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

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

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prectudes the use <strong>of</strong> any acid aithough the addition <strong>of</strong> potassium acetate may have the<br />

desired effect if 4.106 is formed according to the mechanism described by Evans et al.<br />

The yield is however consistent with previous attempts by other groups at generating y-<br />

a~idoglutamates~~ <strong>and</strong> pyroglutamates." The azide 4.106 was then reduced to the amine<br />

4.1û7 in 78% yield under Staudinger type conditions."<br />

CbzH<br />

Pr<br />

Scheme 4.27<br />

CbzH<br />

O 20 40 60 80 100 120<br />

The (minutes)<br />

Figure 4.9: Plot <strong>of</strong> Yîeld (%) versus Tie (minutes) atbr quencbing <strong>of</strong> electrophilic<br />

aziàation <strong>of</strong> Cbz-Glu(0Me)OBO ester 4.69 with T m Azide 4.1û5.<br />

The other diastereomer, 2S94RCbz-Glu(yN3)(OMe)OB0 ester 4.109 was<br />

synthesized by conversion <strong>of</strong> the alcohol <strong>of</strong> 2S94S-CbzGlu(y-OH)(OMe)OBO ester 4.96<br />

176

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