A-o-Mannosides

Hydrolyzes the /3-1-4 glycosidic bond between /V-acetylglucosamine and A-acetylmuraminic acid units in mucopolysaccharides Hydrolyzes a-o-mannosides by removing a-D mannose from the nonreducing end... 

In the field of sugar chemistry Foster and co-workers5 0 have found that diethylmngneeiiim adds to Cia) of methyl 4,6-0-ben2ylidene-2,3-anhydro-a-o-mannoside (Eq. 797), and Richards145 has observed C attack with methyl 4,6-0-benzylidene-2r3-anhydro- -l>-aUo6jde and diphenylmagncsi um (Eq. 798). 

Fig. 13.—A Agar diffusion of immune sera (Se), 1-thio-D-mannose antibodies (A ), and anti-BSA antibodies (A2) against Man-S-BSA (/) and BSA (2). B Agar-diffusion plate of anti-Man-S-antibodies and antibodies oxidized by peroxypropanoic acid for 0, 4, and 8 h. C, D, E, and F Hapten inhibition by agar diffusion, A = purified anti-Man-S antibodies I = antibodies + p-nitrophenyl 1 -thio-a-D-mannopyranoside 12 = antibodies + D-mannose I3 = antibodies + ethyl 1-thio-a-o-mannoside 1 to 6, outer wells contain decreasing concentration of Man-S-BSA. (Reprinted with permission from Journal of Protein Chemistry, Volume 9, J. H. Pazur, B. Liu, Nan Q Li, and Y. C. Lee, pp. 143-150, copyright 1990 Journal of Protein Chemistry.)...

Fig. 1.—Hydrolysis at Different pH Values, in Acetate Buffer, of 6 inM p-Nitrophenyl a-D-Mannoside by Limpet a-D-Mannosidase.4S [A, no addition in the presence of A, 0.1 mM ZnS04 O, 0.1 M NaCl, and , 0.1 M NaCl + 0.1 mM ZnS04. The a-D-man-nosidase activity is expressed as a percentage of the maximum value obtained in the presence of Zn2+ and Cl-.]...

Fig. 2.—Effect of Concentration of Substrate on the Rate of Hydrolysis4 of p-Nitro-phenyl a-D-Mannoside in Acetate Buffer, pH 3.5, at 37° by a Crude Preparation of Limpet a-D-Mannosidase in the Presence of , 0.1 mM ZnS04 and 0.1 M NaCl A, 0.1 M NaCl only and O, 0.1 mM ZnS04 only.

Other human O-glycosylation deficiencies that are not detectable by IEF of ApoC-III affect oligosaccharides in O-mannosidic linkage to a-dystroglycan in Walker-Warburg syndrome and muscle-eye-brain disease [2, 32], and fucosylated N- and... 

An intermediate in Hudson s synthesis4 of D-rhamnose (24) is methyl 2,3,4-tri-0-benzoyl-6-deoxy-a-D-mannoside (25). Frequently, direct replacement of the methoxyl group at C-l of O-acylated hexopyranosides by halide proceeds with difficulty (or not at all) however, treatment of (25) with hydrogen bromide in acetic acid resulted in the slow replacement of the methoxyl group by bromide ion, to give the desired 2,3,4-tri-O-... 

O-p-tolylsulfonyl-a-D-mannoside (39) in 37% yield. Treatment of (39) with sodium iodide in acetone gave the 6-iodo derivative (40), which underwent reduction with hydrogen in the presence of a nickel boride" catalyst" to give methyl 4-0-benzoyl-2,3-0 carbonyl-6-deoxy-o>-D-manno-side (41) in 95% yield. Reaction of (41) with hydrogen bromide in acetic acid effected replacement of the methoxyl group at C-l, affording crystalline... 

Vicinal O-benzylidene derivatives can be opened selectively. Reaction of methyl 2,3 4,6-di-0-benzylidene-a-D-mannoside (230) with butyllithium and... 

Ault, Haworth and Hirst47 first synthesized the methyl a-D-glycoside methyl ester of 2,3,4-tri-O-methyl-D-mannuronic acid by successive treatment of potassium (methyl a-D-mannopyranosid)uronate with dimethyl sulfate and sodium hydroxide, and then methyl iodide and silver oxide. Although no crystalline derivatives were isolated, there is little doubt about its structure, since the authors48 subsequently proved the presence of a pyranose ring in the starting material for the synthesis, methyl 2,3-O-isopropylidene-a-D-mannoside. The uronic acid has also been synthesized by Smith, Stacey and Wilson,28 who oxidized methyl... 

The aromatic phenol was varied to explore the scope of the O-to-C conversion with mannosyl phosphates. Using phosphate 9, the a-C-mannosides of 2-naphthol and 3-benzyloxy phenol (23 and 25, Table 1) were synthesized in excellent yield. O-Mannosides were obtained exclusively with less nucleophilic aromatic systems, such as 3-acetoxy phenol. Several non-phenolic aromatic systems were unsuccessful in the formation of C-aryl or O-aryl glycosides. Reaction of 9 with furan, thiophene, trimethoxybenzene, and indole in the presence of TMSOTf did not result in any product formation. Interestingly, activation of 9 in the absence of any aromatic nucleophiles gave 26 as the major product via an intramolecular C-glycosylation (Figure 1) (79). 

The exo and endo isomers of benzylidene acetals of the carbohydrate series can be obtained separately. Their behavior on reduction with HzAlCl accords with the analysis outlined above frequently only one product is obtained. Thus, the 1,2,4,6-di-O-benzylidene derivatives of glucose (42) and (43 R = H or Bn) cleave rapidly with 1 equiv. of H2AICI at 0 °C (30 min for 42 and 10 min for 43) at the marked bonds." Here, at least, it is clear that steric effects outweigh polar ones. The 2,3-endo and -exo isomers of the a-D-mannoside series (44) and (45) likewise cleave mainly equatorial (78 22) and axial (96 4), respectively, when treated with 1 equiv. of H2AICI at room temperature. The same behavior is seen with the methyl 2,3-benzylidene-a-L-rhamnosides," the methyl 3,4-0-benzylidene-P-L-arabinosides" and... 

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