, 6.49 (d, J = 8 Hz, 1H), 5.04 (t, J = 8 Hz, 1H), 4.46 (m, 2H), 4.25 (dd, J = 8, 20 Hz, 1H), 4.13 (dd, J = 8, 20 Hz, 1H), 3.87 (s, 3H), 3.10 (m, 2H), 2.28