TUD Organische Chemie

Immel

Publications

Poster

Abstract 07

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Structure and Conformational Features of α-Cycloaltrin: a Cyclooligosaccharide with Alternating ⁴C₁/¹C₄ Pyranoid Chairs

Frieder W. Lichtenthaler, Hans J. Lindner, Stefan Immel, and Guido E. Schmitt

9^th European Carbohydrate Symposium (EUROCARB XI), Utrecht, Netherlands, July 6-11, 1997, Abstract C5.

The structural characteristics of α-cycloaltrin (3), readily available from α-cyclodextrin (1) by a straightforward four-step protocol^[1] with 2,3-anhydro-α-cyclomannin (2) as the key intermediate, has been unraveled using X-ray techniques, 800 MHz spectra (D₂O at 30 and 4°C) and molecular modeling (MD in water). In the solid-state, the altropyranoid rings adopt nearly perfect ⁴C₁ and ¹C₄ chairs in an alternating sequence, entailing the macrocycle to be devoid of a through going cavity. From HTA calculations i.e. toward vacuum boundary conditions, the all­skew (twist­boat) ⁰S₂ geometry emerges as the global energy minimum structure. In water, the altropyranoid rings in 3 adopt various conformations within the ¹C₄ ³H₂ ⁰S₂ range.

1		2 (R = SiMe2tBu)
		3

[1] Y. Nogami, K. Fujita, K. Ohta, K. Nasu, H. Shimada, C. Shinohara, and T. Koga, (J. Szejtli, L. Szente, Eds.), Proceedings of the 8^th Internat. Symp. on Cyclodextrins, Kluwer Acad. Publ., Dordrecht, 1996, pp. 99-102.

Additional Graphics: Cycloaltrins