Alkyl fructosides

When the carbonyl compound is a ketose (e.g. fructose) rather than an aldose, the fructosylamine precursor (an N-alkyl fructoside) undergoes a Heyns rearrangement to form a 2-alkylamino-2-deoxy-D-glucose (15). These Heyns compounds are precursors of the browning phenonema. 

Table 10. Effect of the alcohol chain-length on the synthesis of alkyl fructosides. ...

Alkyl fructosides have remained rather inaccessible and have, consequently, received only scant attention. We have found that the reaction of fructose and alkyl alcohols can be achieved by taking special precautions. Initially, furanoid compounds are formed which are in the course of the reaction partly transformed into the /l-fructopyranoside. Separation of the products by preparative HPLC allowed us to study the esterification of structurally homogeneous compounds . 

The alkyl fructosides 19 and 21 represent a novel class of reactants and the investigations are far from complete. It is already clear, however, that in this case also the primary hydroxyl functions are acylated first. 

With long alkyl chain alcohols, the conversion of fructose with 1-octanol to octylfructosides was only 60%, but with 1-decanol and 1-dodecanol the conversion dropped to 40% due to competing of fructose ring opening. However, in 1,2-dimethoxyethane as solvent, a yield in dodecyl-D-fructosides of 60% was obtained after 1.5 h at 83 °C. 

The liquid mixed product of doubtful purity obtained when D-fructose (or a derivative) is allowed to react with alcoholic hydrogen chloride at room temperature until the specific rotation reaches a maximum is called in this article alkyl 7 -D-fructoside (or derivative). In the early literature such a compound was known as y-alkylfructoside. 

Anomeric alkylation of o-fructose in 1-octanol has been performed by use of a sulfonic acid resin-Bayer K 2461. Conversion to octyl fructosides was only 14.2% after 1 h reaction at 548 K [33]. 

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