Sugars unsaturated, synthesis

Synthesis and Reactions of Unsaturated Sugars 6-Deoxyhex-5-enose and 5-Deoxypent-4-enose Derivatives... 

The general approach has been followed for the de novo synthesis of a multitude of differently substituted, unsaturated [112,113] or regiospedfically labeled sugars [102,114]. Unusual branched-chain (42), (43)) and spiro-annulated sugars (45), (46)) have been synthesized from the corresponding aldehyde precursors... 

Intramolecular cycloaddition between an azide and an unsaturated ester (see 300) was the key step in the synthesis of triazole carboxylic acids 302 a, b, prospective anionic sugar mimics (Eq. 33) [79]. 

A. P. Rauter, J. A. Figueiredo, I. Ismael, T. Canda, J. Font, and M. Figueiredo, Efficient synthesis of a,/ -unsaturated /-lactones linked to sugars, Tetrahedron Asym., 12(2001) 1131-1146. 

Lespieau, R., Synthesis of Hexitols and Pentitols from Unsaturated Poly-hydric Alcohols, II, 107-118 Levi, Irving, and Purves, Clifford B., The Structure and Configuration of Sucrose (oipta-D-Glucopyranosyl beta-D-Fructofuranoside), IV, 1-35 Liggett, R. W., and Deitz, Victor R., Color and Turbidity of Sugar Products, IX, 247-284... 

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... 

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

Rauter s group exploited the synthesis of sugar derived bicyclic butenolides ( e.g. 140, Fig. 44),60 which possess cytotoxic and antitumor activities. The key structural feature of such compounds consists of the presence of the a,(3-unsaturated lactone, which allows them to act as Michael acceptors for the addition of enzymes nucleophiles. 

Carbohydrates.—The acid (87), an intermediate in the synthesis of oxaprostaglandin derivatives from D-ribofuranose sugars,84 is obtained from the aldehyde (88) and the sodium salt of (79). The condensation of 2,5-anhydro-D-allose derivatives with (89) gave the expected products (90).85 Similarly, 1,4-furanoses (91) afford (92).86 These unsaturated halides are useful intermediates for further modifications. 

Inverse type hetero-Diels-Alder reactions between p-acyloxy-a-phenylthio substituted a, p-unsaturated cabonyl compounds as 1-oxa-1,3-dienes, enol ethers, a-alkoxy acrylates, and styrenes, respectively, as hetero-dienophiles result in an efficient one step synthesis of highly functionalized 3,4-dihydro-2H-pyrans (hex-4-enopyranosides). These compounds are diastereospecifically transformed into deoxy and amino-deoxy sugars such as the antibiotic ramulosin, in pyridines having a variety of electron donating substituents, in the important 3-deoxy-2-gly-culosonates, in precursors for macrolide synthesis, and in C.-aryl-glucopyranosides. 

Aiming at the pyranose form of sugars, normal type hetero-Diels-Alder reactions were extensively used for the synthesis of functionally substituted dihydropyran and tetrahydropyran systems (5-10) (see routes A - D in the general Scheme 1) which are also important targets in the "Chiron approach" to natural product syntheses (2.) Hetero-Diels-Alder reactions with inverse electron demand such as a, p-unsaturated carbonyl compounds (l-oxa-1,3-dienes) as heterodienes and enol ethers as hetero-dienophiles, are an attractive route for the synthesis of 3,4-dihydro-2H-pyrans (11). 

Our interest in the synthesis of deoxy- and deoxy-amino sugars of the L-series originates from studies (1 ) on the products obtained by the action of fermenting baker s yeasts on such aromatic, a,/9-unsaturated aldehydes as cinnamaldehyde (la) and a-methylcinnamaldehyde (lb ). The transformation proceeds as indicated in Eq. 

Sugar-derived a,(3-unsaturated lactones are relevant motifs considering their ability to act as functionalized substrates for a variety of transformations. Some of them are bioactive [218-222]. An early synthesis of the enantiomer of (+)-altholactone, a natural product with cytotoxic and antitumor activities (for a review on the bioactivity of styryUactones see [223, 224]), involves the preparation of a furanose-fused a,p-unsaturated 8-lactone intermediate 189 [225]. Starting from a a-D-xy/o-pentodialdofuranose derivative 187, aReformatsky reaction with ethyl bromoacetate introduces the carboxyhc side chain necessary for intramolecular lactonization (Scheme 46). 

During the past decade, there has been intense activity in the study of the synthesis and reactions of carbohydrate derivatives containing a carbon-carbon double bond in the sugar chain. Ferrier107 has summarized the status of knowledge in this area, up to 1969, in earlier Volumes of this Series. A wide variety of rare and modified sugars can be synthesized by way of addition reactions to unsaturated sugars ... 

This conversion of readily available 2-furyl alcohols into unsaturated pyranosuloses proved a very effective route to racemic monosaccharides, through stepwise, selective functionalization of the enone grouping in 325. The shortest synthesis of a natural compound by following this scheme involves palladium-catalyzed hydrogenation of the aldosulose (325, R = Me) obtained from l-(2-furyl)ethanol, resulting209 in cinerulose A, the sugar component of the antibiotic cine-rubin. 

Synthesis of the cyclic acetal 25 in 63% yield by reaction of the unsaturated bromo-nitrilo sugar 24 (E configuration) with ethylene glycol in the presence of sodium hydroxide has been reported.40 An extension of this work was given for sugars having a vicinal diol... 

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