A-D-Mannopyranoside, methyl 4-

Because of this situation, the prospect of synthesizing D-rhamnosyl cardenolides containing the unnatural, a-D-linkage was investigated. D-Rhamnose has not been reported to occur naturally, but it has been synthesized by Hudson and co-workers (4) in six steps, starting with methyl a-D-mannopyranoside. An intermediate in the synthesis is methyl... 

Methyl a-D-mannopyranoside was treated in succession with p-toluene-sulfonyl chloride, carbonyl chloride, and benzoyl chloride, and, without isolating the intermediates, there was obtained in 37% yield methyl 4-0-l enzoyl-2,3-O-carbony 1-6-0-(p-tolylsulfonyl ) -D-mannoside. The tos-yloxyl group of the latter was replaced by iodine, and hydrogenation of the 6-iodo derivative in the presence of a nickel boride catalyst gave methyl 4-0-benzoyl-2,3-0-carbonyl-6-deoxy- -D-mannoside. Treatment of the latter with hydrogen bromide in acetic acid gave crystalline 4-0-benzoyl-2,3-0-carbonyl-6-deoxy-a-D-mannosyl bromide (8) (16). The... 

A mixture of d- and l- hexoses also results from the hydroboration of these 5-enes. Hydroboration results in anti-Markownikoff, cw-hydration of the double bond and the amount of each hexose formed varies according to the nature of the substituent groups. For example, hydroboration (23) of methyl 6-deoxy-a-D-ryZo-hex-5-enopyranose (3) affords methyl a-D-glucopyranoside and methyl / -L-idopyranoside in the ratio of 1 2.5 respectively whereas hydroboration of the fris-trimethylsilyl ether of 3 afforded them in the ratio 1 0.6 respectively. The hydroboration method can be used to achieve specific labelling of hexoses with tritium methyl-/ -L-idopyranoside[5-H3] and methyl a-D-glucopyranoside [5-H3] were thus prepared (23). Similarly, hydroboration of the D-Zt/ro-hex-5-eno derivative (14) with diborane-H3 followed by removal of the isopropyli-dene group, afforded methyl a-D-mannopyranoside [5-H3] and methyl / -L-gulopyranoside [5-H3] in the ratio of 1 2 respectively (23). 

To distinguish between these possibilities, Birch and Mylvaganam studied the effect of the sweetness of sucrose and the bitter-sweetness of methyl a-D-mannopyranoside on the bitterness of quinine sulfate, and the effect of the bitterness of quinine sulfate and methyl a-D-mannopyranoside on the sweetness of sucrose. A significantly diminished sweetness-response... 

Thermal phosphitylation of methyl a-D-mannopyranoside (3) with P(NMe2)3 in pyridine or tetramethylurea gave 40% of a-methyl-D-mannopyranoside - 2,3,6-bicyclophosphite (4a). It underwent acetylation giving the corresponding acetate 4b sulfuration, and selenation afforded the corresponding pentavalent thio (4c) and seleno (4d) derivatives, respectively (Scheme 2). The trivalent acetate 4b was found to react with CuBr, Rh(CO)2(acac) and Cl2 [17]. 

The results of a study of the di- and tri-molar methanesulfonylation of methyl a-D-galactopyranoside suggested, amongst the secondary hydroxyl groups, a reactivity order of HO-2 > HO-3 > HO-4, and, from the latter reaction, the 2,3,6-triester could be isolated in 30% yield a similar reaction of methyl a-D-mannopyranoside gave the... 

Additional evidence was provided by Hockett, Dienes and Ramsden,29 who compared the rates of oxidation with lead tetraacetate of styracitol and methyl a-D-mannopyranoside, and also of polygalitol and methyl... 

Fig. 21.—Partial 13C-N.m.r. Spectrum of the Rhamnomannan (16) of Sporothrix schenckii, with Shift Comparisons with Signals of Methyl a-D-Mannopyranoside (Lower Inset Lines) and Methyl a-L-Rhamnopyranoside (Upper Inset Lines). (Solvent, D20 temperature, 33° chemical shifts expressed as 8C, relative to external tetramethyl-silane.)...

Starting with methyl a-D-mannopyranoside there is ready access to the 2,3-0-isopropylidene rhamnoside Treatment of in dichloromethane with DBE and zinc bromide for 5 5 hours at room temperature gives the 2,3-... 

In 1985, Vasella and co-workers provided an efficient synthesis of COTC ((4R,5R,6R)-2-crotonyloxymethyl-4,5,6-trihydroxycyclohex-2-enone 52), a gly-oxalase I inhibitor.Methyl a-D-mannopyranoside was transformed in three synthetic steps into the protected all cis-trihydroxycyclohex-2-enone 163 (34 %, overall) which was then transformed into COTC (52) in four steps. Thus, transformations of our "naked sugar" 32 to 137 — 138 — 163 realize a total, asymmetric synthesis of COTC. Another total synthesis of this natural compound has been reported recently by Koizumi and co-workers, as mentioned earlier. 

A. C. Richardson and J. M. Williams, Selective acylation of pyranosides II. Benzoylation of methyl 6-deoxy-a-D-galactopyranoside and methyl a-D-mannopyranoside, Tetrahedron, 23 (1967) 1641-1646. 

S. Signorella, M. I. Frascaroli, S. Garcia, M. Santoro, J. C. Gonzalez, C. Palopoli, V. Daier, N. Casado, and L. F. Sala, Kinetics and mechanism of the chromium(VI) oxidation of methyl-a-glucopyranoside and methyl-a-D-mannopyranoside,./. Chem. Soc. Dalton Trans. (2000) 1617-1623. 

The reaction of methyl a-D-mannopyranoside with sulfuryl chloride gave methyl 6-chloro-6-deoxy-a-D-mannopyranoside 2,3,4-tri(chloro-sulfate) even treatment of the product with pyridinium chloride for 12 hours at 50° did not effect further substitution.25 In this case, the lack of displacement of the chlorosulfonyloxy group at C-4 is attributed to the presence of an axial group at C-2. In the (hypothetical) transition state 13 (viewed along the C-4-C-3 bond), there would be... 

Several 0-aminoacyl sugars were prepared to study a relationship between taste and chemical structure. Methyl a-D-glucopyranoside, methyl a-D-galactopyranoside and methyl a-D-mannopyranoside were selected as sugar skeletons. As basic amino acids, esters of lysine, ornithine, a,Y-diaminobutyric acid, and a,p-diaminopropionic acid were introduced into 2-0-, 3-0-, and 4-0- positions of sugars leaving only 6-hydroxyl group free. The results of sensory analysis are list in Table VI. O-... 

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