3-DIMENSIONAL STRUCTURE OF CYCLOHEXAPEPTIDES CONTAINING A PHOSPHINIC BOND IN AQUEOUS-SOLUTION - A TEMPLATE FOR ZINC METALLOPROTEASE INHIBITORS - A NMR AND RESTRAINED MOLECULAR-DYNAMICS STUDY

The 3D structures of two phosphinic cyclic hexapeptide inhibitors of bacterial collagenase, cyclo-(Gly(1)-Pro(2)-Phe(3 psi)[PO2-CH2]Gly(4)-Pro(5)-Nle(6)) (compound I) and cyclo(Gly(1)-Pro(2)-D-Phe(3 psi)[PO2-CH2]-Gly(4)Pro(5)Nle(6)) (compound II), inaqueous solution, as derived from NMR spectroscopy and molecular dynamics simulations, are described. The general structures of these cyclic hexapeptides closely resemble the ''canonic'' two-reverse-turn structure, with the proline occupying the (i + 1) position of the turns and the glycine the connecting positions. The phosphinic bond is located between the (i + 2) and (i + 3) positions of one of these turns. However, a striking feature of the backbone structure of these peptides is the presence of double type VIII-turns in compound I, and in compound II of type VIII- and tentatively named type M-turns. The comparison of the 3D structures of these two cyclic hexapeptides shows that the. stereochemistry of the phenylalanylphosphinyl residue influences not only the local conformation but also the global topology of the peptide macrocycle. The differences in the 3D structure of these compounds are discussed in relation to their inhibitory potencies and with the view of using these constrained cyclic peptides as a scaffold for the development of rigid metalloproteases inhibitors.