Sugar aza sugars

Streith J., Defoin A. Aza Sugar Syntheses and Multi-Step Cascade Rearrangements Via Hetero Diels-Alder Cycloadditions With Nitroso Dienophiles Synlett 1996 189-200... 

Because activated 4-0-trimethylsilylated-2, 3, 5 -0-acyluridines such as 3 are also obtained as reactive intermediates in the Friedel-Crafts-catalyzed silyl-Hilbert-Johnson reaction [59, 59 a] of persilylated uracils or 6-azauracils such as 227 with sugars such as l-0-acetyl-2,3,5-tri-0-benzoyl-/9-D-ribofuranose 228 in the presence of SnCl4, treatment of the reactive intermediate 229 with a large excess of pyrrolidine neutralizes the SnCLi. used and aminates 229 to afford the protected 6-aza-cytidine 230, although in 57% yield only [49, 59] (Scheme 4.20). 

Aqueous aza-Diels-Alder reactions of chiral aldehydes, prepared from carbohydrates and with benzylamine hydrochloride and cyclopentadiene, were promoted by lanthanide triflates (Eq. 12.65).137 The nitrogen-containing heterocyclic products were further transformed into aza sugars, which are potential inhibitors against glycoprocessing enzymes. 

Recent research deals with stereoselective 1,3-dipolar cycloadditions of nitrones for the syntheses of alkaloids and aza heterocycles asymmetric synthesis of biologically active compounds such as glycosidase inhibitors, sugar mimetics, /3-lactams, and amino acids synthesis of peptido-mimetics and peptides chemistry of spirocyclopropane heterocycles synthesis of organic materials for molecular recognition and photochemical applications. 

The 1,3-dipolar cycloaddition. The interesting approach to aza-disaccharides in which the aza-part is linked to normal sugar was proposed by Martin.7 The sugar nitrone 1 reacted with 5-O-allyl-galactofuranoside to afford adduct 2 (Fig. 1). 

A simple synthesis of a 7-membered aza sugar from the unsaturated aldehyde 4 was proposed by Moutel.8 The same aldehyde 4 was used in the synthesis of modified aza sugars such as 5 (Fig. 2) 9 An interesting approach to polyhydroxylated 7-membered branched aza sugars (e.g. 8) was proposed by Estevez.10 Nitro sugar 6 underwent the... 

Synthesis of bicyclic aza sugars from D-xylose was reported. A key step involved reaction of the nitrone 9 with ethyl acrylate providing intermediate 10, which was finally converted into aza sugars (Fig. 4).11... 

The 1,3-dipolar cycloaddition of nitrone 12 (derived from D-glucose) was also used for the preparation of bicyclic aza sugars of type 14 (route a Fig. 5).12 Another classical approach (route b) allowed to prepare the analogs (e.g. 17).13,14... 

Fig. 5 Dipolar cycloaddition route towards bicyclic aza sugars.

Interesting structural variation of target aza sugars was initiated from compound 18, readily available in a few standard steps from methyl glucoside (Fig. 6).15... 

A-allylamine 23 (obtained by standard transformations of 6-iodogluco-side 22) underwent cyclization into the monocycle 24. However, when the amine was in situ protected as a Boc derivative it could be subjected to the RCM process. The products were further converted into the bicyclic aza sugar 26.19 A similar approach to eight-membered ring aza sugars was recently reported (Fig. 9).20... 

Fig. 9 Application of RCM in the synthesis of eight-membered ring aza sugars.

Fig. 12 Synthesis of a simple aza sugar based on mercuration of its unsaturated precursor.

Similar derivatives (formally being C-disaccharides with the normal and aza sugar rings) were prepared by Vogel (Fig. 37).52... 

Application of simple sugars as starting materials for the preparation of optically pure complex products represents nowadays the classic methodology of organic synthesis it is covered by many comprehensive reviews, cited here only in references.88 These references provide the precise state-of-art in the synthesis of aza sugars, carbasugars and other derivatives. 

In a similar fashion it should be a relatively simple task to relate the well-known D-gala-L-manno-heptose (XX) to a-rhamnohexose (XXII)81 through the known 1-desoxy-D-gala-L-mcmno-heptitol (syn., 7-desoxy-L-manno-L- aZa-heptitol) (XXI).81 In. this particular case, however, there is already ample proof of the configuration of the latter sugar (XXII) because nitric acid has been found to oxidize the corresponding aldonic acid to mucic acid.82... 

There are three main types of CDs a-cyclodextrin (a-CD), -cyclodexlrin (p-CD), and y-cyclodextrin (y-CD), which are macrocycles formed by six, seven, and eight sugar ring molecules, respectively. The spatial structure of p-CD is shown on Fig. 3. Review [19] generalizes data on the synthesis, modification, physicochemical and theoretical investigations of CDs, and certain applications particularly for enantio-separation and pharmaceutical applications. CDs are able to form host-guest complexes (pseudorotaxanes) with hydrophobic molecules such as aza-dyes... 

DHAP-Dependent Aldolases in the Core of Aza Sugar Synthesis... 

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