A Trefoil Knot Made of Amino Acids and Steroids

摘要

Linear oligoamides made from conformationally restricted non-natural amino acids can form helical or ribbonlike secondary structures.[1] Moreover, amide macrocycles have been shown to build knotted structures if concave structural elements are present in the monomeric units.[2] The concave surface of cholanic acids has often been used as a scaffold in supramolecular chemistry.[3] We have combined all three elements to prepare cyclopeptides from aminocholanic acids. We found that when the amine macrocycles consist of aminocholanic acids they form open cavities, while cyclopeptides composed of aminocholanic acids and natural dipeptides adopt closed-loop structures.[4] Here, we report the unexpected geometry of cyclic oligoamides built from alternating sequences of aminodeoxycholanic acid and a natural amino acid.