Ingrid 't Hart

39 Chemoenzyma�c synthesis of DSGb5 2 2,2,2-Trichloroace�midate 2,3,4,6-tetra-O-acetyl-β-D-galactopyranosyl-(1 → 3)-4,6-di- O-acetyl-2-[(2,2,2-trichloromethoxy)carbonylamino]-β-D-galactopyranoside (7b). A solu�on of disaccharide 13 (350mg, 0.38mmol) in 80%aq AcOH (4 mL) was heated to 80°C for 4 h. The mixture was allowed to cool to room temperature (RT) and was diluted with EtOAc, washed with H 2 O, sat aq. NaHCO 3 (3x), dried (Na 2 SO 4 ), filtered and concentrated in vacuo . The obtained crude was dissolved in pyridine (3 mL) and Ac 2 O (2 mL) was slowly added, followed by DMAP (cat.). A�er 1 h, the reac�on showed complete conversion by TLC and the mixture was concentrated in vacuo . The crude was dissolved in pyridine (3.5 mL) and transferred to a plas�c round bo�om flask. HF·Pyridine (70% HF, 350 µL) was added and the mixture was s�rred overnight. The reac�on mixture was diluted with EtOAc, washed with sat. aq. NaHCO 3 (3x), dried (Na 2 SO 4 ), filtered, concentrated in vacuo and co-evaporated with toluene. Quick silica column purifica�on Hexane:EtOAc (1:0 to 1:3 v/v) provided the intermediate in 81% yield. The obtained intermediate (237 mg, 0.31 mmol) was dissolved in DCM and s�rred with 4 Å molecular sieves at 0°C. 2,2,2-trichloroethyl chloroformate (297 µL, 2.96 mmol) and Cs 2 CO 3 (301 mg, 0.92 mmol) were added a�er 30 min. A�er 22 h the reac�on mixture was concentrated in vacuo and the obtained residue was purified by silica column chromatography using Hexane:EtOAc (1:0 to 1:1 v/v) as the eluent to isolate the α-anomer of the �tle compound (143 mg, 53 %). 1 H NMR (600 MHz, CDCl 3 ) δ 8.75 (1H s, C=NH), 6.57 (1H, d, J = 3.3 Hz, H-1, GalNAc-IV), 5.50 – 5.34 (3H, m, H-4, GalNAc-IV; NHTroc; H-4, Gal-V), 5.28 – 5.20 (1H, m, H-2, Gal-V), 4.99 (1H, dd, J = 10.3, 3.2 Hz, H-3, Gal-V), 4.84 (1H, , J = 12.1 Hz, CHH, Troc), 4.76 (1H, d, J = 8.2 Hz, H-1, Gal-V), 4.62 (1H, d, J = 12.0 Hz, CHH, Troc), 4.41 – 4.34 (1H, m, H-2, GalNAc-IV), 4.31 (1H, t, J = 6.4 Hz, H-5, GalNAc-IV), 4.25 – 4.04 (4H, m, H-6a, GalNAc-IV; H-3, GalNAc-IV; H-6, Gal-V), 4.04 – 3.92 (2H, m, H-5, Gal-V; H-6b, GalNAc-IV), 2.20 (3H, s, OAc), 2.15 (3H, s, OAc), 2.10 (3H, s, OAc), 2.04 (6H, s, 2x OAc), 1.98 (3H, s, OAc). Scheme S4. Synthesis of disaccharide acceptors 12a and 12b from protected lactose 25 . O AcO OAc O TrocHN O AcO OAc AcO AcO O NH CCl 3 O O OBn BnO OBn OMP O HO OBn BnO BnO O O OBn BnO OBn OMP O O O BnO BnO Ph Et 3 SiH, TfOH, DCM, - 78 °C, 12a 25 O CCl 3 NH i) CAN, ACN/H 2 O, 0 °C ii) TCA, DBU, DCM, 0 °C 23 ,TMSOTf, ACN, - 30 °C to 15 °C O O OBn BnO OBn O O O BnO BnO Ph O NBnCbz O O OBn BnO OBn O HO OBn BnO BnO O NBnCbz Et 3 SiH, TfOH, DCM, - 78 °C 26 27 12b O O OBn BnO O O O BnO BnO Ph BnO