62410 3.05390 2.49400 H 0.71280 3.82970 1.59690 O -1.84610-1.88230 2.39150 H -2.54000-1.70180 1.73930 H -1.04530-1.96450 1.85200 O -1.24200 0.66770 3.42700 H -1.47320-0.25810 3.22030 H -2.09240 1.10360 3.54940 O 2.24320 2.39800-0.11350 O 2.92260-0.07260-1.37870 C 4.21580-0.34710-0.87130 H 4.57070 0.47770-0.24300 H 4.21990-1.27350-0.28180 H 4.88020-0.46130-1.72890 C 2.16270 3.56480-0.91210 H 2.91250 4.26210-0.53530 H 2.38170 3.33460-1.96250 H 1.17060 4.02530-0.84680 S31

C 1.48700-2.43720-0.42260 H 2.25410-2.58540-1.19760 H 0.70200-3.19590-0.56940 O 2.04030-2.53740 0.86560 C 2.65760-3.78880 1.07830 H 3.05720-3.78770 2.09260 H 1.93620-4.61010 0.97490 H 3.47810-3.95120 0.36600 O 4.15050-1.11200-1.46010 H -1.07330-0.98310 1.92830 O 0.42730-2.31060 1.41760 C 2.83890 1.04400-2.17530 H 2.54590 0.60460-3.12880 H 2.06120 1.71630-1.80940 H 3.78180 1.58080-2.27820 C -0.13810-3.17860 2.39080 H 0.57390-3.99160 2.53200 Structure α-me4glc-1-oms_tshyd C 0.51670-0.01450 0.95940 C -0.38210-1.21620 1.10420 C -1.22440-1.41310-0.15030 C -1.87900-0.07630-0.47120 C -0.82360 0.98370-0.76870 O 0.25390 0.99230 0.21610 H 1.53170-0.07180 1.33000 H -0.56880-1.72980-0.97190 H -2.47680 0.24630 0.39230 H -0.32660 0.73460-1.71250 O 1.73930-0.96680-0.91770 S 3.05240-0.26340-0.98060 O 3.36820 0.43470 0.30240 H -0.28020-2.65490 3.34470 H -1.09620-3.57910 2.04920 O 2.20090 2.39210 1.88300 H 2.67950 1.77710 1.28840 H 1.83430 3.06320 1.29540 O 0.12080 0.95920 2.80480 H 0.85210 1.60670 2.64200 H 0.39250 0.44510 3.57750 O -2.20520-2.38410 0.13110 O -2.68110-0.16480-1.62590 C -4.07300-0.14290-1.34760 H -4.35480-0.97750-0.69630 H -4.35810 0.80230-0.86870 H -4.58860-0.23460-2.30390 S32

C -2.46410-3.26110-0.95500 H -3.26130-3.93280-0.63440 H -2.78580-2.70670-1.84250 H -1.57180-3.84920-1.20010 C -1.39070 2.38200-0.82480 H -2.09150 2.42340-1.67180 H -0.58330 3.10590-1.01130 O -2.03670 2.64510 0.39280 C -2.64100 3.92150 0.40820 H -3.11670 4.04400 1.38130 H -1.89530 4.71470 0.26780 H -3.39990 4.00880-0.38050 H 0.07750-1.16810-1.62960 O -2.12980-0.06090-1.05050 S -3.38580-1.02910-1.41080 O -3.99870-1.46170-0.16210 O -4.16480-0.29510-2.38090 H -0.51660 1.06480 1.59640 C -2.58260-2.40570-2.18140 H -2.01890-2.03610-3.03740 H -1.93390-2.87280-1.43980 H -3.36410-3.09520-2.50140 O -2.49890-2.62540 2.09550 H -3.20420-2.41810 1.46530 H -1.70130-2.66590 1.54960 Structure α-ac4glc-1-oms C -1.53200-0.20010 0.24670 C -0.77140 1.09720 0.53210 C 0.49120 1.22470-0.30430 C 1.29090-0.07010-0.22040 C 0.42430-1.26920-0.59200 O -0.70170-1.31830 0.29010 H -2.30640-0.35870 0.99350 H 0.25180 1.45750-1.34690 H 1.66770-0.18820 0.79990 O -1.38700-0.32360 3.33600 H -1.86450-1.12980 3.07460 H -2.01320 0.39520 3.17740 O -1.56870 2.23850 0.23770 C -2.57160 2.53180 1.08770 O -2.82820 1.86110 2.06170 C -3.30720 3.76310 0.65350 H -3.75260 3.58560-0.32790 H -4.08110 3.99830 1.38030 H -2.60640 4.59440 0.55750 S33

O 2.36940-0.05820-1.14650 H 3.11520-2.94190 2.90130 C 3.58680 0.31830-0.68630 O 3.77980 0.65640 0.45730 O 1.23430 2.29450 0.27690 C 2.06840 2.99620-0.52360 O 2.16570 2.80380-1.71140 C 4.60220 0.27010-1.78450 H 4.31420 0.98610-2.55800 H 5.58290 0.51910-1.38520 H 4.60830-0.73040-2.22020 C 2.86030 3.98530 0.27840 H 3.60310 3.42530 0.85350 H 3.36070 4.68140-0.39140 H 2.21520 4.51490 0.98000 C 1.18140-2.57890-0.46480 H 0.48090-3.41600-0.49920 H 1.90690-2.66510-1.27370 O 1.84740-2.63400 0.79700 C 3.19720-2.52970 0.79310 O 3.86030-2.49830-0.21660 C 3.73450-2.40150 2.18690 H 4.76440-2.75310 2.21210 H 3.72040-1.33720 2.44260 Structure α-ac4glc-1-oms_tshyd C -1.07920 0.02770 0.44450 C -0.30690 1.32270 0.59980 C 0.99960 1.36460-0.18680 C 1.53130-0.05350-0.38710 C 0.47270-0.86820-1.13060 O -0.76810-0.89210-0.36970 H -1.98640-0.14410 1.00840 H 0.84150 1.83560-1.16210 H 1.77860-0.49890 0.58060 H 0.24510-0.39950-2.09380 O -2.97540 0.72310-0.87800 S -4.02000-0.33380-0.70900 O -3.69890-1.22970 0.44120 O -5.38650 0.19910-0.67240 H -0.09250 1.39950 1.66890 C -3.88950-1.36090-2.15970 H -4.08190-0.74700-3.03930 H -2.88070-1.77370-2.19630 H -4.62530-2.16140-2.08640 O -1.69370-2.90870 1.46830 S34

H -2.44700-2.44620 1.05000 H -1.15990-3.25090 0.73770 O 0.02470-1.01100 2.14200 H -0.61260-1.77020 2.05720 H -0.04300-0.69630 3.05270 O 2.65090-0.08120-1.25420 C 3.88200-0.02210-0.68100 O 4.04650 0.18500 0.49400 O 1.88690 2.15300 0.59440 C 2.86490 2.83000-0.05780 O 2.97420 2.83130-1.25870 C 4.94730-0.22510-1.71330 H 4.83260 0.52360-2.49990 C 2.00160-3.14640 0.55490 O 3.03300-2.70690 0.11080 C 1.81930-3.85190 1.86310 H 2.79060-4.13330 2.26350 H 1.32360-3.15580 2.54570 H 1.17970-4.72690 1.74030 O -1.10490 2.41560 0.18020 C -2.20420 2.66200 0.94520 O -2.41980 2.05110 1.96240 C -3.06060 3.72260 0.33370 H -3.74800 4.11180 1.08180 H -2.45110 4.51960-0.09220 H -3.62300 3.24030-0.47070 H 5.92630-0.13970-1.24730 H 4.82570-1.21360-2.16190 C 3.77110 3.51480 0.91920 H 4.37080 2.74420 1.41110 H 4.42100 4.20770 0.38930 H 3.18930 4.03330 1.68200 C 0.82190-2.32910-1.34440 H 0.05530-2.80350-1.95760 H 1.79610-2.40390-1.82880 O 0.81460-3.02030-0.09640 Structure α-2-f-ac3glc-1-oms C 1.59540-0.56800 0.71780 C 0.39040-1.33960 1.25800 C -0.75480-1.43830 0.26740 C -1.05810-0.03450-0.25460 C 0.20620 0.50830-0.92070 O 1.26140 0.58840 0.03110 H 2.24100-0.25940 1.54070 H -0.50980-2.10910-0.56310 S35

H -1.37180 0.60810 0.57390 H 0.48020-0.16760-1.74600 O 2.33160-1.45390-0.14160 S 3.82020-0.94060-0.55710 O 4.20990 0.12080 0.36220 O 4.62910-2.13390-0.66920 H 0.04140-0.79880 2.14170 C 3.53000-0.25210-2.16130 H 3.06560-1.01520-2.78500 H 2.88470 0.61620-2.03340 H 4.49980 0.04200-2.56330 O 2.44180 2.64810 1.40350 H 3.02320 1.94460 1.07780 H 1.84620 2.81040 0.65590 O 0.04030 1.50970 2.40280 H 0.92120 1.85630 2.16330 H -0.04760 1.66860 3.34940 F 0.80140-2.60000 1.62390 O -2.04270-0.05210-1.27910 O -2.73980-2.87350-0.84840 C -4.20800 0.25490-2.12100 H -4.07870-0.62570-2.75370 H -5.24650 0.35090-1.81200 H -3.90100 1.13390-2.69240 C -3.92640-3.02780 1.25020 H -4.49080-2.11830 1.47340 H -4.57130-3.75030 0.75430 H -3.54090-3.42960 2.18760 C 0.06280 1.91020-1.48840 H 0.94720 2.16300-2.07580 H -0.83070 1.97490-2.11030 O 0.01710 2.87880-0.43770 C -1.20720 3.26030 0.00260 O -2.23110 2.80720-0.44880 C -1.08990 4.27880 1.09470 H -2.07310 4.68670 1.31900 H -0.68300 3.76800 1.97080 H -0.39970 5.07100 0.80050 C -3.33200 0.12790-0.91100 O -3.69500 0.15970 0.23870 O -1.84650-1.97010 1.01240 C -2.79990-2.64760 0.33620 Structure α-2-f-ac3glc-1-oms_tshyd C 1.39780 0.20170 1.03450 C 0.42180-0.82540 1.55860 S36

C -0.56620-1.27300 0.49880 C -1.11350-0.00620-0.15890 C 0.02420 0.74800-0.84440 O 1.15090 0.97340 0.04130 H 2.41910 0.19260 1.38990 H -0.08270-1.92180-0.23650 H -1.61290 0.60850 0.59920 H 0.41920 0.12360-1.65380 O 2.31470-1.37150-0.40630 S 3.69650-0.91880-0.76720 O 4.14310 0.20630 0.10470 O 4.66210-2.01940-0.84570 H -0.13540-0.36370 2.38050 C 3.55250-0.22130-2.40070 H 3.16980-0.98680-3.07530 H 2.86610 0.62530-2.35340 H 4.53850 0.11230-2.72360 O 3.22470 2.64600 1.14830 H 3.62680 1.86380 0.72010 H 2.91640 3.19430 0.41700 O 1.08030 1.70530 2.46500 H 1.83630 2.23510 2.10450 H 1.32470 1.48140 3.37400 O -2.01120-0.28980-1.21650 C -3.33500-0.34940-0.91430 O -3.75060-0.29860 0.21520 O -1.57930-1.97170 1.20750 C -2.30680-2.88690 0.52060 O -2.10280-3.15370-0.63740 C -4.14650-0.49880-2.16320 H -3.80520-1.37850-2.71270 H -5.19840-0.59550-1.90430 H -3.99030 0.38040-2.79230 C -3.38780-3.45720 1.38790 H -4.14070-2.67830 1.53600 H -3.83590-4.31640 0.89350 H -2.98770-3.73540 2.36350 C -0.36900 2.10420-1.39030 H 0.49940 2.57620-1.85240 H -1.16560 1.97770-2.12460 O -0.78240 2.96500-0.33250 C -2.11420 3.09880-0.12960 O -2.94250 2.50410-0.77640 C -2.38470 4.06060 0.98900 H -3.45160 4.08640 1.19750 H -1.82680 3.75060 1.87500 S37

H -2.03240 5.05430 0.70390 F 1.13480-1.87990 2.05360 H 0.07590 1.22870 2.63850 H -0.56530 2.35270 1.82990 O -2.95930 0.16750 2.52720 Structure α-2-f-ac3man-1-oms C 2.03270-0.16940 0.88770 C 1.00230-1.23300 1.25390 C -0.02650-1.43010 0.15230 C -0.57740-0.07870-0.29430 C 0.55990 0.88080-0.64340 O 1.42070 1.02340 0.49130 H 2.65680 0.07060 1.75060 H 0.42570-1.94480-0.70180 H -1.18160 0.34570 0.51390 H 1.12970 0.47650-1.49030 O 2.82060-0.72430-0.16050 S 4.34890-0.16200-0.35210 O 4.84390 0.22420 0.95480 O 5.00890-1.19060-1.12230 C 4.08440 1.28200-1.34350 H 3.61010 0.97600-2.27570 H 3.45630 1.96680-0.77320 H 5.06360 1.72170-1.53520 O -0.66990 1.84130 2.64500 H -2.12780 0.66230 2.62800 H -2.90490-0.25690 1.66060 F 0.34690-0.74160 2.37510 H 1.48790-2.17320 1.52230 O -1.34550-0.21400-1.48360 C -2.67900-0.37990-1.36710 O -3.24370-0.44780-0.29820 O -1.06390-2.22360 0.71980 C -1.76730-3.02840-0.11520 O -1.51770-3.13370-1.29080 C -3.32460-0.48750-2.71090 H -2.95150-1.38900-3.20310 H -4.40440-0.54170-2.59300 H -3.04530 0.37910-3.31230 C -2.88570-3.70170 0.62020 H -3.65100-2.94800 0.82630 H -3.30500-4.49190 0.00120 H -2.53360-4.09740 1.57330 C 0.05080 2.25620-1.03750 H 0.87880 2.96670-1.05010 S38

H -0.41990 2.20800-2.01910 O -0.89650 2.73090-0.07580 C -2.21410 2.73840-0.43160 O -2.58800 2.47950-1.54820 C -3.08610 3.04800 0.74470 H -4.06520 3.36560 0.39180 H -3.19330 2.13080 1.33850 H -2.63230 3.81410 1.37460 O 5.57540-1.16570-0.38770 C 4.40130 0.82060-1.63610 H 4.58900 0.35300-2.60230 H 3.45510 1.36230-1.65120 H 5.21870 1.49130-1.37260 O 1.89470 1.69290 2.18850 H 2.69100 1.31410 1.77010 H 1.47170 2.20640 1.48460 O -0.00060-0.20570 2.05900 Structure α-2-f-ac3man-1-oms_tshyd C 1.31240-0.70300 0.31420 C 0.49150-1.87650-0.12010 C -0.98340-1.51600-0.43030 C -1.17950-0.00700-0.60680 C 0.07170 0.67960-1.15610 O 1.17510 0.43820-0.23890 H 2.07260-0.77970 1.07660 H -1.29240-2.02260-1.34690 H -1.43240 0.40260 0.37310 H 0.34980 0.29000-2.14160 O 3.14500-1.32350-0.82700 S 4.29350-0.45500-0.39780 O 3.97910 0.24590 0.87800 H 0.66390 0.44680 2.38400 H -0.11440-0.88620 2.73380 O -2.20590 0.28030-1.54430 C -3.45700 0.45670-1.03610 O -3.73300 0.22160 0.11230 O -1.78050-1.96930 0.64910 C -2.98420-2.51050 0.32890 O -3.34640-2.68950-0.80690 C -4.38310 0.98450-2.08680 H -4.28190 0.40550-3.00580 H -5.40650 0.94950-1.72020 H -4.09900 2.01870-2.29870 C -3.77390-2.80170 1.56740 H -4.13230-1.84600 1.95930 S39

H -4.62100-3.43740 1.31890 H -3.14390-3.26960 2.32450 C -0.04510 2.19260-1.19560 H 0.86680 2.63020-1.60270 H -0.90860 2.48680-1.79250 O -0.16470 2.66910 0.14580 C -1.41270 2.96950 0.59770 O -2.38620 2.94150-0.11180 C -1.37800 3.27570 2.06390 H -2.34800 3.64890 2.38360 H -1.14240 2.34780 2.59460 H -0.59170 3.99990 2.28300 F 0.57400-2.82820 0.85400 H 0.97810-2.25090-1.02730 S40

2.4. NMR spectra Figure S8. 1 H NMR of 3a (CDCl 3, 400 MHz) S41

Figure S9. 1 H NMR of 4a (CDCl 3, 400 MHz) S42

Figure S10. 1 H NMR of 5b (CDCl 3 400 MHz) S43

Figure S11. 13 C NMR of 5b (CDCl 3, 100 MHz) S44

Figure S12. 19 F NMR of 5b (CDCl 3, 376.5 MHz) S45

Figure S14. 13 C NMR of 6a (CDCl 3, 100 MHz) S47

Figure S15. 19 F NMR of 6a (CDCl 3, 376.5 MHz) S48

Figure S16. 1 H NMR of 6b (CDCl 3, 400 MHz) S49

Figure S17. 13 C NMR of 6b (CDCl 3, 100 MHz) S50

Figure S18. 19 F NMR of 6b (CDCl 3, 376.5 MHz) S51

Figure S19. 1 H NMR of 7 (CDCl 3, 400 MHz) S52

Figure S20. 13 C NMR of 7 (CDCl 3, 100 MHz) S53

Figure S21. 19 F NMR of 7 (CDCl 3, 376.5 MHz) S54

Figure S23. 13 C NMR of 8a (CDCl 3, 100 MHz) S56

Figure S24. 19 F NMR of 8a (CDCl 3, 376.5 MHz) S57

Figure S25. 1 H NMR of 8a/b (CDCl 3, 400 MHz) S58

Figure S26. 13 C NMR of 8a/b (CDCl 3, 100 MHz) S59

Figure S27. 19 F NMR of 8a/b (CDCl 3, 376.5 MHz) S60

Figure S42. 1 H NMR of S1/S2 (CDCl 3, 500 MHz) S75

Figure S43. 13 C NMR of S1/S2 (CDCl 3, 126 MHz) S76

Figure S44. 19 F NMR of S1/S2 (CDCl 3, 376.5 MHz) S77

Figure S45. 1 H NMR of S3 (CDCl 3, 400 MHz) S78

Figure S46. 13 C NMR of S3 (CDCl 3, 100 MHz) S79