Pyranoside moiety

Pikho and co-workers50 found that nonanomeric [6,5]-spiroketals (having a pyranoside moiety with an equatorial CO acetal bond) can be formed under conditions of kinetic control. For instance, 62 undergoes acid catalyzed spiroacetalization giving the anomeric (most stable) acetal 63... 

The plan devised for actinobolin grew out of the observation that sugar-derived a-enones, such as FI, underwent Diels-Alder reactions from the P-face to give annulated pyranosides, such as FII, as the only products [64, 65]. In addition, preliminary experiments had shown that the reactions of these bicyclic molecules were dominated by the conformational preferences of the pyranosidic moiety, these results being in accordance with the predictions of the anomeric effect [66]. Transformations on the carbocyclic annulus could therefore be undertaken on the basis of this established conformational preference. 

The [l8]-crown-6 compound (11) and its isomer with the syn-alignment of the two pyranoside moieties have been synthesized in 14 and 8 yield respectively from methyl 4,6- -benzylldene-a-D-glucopyranoside by alkylation with diethyleneglycol ditosylate a variety of derivatives with different solubility and complex form-Ing characteristics were prepared from compound (11). The bls-dianhydro-D-mannltolo-30-crown-10 derivative (12) was similarly prepared in 14 yield from 1,4 3,6-dianhydro-D-mannitol both compound (12) and its 1 1 1 complexes with primary ammonium cations... 

Consequences of the conformational anomeric effect are largely expressed in monosaccharides and their derivatives. One recognizes the conformational endo-anomeric effect for pyranosides with a polar X group at C(l) (contrasteric electronic stabilization effect Fig. 7A) and conformational exo-anomeric effect for glycosides (acetals) in which the alkyl group of the exocyclic moiety is synclinal (Fig. 7B, C). 

S. Czernecki, S. Horns, and J. M. Valery, Chain-extension of carbohydrates. 5. Synthesis of C-glycosyl amino acid moiety of miharamycins involving stereocontrolled ethynylation of methyl 2,3,4-tri-0-benzyl-a-D-g/nco-hexadialdo-l,4-pyranoside, J. Org. Chem., 60 (1995) 650-655. 

Koskinen and Otsomaa [92] have converted the L-threonine-derived aldehyde 131 (Scheme 13.50) into methyl 4-amino-4,6-dideoxy-gw/6>-pyranosides 134. A modified Homer-Wads worth-Emmons olefination leads to the (Z)-enoate 132. Acidic hydrolysis of the aminal protection affects lactonization giving 133. Double hydroxylation to the sterically less hindered face of the alkene moiety, followed by lactone reduction and methyl glycosidation furnishes 134 in 42% overall yield based on 131. 

K. Kefurt, J. Jary, and Z. Samek, Reaction of methyl 2,3-( -isopropylidene-a-L-rhamno-pyranoside with triphenylphosphite methiodide, J. Chem. Soc. Chem. Common, p. 213 (1969). J. P. H. Verheyden and J. G. Moffatt, Direct iodination of the sugar moiety in nucleosides, J. Am Chem. Soc. 66 2093 (1964). 

This operation introduces the nitrogen moiety with the required configuration. Acetonide methanolysis followed hy methanolysis of the benzoates and acetylation generates pyranoside... 

Co (en)2 and Co (cyclen) (cyclen = 1,4,7,10-tetraazacyclododecane) residues are coordinated by a diolato moiety of a-CD or /3-CD in an aqueous alkaline solution (compare Co (en)2 complexation by a pyranosidic diolato moiety in 109, O Fig. 21). This coordination mode could be confirmed by a large downfield shift of the the carbon atoms involved in the five-membered diolato-chelate ring [159]. 

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