Reaktionsschritte
A suspension of methyl (2R,3S)-3-(9-anthracenesulfonamido)-3-phenyl-2-hydroxypropionate (II, EXAMPLE 11C, 45 mg, 0.1 mmol) in dry toluene (1 ml) is treated with benzaldehyde dimethylacetal (45 μl, 0.3 mmol) in the presence of a catalytic amount of pyndinium toluenesulfonate (2.5 mg, 0.01 mmol) and stirred at 75° under reduced pressure of 15 inch/mercury for 2 hr. HPLC analysis (silica gel with a C-18 group attached; acetonitrile/water, 65/35, flow 1 ml/min and UV 254 nm) showed the final product (70.2%, retention time 15.0 mins) and the (3S)-diasteriomer (3.5%, retention time 17.0 mins). The resulting reaction mixture is diluted with ethyl acetate (15 ml) and washed with water (10 ml). The aqueous phase is extracted again with ethyl acetate (10 ml). The combined organic phase is dried over magnesium sulfate, filtered and the solvent is removed under reduced pressure. Purification by silica gel column chromatography (ethyl acetate/hexane, 10/90) gives the title compound, mp=71-73°; IR (mineral oil) 1762, 1737, 1332, 1216, 1158, 1146, 1116, 1106, 1089, 1076, 1027, 755, 739, 697 and 681 cm−1; NMR (300 MHz, CDCl3) 9.02, 8.39, 7.86, 7.57-7.50, 7.43, 7.30-7.25, 7.07, 6.88, 6.67-6.51, 6.51-6.44, 6.27, 5.94, 4.84 and 3.77 δ; CMR (300 MHz, CDCl3) 170.0, 137.1, 136.2, 133.5, 130,9, 130.5, 128.9, 128.8, 128.6, 128.1, 128.0, 126.9, 125.2, 124.9, 93.1, 81.6, 68.7 and 52.6 δ; MS (m/z) 524 (M++1), 523 (M+), 369, 354, 346, 282,265, 241, 209, 193, 178, 165, 121 and 91; HRMS (m/z) calculated C31H25N1O5S1+H1=524.1531, observed=524.1530.
