Reaction SMILES: Cl[C:2]([O:4][CH2:5][C:6]1[CH:11]=[CH:10][CH:9]=[CH:8][CH:7]=1)=[O:3].[OH:12][C@H:13]1[CH2:17][NH:16][C@H:15]([C:18]([OH:20])=[O:19])[CH2:14]1.C([O-])(O)=O.[Na+].O>CC(C)=O>[OH:12][C@H:13]1[CH2:17][N:16]([C:2]([O:4][CH2:5][C:6]2[CH:11]=[CH:10][CH:9]=[CH:8][CH:7]=2)=[O:3])[C@H:15]([C:18]([OH:20])=[O:19])[CH2:14]1
Reactant: O=C(O)[C@@H]1C[C@@H](O)CN1
Reactant: O=C(Cl)OCc1ccccc1
Agent: O=C([O-])O
Agent: [Na+]
Solvent: CC(C)=O
Solvent: O
Product: O=C(O)[C@@H]1C[C@@H](O)CN1C(=O)OCc1ccccc1
Temperature: 25 °C
Reaction time: 6 h
Yield: 101.8 %

Procedure:
Benzyl chloroformate (8.6 ML, 0.06 mol) was dissolved in acetone (12 mL), and this solution was added dropwise to a stirred solution of trans-4-Hydroxy-L-proline (6.56 g, 0.05 mol) in satd. NaHCO3 (160 mL) and H2O (24 mL). The resulting solution was stirred for 6 h at room temperature. The solution was washed with diethyl ether, and the organic layer was discarded. The aqueous layer was acidified with to pH 3 with 1 M HCl and extracted with ethyl acetate. The organic layer was dried over MgSO4 and concentrated to afford 13.5 g (quantitative yield) of the desired product as an oil. trans-4-TBDMSO-Cbz-L-Proline 4.2. trans-4-Hydroxy-Cbz-L-proline (13.5 g, 0.05 mol) was dissolved in DMF (190 mL), followed by the addition of imidazole (17.0 g, 0.25 mol) and TBDMS-Cl (22.6 g, 0.15 mol). The resulting solution was stirred for 12 h at room temperature. Methanol (150 mL) was added and the solution was stirred for 2 h. The solution was concentrated, the residue was dissolved in ethyl acetate and washed with 1 M HCl. The organic layer was dried over MgSO4 and concentrated. The crude product was purified by column chromatography eluting with methylene chloride/ethyl acetate/acetic acid (2/1/0.03, v/v/v) to afford 18.01 g (95% yield) of the desired product as an oil. trans-5-Hydroxylmethyl-3-TBDMSO-Cbz-Pyrrolidine 4.3. trans-4-TBDMSO-Cbz-L-proline (14.31 g, 0.04 mol) was dissolved in THF and added via cannula to a stirred solution of 2 M Me2S.BH3 in THF (48.0 mL, 0.09 mol). The resulting solution was stirred for 16 h at reflux. The reaction was then quenched with methanol (50 mL) and concentrated. The residued was dissolved in ethyl acetate and washed with brine. The organic layer was dried over MgSO4 and concentrated. The crude product was purified by column chromatography eluting with hexanes/ethyl acetate (3/1, v/v) to afford 9.73 g (70% yield) of the desired product as an oil. trans-5-Methoxymethyl-3-TBDMSO-Cbz-Pyrrolidine 4.4. trans-2-Hydroxylmethyl-4-TBDMSO-Cbz-pyrrolidine (5.02 g, 13.7 mmol) was dissolved in acetonitrile (13.7 mL), followed by the addition of iodomethane (8.55 mL, 0.14 mol) and Ag2O (6.36 g, 27.5 mmol). The resulting reaction mixture was stirred for 12 h at reflux in the dark. The reaction mixture was then filtered through celite and the celite was washed with acetonitrile. The filtrate was concentrated. The crude product was purified by column chromatography eluting with hexanes/ethyl acetate (3/1, v/v) to afford 4.05 g (78% yield) of the desired product as an oil. trans-5-Methoxymethyl-3-Tosyl-Cbz-Pyrrolidine 4.5. trans-2-Methoxymethyl-4-TBDMSO-Cbz-pyrrolidine (8.99 g, 23.6 mmol) was dissolved in THF (237 mL), followed by the addition of 1 M TBAF in THF (23.7 mL, 23.7 mmol). The resulting solution was stirred for 3 h at room temperature. The reaction was quenched with satd. NH4Cl. The solution was concentrated, the residue dissolved in ethyl acetate and washed with brine. The organic layer was dried over MgSO4 and concentrated. The residue was dissolved in methylene chloride (230 mL) and cooled to 0° C. DMAP (3.37 g, 27.6 mmol) and triethylamine (7.7 mL, 66.2 mmol) were added, followed by p-toluenesulfonyl chloride (5.26 g, 27.6 mmol). The reaction solution was stirred for 12 h at room temperature. The solution was washed with brine and the organic layer was dried over MgSO4 and concentrated. The crude product was purified by column chromatography eluting with hexanes/ethyl acetate (2/1, v/v) to afford 8.67 g (90% yield) of the desired product as an oil. cis-5-Methoxymethyl-3-Cyano-Cbz-Pyrrolidine 4.6. trans-5-Methoxymethyl-3-tosyl-Cbz-pyrrolidine (3.55 g, 8.8 mmol) was dissolved in DMSO (8.8 mL). Finely ground NaCN(0.65 g, 13.2 mmol) was added, and the resulting reaction mixture was stirred 4 h at 80° C. The solution was cooled to room temperature, diluted with H2O (9 mL) and brine (9 mL), and extracted with ethyl acetate. The organic extracts were dried over MgSO4 and concentrated. The crude product was purified by column chromatography eluting with hexanes/ethyl acetate (2/1, v/v) to afford 2.09 g (87% yield) of the desired product as an oil. cis-5-Methoxymethyl-Boc-3-Pyrrolidine Carboxylic Acid {cis-Boc-(5-MOM)-PCA-OH} 4.7. cis-5-Methoxymethyl-3-cyano-Cbz-pyrrolidine (1.71 g, 6.2 mmol) was dissolved in concentrated HCl and stirred for 12 h at 50° C. The solution was cooled to room temperature and neutralized with NaHCO3. The solution was concentrated, and the residue was dissolved in methanol (62 mL). Triethylamine (2.6 mL, 18.7 mmol) and Boc2O (1.63 g, 7.5 mmol) were added, and the solution was stirred 12 h at 50° C. The solution was concentrated and the residue was dissolved in H2O. The aqueous solution was washed with diethyl ether, and the organic layer was discarded. The aqueous layer was acidified with to pH 3 with 1 M HCl, and extracted with ethyl acetate. The organic layer was dried over MgSO4 and concentrated to afford 1.40 g (86% yield) of the desired product as an oil. cis-5-Methoxymethyl-Boc-3-Pyrrolidine Benzyl Ester Acid {cis-Boc-(5-MOM)-PCA-OBn} 4.8. cis-5-Methoxymethyl-Boc-3-pyrrolidine carboxylic acid (1.4 g, 5.3 mmol) was dissolved in DMF (26.5 mL). Cs2CO3 (1.73 g, 5.3 mmol) and benzyl bromide (0.76 mL, 6.4 mmol) were added, and the reaction mixture was stirred 24 h at room temperature. The reaction mixture was concentrated, and the residue was dissolved in H2O. The aqueous solution was extracted with ethyl acetate. The organic layer was dried over MgSO4 and concentrated. The crude product was purified by column chromatography eluting with ethyl acetate/hexanes (1/1, v/v) to afford 1.88 g (85% yield) of the desired product as an oil. 2. Oligomer Synthesis