Reaction Steps
A solution of biotin (0.59 g, 2.42 mmol, 1.5 eq), HBTU (0.79 g, 2.10 mmol, 1.3 eq) and DIEA (0.45 mL, 2.60 mmol, 1.6 eq) in DMF (15 mL) was stirred for 20 min at 21° C. before being added dropwise to a solution of tert-butyl-N-(2-(2-(2-aminoethoxy)ethoxy)ethyl)carbamate (400 mg, 1.61 mmol, 1 eq) in DMF (10 mL). The reaction mixture was stirred for 2 h at 21° C., after which the DMF was removed in vacuo to give a yellow residue. The crude product was purified by column chromatography (gradient 2-10% MeOH/CH2Cl2) to yield the desired compound as a white solid (0.61 g, 1.29 mmol, 80% yield). m.p. 106-108° C.; [α]D20.0+23.0 (c 0.6, CH2Cl2); 1H NMR (500 MHz, CDCl3) δ 4.55 (dd, J=5.0, 7.5 Hz, 1H, NHC(O)NHCH), 4.36 (dd, J=5.0, 7.5 Hz, 1H, NHC(O)NHCH), 3.62 (bs, 6H, OCH2), 3.59-3.55 (m, 2H, OCH2), 3.46 (m, 2H, NCH2), 3.31 (m, 2H, NCH2), 3.17 (dt, 3.0, 5.0 Hz, 1H, SCH), 2.92 (dd, J=5.0, 13.0 Hz, 1H, SCHH), 2.79 (d, J=13.0 Hz, 1H, SCHH), 2.27 (t, J=7.0 Hz, 2H, NHC(O)CH2CH2CH2), 1.71 (m, 4H, NHC(O)CH2CH2CH2CH2), 1.47 (br, 11H, C(CH3)3 & NHC(O)CH2CH2CH2CH2); 13C NMR (125 MHz, CDCl3) δ 173.69 (s), 163.92 (s), 155.99 (s), 79.14 (s), 70.03 (t), 69.69 (br t), 61.58 (d), 60.06 (d), 55.19 (d), 40.16 (t), 39.96 (t), 38.91 (t), 35.44 (t), 28.09 (q), 27.80 (t), 27.67 (t), 25.23 (t), * 2 t absent; IR (neat) 3307, 2933, 1691 cm−; HRMS (ES) calcd for C21H38N4O6NaS [M+Na]+ 497.2410, observed 497.2423.
