Download (3249Kb) - D-Scholarship@Pitt - University of Pittsburgh

mixture was filtered over a pad of silica gel using a fritted funnel, eluting with hexanes/EtOAc 2
: 1 (100 mL). The filtrate was concentrated under vacuum and the resulting pale yellow oil was
purified by flash chromatography (hexanes/EtOAc, 20 : 1, v/v) to give 60 (187 mg, 73%) as a
colorless oil and a 1 : 1 mixture of diastereomers.
1 H NMR (300 MHz, CDCl3): δ 5.52-5.42 (m, 1H), 5.32 (br d, J = 7.4 Hz, 1H), 4.36-4.30 (m,
1H), 4.08-4.03 (m, 1H), 3.81 (dd, J = 10.0, 2.9 Hz, 1H), 2.45 (d, J = 2.1 Hz, 0.5H), 2.41 (d, J =
2.1 Hz, 0.5H), 1.50 (d, J = 6.7 Hz, 1.5H), 1.49 (d, J = 6.6 Hz, 1.5H), 1.44 (s, 9H), 1.85 (s, 4.5H),
1.85 (s, 4.5H), 0.03-0.01 (m, 6H); 13 C NMR (75 MHz, CDCl3): δ 169.6, 155.4, 155.3, 81.6, 79.8,
73.3, 73.2, 63.6, 63.5, 61.1, 55.7, 55.6, 28.3, 25.7, 25.7, 21.3, 21.2, 18.1, -5.6; IR (thin film): ν
3451, 3314, 2932, 2122, 1750, 1720 cm -1 ; MS m/z (%) 372 (11), 316 (22), 258 (51), 206 (43), 57
(100); EI-HRMS calcd for C18H34NO5Si m/z [M+1] + 372.2206; found 372.2201.
TBDMSO
Bz NH
2-Benzoylamino-3-(tert-butyldimethylsilyloxy)propionic acid 1-methylprop-2-ynyl ester
(61). Boc-protected amine 60 (1.48 g, 3.98 mmol) was dissolved in TFA (5 mL) and stirred for 5
min at rt, and then the excess TFA was removed under vacuum (rotary evaporator was used with
a dry ice-cooled trap to collect the TFA). The brown oil was purified by flash chromatography
(hexanes-EtOAc, 3 : 1, v/v then EtOAc). After evaporation of the solvents the resulting residue
(1.54 g) was dissolved in CHCl3 (20 mL) and Et3N (1.65 mL, 12.0 mmol) was added followed by
benzoyl chloride (444 µL, 3.84 mmol) at 0 °C under nitrogen. The reaction mixture was stirred
for 1 h after which it was diluted with CHCl3 (120 mL). The organic phase was washed with 5%
aq. AcOH (50 mL) and then sat’d aq. NaHCO3 (50 mL), dried over MgSO4 and concentrated
under vacuum. Purification of the crude residue by flash chromatography (gradient elution,
61
152
O
O