The synthesis, solution NMR investigation and solid-state structural characterization of a new difunctionalized beta -cyclodextrin (beta -CD) are reported. 6(I),6(II)-Dideoxy-6(I),6(II)-bis[2-(2-pyridyl)ethylamino]-beta -cyclomaltoheptaose is synthesized for the first time using a regioselective synthetic procedure. On the basis of an aqueous solution NMR investigation, the intramolecular interaction of the two pyridine rings with the upper rim of the cavity is proposed. 6(I),6(II)-Dideoxy-6(I),6(II)-bis[2-(2-pyridyl)ethylamino]-beta -cyclomaltoheptaose, C56H86N4O33, crystallizes in the monoclinic P2(1) space group with cell dimension a=26.303(5), b=15.670(5), c=8.276(2) Angstrom and beta =103.60(2)degrees, and 5.5 molecules of water for each independent beta -cyclodextrin molecule. The structure refines to R=0.103 for 2270 observed reflections [I greater than or equal to3 sigma (I)] and represents the first example of a complete structural characterization of a branched difunctionalized beta -cyclodextrin. In the solid state, the macrocycle structure maintains an approximate seven-fold symmetry with only small changes occurring in the cyclic carbohydrate conformation where two consecutive primary hydroxy groups are substituted with bulky moieties. The two aminoethylpyridine groups linked to contiguous glucosidic units show different behaviour, with one group extending away from the cavity of the beta -CD, the other remaining in the proximity of the 'mouth' of the cavity. However, in the crystal the aminoethylpyridine group extending away from the cavity of the beta -CD is deeply inserted into the cavity of the adjacent beta -CD molecule translated along the c axis, giving rise to long rows of beta -CD molecules stabilized by these host-guest interactions. The resulting polymeric arrangement has already been observed in crystal structures of other monosubstituted beta -CDs.
|Titolo:||Difunctionalized beta-cyclodextrins: synthesis and X-ray diffraction structure of 6(I),6(II)-dideoxy-6(I),6(II)-bis[2-(2-pyridyl)ethylamino]-beta-cyclomal toheptaose|
|Data di pubblicazione:||2001|
|Appare nelle tipologie:||1.1 Articolo in rivista|