A mixture of 3,4-diethoxybenzoic acid (0.19 g; 0.904 mmol), a product of Step D (0.25 g; 0.904 mmol) and EDC (0.27 g; 1.4 mmol) in anhydrous DMF (2 ml) was stirred at ˜60° C. for 1 h, then cooled to room temperature and diluted to 20 ml with EtOAc. This was washed with H2O (2×5 ml), brine, dried over anhydrous MgSO4, filtered and filtrate evaporated to dryness. The residue was diluted to 3 ml with anhydrous diglyme and 1M TBAF in THF (0.5 ml) was added and the resulting mixture was stirred at ˜80° C. for 1 h, then solvents were removed in vacuo. The residue was purified by crystallization from MeOH, to give the title compound (0.084 g; 20%) as greyish solid. 1H-NMR (CDCl3) 1.4-1.6 (m, 15H+H2O); 4.14-4.24 (m, 4H); 4.7-4.76 (m, 4H); 6.97 (d, 1H, J=6 Hz); 7.32-7.4 (m, 1H); 7.66 (d, 1H, J=3 Hz); 7.78 (dd, 1H, J=3, 9 Hz); 8.02-8.08 (m, 2H).
