All reagents and chemicals commercially available were used without further purification. Solvents were dried using standard techniques. NMR spectra were recorded on a Bruker III 300 ( 1 H, 300 MHz ; In a Schlenk tube under an argon atmosphere, the compound 2 (500 mg, 0.54 mmol, 1 equiv.) was suspended in a THF/MeOH/H2O mixture (1/1/1 v/v/v, 9 mL). NaOH (216 mg, 5.4 mmol, 10 equiv.) was added and reaction was stirred overnight at 80 °C. Water was added to the reaction until complete dissolution of the media and the resulting solution was heated for a further 30 min at 80 °C. After going back to room temperature, MeOH and THF were removed under reduced pressure. The resulting solution was acidified to pH = 2 using a 10 % HCl solution. The orange precipitate was filtrated on a sintered glass funnel. The obtained solid was washed by H2O, EtOH and Et2O. The product L was obtained as a dark brown solid (395 mg, 84 %).