Carbohydrates carboxylic acids, preparation from

The reaction of type i is utilized for the preparation of a variety of dicarboxylic acids. Scheme 25 shows the synthesis of a C-disaccharide (73) from a carbohydrate carboxylic acid (72) [98]. 

The obvious approach for chiral synthesis would be to find a chiral starting material, such as a natural amino acid, carbohydrates, carboxylic acids or terpene. The major source of these chiral starting materials sometimes called chirons is nature itself. The synthesis of a complex enantiopure chemical compound from a readily available enantiopure substance such as natural amino acids is known as chiral pool synthesis. For example, chiral lithium amides 1.39 that are used for several types of enantioselective asymmetric syntheses can be prepared in both enantiomeric forms starting from the corresponding optically active amino acids, and these are often available commercially. 

Native and microcrystalline cellulose precoated plates are used in the life sciences for the separation of polar compounds (e.g. carbohydrates, carboxylic acids, amino acids, nucleic acid derivatives, phosphates, etc) [85]. These layers are unsuitable for the separation of compounds of low water solubility unless first modified, for example, by acetylation. Several chemically bonded layers have been described for the separation of enantiomers (section 10.5.3). Polyamide and polymeric ion-exchange resins are available in a low performance grade only for the preparation of laboratory-made layers [82]. Polyamide layers are useful for the reversed-phase separation and qualitative analysis of phenols, amino acid derivatives, heterocyclic nitrogen compounds, and carboxylic and sulfonic acids. Ion-exchange layers prepared from poly(ethyleneimine), functionalized poly(styrene-divinylbenzene) and diethylaminoethyl cellulose resins and powders and are used primarily for the separation of inorganic ions and biopolymers. 

Further acylations/selective acylations of carbohydrates are compiled in Table 3—11. The acylations are carried out either by using imidazolides prepared in situ from the carboxylic acid and CDI (method A), or by using the isolated carboxylic acid imidazolides (method B). 

Carboxylic Acids Obtained by Fermentation of Carbohydrates Lactic (2-hydroxy-propionic) acid obtained by fermentation of glucose and polysaccharides is used by NatureWorks (Cargill/Dow LLC) to prepare polylactide (PLA), a biodegradable or recyclable polymer with a potential production of 140000 t a-1 (Scheme 3.4) [23], This and other potential useful reactions from lactic acid have been reviewed by Datta and Henry [24],... 

Furoic acid (furan-2-carboxylic acid, or pyromucic acid) is used as a bactericide, and the furoate esters are used as flavoring agents, as antibiotic and corticosteroid intermediates. It is obtained by the enzymatic or chemical/catalytic aerobial oxidation of furfural (2-furalaldehyde) the latter is the only unsaturated large-volume organic chemical prepared from carbohydrates today. D-Xylose and L-ara-binose, the pentoses contained in the xylan-rich portion of hemicelluloses from agricultural and forestry wastes, under the conditions used for hydrolysis undergo dehydration to furfural. 

Radicals from Carboxylic Acids. Carboxy radicals appear to be involved in three venerable reactions in preparative carbohydrate chemistry, the Ruff degradation, the Hunsdiecker reaction and the Kolbe electrolysis. 

Pinitol has been prepared from a non-carbohydrate source by a Diels-Alder condensation of furan and trainj-l,2-bis-phenylsulfonyl ethylene and resolved using an intermediate camphanic acid ester. (+)-Cyclophellitol and its (1/ , 6S)-enantiomer have been prepared from a 7-oxabicyclo[2.2.1]hept-5-ene-2-e i/o-carboxylic acid. ... 

Smoking is a slow process and it is not easy to control the process. Smoke contains phenolic compounds, adds, and carbonyls and smoke flavor is primarily due to the volatile phenolic compound [10,20,34]. Wood smoke is extranely complex and more than 400 volatiles have been identified [43]. Guillen and Manzanos [26] identified around 140 compounds in liquid smoke prepared from Thymus vulgaris wood. Polycyclic aromatic hydrocarbons are ubiquitous in the environment as pyrolysis products of organic matter. Their concentrations in smoked food can reach levels hazardous for human health, especially when the smoking procedure is carried out under uncontrolled conditions [46]. Wood smoke contains nitrogen oxides, polycyclic aromatic hydrocarbons, phenolic compounds, furans, carbonylic compounds, aliphatic carboxylic acids, tar compounds, carbohydrates. 

However, it was originally prepared (over a century ago) from pentoses (five-carbon carbohydrates see Chapter 11), which, on sulfuric acid treatment, produce furfural (furan 2-carboxaldehyde) (Scheme 8.75), and which, in turn, can be easily oxidized to the corresponding carboxylic acid (2-furoic acid). The acid (2-furoic add) is then readily decarboxylated (i.e., loss of CO2) to furan (oxa-2,4-cyclopentadiene) and the resulting product is catalytically reduced with hydrogen (H2) (Scheme 8.102) over a Ni catalyst to yield the desired five-membered heterocyclic compound (oxalane, oxacyclopentane,THF). 

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