Glycoside allyl

A novel latent-active glycosylation strategy was reported. This strategy is based on a rhodium-catalyzed isomerization of substituted allyl glycosides followed by a Lewis acid-mediated glycosylation reaction (Scheme 46).76 77... 

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. 

Allyl glycosides can be obtained either by Fischer or Koenigs-Knorr type glycosylations. They can be oxidized by the RuCl3-NaI04 system,53... 

C-Allyl glycosides can be prepared by the reaction of glycal epoxides with allyltributyltin in the presence of tributyltin triflate as a Lewis acid,281 and aldonitrones can be allylated with trimethylsilyl triflate as a catalyst (Equations (101) and (102)).282... 

Compound 10 was converted into allyl glycoside 11 in 73 yield in two steps, (a) Bu2Sn0CH2CH=CH2—SnCl,(4), and (b) MeONa—MeOH. Treatment of 11 with dimethoxypropane and TsOH, and then with benzyl bromide— NaH—DMF afforded compound 12 in 51% yield. Solvolysis of compound 12 in MeOH—AcOH, and then monobenzylation by the stannylation— alkylation method(5) gave the desired glycosyl acceptor 8 in 67% yield. Acetylation of compound 8 and then deallylation with PdCl2— AcONa in aq.AcOH(6) afforded a 93% yield of hemiacetal 13, which was treated with (a) SOCI2—DMF in dichloroethane(7) and (b) AgF— CH CN(8) to give the desired fluoride 9 in 73% overall yield. 

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

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... 

The allyl glycosides have been synthesized from allyl alcohol and the free carbohydrate, or the per-O-acetylglycosyl halide in the presence of acid, or mercury cyanide, as the catalyst. The condensation of the alcohol occurs with both anomers of the carbohydrate, and a mixture of the a- and /3-glycosides is obtained. The anomers can be separated by preferential, solvent extraction,12 or by chromatography on... 

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. 

In the preparation of the non-reducing unit the 4,6-0-benzylidene allyl glycoside was benzylated at position... 

Kitajima et al. [264] used the mixture of mercury salts and molecular sieves in 1,2-dichloromethane to condense (370) with the trisaccharide derivative (382) to give similar tetrasaccharides [on the primary hydroxyl group of (382)] with again equal amounts (30% each) of a- and (3-linked derivatives. With the allyl glycoside (383) under the same conditions 48 % of a- and 33 % of P-linked glycosides were obtained [265]. The a-isomer was used to prepare [265] the undecasaccharide characteristic of the complex type of glycan of glycoproteins. 

A-l-Allyl-2-formylpyrrole, cyclohydrocarbonylation, 11, 521 Allyl glycosides, isomerization, 10, 91 Allyl halides, in copper-mediated substitutions, 9, 549-550 Allylic alcohols... 

Hydrosilylation of the protected allyl-glycoside 1 with the carbosilane 2 (by means of Silopren , a platinum-siloxane complex from Bayer AG) led via Si-C bond formation to a glycosidic carbosilane dendrimer (Fig. 4.42) [82]. 

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