Organofluorine compounds and fluorinating agents. 14. Thermotropic Liquid-Crystalline Glycosyl Fluorides

Abstract

The liquid crystalline 6‐O‐alkyl‐α‐D‐galactopyranosyl fluorides (3a–f) and the mesogenic 6‐O‐dodecyl‐α‐D‐glucopyranosyl fluoride (7) were prepared from the homologous 6‐O‐alkyl‐1,2:3,4‐di‐O‐isopropylidene‐α‐D‐galactopyranosides (1a–f) and from the methyl 2,3,4‐tri‐O‐benzyl‐glucopyranoside (4), respectively, in two and three steps. The fluorinations of 1a–f to the α‐fluorides 2a–f and of 5 to the α‐fluoride 6 were carried out with the reagent system HF/nitromethane/acetic anhydride, which simultaneously effects the complete exchange of the isopropylidene groups (1a‐f) and of the benzyl groups (5) for acetyl functions in the non‐glycosidic positions. Moreover, the 6‐O‐dodecyl‐2,3,4‐tri‐O‐acetyl‐α‐D‐galactopyranosyl fluoride (11) was prepared in three steps from the 6‐O‐dodecylgalactopyranose (8). The stereoselective introduction of the fluoride into the β‐anomeric position (10 → 11) was achieved by bromide‐fluoride exchange with the two‐phase system triethylamine‐trishydrofluoride/petroleum ether. Dodecyl 6‐deoxy‐6‐fluoro‐α‐D‐glucopyranoside (13), prepared from the glucoside 12 with the fluorinating agent DAST, shows a narrow monotropic SA‐phase and lyotropic liquid crystalline behaviour in contact with water. Dodecyl 6‐deoxy‐6‐fluoro‐β‐D‐galactopyranoside (17), prepared in three steps from the acetal 14, does not form mesophases. The liquid crystalline behaviour of the amphiphilic glycosyl fluorides 3a–f, 7, and of the 6‐deoxy‐6‐fluoro derivative 13 is described.

Thermotrop fl�ssigkristalline Kohlenhydrat-Amphiphile

“…Stabilitiit von columnaren (discotischen) Mesophasen: Aldose-Dialkyldithioacetale mit ihren zwei geminal angeordneten lipophilen Ketten erfiillen bekanntlich [97,100,1021 neue Erkenntnisse gewonnen werden, die zu alternativen Strukturvorschlagen fuhren [106]. Der am Beispiel der 6-Desoxy-aldosedithioacetale gefundene Verlust mesogener Eigenschaften [97,102] ist auf eine empfindliche Storung im Zentrum des hydrophilen Bereichs zuriickzufuhren und unterstutzt damit die bisherigen Modellvorstellungen fur Mesophasen des columnaren TYPS-Mesogene GlycosylJl'uoride: Mit den homologen 6-0alkyl-a-D-galactopyranosylfluoriden 65 [86] (Alkylkelten 2 C7), dem 6-0-Dodecyl-a-D-glucopyranosylfluorid 66 [86] und den langkettigen N-Acyl-2-desoxy-2-aminoa-D-glucopyranosylfluoriden 67 [ 1051 wurden die ersten thermotropen Glycosylhalogenide aufgefunden (Formelbild 10). Oberhalb des Schmelzpunktes beobachtet man bei diesen Verbindungen allerdings bereits eine HF-Abspaltung, so darj die gefundenen Klarpunkte nicht denen der reinen Glycosylfluoride entsprechen.…”

“…Das Nonyl-Derivat zeigt allerdings noch monotropes Verhalten. [45], 24 [86]; 25, 26, 28, 29 [43], 27 [86], 30-32 [89]. [88].…”

Triethylamine Trishydrofluoride in Synthesis

“…Nucleophilic substitutions with inversion of the configuration of abromine substituents at the anomeric centre with fluorine were effectively realized by refluxing of 7 with a large excess of Et3N.3HF in a two-phase system with CC14 to give 8 [6]. Several similar transformations of other protected a-bromo sugars 151 and protected sugar analogues like 9 and 11 [7,8] have been realized.…”

Amphiphilic and mesogenic carbohydrates IX. Perfluoroalkyl substituted monosaccharides: a new group of amphiphilic liquid crystals

“…70´5± 72´5ß C, c.p. 141ß C) [22 ]. The latter is a typical hydrocarbon tailed amphiphilic carboacetalation from methyl b-d-galactopyranoside and hydrate with a SmA texture.…”