Crystal structures of cyclosporin derivatives: O-acetyl-(4R)-4-(E-2-butyl)-4,N-dimethyl-L-threonyl-cyclosporin A and O-acetyl-(4R)-4-[E-2-(4-bromobutyl)]-4,N-dimethyl-L-threonyl-cyclosporin A

The structures of O-acetyl-(4R)-4-(E-2-butyl)-4,N-dimethyl-L-threonyl-cyclo sporin A (1) and O-acetyl-(4R)-4-[E-2-(4-bromobutyl)]-4,N-dimethyl-L-threon yl-cyclosporin A (2) were determined by X-ray diffraction methods and compa red with the structure of related cyclosporins. In contrast to expectation, neither the acetylation nor the subsequent bromination of 1 affects the co nformation and packing of cyclosporins in the solid state. Both compounds a re isomorphous and crystallize in the orthorhombic space group P2(1)2(1)2(1 ) with a = 12.936(2) Angstrom, b = 15.590(2) Angstrom, c = 36.280(3) Angstr om, and a = 12.916(3) Angstrom, b = 15.675(4) Angstrom, c = 36.715(7) Angst rom, for 1 and 2, respectively.