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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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Dehydroamino acids have also been used as intermediates towards the solid-phase<br />

synthesis <strong>of</strong> a-amino acids? Radical additions to resin-b<strong>and</strong> dehydroamino acids 6.7<br />

provided various racemic a-amino acids 6.8 in both hi& yield <strong>and</strong> punty (Scheme 6.4).<br />

Scheme 6.4<br />

Polyrner supported a-imino acetates 6.9 have been used to synthesize a-amino<br />

libraries via a Mannich-type reaction with various silyl nucleophiles to afford resin-<br />

bound y-0x0-a-amino acids 6.10 (Scheme 6.5)? Cleavage <strong>of</strong>f the resin gave the desired<br />

products in 69-94% yield <strong>and</strong> high purity although no comrnents were made regarding<br />

enantioselectivity in the Mannich-type reaction.<br />

Scheme 6.5<br />

H SdOTih Nu, o%~l 11NaOMe<br />

CH2ClflffiN 2) ~cvdioxane-<br />

NAr NHAr NHAr<br />

3-Substituted prolines 6.14 have been synthesized diasterroselectively by amino-<br />

zinc-enolate cyclization chemistry (Scheme 6.6).= Esterification with the oxy anion gave<br />

6.11 which was cyclized to give the cyclic organozinc derivative 6.12. Iodonolyzation<br />

gave 6.13 which could be further derivatized via nucleophilic substitution then cleaved<br />

307

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