N-Methyl-L-Val-OMe*HCl; N-ethyl-N,N-diisopropylamine; PyCloP in dichloromethane 16 h; Ambient temperature;

1: 1.) ethyl chloroformate, Et3N, 2.) Et3N / 1.) CHCl3, 30 min, room temp., 2.) CHCl3, THF, room temp., 30 min, then reflux, 10 min 2: 100 percent / 0.5 h / 200 °C View Scheme

1: t-Boc-L-valine With chloroformic acid ethyl ester; triethylamine in tetrahydrofuran T=0 - 20°C; 2: L-proline in tetrahydrofuran T=0 - 20°C;

1: 81.2 percent / HOBt; EDCI / dimethylformamide / 20 °C 2: 93.5 percent / aq. NaOH / methanol / 2 h / 20 °C View Scheme

1: Et3N / -15 °C 2: -5 deg C to room t. 3: 93 percent / H2O / CF3CO2Ag / tetrahydrofuran; triethylamine / 3 h / -25 deg C to room t. View Scheme

2: 1-hydroxybenzotriazole hydrate, dicyclohexylcarbodiimide, triethylamine / dimethylformamide / 96 h / Ambient temperature View Scheme

1: DMAP, DCC / CH2Cl2 / 12 h / 0 °C 2: AcOH, NaBH4 / CH2Cl2 / 8 h / -5 °C 3: 94 percent / toluene / 3 h / Heating 4: 75 percent / NaOH / H2O; acetone / 0.5 h / 22 °C View Scheme

1: 1-hydroxybenzotriazole (HOBT), 1-ethyl-3-<3-(dimethylamino)propyl>carbodiimide hydrochloride (EDC) / dimethylformamide / 18 h / Ambient temperature 2: triethylamine / 1,2-dimethoxy-ethane / 18 h / Ambient temperature 3: HCl (gas) / ethyl acetate / 0.33 h / -25 °C View Scheme

Multistep reaction;

1: 454 mg / DEBPT; i-Pr2NEt2 / tetrahydrofuran / 18 h / 20 °C 2: 2,6-lutidine / CH2Cl2 / 1 h / 20 °C 3: 143 mg / aq. LiOH / 2-methyl-propan-2-ol / 16 h / 20 °C 4: 78 percent / 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide*HCl; 1-hydroxybenzotriazole / dimethylformamide; CH2Cl2 / 24 h / 0 - 20 °C 5: 88 percent / β-bromocatecholborane / CH2Cl2 / 0.5 h / -78 °C 6: H2; 2,2'-bipyridyl / Pd/C / methanol; ethyl acetate / 2 h 7: 37.7 mg / 2,4,6-collidine / CH2Cl2 / 3 h / 20 °C 8: Dess-Martin periodinane / CH2Cl2 / 1.25 h / 0 - 25 °C 9: aq. NaClO2; NaH2PO4*2H2O / 2-methyl-propan-2-ol; various solvent(s) / 0.33 h / 25 °C 10: 28.4 mg / 3-(diethoxyphosphoryloxy)-1,2,3-benzotriazin-4(3H)-one; i-Pr2NEt2 / tetrahydrofuran / 18 h / 20 °C 11: 77 percent / MTBD / dimethylformamide / 1.5 h / 20 °C 12: 96 percent / n-Bu4NF; AcOH / tetrahydrofuran / 3 h / 20 °C 13: 74 percent / β-mercaptoethanol; DBU / dimethylformamide / 0.5 h / 20 °C 14: 85 percent / H2; aq. HCl / Pd black / ethanol / 2 h View Scheme