SYNTHESIS OF CYCLOPROPANE AMINO-ACIDS AND THEIR INCORPORATION INTO BIOACTIVE PEPTIDES AS CONFORMATIONAL CONSTRAINT

Cyclopropane amino acids are the amino acid derivatives which contain the cyclopropane ring in their side chain. Various cyclopropane amino acids were isolated from many different natural sources. Along with many efforts to synthesize these natural compounds, studies on the structure-activity relationships of bioactive peptides have highlighted the usefulness of cyclopropane amino acids. Incorporation of cyclopropane amino acids has been achieved for some neuropeptides, hormones, and enzyme inhibitors and these sterically rigid cyclopropane amino acids were found to be a key constituent not only as conformational constraint but also as a structural element to avoid enzymatic degradations. Several distinct success stories have prompted organic chemists to challenge the asymmetric synthesis of optically active cyclopropane amino acids in these years.