Ingrid 't Hart

37 Chemoenzyma�c synthesis of DSGb5 2 Dimethylthexylsilyl 4,6-O-benzylidene-2-[(2,2,2-trichloromethoxy)carbonylamino]- β-D-galacto-pyranoside (10). Benzaldehyde dimethyl acetal (4.57 mL, 30.4 mmol) and pTsOH·H 2 O (1.05 g, 5.5 mmol) were added to a solu�on of compound 24 (13 g, 26 mmol) in CH 3 CN (90 mL). A�er 1 h the mixture was quenched with Et 3 N, concentrated in vacuo and the obtained residue was purified by silica column chromatography using Hexane:EtOAc (1:0 to 3:1 v/v) as the eluent to obtain compound 10 (4.6 g, 30%). 1 H NMR (400 MHz, CDCl 3 ) δ 7.55 – 7.48 (2H, m, H-Ar), 7.43 – 7.35 (3H, m, H-Ar), 5.57 (1H, s, CH-C 6 H 5 ), 5.05 (1H, s, NH), 4.80 (1H, d, J = 7.8 Hz, H-1), 4.69 (2H, s, CH 2 , Troc), 4.28 (1H, d, J = 12.3, 1.3 Hz, H-6a), 4.20 (1H, d, J = 3.6 Hz, H-4), 4.07 (1H, d, J = 12.4, 1.8 Hz, H-6b), 3.92 (1H, d, J = 8.9 Hz, H-3), 3.63 (1H, d, J = 9.4 Hz, H-2), 3.47 (1H, s, H-5), 2.73 (1H, d, J = 9.0 Hz, OH), 1.66 – 1.58 (1H, m, CH, TDS), 0.94 – 0.78 (12H, m, 4x CH 3 , TDS), 0.22 (3H, s, CH 3 -Si), 0.17 (3H, s, CH 3 -Si). 13 C NMR (101 MHz, CDCl 3 ) δ 154.7 (C=O, Troc), 137.5 (C, Ar), 129.3, 128.5, 128.3, 126.4, 101.4 (CH-C 6 H 5 ), 95.7 (C-1), 75.0 (C-4), 74.7 (CH 2 , Troc), 70.4 (C-3), 69.3 (C-6), 66.5 (C-5), 57.8 (C-2), 34.0 (CH, TDS), 20.1 (CH 3 , TDS), 20.1 (CH 3 , TDS), 18.5 (CH 3 , TDS), 18.5 (CH 3 , TDS), -1.7 (CH 3 -Si), -2.9 (CH 3 -Si). ESI HRMS (m/z): [M + Na] + calcd for C 24 H 36 Cl 3 NO 7 Si, 606.1224; found 606.1227. [α] 25/589 = -22.5° (C = 1; CHCl 3 ). Scheme S2. Chemical glycosyla�on of donor 9 and acceptor 10 and forma�on of disaccharide donor 7a . Dimethylthexylsilyl 2,3,4,6-tetra-O-acetyl-β-D-galactopyranosyl-(1 → 3)-4,6-O- benzylidene-2-[(2,2,2-trichloromethoxy)carbonylamino]-β-D-galactopyranoside (13). A mixture of acceptor 10 (1.0 g, 1.7 mmol), donor 9 (1.3 g, 2.6 mmol) and 4 Å molecular sieves was s�rred in DCM (5 mL) for 2 h. The reac�on mixture was cooled to -35°C and TMSOTf (62 µL, 0.3 mmol) was added. A�er 30 min the reac�on was quenched with Et 3 N, filtered over a pad of Celite and concentrated in vacuo . The obtained residue was purified by silica column chromatography using Toluene:EtOAc (1:0 to 8.5:1.5 v/v) as the eluent to afford compound 13 (878 mg, 56 %). 1 H NMR (400 MHz, CDCl 3 ) δ 7.58 – 7.52 (2H, m, H-Ar), 7.42 – 7.31 (3H, m, H-Ar), 5.55 (1H, s, CH-C 6 H 5 ), 5.36 (1H, dd, J = 3.4, 0.8 Hz, H-4, Gal-V), 5.32 – 5.26 (1H, m, NH), 5.21 (1H, d, J = 7.9 Hz, H-1, GalNAc-IV), 5.13 (1H, d, J = 7.7 Hz, H-2, Gal-V), 4.96 (1H, dd, J = 10.4, 3.5 Hz, H-3, Gal-V), 4.78 (1H, d, J = 7.9 Hz, H-1, Gal-V), 4.75 – 4.60 (2H, m, CH 2 , Troc), 4.46 (1H, dd, J = 11.1, 2.7 Hz, H-3, GalNAc-IV), 4.29 (1H, d, J = 3.3 Hz, H-4, GalNAc-IV), 4.25 (1H, d, J = 12.2, 1.1 Hz, H-6a, GalNAc-IV), 4.22 – 4.07 (2H, m, H-6, Gal-V), 4.03 (1H, d, H-6b, GalNAc-IV), 3.88 (1H, t, J = 6.3 Hz, H-5, Gal-V), 3.54 – 3.36 (2H, m, H-2, GalNAc-IV; H-5, GalNAc-IV), 2.15 (3H, s, OAc), 2.06 (3H, s, OAc), 2.04 (3H, s, OAc), 1.97 (3H, s, OAc), 1.63 (1H, p, J = 13.7, 6.9 Hz, CH, TDS), 0.92 – 0.78 (12H, m, 4x CH 3 , TDS), 0.19 (3H, s, CH 3 -Si), 0.13 (3H, s, CH 3 -Si). 13 C NMR (101 MHz, CDCl 3 ) δ 170.2 (C, OAc), 170.0 (C, OAc), 169.3 (C, OAc), 153.8 (C=O, Troc), 138.0 (C, C 6 H 5 ), 129.0, 128.2, 126.3, 101.6 (C-1, Gal-V), 100.7 (CH-C 6 H 5 ), 95.20 (CCl 3 ), 94.5 (C-1, GalNAc-IV), 76.1 (C-4, O O O HO TrocHN Ph OTDS O O O O TrocHN O AcO OAc AcO AcO Ph OTDS 9 10 O O O HO TrocHN Ph OTDS O O AcO OAc AcO AcO O O O O TrocHN O AcO OAc AcO AcO Ph O NH CCl 3 CCl 3 NH TMSOTf, DCM, -35 °C + 56% 7a O O O O TrocHN O AcO OAc AcO AcO Ph 13 OTDS i) HF.pyridine, pyridine ii) Cs 2 CO 3, Cl 3 CCN, CH 2 Cl 2, 0 °C 71%