A Strategy for the Asymmetric Aminohomologation of α,β-Dihydroxy Aldehydes: Application to the Synthesis of the Southwest Tripeptide Segment of Echinocandin B
作者:Claudio Palomo、Mikel Oiarbide、Aitor Landa
DOI:10.1021/jo990964c
日期:2000.1.1
The synthesis of the (2S,3S,4S)-3,4-dihydroxyhomotyrosine amino acid segment, present in echinocandin B, in its activated form ready for peptide coupling is described. The key steps of the approach are the enantioselective AD reaction of 4-methoxycinnamic acid methyl ester, a completely diastereoselective [2 + 2] hydroxyketene-imine cycloaddition, and the TEMPO-assisted cyclo-expansion of the resulting 3-hydroxy beta-lactam to the corresponding alpha-amino acid N-carboxy anhydride (NCA). The smooth opening of the latter upon treatment with L-Thr((OSiBuPh2)-Bu-t)OMe and further acylation with the N-Cbz protected L-4-tert-butyldiphenylsilyloxy proline rendered the southwest portion of echinocandin B.