D-Mannofuranose

Fig. 3.—A. Initial Slope Approximation to Determine the Initial, Nonselective, Spin-Lattice Relaxation Rate of H-S of 2,3 S,6-Di-0-isopropylidene-a-D-mannofuranose (2) in Me2SO-d Solution. (Points between 0.01 and l.SS s were selected for tracing the best straight line.) B. The Same as in A for H-1 of a Partially Deuterated Sample of 1,6-Anhydro- -cellobiose Hexaacetate (3). [Note that the relaxation of H-1 is strongly dependent on the choice of I value. An R (ns) value of 0.24s was obtained from the data points 0 t 5s, where a value of 0.18 s was obtained from the terminal decay 5 lOs (see text).]...

C6H1206 Ca2+ Cl2 4 H20 yS-D-Mannofuranose calcium chloride, tetrahydrate MANCAC 30 465... 

For 2,3 5,6-di-O-isopropylidene-a-D-mannofuranose (183), separation of the anomeric products (184 and 185) was possible,135 and their structures were elucidated by periodate-oxidation studies. The configurational assignment for these products was based on the greater value of the specific rotation for the a anomer, as compared with that of the j3 anomer. The higher chromatographic mobility of one of the... 

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). 

Optically active dihydrooxazines 230 are produced by the reaction of the chiral a-chloronitroso compound 228 derived from D-mannofuranose with a variety of 1,3-dienes in the presence of ethanol at low temperatures via the primary adducts 229 (equation 122). Penta-1,3-diene, for instance, yields a mixture of the regioisomers 231 and 232113. 

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... 

As a matter of fact the high value of A in the equilibrium solution (344.4) is a sign that a very large proportion of D-mannofuranoses is present in this connection it must be borne in mind that the cis as well as the trans modification has in this case two favorably situated adjacent hydroxyl groups attached to carbon atoms 2 and 3. Since a-(trans)-T>-mannose has not been examined, no further conclusions can be drawn. 

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]. 

Examples of sugar homologation based on the use of 2-lithio-l,3-dithiane (2-LDT, 13) are surprisingly rare relative to the popularity of this reagent [25]. Stereoselective chain extension of a partially protected hexose, 2,3 5,6-di-0-isopropylidene-ot-D-mannofuranose (14), into a D-glycem-D-galacto-heptose derivative (16) was reported by Paulsen and his coworkers several years ago [26] (Scheme 5). 

The fragmentation of l,2 5,6-di-0-isopropylidene-a-D-gIucofuranose (29) or 2,3 5,6-di-0-isopropylidene-D-mannofuranose starts with cleavage of the bond between C-4 and C-5. 

Fig. 5.6 illustrates that D-ribose equilibrates in a- and -pyranoses and furanoses when dissolved in water [132 b]. High-field 13CNMR also detected 0.6% a- and 0.3% /1-D-mannofuranose in aqueous D-mannose solution [132 c]. 

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... 

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