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

Oxidation to the aldehyde 6.34 and ketone 6.35 was more difficult than in
solution phase for a number of reasons. Swern oxidation required transfer of the alcohol
into a -78°C mixture of the generated chiorosulfonium salt which proved to be difficult
since the alcohol was bound to the resin. TentaGe1 PHBa resin was particularly
troublesome due to its "sticky" nature (a consequence of the PEG spacer) in cornparison
to Wang resin. However, after numerous different experimental setups, the arrangements
depicted in figure 6-3 were found to be most convenient: (a) for additions of resin 400
mg and (b) for >500 mg.
Figure 6.2: MAS 'H-NMR (500 MHz) with spinseho puise program of 6.34
W=W~W).