Synthesis and enzymatic resolution of C-alpha-dialkylated alpha-azido carbox-amides: New enantiopure alpha-azido acids as building blocks in peptide synthesis

摘要

alpha-Azido carboxylic acids have recently emerged as versatile N-protected equivalents for alpha-amino acids, especially valuable when the sterically hindered C-u-dialkylated alpha-amino acids have to be incorporated. Unsymmetrically substituted C-u-dialkylated alpha-azido carboxylic acids can be obtained in enantiomerically pure form by enzymatic resolution of alpha-azido carboxamides. A L-amidase from Ochrobactrum anthropi NCIMB 40321 accepts 2-azido-2,4-dimethylpentanamide as the substrate and provides both the corresponding S-configured alpha-azido carboxylic acid and the R-configured alpha-azido carboxamide in excellent enantiomeric purity. The former is a valuable synthetic precursor of alpha-methylleucine [(alpha-Me)Leu] in peptide synthesis, as demonstrated by the successful synthesis of a (alpha-Me)Leu containing efrapeptin C analogue.