Lobry de Bruyn-van Ekenstein transformation

Scheme 5.2 Lobry de Bruyn-van Ekenstein transformation of D-glucose.

MPa H2. To suppress the isomerization of D-glucose to D-mannose and D-fructose (Lobry de Bruyn-van Ekenstein transformation) (Scheme 5.2) and the Cannizzaro reaction, which were both promoted in an alkaline medium, the pH value was maintained between 5.5 and 6.5. Under the conditions that were optimized to minimize the side reactions, the formation of gluconic acid and mannitol was reduced to less than 1% each at 99.5-99.6% conversion, while with a normal nonpromoted Raney Ni 1.5-2.1% of gluconic acid and 1.3-1.9% of mannitol were formed at 99.5-99.7% conversion. 

Lobry de Bruyn-van Ekenstein transformation. Isomerization of carbohydrates in alkaline media, considered to embrace both epimerization of aldoses and ketoses and aldose-ke-tose interconversion. 

This reaction is related to the Lobry de Bruyn-van Ekenstein transformation of aldoses involving the rearrangement of A-alkylamino-D-glucopyranosides into 1-alkylamino-l-deoxy-D-fructoses. ... 

This reaction was first reported by Lobry de Bruyn in 1895, and explored extensively by Lobry de Bruyn and Alberda van Ekenstein. It is the reciprocal interconversion of carbohydrates into their isomers in an alkaline solution through the enediolic intermediate. The name of reaction given here is probably the only one time the full name of the people who discovered such reaction. It is known as the Lobry de Bruyn-Alberda van Ekenstein rearrangement, Lobry de Bruyn-Alberda van Ekenstein transformation, Lobry de Bruyn-Albreda van Ekenstein C-2 epimerization, or Lobry de Bruyn-van Ekenstein transformation. ... 

The former base-catalyzed aldose-ketose isomerization is named the Lobry de Bruyn-van Ekenstein transformation (Scheme 6.25). Deprotonation of the a-carbonyl carbon of aldose (glucose) requires a base, and results in the form of a series of enolate intermediates. Solid bases such as cation-exchanged zeolites and Mg-Al HT catalyze glucose isomerization in water [176-178]. 

Lobry de Bruyn-van Ekenstein Transformation Loftier (see Hofmann-Loffler-Freytag Reaction)... 

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 ... 

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. 

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... 

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