Analysis and modelling of the structures of beta-cyclodextrin complexes

A systematic computer graphics study of all available beta-cyclodextrin crystal structures has been carried out specifically to aid in the modelling and design of beta-cyclodextrin-drug complexes. The analyses show that the basic conformation of the molecule remains constant among natural, mono-substituted and partially permethylated beta-cyclodextrins, with major changes observed only in the case of full permethylation. In all the structures, however, there are no significant perturbations caused by guest molecule inclusion. On the basis of these observations models are proposed for the structures of beta-cyclodextrin-indomethacin complexes, the principal features of which are shown to be consistent with the data obtained in 1H-NMR studies.

Crystal structure of 2-O-[(S)-2-hydroxypropyl]cyclomaltoheptaose

2-O-[(S)-2-Hydroxypropyl]cyclomaltoheptaose crystallises in the monoclinic space group P2(1) with unit-cell dimensions a = 15.072(1), b = 10.409(1), c = 20.623(2) A, and beta = 108.52(1) degrees. The structure was solved by X-ray diffraction and refined to an R-value of 0.096. The macrocyclic ring of the cyclomaltoheptaose moiety is less symmetrical than that in cyclomaltoheptaose. The glucose residue that carries the hydroxypropyl group inclines much more with its primary hydroxyl side towards the inside of the macrocycle than the other glucose residues. The molecules are arranged in a herring-bone fashion to form a cage-type packing structure. The hydroxypropyl group is inserted into the cavity of an adjacent molecule related by a two-fold screw axis, and the hydroxyl group is linked to an HO-6 via OH...water...OH hydrogen bonds. The crystal contains 8.5 water molecules which occupy 11 sites. Two water molecules are included at the primary hydroxyl side of the cyclomaltoheptaose cavity.

Structure of inclusion complexes of cyclomaltoheptaose (cycloheptaamylose): crystal structure of the 1-adamantanemethanol adduct

Cyclomaltoheptaose (cycloheptaamylose) has been crystallized with 1-adamantanemethanol as the guest molecule. The complex crystallized in space group C222(1), with unit-cell dimensions a = 19.162 (13), b = 23.965 (17), and c = 32.597 (27) A. The structure was solved by rotation-translation search-methods. The cyclomaltoheptaose exists as a dimer in the crystal by means of extensive hydrogen-bonding across the secondary hydroxyl ends of two cyclomaltoheptaose molecules. The two halves of the dimer are related by a crystallographic two-fold axis. The primary hydroxyl ends of two adjacent cyclomaltoheptaose molecules are also related by a crystallographic two-fold axis, but do not directly hydrogen bond to one another. Instead, they are held in place by a strong hydrogen bond from the hydroxyl group of the 1-adamantanemethanol to a primary hydroxyl group on an adjacent cyclomaltoheptaose molecule. Other stabilizing hydrogen bonds are formed via three water molecules which are situated at the primary hydroxyl interface, and others that form parallel columns stabilizing the crystal structure. A unique feature of this complex is the presence of trapped water in the cavity at the secondary hydroxyl interface. This water is distributed over 3 disordered sites. Its presence blocks one possible site for the 1-adamantanemethanol, which, instead, binds near the primary hydroxyl end, with its hydroxyl group and part of the adamantane moiety protruding from the cyclomaltoheptaose.