1H NMR (600 MHz, DMSO‑d 6) δ 8.55 (t, J = 5.8 Hz, 1H), 8.33–8.27 (m, 2H), 8.26 (s, 1H), 8.13 (s, 1H), 7.96–7.88 (m, 2H), 7.37 (br. s, 2H), 6.09 (d, J = 2.8 Hz, 1H), 5.32 (dd, J = 6.3 Hz, 2.9 Hz, 1H), 4.89 (dd, J = 6.3 Hz, 3.0 Hz, 1H), 4.16 (td, J = 5.9 Hz, 3.0 Hz, 1H), 3.24–3.10 (m, 2H), 1.50 (s, 3H), 1.27 (s, 3H).