Mannofuranose preparation

Carbohydrate lactones have been used as the carbonyl reagent in the Reformatsky reaction. Thus, 2,3 5,6-di-O-cyclohexylidene-D-mannono-1,4-lactone [44, obtained by oxidation of the mannofuranose derivative (49)] reacted with ethyl bromoacetate and zinc to give the protected 2-deoxy-3-octulosonic acid ethyl ester (45a) in 69% yield (50). Ketonic hydrolysis with potassium hydroxide in aqueous methanol, followed by acidification and heating, afforded the 1-deoxyheptulose derivative 45b. Similarly, starting from compound 44, the 1-C-substituted allyl and propar-gyl lactols were prepared on reaction with allyl or propaigyl bromides in the presence of zinc (51). 

Vinyl glycosides are difficult to prepare by conventional vinylation procedures although it has been reported that 2,3 5,6-di-0-isopropyl-idene-D-mannofuranose with acetylene in the presence of potassium hydroxide afforded vinyl mannosides A much better transvinylation procedure was used by Fletcher and coworkers as shown in Scheme 12 to give mixed products which, after chromatographic separation, were converted to vinyl a- and p-D-glucopyranosides by treatment with sodium in liquid ammonia... 

The strategy for the synthesis of carba-hexofuranoses and -pentofuranoses is summarized in Scheme 16. Five new carbaanalogues of hexofuranoses were synthesized 74, 73 and the enantiomer a-L-mannofuranose, and the a-L and /3-D-glucofuranoses. The carba-analogues of the 5-deoxyhexofuranoses with a-L- and -D-lyxo-, and a-L-xyZo-configurations, which we have also prepared [98b], have recently been described, either with the same configuration, or as the enantiomeric compound, or as a racemic mixture [86]. Several of the hitherto known compounds were now obtained in a crystalline state... 

Two reports on the preparation of polyhydroxylated [13]thiazolo[3,2a]azepane derivatives have been published. The one reports the synthesis of the p-tum mimetic 22 from D-glucurono-3,6-lactone and L-cysteine <99TL477>, whilst the other describes, for example the preparation of 23 in 78% yield from 6-0-tosyl-23-0 isopropylidene-D-mannofuranose and 2-aminothioethanol <99S839>. 

The second example concerns the study of acetonation of o-mannose (see Scheme 8) and allows a clear distinction between the use of 2,2-dimethoxypropane and 2-methoxy-propene. Thus, whereas D-matmose gives 2,3 5,6-di-0-isopropylidene-D-mannofuranose 5 by reaction of the free sugar with acetone [5,6] as well as with 2,2-dimethoxypropane [96], the major compound (more than 85%) obtained with 2-methoxypropene is 4,6-0-isopropylidene-D-mannopyranose 6 [52]. Once again, a confirmation of the better stability of furanoid acetals in this series is given by the selective hydrolysis of the 2,3 4,6-di-O-isopropylidene-D-mannopyranose 7 (by-product of the preceding reaction or quantitatively obtained by action of 2-methoxypropene on acetal 6), witch gives the furanoid monoacetal 8. Actually, the pyranoid monoacetal 9 can be easily prepared as soon as the anomeric hydroxyl group is protected by acetylation [52]. 

Pyranoid examples have been prepared in all possible configurations altro,396,397 ido39 399 manno39S,40° and talo.185 396 From the furanose group, 2,6-anhydro-D-mannofuranose and its derivatives are known.366,401,402... 

Taylor s group also showed that the Horner-Wadsworth-Emmons (HWE)/conjugate-addi-tion sequence can be an efficient alternative to the thioetherification-oxidation reactions for the preparation of the required sulfones [59]. This was illustrated in the synthesis of the /3-(1 6)-mannofuranose-a-Glu C-dimer [60] (O Scheme 21). 

The (+ )-isomers were prepared from 2,3-0-isopropylidene-D-ribofuranose (179) as shown Scheme 20. A very similar route from 2,3-0-isopropylidene-D-mannofuranose (180) led to the (-)-isomers. The naturally occurring isomers [( + )-173 and (-)-174] having the (2i )-configuration tasted more fruity, the configuration at C-4 having litde influence on Ae taste. 

Jerkeman attempted to prepare c-mannofuranose pentaacetate by the acetolysis of 2,3 5,6-di-0-isopropylidene-D-mannofuranose. Deaeetylation... 

Mannojirimycin (1) and 1-deoxymannojirimycin (2) were prepared from 2,3 5,6-di-0-isopropylidene-a-D-mannofuranose (26) (Scheme 5). The oxime 27, prepared from 26, underwent reduction by hydrogenation in the presence of Raney nickel, and subsequent removal of the trityl group afforded the amines 28 and 29. Acid hydrolysis of 28 afforded 30 (21%), which was converted to 31 (28%) that upon treatment with Dowex 1 (OH ) resin afforded 1. On the other hand, hydrogenation of 28 gave 32, which upon removal of the... 

It is worth to note that P-acetoxy-a-diazoesters were also readily accessible through the reaction of monosaccharides in their hemiacetal form. However, such a reaction required the use of an equimolecular amount of diethylzinc creating likely very reactive zinc diazointermediates which react smoothly with aldehydes [l 02]. Applying this procedure KO and its 3-epimer were prepared, starting from 2,3 5,6-di-0-isopropylidene-D-mannofuranose [101]. 

K. Bock and C. Pedersen, Reaction of carbohydrates with hydrogen bromide. Preparation of some 6-deoxy-D-mannofuranoses, Acta Chem. Scand., B31 (1977) 248-250. 

Details of the synthesis and reactions of glycofuranosylethynes, prepared via the reaction of 2,3 5,6-di-0-isopropylidene-a-D-mannofuranose with ethynyl magnesium bromide, have been published (see Vol. 8, p. 27). It is noteworthy that the glycofuranosylethynes do not obey Hudson s rules of isorotation. 

The phosphitylation of D-mannose with phosphorous triazolides has afforded primarily the mannofuranose 2,3,6-O-phosphite 12. The complexes formed separately between o-fructose and L-sorbose with 1,10-phenanthroline and Co(III) ions have been characterised, while composites prepared by the reaction of simple sugars with tetraethoxysilane and water have been shown to be capable of resolving racemic cobalt and chromium ion complexes. Sodium alkoxide salts of free sugars have been treated with ferric chloride to give iron-sugar complexes and five-fold deprotonated D-mannose forms dinuclear metalates [X2(P-D-Man-/)2] of trivalent (X = Fe, V, Cr and Al) with O-1,2,3,5 and 6 involved in complexation. ... 

C-Hydroxymethyl-2,3 5,6-di-O-isopropylidene-D-mannofuranose has been converted conventionally to 6-deoxy-2-C-methyl-D-mannitol (21) and 2-C-hydroxymethyl-D-mannitol (22) as potentially sweet compounds but neither were sweeter than sucrose. The related branched-chain mannitols (23) have also been prepared as potential asymmetric ligands for lithium aluminium hydride reagents, but these only show-... 

Guijar et al. converted a C-allyl glycoside to a CAA by hydroxylation of the double bond followed by Jones oxidation [38]. An acid ftmction was also introduced by reacting the free anomeric center with methyl(triphenylphosphor-anylidene) acetate in a Wittig reaction and followed by conversion to a C-glycoside by intramolecular Michael addition, cf. Scheme 5 for the preparation of 36 from 2,3 5,6-di-O-isopropylidene-D-mannofuranose (34) [6]. A disadvantage of this... 

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