THE STRUCTURE OF A NEW CYCLOSPORINE-A SOLVATED FORM

The structure of cyclosporin A dimethyl isosorbide solvate (C62H111N11 O12. C8H14O4, CsA . DMI) was solved using direct methods and refined a nisotropically to the R value of 0.091 for 7120 observed independent r eflections. The title compound crystallizes in the monoclinic space gr oup P2(1) with lattice parameters a = 15.521(2) Angstrom, b = 20.833(3 ) Angstrom, c = 12.949(3) Angstrom, beta = 100.21(1)degrees, Z = 2. In comparison with the structures of CsA monohydrate or dihydrate, the m olecular shape of CsA . DMI differs in the backbone conformation (psi( 1), psi(7), psi(8)) and in the opposite MeBmt(1) side-chain orientatio n (chi(1)), which permits to form the new H-bond contact MeBmt(1)OH-Sa r(3)CO. The H-bond contact D-Ala(8)NH-MeLeu(6)CO is absent in the stru cture of CsA . DMI.