Asymmetric synthesis of N-protected amino acids by the addition of organolithium carboxyl synthons to ROPHy/SOPHy-derived aldoximes and ketoximes |
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Authors: | Cooper Tracey S Laurent Pierre Moody Christopher J Takle Andrew K |
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Affiliation: | Department of Chemistry, University of Exeter, Stocker Road, Exeter EX4 4QD, UK. |
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Abstract: | A new asymmetric synthesis of alpha-amino acids is described in which the key step is the highly diastereoselective addition of organolithium carboxyl synthons (2-furyllithium, phenyllithium, vinyllithium) to (R)- and (S)-O-(1-phenylbutyl) oximes to give hydroxylamines, with vinyllithium being the most satisfactory nucleophilic reagent. Subsequent reductive cleavage of the N-O bond in hydroxylamines, followed by N-protection, and oxidative cleavage of the carboxyl precursor gave a range of N-protected amino acids and esters. The method was exemplified by the synthesis of a range of derivatives of non-proteinogenic amino acids such as 4-bromophenylalanine, tert-leucine, norvaline, cyclohexyl- and aryl-glycines, 2-amino-8-oxodecanoic acid (Aoda) and alpha-methylvaline. |
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