Mannosyl fluorides

Cellovibrio japonicus.33 They ensure high yields and employ easily available a-mannosyl fluorides. 

Intriguing approaches have been developed using mannosyl fluorides,30,31 phosphites,32 and thioglycosides (Scheme 7.8).33 However, their generalities, particularly in terms of applicability to complex and biologically relevant systems, are yet to be clarified. Quite probably, the most successful donor for direct P-mannosylation is the sulfoxide developed by Crich and coworkers (Scheme 7.9).34-37 Glycosyl sulfoxides were originally developed by Kahne and have proved... 

Suzuki, K, Maeta, H, Suzuki, T, Matsumoto, T, Cp2ZrCl2-AgBF4 in benzene a new reagent system for rapid and highly selective a-mannoside synthesis from tetra-O-benzyl-D-mannosyl fluoride. Tetrahedron Lett., 30, 6879-6882, 1989. 

Kim, W-S, Sasai, H, Shibasaki, M, P-Selective glycosylation with a-mannosyl fluorides using tin(II) triflate and lanthanum perchlorate, Tetrahedron Lett., 37, 7797-7800, 1996. 

The glycosynthase methodology has been successfully extended to the enzymatic synthesis of /3-mannoside. The Glc519Ser mutant of the retaining /3-mannosidase (Man2a) proved to afford a catalytic conversion of the various acceptors with the a-mannosyl fluoride 97 as a readily accessible donor [159] (O Scheme 49). The chitobiose and GlcNAc derivatives, however, would not function as the acceptor. 

Utilizing the enpirical results of the glycosidation reactions and the information obtained in a solvent effect study, we developed plausible mechanisms for the glycosidation reactions of the (2- phenylthio)glycosyl fluorides. As previously stated, it was expected that the (2-phenylthio) mannosyl fluoride (51, Figure 11), which... 

Pathak et al. developed an IL-supported convergent solution-phase synthesis of homolinear a(l->6)-linked octa-maimoside from imidazolium cation-tagged mannosyl fluoride 141 and thiomannoside 143 (Scheme 18) [55]. Glycosylation of IL-supported mannosyl fluoride donor 141 with thiomannoside acceptor 142 in the presence of coupling... 

Hashimoto found that low-temperature activation of mannosyl chlorides with silver triflate in the presence of alcohols leads to varying ratios of a- and P-linked mannosides [45, 126, 127]. A study of the factors controlling stereoselectivity in silver triflate-mediated mannosylation has been published [128]. Activation of O-benzyl-protected mannosyl fluorides by a combination of Sn(OTf)2 and La(C104)3 has been reported by Shibasaki to afford mixtures of a- and P-mannosides [129]. The large proportions of a-mannosides formed in the homogeneous reactions outlined in this section indicate the involvement of oxocarbonium-ions enabling the anomeric effect to dictate the steric outcome. Because the stereoselectivity of these approaches is crucially dependent on the reacting partners and conditions their scope remains limited. 

Triazolylphenyl and pyrazolylphenyl mannosides (Scheme 4). Mannosylation of the phenols 14a,b and 17a,b (see Scheme 3A B) with mannosyl fluoride 7 and BF3 EtaO as promoter, yielded exclusively the ot-mannosides 24a,b and 27a,b. Deacetylation ( 25a-c and 28a,b) followed by ester hydrolysis gave the test compounds 26a,b and 29a,b. 

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