13C NMR (125 MHz, DMSO‑d 6) δ 156.1, 156.0, 152.5, 152.4, 149.3, 149.0, 139.8, 139.8, 119.3, 119.2, 87.6, 86.3, 86.2, 82.4, 81.2, 72.5, 71.9, 69.2, 68.0, 62.0, 56.2, 54.0, 53.7, 28.3, 19.8, 13.8.