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

6 158.9 (CONH), 107.4 (OB0 ester C-O), 76.3 ( B a , 72.7 (OB0 ester a20), 62.8
(CbzW20). 30.8 (OB0 ester Gag), 24.7 (mz), 14.1 (OB0 ester Ca3), -1 -1
(Si(CH3)3); Anal. Calcd for C&&NSiOs: C, 51.80; H, 7.69; N, 4.65. Found: C, 52.09; H,
7.96; N, 4.34.
3.4*7 Acid Hydrolysis of Cbz-L-Gly(-CH=CHt)aBO ester 3.38 with 6N HCI. (2S)-
2-amiao-3-butenoic acid, 3-7.
Cbz-L-Gly(-CH=CH+OBO ester 3-38 (0.230 g, 0.720 rnmol) was rnixed with 6N HCI
(2.0 mL) and refluxed for 1 h. The solution was reduced in vacuo then cooled,
neutralized with a sahirated solution of NaHC03 (approx. M mL) and loaded on an anion
exchange column (Bio-Rad AG 1-X4 100-200 mesh, chloride forrn, converted to
hydroxide fonn by prewashing with 4N NaOH). The column was rinsed with H20 (5
column lengths) and eluted with IN AcOH, then lyopholized to give 0.0109 g (79%) of a
colourless powder. Recrystallization (H20/acetone) gave 0.010 g (72%) of a white solid.
Derivatisation and analysis by HPLC indicated 86% ee (conditions as described in
Section 2.4.1 Sa) (L-viny lgl ycine 26.5 min; D-viny lglycine 28.4 min).
mp 1 78- 1 80°C (dec); TLC (1 : 1 : 1 : 1, EtOAc:nBuOH:AcOH:H20) Rf 0.46; 'H NMR
(Da, 250 MHz) 6 5.85 (ddd, lH, J = 7.4, 10.1, 17.4Hz, B-CH), 5-38 (d, lH, J = 17.2Hz,
y-CHH), 5.38 (d, 1H, J = 10.4Hz, y-CHH), 4.27 (d, lH, J = 7.3Hz. a-CH); 'k NMR
(D2O, 50.3 MHz): 6 174.7 GO2H), 132.0 (B-CH), 124.8 (y-CH2), 59.1 (a-CH); ESI-MS
(M + He) 102.22.