Molecular modeling of saccharides, part 27 Synthesis and molecular geometry of an achiral 30-crown-12 polyacetal from alpha-cyclodextrin

• Published in: Chemistry : a European journal Vol. 6; no. 18; pp. 3366 - 3371
• Main Authors: Immel, S, Nakagawa, T, Lindner, HJ, Lichtenthaler, FW
• Format: Journal Article
• Language: English
• Published: BERLIN Wiley 15.09.2000
• Subjects: Chemistry; Chemistry, Multidisciplinary; Physical Sciences; Science & Technology; OXYGEN; 17-CROWN-6; oligosaccharides; CATION-BINDING; CROWN-ETHER ACETALS; cyclodextrins; crown acetals; macrocyclic polyacetals; CYCLOALTRIN; FORMALS; 14-CROWN-5
• ISSN: 0947-6539
• DOI: 10.1002/1521-3765(20000915)6:18<3366::AID-CHEM3366>3.0.CO;2-9

Periodate oxidation of alpha-cyclodestrin followed by borohydride reduction readily provided an octadecahydroxymethyl-substituted 30-crown-12 polyacetal 1, its 30-membered macrocycle being composed of six meso-butanetetrol/glycolaldehyde acetal units, which is, consequently, optically inactive, Its solid-state molecular geometry emerged from the X-ray structural analysis of the well-crystallizing octadeca-acetate 2, which revealed the undulated macrocycle to be molded into three loops with a unique order of succession of the -CHR-CHR-O-CHR-O- units: alternating gauche- and anti-conformations of the meso-butanetetrol portions and consecutive disposition of the glycolaldehyde-acetoxymethyl groups above and below the mean-plane of the macrocycle. In solution, however, as evidenced by H-1- and C-13-NMR spectra, the macrocycle is highly flexible at ambient and higher temperatures, its mobility becoming distinctly restricted only below - 20 degrees C.