To a solution of N-(2-aminomethyl-5-tert-butyl-3-thienyl)-N′-(4-methylphenyl)urea (0.20 g, 0.63 mmol) and N-carbo-tert-butoxyglycine (0.11 g, 0.63 mmol, 1.0 equiv) in THF (2 mL) at room temp. were added dicyclohexylcarbodiimide (0.13 g, 0.63 mmol, 1.0 equiv) and 1-hydroxybenzotriazole monohydrate (0.008 g, 0.06 mmol, 10 mol %). The resulting mixture was allowed to stir 18 h, diluted with EtOAc (5 mL), and washed with a saturated NaCl solution. The organic layer was dried (MgSO4) and concentrated under reduced pressure. The residue was purified by flash chromatography (gradient from 30% EtOAc/hexane to 50% EtOAc/hexane) to afford N-(2-(N-(N-carbo-tert-butoxyglycyl)aminomethyl)-5-tert-butyl-3-thienyl)-N′-(4-methylphenyl)urea (0.12 g, 40%, Example 52): mp 174-176° C.; 1H NMR (CDCl3) δ1.38 (s, 9H), 2.27 (m, 3H), 4.38 (m, 2H), 6.67 (bs, 1H), 6.89 (m, 1H), 7.27 (m, 1H), 7.33 (m, 2H), 8.58 (bs, 1H); FAB-LRMS m/z 475 (M+H).
