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Molecular Modeling of Saccharides, Part XII.

Sucrose as a renewable organic raw material: New, selective entry reactions via computersimulation of its solution conformations and its hydroxyl group reactivities

F.W. Lichtenthaler, P. Pokinskyj und S. Immel

Zuckerind. (Berlin) 1996, 121, 174-190.

This account describes the application-oriented development of novel, highly selective and practicable "entry reactions" for the derivatization of sucrose, utilizing modern molecular modeling procedures, which allow the realistic simulation of the preferred conformation protic (water) and aprotic solvents (DMF, pyridine) as well as the different reactivities of the eight hydroxyl groups. - Due to the persistence, in DMF solution, of a hydrogen bond between the glucose and fructose portions, of the type 2g-O ··· HO-1f and 2g-O ··· HO-3f, two conformations are preferred, of which the MOLCAD-generated electrostatic potential (MEP) proves the 2g-OH the by far most electropositive, i.e. the most acidic one and, hence, the one to be deprotonated first. This insight was transferred into practicable chemistry: deprotonation of sucrose in DMF with base (1 molar equiv.) and quenching the monoalkoxide with benzyl bromide generates 2g-O-Benzyl-sucrose (> 80%) - a new entry reaction that made readily accessible a series of 2g-modified products: 2-deoxy-sucrose, sucrosamine, sucrose-2,3-epoxide, and enantiopure dihydropyranone, all compounds with industrial application potential. - An entry into glucosyl-C-4-modified sucroses is possible via pivaloylation to the 4g-OH-free heptapivaloate (> 50%) which through oxidation, oximation, reduction and β-elimination provides a similar set of new application-profiled products. - Another, highly selective entry reaction for the chemical modification of sucrose, and already realized on an industrial scale, is the enzymatically induced 2f-O -> 6f-O-glucosyl shift to isomaltulose - a transformation, that on the basis of molecular modelings can be readily understood as a closed shell process. Being more easily derivatizable than sucrose, isomaltulose is readily converted into products with industrial application profiles: air-oxidation generates glucosyl-α (1→5)-arabinonic acid, reductive amination isomaltamine, each being convertible in one more step - amidation with fat-amines or N-acylation with fatty acids - into products with interesting detergent and liquid crystal properties; acidic dehydration transforms isomaltulose into glucosyloxymethyl-furfural (α- GMF) in a surprisingly uniform reaction, which - like its parent compound HMF - is amenable to various ensuing reactions, e.g. to α-GMF-acrylic acid esters, that, on polymerization, are apt to provide new, biologically degradable polymers.

Additional Graphics: Sucrose

© Copyright PD Dr. S. Immel