5 (0.54 g, 2.4 mmol, 1.05 eqv.) was dissolved in dry THF (5 mL) and DMAP (0.14 g, 1.2 mmol, 0.5 eqv.) was added to the solution under nitrogen. After cooling on ice, a dexamethasone solution (0.91 g, 2.3 mmol, 1 eqv.) in dry THF (25 mL) and DCC (0.525 g, 2.5 mmol, 1.1 eqv.) were added to the mixture. The reaction mixture was slowly warmed to room temperature and stirred overnight at RT. The completion of the reaction was confirmed by TLC (EtOAc/Hex, 20:1 (v/v), Rf: 0.24). Most of the solvent was evaporated and the remaining solution was purified on a 20 cm silica gel column (EtOAc/Hex, 20:1 (v/v)). 1 g (73% yield) DMSL2 was obtained as a yellow fluffy solid.
