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

(threo-L-254: 33.0 min, threo-D-2.54: 34.1 min, erythro-L-2.54: 37.2 min, erythro-D-
2.54: 38.1 min).
TLC ( 1 : 1 : 1 : 1. Et0Ac:nBuOH:MeOH:Hfi) Rf = 0.48; 'H NMR (DzO, 250 MHz) 6 3.85
(dt. 1H. J = 4.9, 8.2Hz, B-CH), 3.57 (d, 1H. J = 4.4Hz, a-CH). 1.57-1.32 (m, ZH,
CHKHz), 0.87 (t, 3H, J = 7.4Hz. CH3CH2); 13c NMR (&O. 63 MHz) 6 178.3 (COzH),
75.2 @-CH), 62.2 (a-CH), 30.0 (CH3_&), 1 3.1 cH3CH2); ESI-MS (M + H+) 1 34.19.
2.4.17 Deprotection of BoclSer(viny1)OBO ester 2.51: (2S,3R)-2-smino-3-hydroxy-
4-pentenoic acid, 2.55.
Boc-Ser(vinyl)OBO ester 2.51 (0.041 g, O. 13 mmol) was deprotected as described in
procedure 2.4.15 and lyophilized to give 8 mg (40%) of a white powder. HPLC analysis
performed as described in 2.4.15a indicated a threo:erythrû ratio of 89: 11 with 97% ee
(threo-L-2.55: 37.2 min, threo-D-2.55: 40.1 min, erythro-L-2.55: 43.6 min, erythro-D-
2.55: 45.2 min).
TU3 (1 : 1: 1: 1, EtOAc:nBuOH:MeOH:HzO) Rf = 0.46; 'H NMR (DD, 250 MHz) 6 5.89
(ddd, lH, J = 5.3, 10.9, 16.8Hz, CH2=CH), 5.39 (br d, 1H, J = 17.OHz, CHH=CH), 5.22