Crystal Structures of Two Modifications of [3,O‐didehydro‐mebmt1, val2]‐cyclosporin and comparison of three different X‐ray data sets

Abstract The crystal structure of [3,O‐didehydro‐MeBmt1, Val2]cyclosporin (PSC‐833; 1) was investigated by X‐ray analysis. Data were collected from two different crystal modifications. Modification I crystallizes in P3121, a = b = 21.419 (2) Å, c = 32.101 (3) Å with one molecule in the asymmetric unit, modification II in P3221, a = b = 21.313 (2) Å, c = 62.053(3) Å with two molecules per asymmetric unit. This non‐immunosuppressive analogue of cyclosporin A adopts a similar backbone conformation to that found in the crystal structure of cyclosporin A and other analogues. Three different data sets of modification I were collected using an Enraf‐Nonius‐CAD4 diffractometer with CuKα radiation at 20°, a Stoe‐Siemens four‐circle diffractometer with MoKα radiation at − 120°, and an EMBL image‐plate scanner with synchrotron radiation at 12°. The quality of the data sets was evaluated by internal consistency, independent structure solution, and refinement. The structural parameters reported here for modification I are based on the synchrotron data.