Molecular conformation of a D,L stereoisomeric analogue of valinomycin, cyclo[‐(L‐Val‐L‐Hyi‐L‐Val‐D‐Hyi)₂‐(D‐Val‐L‐Hyi‐L‐Val‐D‐Hyi)‐]

The crystal structure of a synthetic analogue of valinomycin, cyclo[‐(L‐Val‐L‐Hyi‐L‐Val‐D‐Hyi)₂‐(D‐Val‐L‐Hyi‐L‐Val‐D‐Hyi)‐] ([L‐Val¹, L‐Val⁵]meso‐valinomycin), C₆₀H₁₀₂N₆O₁₈, has been determined. Crystals grown from petroleum ether are orthorhombic, space group P2₁2₁2₁, with cell parameters a = 16.41(1), b = 18.76(1), c = 25.86(1) Å, and Z = 4. The atomic coordinates for nonhydrogen atoms, except those of terminal carbons on one side chain, were refined in the anisotropic thermal motion approximation. The coordinate parameters of the H atoms were incorporated into the structure factor calculations at geometrically expected positions. Values of the standard and weighted R factors after refinement are 0.074 and 0.083, respectively. The crystal structure of the molecule is asymmetric and adopts a conformation with four 4 → 1 type and one 6 → 1 type intramolecular hydrogen bonds between amide nitrogens and carbonyl oxygens. Valinomycin binds potassium more than 100 times strongly than the D,L Stereoisomeric analogue, as a result of a different spatial orientation of potentially interacting carbonyl groups.