TUD Organische Chemie

Immel

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Abstract 35

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Molecular Modeling of Saccharides, Part XXX.

Two Stereoisomeric 3^I,2^II-Anhydro-α-cyclodextrins: A Molecular Dynamics and Crystallographic Study

S. Immel, K. Fujita, M. Fukudome, and M. Bolte

Carbohydr. Res. 2001, 336, 297-308.

Regioselective epoxide ring opening of 2^I,3^I-(2^IS)-anhydro-α-cyclodextrin (1) through intramolecular attack of hydroxyl groups of neighboring glucose rings occurs in diequatorial fashion to yield 3^I,2^II-anhydro-α-cyclodextrin (3) with a rigid glucopyranose-dioxane-glucopyranose tricyclic ring system, the usual diaxial opening and the gluco/altro-configurated stereoisomer 2 cannot be detected. Molecular dynamics simulations in water were used to analyze the conformations of 1 - 3 and the stereochemical implications of this reaction. Due to the contracted 2,3-OH side of the torus, 3 features an inverted conicity compared to the parent α-cyclodextrin. A crystallographic study on the bis-3 ^. 3 n-PrOH nonahydrate not only displays little variations between the solid-state and solution geometries of 3, but also provides a molecular picture of a unique inclusion complex in which three n-propanol molecules are distributed in the cavity of a dimeric unit of 3 (monoclinic, space group P2₁, a = 14.257(1), b = 22.623(2), c = 16.644(1) Å, β = 104.82(1), all 19278 reflections with I > 2s(I) yield R(F) = 0.1017).

Additional Graphics: Anhydro Cyclodextrins