A suspension of H-Thr(Bzl)-OH (3.0 g, 14.34 mmol) in DMF (60 ml) was mixed with Et3N (2 ml) and Boc-Val-OSu (4.96 g, 15.78 mmol) at 0° C for 2 hours and then at 25° C for 24 hours. Acetic acid was added to about pH 3 and the solvents removed under reduced pressure. The product was extracted into EtOAc, washed with 5% AcOH and water, dried (MgSO4) and evaporated to clear oil which crystallized from EtOAc with petroleum ether to yield 4.9 g (83.1%); mp 132°-135° C; [α]D25 +21.5° (c, 1, CHCl3). Anal. Calcd for C21H32N2O6 (408.49): C, 61.74; H, 7.89; N, 6.85. Found: C, 61.61; H, 7.76; N, 6.80.
