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

TLC (4: 1, CH2C12:EtOAc) Rf = 0.58; 'H NMR (CDC13, 250 MHz) 6 7.51-7.25 (m, SH,
ArH), 5.69 (br d, 0.88H, J = 10.3Hz. threo NH), 5.30 (br d, 0.12H, J = 10.3Hz, erythro
NH), 4.93-4.8 1 (m, 1 H, &CH), 3.9 1 (s, 6H, OB0 ester CHD). 3.72 (dd, 1 H, J = 3.4,
10.3Hz, a-CH), 1.43 (s, 9H, (CH3)Ç), 0.79 (s, 3H, OB0 ester CCH3); 13c NMR
(-13,63 MHz) 6 1 56.8 (CONH), 136.7 (ArsC-=), 128.3, 127.7, 127.6 (&=CH), 108.1
(OB0 ester C-O), 79.3 ((CH3)3C), 72.4 (OB0 ester GHzO), 69.1 (8-H), 57.5 (a-CH),
30.4 (OB0 ester WH3). 28.3 ((Q13)3C), 13.9 (OB0 ester CCH3); HRMS (FAB)
calculated for (M + H+) Cl&aNOs 366.4309, found 366.4365; Anal. calcd for
ClgH27NOs C, 62.45; H, 7.45; N, 3.83. Found: C, 62.73; H, 7.75; N, 3.91.
2-4-15 Deprotection of Boc-Ser(Me)OBO ester 2-49: (2S,3R)-2-amino-3-
hydroxybutanoic acid, L-Tb, 2.53.
Boc-Ser(Me)OBO ester 2.49 (0.210 g, 0.69 mmol) was dissolved in CH2C12 (5 rnL) to
which TFA (1 mL) was added. The mixture was stirred for 30 min and the solvent then
removed under reduced pressure. The mixture was nnsed with Fresh CH2CI2 then
reduced again and repeated once more. The mixture was dissolved in MeOH:H20 (5 rnL,
4: 1) then t mL of a 10% (wthol) Cs2C03 solution was added. The mixture was allowed
to stir for 18 h at room temperature before king acidified to pHd with 3 N Hel. The
solution was then Ioaded ont0 a cation exchange resin column (Bio-Rad AGa SOW-X8
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