Ingrid 't Hart

45 Chemoenzyma�c synthesis of DSGb5 2 N-(Benzyl)-benzyloxycarbonyl-5-aminopentyl 2-O-benzyl-4,6-O-di-tert-butylsilanediyl- β-D-galactopyranosyl-(1 → 4)-2,3,6-tri-O-benzyl-β-D-galactopyranosyl-(1 → 4)-2,3,6- tri-O-benzyl-β-D-glucopyranoside (8b). β-Pinene (71 µL, 0.45 mmol) and DDQ (51 mg, 0.22 mmol) were added to a s�rring solu�on of compound 15b (2.1 g, 1.4mmol) in DCM/H 2 O (9/1 mL). The reac�on mixture was kept in darkness and s�rred overnight. The mixture was diluted with DCM, washed with sat. aq. NaHCO 3 (2 x), dried (Na 2 SO 4 ), filtered and concentrated in vacuo . Purifica�on by silica column chromatography using Toluene:EtOAc (1:0 to 10:1.2 v/v) as the eluent provided compound 8b (105 mg, 59 %). 1 H NMR (400 MHz, CDCl 3 ) δ 7.42 – 7.09 (45H, m, Ar-H), 5.15 (2H, d, J = 7.0 Hz, CH 2 ), 5.05 (1H, d, J = 11.6 Hz, CHH), 4.98 (1H, d, J = 3.2 Hz, H-1, Gal-III), 4.89 – 4.80 (1H, m, CHH), 4.80 – 4.26 (16H, m, H-1, Gal-II; H-1, Glc-I), 4.23 (1H, d, J = 2.8 Hz, H-4, Gal-III), 4.09 – 3.68 (10H, m, H-3, Gal-III), 3.65 (1H, dd, J = 9.9, 3.2 Hz, H-2, Gal-III), 3.61 – 3.09 (10H, m, H-2, Gal-II; H-2, Glc-I), 2.39 – 2.31 (1H, m, OH), 1.78 – 1.42 (4H, m, 2x CH 2 , pentyl), 1.38 – 1.18 (2H, m, CH 2 , pentyl), 0.97 (9H, s, t-Bu), 0.90 (9H, s, t-Bu). 13 C NMR (101 MHz, CDCl 3 ) δ 139.4, 138.6, 138.4, 138.4, 138.2, 128.5, 128.4, 128.3, 128.3, 128.2, 128.2, 128.1, 128.0, 127.9, 127.8, 127.7, 127.7, 127.6, 127.6, 127.5, 127.4, 127.3, 127.1, 103.5 (C-1, Glc-I), 103.0 (C-1, Gal-II), 99.4 (C-1, Gal-III), 82.6, 81.7 (C-2, Glc-I), 81.0, 78.9 (C-2, Gal-II), 77.2, 75.5 (C-2, Gal-III), 75.1, 75.0, 74.9, 73.9 (C-4, Gal-III), 73.2, 73.1, 73.1, 73.0, 72.2, 70.1 (C-3, Gal-III), 68.4, 67.5, 67.1, 66.7, 29.4, 27.5 (CH 3 , t-Bu), 27.2 (CH 3 , t-Bu), 23.4, 23.2 (C, t-Bu), 20.6 (C, t-Bu). [α] 25/589 = -53° (C = 0.01; CHCl 3 ). Table S1. Glycosyla�on condi�ons of trisaccharide acceptor 8a and disaccharide donor 7a or 7b to afford protected Gb5 ( 16a , 16b ). Donor Ac�vator Temperature Total product Isolated β-product 7a TMSOTf (0.2eq) -30 °C 56-59% 37-42% 7a TMSOTf (0.2-0.3eq) -60 °C 72-76% 42-45% 7a TfOH (0.1eq) -10 °C 32% 32% 7a TfOH (0.1eq) -50 °C 43% 24-28% 7b TfOH (0.1eq) -10 °C 19-44% 19-44% 7b TfOH (0.1eq) -50 °C 52% 52% The highest overall yield of the glycosyla�on was obtained at the coldest ac�va�on temperature. However, changes in temperature or ac�vator did not improve β/α selec�vi�es when donor 7a was used. The glycosyla�on proved most successful with donor 7b and acceptor 8a in DCM with molecular sieves at -50 °C, since no α-product was formed. O O O HO BnO O O OBn BnO OBn O O O OBn BnO BnO Si NBnCbz O R 1 O OR 2 O TrocHN O AcO OAc AcO AcO O NH CCl 3 O O O HO BnO O O OBn BnO OBn OMP O O OBn BnO BnO Si 8a O R 1 O OR 2 O TrocHN O AcO OAc AcO AcO O O O O BnO O O OBn BnO OBn OMP O O OBn BnO BnO Si + R 1 :R 2 = CHPh ( 7a ) R 1 = R 2 = OAc ( 7b ) R 1 :R 2 = CHPh ( 16a ) R 1 = R 2 = OAc ( 16b ) Activator