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

ffom CH2Cl2) 3338,2962,2875, 1732, 1522, 1455, 1262, 1214, 1 176, 1053.98 1; Anal.
calcd for CUH29N&: C, 65.92; H, 6.42; N, 3.07. Found: C, 65.65; H, 6.27; N, 3 .M.
4.4.7 5-Methyl-(2S)-2-[(benzyloxy)cartw,nyl ]~~l-(4-me~yI-2,6,7-~o~bicycIo-
[2.2.2]oct-1-yl)pntanmte, Cbz-L-Glu(0Me)-OB0 ester, 4.69.
Cbz-L-Glu(QMe)-oxetane ester 4.65 (5.40 g, 14.2 rnmol) was dissolved in dry CHK12
(225 rnL) while stimng under Ar. The mixture was cwled to 0°C then BF3. Et20 (90&
0.64 mmol) was added by syringe. The mixture was allowed to warm to room
temperature and stir for 6 hours after which a TLC indicated the reaction was complete.
Et3N (0.39 mL, 2.58 mrnol) was then added and the mixture stirred an additional 30 min
before the solvent was removed in vacuo. The resulting oïl was dissolved in EtOAc (150
mL) and extracted with 3% -1 (2 x 25 mL), saturated NaHC03 (25 mi,), brine (25
rnL) and dried over MgS04. The solvent was removed under reduced pressure to reveal a
light coloured oil which was purified by flash chromatography (1: 1 Et0Ac:Hex) to give a
clear oil in 9146 yield (4.45 g) which crystallized upon standing. The product can be
recrystallized ftom a mixture of diethyl ether:petroleum ethers (30-60):hexanes to give
3.54 g (65.5% yield) of white, needles.
m.p. 50.5-51.5 OC, [a120D = -33.0 (c = 1.0, EtOAc); TLC (1: 1, EtOAc:Hex), Rr = 0.56; 'H
NMR (Acetone-6, 300 MHz) 8 7.38-7.26 (m, SH, ArH), 5.74 (d, 1H, J =10.3Hz, NH),
5.10 (d, lH, J = 12.7Hz, CbzCHHO), 5.03 (à, lH, J = 12.7Hz, CbzCHHO), 3.89 (s, 6H,
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