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

found 470.21822. Anal. calcd for CA1N07: C, 66.51; H, 6.65; N, 2.98. Found: C,
66.60; H, 6.62; N, 3.04.
4.4.19 Be~1zyI-N-[(3R~S)-5-metbyl-210xotetrahyd~ 4.W.
Cbz-L-Glu(0Me)-OB0 ester 4.69 (0.077 g, 0.20 rnmol) was dissolved in THF (IO mL)
then cooled to -30°C whilst stimng under Ar. DIBAL-H ( 0.60 mL, 0.60 mmol) was
then added and the mixture allowed to warm to room temperature. After 6 h a TU3
indicated the reaction complete and so 20% AcOH (4 mL) was added and the mixture
stirred for 30 min before saturated potassium sodium tartrate (50 mL) was added and the
mixture stirred for 1 h. The mixture was extracted with EtOAc (3 x 100 rnL), the organic
fractions pooled then extracted with brine (50 mL) and dried over MgS04. The solvent
was then removed under reduced pressure and the resulting oil dned under high vacuum.
The light yellow oil was taken-up in benzene to which p-TsOH (10 mg) was added and
the mixture stirred ovemight at 60°C. The solvent was removed in vucuo and the
resulting oil taken up in Et0AC:Hexanes (1:l) then passed through a silica plug to
rernove any polar by-products to give 21 mg of crude 4.84 (40% yield).
1 H NMR (CDCl3, 3ûûMHz) 6 7.39-7.25 (m, 5H, ArH), 5.56 (br s, 1 H, NH), 5.10 (s, 2H,
CbzCHzO), 4.56-4.43 (m, 1 H, a-CH), 4.23 (dd, 1 H, J = 5.3, 1 1.3Hz, C02CHH), 3.97 (dd,