g 84 of t butyloxy carbonyl urocanic acid melting point transition at 155 u00b0 c 218 u00b0 219 u00b0 c a suspension of 23 1 g 97 mmol of t butyloxy carbonyl urocanic acid 13 4 g 97 mmol of p nitrophenol and 1 g of p dimethylaminopyridine dmap in 150 ml of ch 2 cl 2 is cooled in an ice bath and treated with 20 0 g 97 mmol of dicyclohexylcarbodiimide the ice bath is removed and the reaction stirred at room temperature overnight the reaction mixture is filtered and rinsed with 50 ml portions of 0 1 n hcl water saturated nahco 3 and twice with brine the solution is dried na 2 so 4 concentrated in vacuo and triturated with hot chcl 3 hexanes to afford 28 3 g 81 of t butyloxy carbonyl urocanic acid p nitrophenol ester melting point 158 u00b0 159 u00b0 c d a solution of 12 9 g 70 4 mmol of l proline t butyl ester and 9 8 ml 69 4 mmol of triethylamine in 150 ml of ch 2 cl 2 is cooled in an ice bath under nitrogen and treated with 25 g 69 4 mmol of t butyloxy carbonyl urocanic acid p nitrophenol ester added in three portions over a thirty minute period the reaction is allowed to warm to room temperature overnight then diluted with 750 ml of ethyl acetate and rinsed with portions of 1 n aqueous nh 4 oh totaling 1 5 liters the ethyl acetate solution is finally washed with brine 10 khso 4 saturated nahco 3 brine dried na 2 so 4 and concentrated in vacuo the.