Solution and Solid Phase Synthesis of Unusual a-Amino Acids From

6.4 Experimental
Wang (1.04 mmoVg to 0.74 mmoVg) and TentaGel PHB@ (0.33 mmoVg to 0.29
mrnoVg) resin were purchased €rom Advanceci ChemTech or Novabiochem. Al1 NMR
spectra were acquired using a BRiker AMX-500 NMR. Approximately 1-2 mg of resin
was placed in a 4 mm MAS zirconia rotor with Kel-F cap and a spherical insert (diameter
2.6 mm). Sarnples were spun at the magic angle at a rate of 4 kHz and were run in
CWl2 and referenced interndly to residual CH2C12.
6.4.1 (3-Methyl-3-oxetanyl)methyl (~JR)-2-[(beazyIoxy)carbonyl]amin0-3-
hydroxybutanoate, Cbz-Thr oxetane ester, 6.24.
Cbz-L-Thr 6.23 (5.06 g, 0.02 mol) and Cs2C03 (3.91 g, 0.012 mol) were combined and
dissolved in &O (100 rd). The water was then nmoved in vacuo and the resulting oil
lyophilized for 12 hours to give a white foam. To this foam was added oxetane tosylate
2.38 (5.38 g, 0.021 mol) and Na1 (0.6 g, 4.0 rnmol) which was then taken up in DMF
(200 mL) and allowed to stir under Ar for 48 hours. The DMF was then removed in
vacuo and the resulting solid dissolved in EtOAc (300 mL) and Hfl (100 rnL) and
extracted with 10% NaHC03 (2 x 50 mL), saturated NaCl (50 mL) and dried over
MgS04. The solvent was removed under reduced pressure to yield a yellow oil which
was recrystailized from ethyl acetate to give long, clear crystals in 96.8% yiefd (6.80 g).
mp 49-5 I0C; [al2'o = - i 8.2 (c = 1.12, EtOAc); TLC (3: 1 EtOAc: hexane), Rr = 0.46; ' H
NMR (-13, 250 MHz) 6 7.32-7.36 (m, SH, ArH), 5.66 (d, lH, J = 8.9 Hz, NH), 5.14