To a 500 mL round bottom flask, charged with 9.00 g (36.8 mmol) of biotin (Sigma Chemical Company), 7.93 g (40.5 mmol, 1.1 equiv.) of amine hydrochloride 12, and 200 mL of anhydrous dimethylformamide was added 17 mL of triethylamine (120 mmol) followed by 17.1 g (38.7 mmol, 1.05 equiv.) of benzotriazolyloxytris(dimethylamino)phosphonium hexaphosphonate (BOP, commercially available from Aldrich Chemical Company and Chem-Impex International, Wood Dale, Ill.) coupling agent. The reaction was stirred at room temperature for 13 h and then concentrated. The residue was diluted with 100 mL of 2-propanol and 300 mL of methylene chloride and the resulting mixture was washed with 2×150 mL aliquots of 1N aqueous HCl and then with 150 mL of de-ionized water. The organic phase was dried with anhydrous magnesium sulfate and vacuum filtered. The solids were rinsed with 100 mL of 25% 2-propanol/methylene chloride. The combined filtrates were concentrated. The residue was chromatographed on 9×22 cm of silica gel, eluting with 20% methanol/ethyl acetate. The fractions containing product (13) were combined and concentrated via rotary evaporation. The residue was chromatographed on 7×18 cm of RP-18 silica gel, eluting with 800 mL of 50:50 methanol/water, 1 liter of 55:45 methanol/water and 2 liters of 60:40 methanol/water. The fractions containing product (13) were combined and concentrated, first via rotary evaporation and finally under full vacuum pump pressure (<0.5 mm Hg) to afford 11.58 of the product (13) as a near colorless oil: 1H NMR (d6-DMSO) d 6.42 (1H, s), 6.33 (1H, s), 4.29 (1H, m), 4.12 (1H, m), 3.57 (3H, s), 3.22 (2H, t), 3.09 (1H, m), 2.91 and 2.77 (3H, 2 s), 2.81 (1H, dd), 2.57 (1H, d), 2.34-2.19 (4H, m) and 1.70-1.10 (12H, m) ppm; 1H NMR (CD3pk OD) d 4.48 (1H, dd), 4.29 (1H, dd), 3.63 and 3.62 (3H, 2 s), 3.34 (2H, t), 3.20 (1H, m), 3.02 and 2.88 (3H, 2 s), 2.91 (1H, dd), 2.68 (1H, d), 2.43-2.27 (4H, m) and 1.80-1.20 (12H, m) ppm; Thin Layer Chromatography (Visualization with p-aminocinnimaldehyde spray); Silica Gel, Rf=0.31 ({fraction (80/20)} ethyl acetate/methanol); RP-18 Silica Gel, Rf=0.29 ({fraction (60/40)} methanol/water).
