Synthesis and Structural Confirmation of (2S,3R,4R,6E)-2-Acetylamino-3-hydroxy-4-methyl-6-octenoic Acid, a New Amino Acid Produced byNeocosmospora vasinfecta

Abstract

An unusual amino acid, (2S,3R,4R,6E)-2-acetylamino-3-hydroxy-4-methyl-6-octenoic acid (2a) and its stereoisomer (2b), were synthesized by the aldol condensation of (2R,4E)-2-methyl-4-hexenal (5) with tert-butyl isocyanoacetate (6) as the key reaction via trans-oxazoline derivative 7, in which two continuous chiral centers were newly formed. The oxazoline derivative was efficiently hydrolyzed to afford separable N-formyl-β-hydroxy amino acid esters 8a and 8b in a 1:1 ratio. Each diastereomer was transformed into target N-acetyl amino acids 2a and 2b via corresponding amino acids 1a and 1b.