Synthesis of 3- and 4-Hydroxy-2-aminocyclohexanecarboxylic Acids by Iodocyclization

Regio- and diastereoselective fluorination of alicyclic β-amino acids

A regio- and stereoselective approach to fluorinated β-aminocyclohexene or cyclohexane esters has been developed, starting from a bicyclic β-lactam (1). The procedure involves six or seven steps, based on regio- and stereoselective iodolactonization, lactone opening and hydroxy-fluorine exchange. The method has been extended to the synthesis of fluorinated amino ester enantiomers.

The First Direct Enzymatic Hydrolysis of Alicyclic β-Amino Esters: A Route to Enantiopurecis andtrans β-Amino Acids

The first direct enzymatic method is reported for the synthesis of cis and trans beta-amino acid enantiomers through the lipase-catalyzed enantioselective hydrolysis of alicyclic beta-amino esters in organic media. High enantioselectivities (E usually >100) were observed when the Candida antarctica lipase B catalyzed reactions were performed with H2O (0.5 equivalents) in iPr2O at 65 degrees C. The resolved products, obtained in good yields (>or=42%), could be easily separated.

An Efficient Enzymatic Synthesis of Benzocispentacin and Its New Six- and Seven-Membered Homologues

A very efficient enzymatic method was developed for the synthesis of new enantiomeric benzocispentacin and its six- and seven-membered homologues through the Lipolase (lipase B from Candida antarctica) catalyzed enantioselective (E > 200) ring opening of 3,4-benzo-6-azabicyclo[3.2.0]heptan-7-one, 4,5-benzo-7-azabicyclo[4.2.0]octan-8-one, and 5,6-benzo-8-azabicyclo[5.2.0]nonan-9-one with H2O in iPr2O at 60 degrees C. The (1R,2R)-beta-amino acids (ee > or = 96%, yields > or = 40%) and (1S,6S)-, (1S,7S)-, and (1S,8S)-beta-lactams (ee > 99%, yields > or = 44%) produced could be easily separated. The ring opening of racemic and enantiomeric beta-lactams with 18% HCl afforded the corresponding beta-amino acid hydrochlorides.

Application of alicyclic β-amino acids in peptide chemistry

The self-organizing beta-peptides have attracted considerable interest in the fields of foldamer chemistry and biochemistry. These compounds exhibit various stable secondary structure motifs that can be exploited to construct biologically active substances and nanostructured tertiary structures. The secondary structures can be controlled via the beta-amino acid sequence, and cyclic beta-amino acid residues play a crucial role in the design. The most important procedures for the preparation of cyclic beta-amino acid monomers and peptides are discussed in this tutorial review. Besides the secondary structure design principles, the methods of folded structure detection are surveyed.