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

3.43 Acid Hydrolysis of Cbz-ESer(CHtTMS)IOBO Ester 3.45 witb 6N HCI. (249-2-
amino-3-butenoie acid, 3.7.
Cbz-L-Ser(CHzTMS)-OB0 ester 3.45 (0.140 g, 0.34 rnmol) was mked with 6N HCI
(10.0 mL) and refluxed for 3 h. The solution was cmled extracted twice with ether (2 x 5
mL), neutralized with a saturated solution of NaHC03 (approx. 50 mL), then loaded on
an anion exchange column (Bio-Rad AG 1-X4 100-200 mesh, chloride form, converted
to hydroxide form by prewashing with 4N NaOH). The column was rinsed with HzO (5
cloumn lengths) and eluted with LN AcOH, then lyopholized to give 0.028 g (8 1%) of a
colourless powder. Recrystallization (wlacetone) gave 0.025 g (74%) of a white solid.
Derivatisation with O-phthaladehyde and N-isobutyryl-L-cysteine, and analysis by HPLC
indicated 95% ee (conditions as described in 2.4.1 Sa and retention times as in 3.4.7).
mp 177-1 80°C (dec); TLC (1 : 1 : 1 : 1, EtOAc:nBuOH:AcOH:H20) Rr 0.46. 'H NMR (DzO,
250 MHz) 6 5.85 (ddd, lH, J = 7.4, 10.1, 17AHz, B-CH), 5.38 (d, IH, J = 17.2Hz, y-
CHH), 5.38 (d, lH, J= 10.4&, y-Cm, 4.27 (d, IH, J = 7.3Hz. a-CH); "C NMR (D20,
50.3 MHz): 6 174.7 (ÇOtH), 132.0 ($-CH), 124.8 (y-CH2), 59.1 (a-C-); ESI-MS (M +
H+) 102.29.