Mannofuranose synthesis

Szarek et al. were the first to develop this mode of glycosylation, which was demonstrated for ribonudeoside synthesis. In the reaction, a protected mannofuranose... 

Similarly, starting from 2,3 5,6-di-0-isopropylidene-D-mannofuranose 72, a one-pot procedure that implies the synthesis of glycosyl sulfones by Horner-Wadsworth-Emmons olefination with phosphonate 73, followed by subsequent Michael addition and Ramberg-Backlund reaction92 gives compound 74 in 78% yield93 (Scheme 24). 

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>. 

An asymmetric synthesis of aminocyclopentitols 134-137 has been used in the synthesis of trehazolin via free-radical cycloisomerization of enantiomerically pure, alkyne-tethered oxime ethers derived from D-mannose (Scheme 17).84 Treatment of 2,3 5,6-di-(9-isopropylidene-D-mannofuranose (128)85 with ethynylmagnesium bromide gave compound 129, which underwent sequential one-pot acid hydrolysis plus diol cleavage to give 130, oximation of which afforded the radical precursor 131, in 41% overall yield from 129. The free hydroxyl group of 131 was protected as acetate 132 and tert-butyldimethylsilyl ether 133, which were isolated as inseparable... 

A common procedure for the efficient synthesis of 1,6-anhydrofuranoses is based on cycliza-tion of the 6-O-tosyl derivative of furanose with the free anomeric position and protected hydroxyl function at the C-5 position. Synthesis of 1,6-anhydro-D-mannofuranose is a good example of such a strategy (O Scheme 10) [22]. 

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). 

Synthesis from o-mannose A total synthesis of D-(- -)-biotin (1) from D-mannose has also been reported (Scheme Treatment of 2,3 5,6-di-0-isopropylidene-a-D-mannofuranose (17) with benzoyl chloride followed by selective hydrolysis of the terminal acetal group afforded 1-0-benzoyl-2,3-0-isopropylidene-a-D-mannofuranose (18). Subsequent periodate oxidation and chain extension with the proper phosphorane followed by hydrogenation gave the uronate derivative 19. Treatment of 19 with NaOCHs followed by reduction of the resulting aldehyde with sodium borohydride afforded compound 20. 

Bock, K. Pedersen, C. Reaction of sugar esters with hydrogen fluoride. X. Derivatives of D-glucofuranose and D-mannofuranose. Acta Chem. Scand. 1972, 26, 2360-2366. Ajmera, S. Bapat, A.R. Stephanian, E. Danenherg, P.V. Synthesis and interaction with uridine phosphorylase of 5 -deoxy-4, 5-difluorouridine, a new prodrug of 5-fluorouracyl. J. Med. Chem. 1988, 31, 1094-1098. 

A new synthesis of glycosyl azides has been reported which involves sequential treatment of an aldose, in which all hydroxy-groups other than that at C-1 are blocked (acetals or ethers), with HMPT and mesityleneoxytris(dimethylamino)-phosphonium azide. The glycosyl azides are usually formed in overall yields of 65-80% yields and the 1,2-cw-isomers are formed exclusively. The method has been applied successfully to 2,3 5,6-di-O-isopropylidene-D-mannofuranose and its a//o-isomer, 2,3-0-isopropylidene-5-0-trityl-D-ribofuranose, 2,3 4,6-di-(9-benzylidene-D-mannopyranose, and 2,3,5-tri-O-benzyl-D-arabinofuranose. The products are useful for the synthesis of nucleoside analogues. 

Periodate oxidation of l-0-benzoyl-2,3-0-isopropylidene-a-D-mannofuranose has afforded access to several derivatives of D-lyxuronic acid, and glyco-furanosyl halides of D-riburonic acid, which are of value in nucleoside synthesis, have been made by way of the corresponding thiofuranosides (see Chapter 7). 

The first asymetric synthesis of (+)-biotin (Scheme 30) was reported by Ohrui and Emoto 68). The starting material was diacetone mannose (2,3 5,6-di-O-isopropylidene mannofuranose), (116). Although... 

A synthetic approach towards goniobutenolides A and B 63 and 64 from 2,3 S,6-di-0-isopropylidene-D-mannofuranose was thwarted by decomposition accompanying attempted deacylation of 60 and 61. The synthesis was completed altonatively by dehydration of the known triol butenotide 62 which provided a mixture of the isomoric natural products (Scheme 16). 

Full details of the synthesis of adenine and imidazole nucleosides of d-mannofuranose from 2,3 5,6-di-O-isopropylidene-D-mannofuranosylamine have now appeared (see Vol. 11, p. 171). The same group has also synthesized the arabinofuranosyl 5-aminoimidazole-4-carboxylate (14) by condensation of 2,3,5-tri-O-benzyl a-D-arafemo-furanosyl chloride with the parent base followed by hydrogenation. 1,3-Dipolar cycloaddition of glycosyl azides to 1,4-naphthoquinone or 2-methyl-1,4-benzoquinone gave the nucleosides (15), (16), and (17), which were shown to exhibit some cytostatic activity... 

The synthesis of the 2,5-disubstituted pyrrolidine 43 from D-mannitol by standard chemistry and the synthesis of pyrrolidines 44 by addition of azomethine ylides to vinylene carbonate " as well as the synthesis of the imino-heptitol 45 from 2,3 5,6-di-0-isopropylidene-a-D-mannofuranose have been reported. 

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. 

Mootoo and his team devised a fairly short synthesis of (—)-swainsonine (378) from the acetal-protected mannofuranose derivative 593 (Scheme 80). " ... 

The leaving group properties of sulfonate groups were first exploited in p-manno-side synthesis by Perlin [94, 95]. In the first step of this approach mannofuranose 18 is treated with Tf20 to afford the anomeric triflate 19. This is converted in situ to the bromide 20 by Bu4NBr. Subsequent addition of MeOH led to a 2 3 mixture of the methyl a- and p-mannosides 21 without heavy metal promoters (Scheme 7). 

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