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

(MgS04), and evaporated to dryness. The product was purifieci by flash chromatograph y
(4: 1, C&C12:EtOAc) to give a white solid (2.84 g) in 68% yield.
mp 128- 129°C; [a]20ss = - 15.2 (c = 1 .CM, CH2C12); TU= (4: 1, CH2CI2:EtOAc) Rf = 0.39;
'H NMR (CDC13, 250 MHz) 6 5.06 (br d, lH, J = 10.4Hz, NH), 4.3 1 (br q, 1 H, J =
6.4Hz, B-CH), 3.89 (s, 6H, OB0 ester CH20), 3.63 (d, lH, J = 10.4Hz, a-CH), 2.88, (br
S. I H, OH), 1.42 (s, 9H, (CH&C), 1 .O6, (d, 3H, J = 6.4H.2, P-CH3). 0.79 (s, 3H, OB0
ester CCH3); I3c C (CDCb, 63 MHz) 6 156.3 (CONH). 108.8 (OB0 ester Ç-O), 79.2
((CH3)3ç), 72.6 (OB0 ester cm), 65.3 (B-_CH), 57.1 (a-CH), 30.5 (OB0 ester WH3),
28.3 cH&C), 18.9 @-CH3), 14.3 (OB0 ester CÇH3); IR (cast from CH2C12) 3386,2975,
1715, 1506, 1365, 1169, 1049; HRMS (FAB) calculated for (M + EI+) CIJ&NO6
304.1761, found 304.1732; Anal. calcd for C1&5N06: C, 55.43; H, 8.30; N, 4.61.
Found: C, 55.63; H, 8.56; N, 4.92.
2.4.8 1-[N~ert-Butoxy~~1rbonyl-(lS)-1-amin012-0xoethyl]-4-methy1-2,6,7-
trioxabicyclo [2.2.2]octane, Boc-L-Ser(a1d) OB0 ester, 2.46.
Boc-Ser OB0 ester 2.44 (1.12 g, 3.87 mmoi) was dissolved in freshly distillai CH2C12
(15 mL) under Ar and cooled to -78OC in flask 1. Oxalyl chloride (0.54 mL. 6.19 mrnol,
1.60 equiv) was added to CH2C12 (120 mL) in a separate round bottom fiask (flask 2)
under Ar, and cooled to -78OC. Dry DMSO (0.91 mL, 12.8 mrnol, 3.30 equiv) was added
to the oxalyl chloride solution (flask 2) and the mixture was stirred at -78OC for 15