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

(br d. IH. J= 10.6Hz, CHH-CH), 4.634.52 (m, 1H. P-CH), 3.88 (d, IH, J=4.0Hz, a-
CH); "C NMR @20, 63 MHz) 6 175.3 (C02H), 136.9 (CH2=CH), 12 1.1 m2=cH)7
73.2 (p--m, 62.0 (a--; ESI-MS (M + HC) 13 1.92.
2.4.18 Deprotection of Boc-Ser(Ph)OBO ester 2.52: (~~R)-2-Pmino-3-hydroxy-3-
pheny Bpmpanoic acid, 2.56.
Boc-Ser(Ph)OBO ester 2.52 (0.073 g, 0.20 mmol) was deprotected as described in
procedure 2.4.15 and lyophilized to give 23 mg (66%) of a white powder. HPLC analysis
performed as described in 2.4.15a (linear gradient to 5050 30mM sodium acetate: MeOH
over 25 min) indicated a threo:erythro ratio of 90: 10 with 98% ee (threo-L-2.56: 35.1
min, threo-D-2.56: 38.1 min, erythro-L-2.56: 40.6 min, erythro-D-2.56: 4 1 -3 min).
TU3 (1: 1: 1: 1, EtOAc:nBuOH:MeOH:H20) Rr = 0.61; 'H NMR 020, 250 MHz) 6 7.4 1 -
7.29 (m, SH, ArH), 5.3 1 (d, O. IH, / = 4.0Hz, erythro p-CH), 5.25 (d, 0.9H. J = 4.OHz,
threo p-CH), 4.08 (d, lH, J = 4.0Hz, a-CH); 13c NMR (D20, 63 MHz) 6 175.0 (C02H),
140.9 (-=), 131.0, 129.9, 128.1 (mH), 73.9 (p-GH), 63.1 (a-CH); ESI-MS (M +
182.01.
2.4.19 Reduction of recovered Boc-Ser(ald)-OB0 ester 2.46 fmm section 2.4.11.
91