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

5-430 (2S)-2-Amin013-hydn,xgbutanedioic acid, Asp(p-OWH, 5.5-
Same procedure as in section 5.4.14 to give 0.029 g (62%) of 53.
"XCO*"
H2 C02H
2S,3S-5.5: [a120~ = 4.4 (c = 1.5, 1N HCl), (lit." = +1.3 (c = 3.12, 1N HCI); 'H
NMR (D20.300 MHz) 6 4.89 (d. 1 H, J = 3.6Hz, p-CH) 3.82 (d, 1 H, J = 3.6Hz, a-CH);
13c NMR (&O, 75 MHz) 6 178.2 -1, 173.7 cd), 69.3 (p-CH), 61.5 (a-CH); ESI-
MS 149.91.
5-4-21 1 -[(2S)-2-[(Be11~yloxy)~bo~y1]smin011-(rne~yl-
2,6,7-trioxabicyclo[2.2.2 Joct-l-yl)ethyl]-l,2-~azadien-2-ium, Cbz-L-Asp(p-
N3)(OMe)OBO ester, 5-53,
Cbz-Asp(0Me)OBO ester 5-38 (0.370 g, 1.01 mmol) was dissolved in dry THF (3 rnL)
then added by cannula to a Bask containing LiHMDS ( 3.03 rnL, 3.03 mmol) in dry TH.
(5 mL) at -78°C under Ar. After 1 h. trisyl azide 4.105 (0.624 g, 2.02 mmol) dissolved
in dry THF (3 mL) was slowly added by syringe. Mer 18 h at -78"C, the mixture was
allowed to warm to room temperature then poured into Et20 (50 mL) and extracted with
3% NHKl (2 x 20 mL), 10% NaHCO3 (?O mL), brine (20 mL) and dried over MgS04
and the solvent removed under reduced pressure to give a bright yelIow oil which was
purified by flash chromatography to give 5.53 in 28% yield (0.1 14 g).