beta-Maltose → 63-O-alpha-D-Glucosylmaltotriose

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Pullulane52 (100 g) was dissolved in water (1 l) by heating and added to a solution of acetic acid (ca 15 ml) and sodium acetate (41 g) in water (5 l). The solution was adjusted to pH 5 and pullulanase and β-amylase (200 and 200000 units respectively) were added. The reaction mixture was stirred at 37° for 24 h (TLC: SiO2, acetone:isopropanol:0.1M lactic acid; 2:2:1) and then heated at 120° for 20 min (autoclave). The solution was concentrated (final volume: 1.5 l) and treated with ion-exchange resin (Duolite C-26 (H+); 0.5 l). The resin was washed with water and the combined water solutions (ca 4 l) were ultrafiltered (Millipore PSAC 14205 NMWL 1000) which gave a colorless solution. Freeze-drying gave 91 (72 g) contaminated with glucose, maltose and maltotriose. Pure 91 was obtained by treating 92 (1.0 g) with methanolic sodium methoxide (50 ml; from ~1 mg of sodium) at room temperature while monitoring the reaction by TLC (SiO2, chloroform:methanol:water 65:35:10, lower phase). After 24 h, the reaction mixture was neutralized with dry Duolite (H+) resin, filtered, concentrated and chromatographed (Waters Preppak-500/C:water) to give 91 (337 mg, 63%, >99.5% pure by HPLC). [α]D25 +165° (c 0.8, water). Lit.25 [α]D20 +179° (c 1.14, water). 1H-NMR (D2O, TSP) δ 5.40, 5.38 (2d, each 1H, J=3.8 and 3.5 Hz, H1' and H1"), 5.26 (d, ~0.3H, J=3.7 Hz, H1), 4.99 (d, 1H, J=3.7 Hz, H1"'), 4.68 (d, ~0.7H, J=7.9 Hz, H1). 13C-NMR (D2O, TSP) δ 102.6, 102.2, 100.8 (C1', C1∆, C1"'), 98.5, 94.7 (Cl), 79.9, 79.8, 79.6, 78.9, 77.3, 76.7, 76.0, 75.97, 75.8, 74.7, 74.6, 74.4, 74.3, 74.2, 74.1, 73.9, 72.7, 72.3, 72.1, 68.6, 63.4, 63.3, 63.2. The structure of 91 was confirmed by methylation analysis26.

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