Allyl glycosides syntheses

Therefore, taking into account the potentialities of such lactones as carbohydrate delivery synthons (vide infra), several routes leading to carboxymethyl glycosides (and thus subsequently to the lactones) were investigated, in order to get as many structural variations as possible for widening the scope of their use in synthesis. In addition to the isomaltulose oxidation method (route a), the oxidation of allyl glycosides (route b), and the anomeric alkylation with tert-butylbromoacetate (route c) were studied (Scheme 11). These three methods are detailed in the following sections. 

Fig. 30 Synthesis of 2,3-unsaturated allyl glycosides or glycosyl cyanides...

C-Glycoside synthesis may be achieved in twro ways. Intermolecular radical addition reactions are observed with (i) polarized, electron-deficient alkenes, (ii) alkenes that provide a high level of stabilization to the initial radical adduct and (in) substrates that undergo a facile fragmentation (e.g. allyl stannanes). Additions to less reactive substrates, though not favored for intermolecular processes, are observed if the two components are tethered in an intramolecular array. 

The latter approach has been followed in our laboratory. For instance, in studies related to the synthesis of potent multivalent sialoside inhibitors of influenza virus hemagglutinin [34], it became of interest to evaluate the immunogenicity of neoglycoproteins containing sialosides as sole immunodominant hapten. To this end, acetochloroneuraminic acid (1) was transformed into allyl glycoside 2 (Scheme 1) which upon reductive ozonolysis afforded aldehyde 3 in excellent overall yields [35], Reductive amination of 3 to bovine serum albumin (BSA) and tetanus toxoid provided immunogenic vaccines from which specific rabbit IgG anti-sialic acid antibodies were obtained [36]. In order... 

R. R. Schmidt and W. Klotz, Glycoside bond formation via anomeric (7-alkylation How many protective groups are required Synlett p. 168 (1991). W. Klotz and R. R. Schmidt, Anomeric (7-alkylation of (7-unprotected hexoses and pentoses —-convenient synthesis of decyl, benzyl and allyl glycosides, Liebigs Ann. Chem. 683 (1993), and references therein. 

Copolymerization of allyl glycosides with acrylamide is a simple, direct method for the synthesis of non-protein-based NGCs,110 and has been used by Verez-Bencomo and co-workers111 to prepare leprosy-related conjugates. The same limitations as before apply to the preparation and use of allyl glycosidic substituents. 

Oxidative removal of the 4-methoxyphenyl group in 61, followed by oxidation and deprotection as for the synthesis of 55, gave the allyl glycoside (62) of the... 

The direct allylation of radical precursors (e.g., alkyl hahdes, thioacyl derivatives) with allyltributylstannane in the presence of an initiator represents a well-established protocol for carbon-carbon bond formation [29,30]. This methodology provides a convenient means for introducing an allyl group to the anomeric carbon of carbohydrates [31]. hi their recent work on the preparation of building blocks for C-glycoside synthesis, Postema and coworkers... 

Kunz, H, Zimmer, J, Glycoside synthesis via electrophile-induced activation of A-allyl carbamates. Tetrahedron Lett., 34, 2907-2910, 1993. 

Araki, Y, Kobayashi, N, Watanabe, K, Ishido, Y, Synthetic studies by the use of fluorinated intermediates. Part 2. Synthesis of glycosyl cyanides and C-allyl glycosides by the use of glycosyl fluoride derivatives, J. Carbohydr. Chem., 4, 565-585, 1985. 

The starting materials for the synthesis of the various derivatives used in these studies were the appropriate allyl glycosides which have the general structure indicated in (X). Allyl derivatives may be the most general precursor for the synthesis of epoxides. The various allyl glycosides were synthesized by the following procedure of Thomas (1970)forallyl-2-acetamido-3,4-6-tri-0-acetyl-2-deoxy-/ -D-glycopyra-... 

Schmidt and co-workers have also independently developed the self-cleavable diene linker 14 and solid-phase synthesis of the branched hexasaccharide 16 has been achieved (O Scheme 6) [12], The ring-closing metathesis of 15 provided the allyl glycoside 16 from which the allyl protecting group was readily removed by Ir-mediated isomerization followed by hydrolysis. 

G. O. Aspinall, N. K. Khare, R. K. Sood, D. Chatterjee, B. Rivoire, and P. J. Brennan, Structure of the glycopeptidolipid antigen of serovar 20 of the Mycobacterium avium serocomplex, synthesis of allyl glycosides of the outer di- and tri-saccharide units of the antigens of serovars 14 and 20, and serology of the derived neoglycoproteins, Carbohydr. Res., 216 (1991) 357-373. 

SCHEME 22. Allyl glycosides in the active—latent strategy for oligosaccharide synthesis.147... 

SCHEME 13. Early synthesis employing allyl glycoside to glycosyl chlorides. 

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