Details

Autor(en) / Beteiligte

• Grochulski, P.
• Smith, G. D.
• Langs, D. A.
• Duax, W. L.
• Pletnev, V. Z.
• Ivanov, V. T.

Titel

Molecular structure of cyclo[-(D-Val-L-Hyi-L-Val-D-Hyi)2-] revealed by X-ray analysis

Ist Teil von

• Biopolymers, 1992-07, Vol.32 (7), p.757-764

Ort / Verlag

Hoboken: Wiley Subscription Services, Inc., A Wiley Company

Erscheinungsjahr

1992

Link zum Volltext

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• The crystal structure of a synthetic analogue of valinomycin, cyclo [‐(D‐Val‐L‐Hyi‐L‐Val‐D‐Hyi)2‐] (octa‐meso‐valinomycin) (I) (C40H68N4O12 · 1.5 · C4H8O2, Mr = 937.01 + 88.10), has been determined. Crystals grown from dioxane are monoclinic, space group P21/a, with cell parameters a = 21.487(8), b = 16.836(5), c = 16.089(4) Å, β = 111.70(4), and Z = 4. The atomic coordinates for nonhydrogen atoms were refined in the anisotropic thermal motion approximation. H atom positions were included in the structure factor calculations at their geometrically expected positions. Values of the standard and weighted R factors after refinement are 0.11 and 0.13, respectively. The conformation of the depsipeptide crystallized from dioxane is different from that crystallized from chloroform (II). The molecule adopts a rectangular shape with two type IV β–turns containing a hydrogen bond and possesses pseudorotational symmetry. The side chains are located on the molecular periphery. The orientation of the carbonyl groups of the molecule is not conducive for efficient metal‐ion coordination and in the observed conformation cannot behave as an ionophore. In the crystal the molecules form infinite chains parallel to the c axis, and are stabilized by two intermolecular hydrogen bonds that are shorter and have better geometry than the intramolecular hydrogen bonds. A ϕ/Ψ plot for dodecadepsipeptides with a (DLLD)3 sequence has well‐defined areas for Val and Hyi residues only in cases when the crystals have been grown from nonpolar or medium‐polar solvents. The Φ/Ψ plot for octadepsipeptides crystallized from chloroform (II) shows this behavior also. There also is a correlation between the polarity of the solvent from which crystals of octa‐meso‐valinomycin or valinomycin analogues with a (DLLD) sequence of configuration have been grown and the number of the intramolecular hydrogen bonds that are formed. The more polar the solvent the fewer the number of intramolecular hydrogen bonds. Empirical energy calculations on octa‐meso‐valinomycin indicate that for isolated molecules, the energy of the bracelet form (II) is 4.7 kcal/mole lower than that of the rectangular form (I).