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

CH), 3.85 (s, 6H, OB0 ester CH20), 3.68 (ddâ, lH, J= 2.9, 10.4, 12.2Hz, a-CH), 3.57
(s, 3H, C02CH3), 2.86 (br s, 2H, y-NH2), 2.24 (ddd, IH, J = 2.4, 10.7, 1 3.7H2, p-CHH),
1.88 (ddd, lH, J = 3.4, 12.2, 13.7Hz, p-CHH), 0.76 (S. 3H, OB0 ester CCH3); I3c NMR
(Acetone-4, 75 MHz) 6 172.0 156.1 (ÇONH), 137.7 (a-=), 128.4, 127.7,
127.7 (Cbz===), 108.5 (OB0 ester C-O), 72.3 (OB0 ester CJ120), 65.6 (CbzW20),
59.5 (y-cm, 5 1.8 (a-CH), 5 1.1 (COD3), 33.0 (OB0 ester ÇCH3), 30.3 (B-w2), 1 3.4
(OB0 ester CQi3); IR (cast fkom CHC13) 3374, 2949, 2880, 1730, 15 16, 1224, 1046,
101 1; ESI-MS (M + H+) 394.90. Anal. caicd for Ci9Hz&J2@: C, 57.86; H, 6.64; N, 7.10.
Found: C, 58.08; H, 6.75; N, 7.12.
4-4-38 Metbyl-(2S,4S)-2-[(be11zyloxy)carbnyl ]am
wthyI-2,6,7-trioxabicyc10[2~2.2~0~t-l-y~ Cbz-L-Glu(~OMs)(OMe)OBO
ester, 4.108.
Cbz-L-Glu(y-OH)(OMe)OBO ester 4.% was dissolved in dry CHzC12 (5 mL) then cooled
to 0°C. Et3N (57 pL, 0.42 rnmol) was then added followed by mesyl chloride (16 pL,
0.21 rnmol). The mixture was allow to stir for 12 h before the solvent was removed in
vacuo der which the desired product could be purifieci by flash chromatography to give
4.108 in 80% yield (76 mg). However, the mesylate was generally displaced by azide
without isolation.