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

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mp 8748°C; [al2O5,, = -3 1.8 (c = 1 .O6, EtOAc); TLC (4: 1, CH2CI2:EtOAc) Rt = 0.55; 'H
NMR (CDC13, 250 MHz) 6 5.01 (br d, lH, J = 10.3Hz, NH), 3.87 (s, 6H, OB0 ester
CH20), 3.75 (d, 1 HT J = 10.3Hz, a-CH), 3.18, (br s, IH, OH), 1.47 (q, 2H, J = 7 SHz,
CH3CH2), 1.41 (s, 9H, ((C&)gC), 1.23 (s, 0.98H. threo $-CH3), 1.19 (s, 0.02H, erythm
P-CH3), 0.84 (t, 3H. J = 7.5H2, CH3CH2) 0.77 (s, 3H, OB0 ester CCH3); 13c NMR
(Cml3,63 MHz) 6 156.1 (CONH), 109.6 (OB0 ester C-O), 79.1 ((CH3)3Q, 74.7 (B-C),
72.3 (OB0 ester CH#), 58.3 (a-CH), 3 1.7 (CH3_CH2), 30.4 (OB0 ester mH3), 28.4
((çH3)3C), 24.3 (&CH3), 14.3 (OB0 ester CÇH3), 8.0 (CH3CH2); IR (neat) 3380, 2975,
1715, 1505, 1362, 1169, 1051; HRMS (FAB) calculated for (M + H') C1&&06
332.2073, found 332.2061; Anal. cdcd for C16H29N06: C, 57.98; H, 8.85; N, 4.22.
Found: C, 58.13; H, 9.02; N, 4-38,
2.4.22 Deprotection of Boe-Thr(Me)OBO ester 2.57: (2S)-2-amino-3-hydroxy-3-
methylbutanoic acid, 2.59,
Boc-Thr(Me)OBO ester 2.57 (0.210 g, 0.66 mrnol) was dissolved in CH2C12 (10 mL) to
which TFA (2 rnL) was added. The mixture was stirred for 30 min and the solvent then
removed under reduced pressure. The mixture was rinsed with fresh CH2Clz then
reduced again and repeated once more. The mixture was dissolved in Me0H:Hfi (5 mL,
4: 1) then 1 rnL of a 10% (wthol) Cs2C03 solution was added. The mixture was allowed
to stir for 18 h at room temperature before king directly loaded onto an anion exchange
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