Ekenstein transformation

Angyal SJ (2001) The Lobry de Bruyn-Alberda van Ekenstein Transformation and Related Reactions. 215 1-14... 

Albrecht M (2004) Supramolecular Templating in the Formation of Helicates. 248 105-139 Ando T, Inomata S-I, Yamamoto M (2004) Lepidopteran Sex Pheromones. 239 51-96 Angyal SJ (2001) The Lobry de Bruyn-Alberda van Ekenstein Transformation and Related Reactions. 215 1-14... 

Aldoses generally undergo benzilic acid-type rearrangements to produce saccharinic acids, as well as reverse aldol (retro-aldol) reactions with j3-elimination, to afford a-dicarbonyl compounds. The products of these reactions are in considerable evidence at elevated temperatures. The conversions of ketoses and alduronic acids, however, are also of definite interest and will be emphasized as well. Furthermore, aldoses undergo anomerization and aldose-ketose isomerization (the Lobry de Bruyn-Alberda van Ekenstein transformation ) in aqueous base. However, both of these isomerizations are more appropriately studied at room temperature, and will be considered only in the context of other mechanisms. 

The reaction of carbohydrates in alkaline or acidic aqueous solutions results in a myriad of products, many of which have been recognized for well over a century. The number of identified products has greatly increased in recent years, owing to the development of sophisticated techniques for separation and identification. With the exception of anhydro sugars and oligosaccharides, found as concentration-dependent, equilibrium constituents (reversion products) in acidic solutions, all of the products result from reactions of intermediates present in the Lobry de Bruyn-Alberda van Ekenstein transformation. 

These enzymes vary widely in secondary and tertiary structure.1273 Mannose-6-phosphate isomerase is a 45 kDa Zn2+-containing monomer. The larger 65 kDa L-fucose isomerase, which also acts on D-arabinose, is a hexameric Mn2+-dependent enzyme.1273 L-Arabinose isomerase of E. coli, which interconverts arabinose and L-ribulose, is a hexamer of 60-kDa subunits128 while the D-xylose isomerase of Streptomyces is a tetramer of 43-kDa subunits.129 The nonenzymatic counterpart of the isomerization catalyzed by the enzyme is the base-catalyzed Lobry deBruyn-Alberda van Ekenstein transformation (Eq. 13-25).130... 

Lobry de Bruyn-Alberda van Ekenstein transformation 693 Lock and key theory 478 Log phase of growth 470 Lon protease 628 Loricin 439... 

Speck, John C., Jr., The Lobry de Bruyn-Alberda van Ekenstein Transformation, 13, 63-103 Spedding, H., Infrared Spectroscopy and Carbohydrate Chemistry, 19, 23-49 Sprinson, D. B., The Biosynthesis of Aromatic Compounds from d-G1u-cose, 16, 235-270... 

The complex reactions of alkalies with reducing sugars have been described extensively. The origin of the initial products that are obtained is usually explained by the classical Lobry de Bruyn and Alberda van Ekenstein transformation,80 in which an enediol (XLVI) is proposed as the key intermediate. In recent studies Sowden and Schaffer61 used D-glucose-l-C14, D-fructose-l-C14, and D-glucose in D20 to... 

It has been postulated (37) that lactulose is formed from lactose by the Lobry de Bruyn and Alberda van Ekenstein transformation, whereby glucose is isomerized to fructose via an enol intermediate. In turn, two mechanisms have been proposed for the degradation of this intermediate (38)- One involves the addition of a proton to the enediol resulting in epimeric aldoses and the original ketose, while the other involves 8-elimination to yield galactose and saccharinic acids. The authors experimental data would tend to better support the second pathway. 

The synthesis of D-psicose as a colorless sirup ([< ]% + 3.1° in water) by Steiger and Reichstein13 may be regarded as the first authentic preparation of this ketohexose. The Kiliani-Fischer cyanohydrin synthesis furnished D-allonic lactone (VII) from D-ribose. This lactone, on reduction with sodium amalgam, gave D-allose (VIII) which was transformed into D-psicose (I) by refluxing with pyridine. Pyridine had been introduced into the Lobry de Bruyn-Van Ekenstein reaction by Fischer, Danilov and their coworkers.13 ... 

In 1895 Dull,9 who was studying inulin and its products of hydrolysis, found that when either fructose or sorbose was treated with an aqueous solution of oxalic acid under pressure, a substance was obtained which had the formula CeHeOa and resembled furfural in its properties. This substance was further investigated by Kiermayer4 who found that fructose and sucrose were the best sources when they were heated with 0.3% aqueous oxalic acid at 120°. It was however only the fructose portion of the sucrose molecule which was transformed since the glucose moiety was recovered unchanged. Kiermayer prepared several derivatives of CeH Os and from its reactions concluded that its structure was probably /3-hydroxy-S-methylfurfural (III). Van Ekenstein and... 

Lipoaldehydes, II, 123 Lipositol, III, 47, 343 Lithium aluminum hydride, for hydrogenation of 1,2-epoxides, V, 22 Lithium chloride, influence upon the activity of pancreatic amylase, V, 237 Lithium hypochlorite, III, 137 Liver, fat conversion by isolated, II, 141 ketogenesis in isolated, II, 155 Lobry de Bruyn-Alberda van Ekenstein transformation, III, 113 Locust bean mucilage, IV, 267 Lucerne seed, emulsins, V, 63 Lucerne seed, mucilage, IV, 266, 267 Lupinus albus, galactan from seed of, II, 248... 

In weakly alkaline solutions aldoses and ketoses undergo rearrangements. An example is the Lobry de Bruyn -Alberda van Ekenstein transformation of... 

Fig. 2-32. Lobry de Bruyn-Alberda van Ekenstein transformation of sugars. 1, D-Glucose 2, 1,2-enediol 3, D-mannose 4, D-fructose 5, 2,3-enediol 6, D-allulose.

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