A mixture of 3.5 g of 1,1-dimethylethyl 4-[6-(benzyloxy)-3-(3,4-dimethoxybenzyl)-2,4-dioxo-3,4-dihydroquinazolin-1(2H)-yl]piperidine-1-carboxylate obtained in stage 1.5 and 25 ml of TFA in 50 ml of DCM is stirred at AT for 2 h 00. The mixture is neutralized with K2CO3. It is filtered and the filtrate is evaporated under reduced pressure. The residue is taken up in DCM and washed with a saturated NaHCO3 solution and then with an 8% NaOH solution. The solution is dried over Na2SO4 and filtered, and the solvent is evaporated under reduced pressure to give 2.67 g of the expected product.
