Approaches to (R)- and (S)-1′-(1-aminoethyl)ferrocene-1-carboxylic acid derivatives

Lipase-catalyzed esterification of (±)-methyl 1′-(1-hydroxyethyl)ferrocene-1-carboxylate 4 afforded its (R)-acetate (−)-5 (ee = 99%) and (S)-(+)-4 (ee = 90%). Stereoretentive azidation/amination/acetylation of (R)-(−)-5 gave (R)-(+)-methyl 1′-(1-acetamidoethyl)ferrocene-1-carboxylate (R)-3 (ee = 98%). In a similar manner (S)-(+)-4 was converted into (S)-(−)-3 (ee = 84%). Both enantiomers of 3 were obtained in high chemical yields without a loss of enantiomeric purity. The title compounds can be coupled with natural amino acids and peptides on both C- and N-termini.