Monosaccharides protecting groups

Scheme 25. Monosaccharide derivatives containing protecting groups whose cleavage can be achieved by Montmorillonite K-10 in aqueous methanol.

As part of a strategy of employing monosaccharides as a convenient source of chirality, organometallic additions to protected L-erythrulose derivatives have been carried out. Employing silyl, benzyl, trityl, and acetonide protecting groups, the diastereoselectivities obtained are discussed in terms of chelation to the a-and/or the /3-oxygen, and are compared with results for similar aldehydes. 

Nucleoside 5 -phosphates are employed as starting materials to prepare the activated derivatives (56). Their synthesis has been discussed in a Chapter in this Series.266 The methods used most frequently for preparing glycosyl phosphates involve the interaction of protected glycosyl bromides with diphenyl phosphate and subsequent removal of the protective groups,267 or by fusion of the peracetylated monosaccharides with anhydrous phosphoric acid.268... 

D. Plusquellec and M. Lefeuvre, Sugar chemistry without protecting groups A regioselective addition of the primary hydroxyl of monosaccharides to alky lisocyanates, Tetrahedron Lett., 28 (1987) 4165—4168. 

In addition to their work on tricyclic systems, Chmielewski and co-workers have used monosaccharides to obtain polycyclic derivatives of oxacepham. For instance, cyclization of 479 (R2 = Tos or TIBS) in a two-phase system including a phase-transfer catalyst and potassium carbonate gave 480 in 65-90% yields. The protecting group R1 was lost if it was a silyl group, for example, TMS, TBDMS <1998T14065>. 

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