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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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Rotected ~-aminoaspartate Sm6 was synthesized by the oxidative dimenzation <strong>of</strong><br />

glycinate Sm25 in the presence <strong>of</strong> iodine to give threo derivative S.%? This was then<br />

deprotected <strong>and</strong> reprotected to give protected B-aminoaspartate in excellent<br />

diastereoselectivity, enantioselectivity <strong>and</strong> yield (Scheme 5.14).<br />

Scheme 5.14<br />

A variety <strong>of</strong> B-alkylated aspartate denvatives were synthesized from protected 4-<br />

ketoproline 5.27.' Bredereck's reagent 430 gave an enaminone which when reacted<br />

with a Grignard reagent gave enone 538 that was cataiytically hydrogenated to give only<br />

the cis-isomer 5.29 (Scheme 5.15). Baeyer-Villiger oxidation gave 530 <strong>and</strong> after<br />

hydrolysis protected p-alkylaspartic acid denvatives were isolated in good yield as single<br />

diastereomers. Direct alkylations on the enolate <strong>of</strong> 5.30 were also attempted, however,<br />

diastereoselectivities ranged fkom 1 : 1 to 4: 1 <strong>of</strong> the transxis isomers.<br />

Scheme 5-15

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