Frieder W. Lichtenthaler

Towards improving the utility of ketoses as organic raw materials

Abstract Although three ketoses are bulk scale-accessible and inexpensive, i.e. d -fructose, l -sorbose, and isomaltulose, their utilization as organic raw materials in chemical industry is modest—not surprising in fact, as their chemistry has not developed at a rate comparable with the other common monosaccharides. This account gives an overview over older and very recent efforts of chemically transforming these three ketoses into building blocks with industrial application profiles, be it bulk, fine, or specialty chemicals, pharmaceuticals, or simply enantiopure building blocks for organic synthesis.

Is Isoprene Emitted by Plants Synthesized via the Novel Isopentenyl Pyrophosphate Pathway

Abstract The incorporation of deuterium labeled 1-deoxy-ᴅ-xylulose into isoprene, emitted by three higher plants upon illumination, was analysed by headspace GC-MS. A high extent of incorporation into isoprene was found, indicating that isoprene is synthesized in higher plants via the novel isopentenyl pyrophosphate pathway, of which 1-deoxy-ᴅ-xylulose-5-phosphate is an intermediate. A new chemical synthesis of methyl [ 1-2H1]-1-deoxy-α/β-ᴅ-xyluloside from ᴅ-xylulose is presented.

N.M.R.-studien an zuckern und cyclanolen : V. Zusammenhang zwischen sterischer orientierung von O- und N-acetyl-gruppen und der signallage ihrer methyl-resonanzen bei cyclit- und aminocyclit-polyacetaten

Abstract Absorption ranges are deduced for axial and equatorial O - and N -acetyl-resonances of cyclitol and aminocyclitol polyacetates on the basis of 41 (CDCl 3 ) and 22 (Me 2 SO- d 6 ) compounds, allowing configurational and conformational assignments. Scope and limitations are discussed; in particular, application to compounds having substituents other than acetoxy and acetamido groups.

Bromine as an oxidant for direct conversion of aldehydes to esters

Examples illustrate the direct conversion of aldehydes to esters using bromine in alcohol solvents with sodium bicarbonate buffer. The convenient and efficient one-pot procedure is compatible with secondary hydroxyl groups as well as a variety of O-protecting units such as MOM, MEM, Ph2tBuSi, benzyl, benzoyl, and isopropylidene functions.

Boron trifluoride-catalyzed oxidation of glycal esters: An effective and mild method for their conversion into α,β-unsaturated lactones☆

An effective, one-step procedure for conversion of glycal and 2-acyloxyglycal esters to 2,3-unsaturated lactones has been developed, involving BF3-induced removal of the allylic acyloxy function and oxidation with m-chloroperbenzoic acid or pyridinium chlorochromate.

Guest-induced conformational change in a flexible host: mono-altro-β-cyclodextrin †

Mono-altro--cyclodextrin 1 ,a -cyclodextrin with one of the seven glucose units being configurationally changed to an altrose, is shown to be a flexible host undergoing a distinct conformational change within its altropyranose geometry upon intracavity inclusion of adamantanecarboxylate, thus representing an induced-fit model of binding rather than one following the rigid lock-and-key type pattern.

Cyclodextrins, cyclomannins, and cyclogalactins with five and six (1→4)-linked sugar units: A comparative assessment of their conformations and hydrophobicity potential profiles1

Abstract A molecular modeling study of the (1→4)-linked cyclooligosaccharides containing five and six α- D -glucose, α- D -mannose, and β- D -galactose units, respectively, provide a clear conception of their overall conformations, their contact surfaces, and their cavity proportions. A MOLCAD-based generation of their molecular lipophilicity potential (MLPs) gives a lucid picture of their hydrophobic and hydrophilic surface areas, and hence, a first estimation of their inclusion properties.

α-D-Glucopyranosyl-D-fructoses: distribution of furanoid and pyranoid tautomers in water, dimethyl sulphoxide, and pyridine. Studies on ketoses. Part 4

The tautomeric distributions of trehalulose (2), turanose (3), maltulose (4), leucrose (5), and palatinose (6) have been established using an 1H NMR methodology based on integration of the low-field anomeric OH singlets in dimethyl sulphoxide. Equilibration in dimethyl sulphoxide being exceedingly slow the method can be applied to determine tautomeric ratios in essentially any solvent, by freezing a small probe of the respective solution (liquid N2), dissolving the resulting ice-matrix in (CD3)2SO and rapid recording of the intensities in the low-field OH-region. In dimethyl sulphoxide, fructose, trehalulose (2), turanose (3), and maltulose (4) adopt equilibria with a high proportion of the furanoid tautomers (∼ 60% at 20 °C) in an approximate 2:1 β-f/α-f-ratio versus 10:1 for the β-p/α-p-forms. For leucrose (5), the β-p⇌α-p equilibrium lies at the β-p side with a 9:1 preference, whereas palatinose (6) establishes an 11 :4 β-f⇌α-f equilibrium with a comparably high proportion of the acyclic keto-form (6%), that, in all other cases, is ⩽ 1%. There is little temperature dependence of the anomeric compositions in the 20–70 °C range. In water, the β-p form invariably is the most abundant at equilibrium, decreasing substantially though with rising temperature in favour of the β-fand α-f-tautomers. The equilibrium compositions of fructose, trehalulose, and maltulose being almost identical, that of turanose is markedly shifted towards higher proportions of furanoid forms, amounting to two-thirds of the mixture at 70 °C. Aqueous solutions of leucrose contain the β-p form almost exclusively, palatinose establishes a 5:1 to 3:1 β-f⇌α-f equilibrium over the 1–70 °C range. In pyridine, equilibrium tautomeric compositions are similar to those found for water, except for distinctly slower tautomerization rates. The preparative implications for derivatizations of these glycosyl-fructoses in pyridine are discussed, their now predictable outcome being strongly dependent on the mode of dissolution of the substrate, and the temperature of the reaction.

Building blocks from sugars. Part 23. Hydrophilic 3-pyridinols from fructose and isomaltulose☆

Abstract Brief exposure to bromine in water-methanol at 0°C smoothly and effectively converts furfurylamines with hydroxymethy ( 5 ) or glucosyloxymethyl substituents ( 16 ) into the respective 6-substituted 3-pyridinols 9 and 19 , whereas the N -methyl-furfurylamines 10 and 17 elaborate the N -methyl-pyridinium betaines 13 and 22 . Combination of this multistep one-pot reaction with the large scale-feasible generation of hydroxymethylfurfural ( 4 ) from D-fructose and its O -glucosyl analog 15 from isomaltulose, together with their ready conversion into furfurylamines by reductive amination, opens up a preparatively satisfactory, 3-step “reaction channel” from inexpensive sugars to hydrophilic 3-pyridinols, of interest as intermediate chemicals for drugs of the pyridostigmine type and agrochemicals.

A convergent total synthesis of (−)-anamarine from D-glucose

The di-acetonide of 6-deoxy-aldehydo-D-glucose 12 and (S,S)-2-ethoxy-6-triphenylphosphoniomethyl-dihydropyran iodide 8 are elaborated from D-glucose each in practicable procedures of 5 and 10 steps, resp., and subsequently joined to give, after oxidation, deprotection and acetylation, (−)-anamarine (ent-1). The synthesis proves the absolute configuration of natural (+)-anamarine (1).