TRIPODAL PEPTIDES WITH CHIRAL CONFORMATIONS STABILIZED BY INTERSTRAND HYDROGEN-BONDS

C3 symmetric trispeptides are described that form chiral conformations and are therefore eminently suited to provide a new family of chiral receptor molecules when extended by appropriate binding sites. These trispeptides are composed of C3 symmetric trisamines as anchors and three symmetrically extending chiral amino acid residues. Their conformations in apolar solvents fall into two main classes. One is comprised of propeller-like conformations of preferred chiral sense that are stabilized by a belt of intramolecular H-bonds (hydrogen bonds) between adjacent strands. The other class has two of its strands connected by two H-bonds to form a 10-membered ring, while the third strand may hydrogen-bond to one of the other two. The effect of the anchors and amino acids on the relative stability of the H-bonded, chiral conformations has been established by a combination of spectroscopic and theoretical means. Trispeptides derived from more lipophilic alpha-amino acids show a higher population of the chiral conformations. Moreover, trispeptides that are based on tris(2-aminoethyl)amine (TREN) as anchor form stronger H-bonds than those relying on 1,3,5-tris(aminomethyl)benzene (TRAM).