Reaction Steps
A solution of the product of Example 4 (40 mg, 0.065 mmol) in THF (1 ml) was treated with 1.0 M TBAF (0.32 ml, 0.32 mmol) at 0° C. The reaction was stirred for 3 h and then poured into water and extracted with ether. The ether extracts were washed with brine, dried and concentrated. The ethereal solution was then treated with an excess of freshly prepared diazomethane in ether to convert the free acid to the product. Flash column chromatography (silica gel, 4% MeOH/CH2Cl2) afforded the pure product in 90% yield. 1H NMR (500 MHz, C6D6): δ 6.55 (dd, J=15.5 Hz and 10.9 Hz, 1H), 6.16 (dd, J=15.2 Hz and 11.0 Hz, 1H), 6.05 (dd, J=15.5 Hz and 5.3 Hz, 1H), 5.70 (d, J=16.2 Hz, 1H), 5.61 (dd, J=14.6 Hz and 5.5 Hz, 1H), 5.58 (d, J=14.7 Hz, 1H), 4.28 (t, J=5.8 Hz, 1H), 4.06 (dd, J=11.2 Hz and 5.3 Hz, 1H), 3.65 (dd, J=1.0 Hz and 6.7 Hz, 1H), 3.30 (s, 3H), 2.36 (m, 2H), 2.06 (t, J=6.9 Hz, 2H), 1.72 (m, 2H), 1.59 (m, 2H), 1.27 (m, 2H), 0.74 (t, J=7.4 Hz, 3H). 13C NMR (125 MHz, C6D6): δ 173.819, 145.219, 141.143, 136.647, 130.007, 111.340, 109.915, 92.672, 85.857, 84.082, 81.330, 73.505, 70.225, 62.533, 51.488, 37.097, 33.599, 29.912, 28.658, 20.615, 9.451. HPLC: Beckman Ultrasphere reverse phase column (30% water in MeOH, 3.8 ml/min, 252 bar): elution time=5.41 min.
