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This paper is dedicated to Dr. 0. E. (Ted) Edwards J.-P. PRALY and R. U. LEMIEUX. Can. J. Chem. 65, 213 (1987). A novel application of I3c nuclear magnetic resonance provided the effects of solvent polarity and hydrogen-bond formation on the conformational equilibria for a range of 2-substituted tetrahydropyrans and the results are interpreted in terms of how solvent affects the competition between the endo-and exo-anomeric effects in determining the magnitude of the anomeric effect. In accord with the generally accepted origin of the endo-and exo-anomeric effects (anti-periplanar n-a* interaction of the oxygen lone-pair orbital with the antibonding orbital of the adjacent C-0 bond), the exo-anomeric effect for the a anomer is expected to be weaker because charge delocalization from the glycosidic oxygen to anomeric center is in competition with delocalization from the ring-oxygen atom. The effects of solvent on the relative magnitudes of the endo-and exo-anomeric effects are then considered to arise from the formation of specific complexes with the solvent, and the exo-anomeric effect of a P-glycoside is more strongly influenced. It is contended that hydrogen bonding of solvent to the ring oxygen increases the exo-anomeric effects. For this reason water is particularly effective for the strengthening of the exo-anomeric effect and, thereby, the conformational rigidity of glycosides. Experimental evidence is presented that indicates that the anomeric hydroxyl groups of free sugars dissolved in water tend to prefer the equatorial orientation because these provide stronger hydrogen bonds as proton donors to water.

It was discovered that olefinic double bonds are readily oxidized in an aqueous solution of periodate which contains only catalytic amounts of permanganate. The data suggest that in the effective pH range of 7 to 10 the permanganate is not reduced at once beyond the manganate state and that it is regenerated from this state by periodate action. Evidence was obtained that the main course of the oxidation of an olefin of type —CH=CH— involves first permanganate oxidation to hydroxyketones which are then rapidly cleaved by periodate to products which may subsequently be oxidized by the permanganate.

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Further evidence is presented (8) that changes in optical rotation at the D-line of sodium which occur with changes in solvent largely reflect changes in conformational equilibria.Changes in the nuclear magnetic resonance spectrum of 4,4,5,5-tetradeuterio-2-methoxytetrahydropyran and in the rotation of s(+)-2-methoxytetrahydropyran with changes in solvent are interpreted to show that solvents capable of donating a hydrogen to a hydrogen bond have an effect on the magnitude of the anomeric effect which is greater than that resulting from the change in the dielectric constant of the solvent. In the case of methyl 2-deoxypyranosides with the methoxy group in axial orientation, water appears to have an especially profound influence in stabilizing that orientation of the methyl group which brings it into garrche relationship with both the C2-grouping and the anomeric hydrogen; that is, counter to the anomeric effect.The methyl 2-deoxy-e-L-erythro-pentopyranoside was synthesized from di-0-acetyl-L-arabinal by way of an iodomethoxylation. Deuterolysis of the resulting 1,2-trans-acetylated methyl 2-deoxy-2-iodopentosides is shown to proceed in one case with extensive inversion of configuration and with extensive retention in the other case and offers a route to the preparation of 2-deoxy-2-deuterio-erythropentose with a high proportion (> 75%) of the diastereoisomer with the arabino-configuration.

1 P. V. NIKRAD, H. BEIERBECK, and R. U. LEMIEUX. Can. J. Chem. 70, 241 (1992).The relative potencies of both the monodeoxy and mono-0-methyl derivatives of the Leb-OM^ tetrasaccharide (a-LFuc-(1 + 2)-P-D-Gal-(1 + 3)-[a-L-Fuc-(I + 4)]-P-D-GlcNAc-OMe) as inhibitors of the complexation of a Leb artifi; cia1 antigen by the lectin IV of Gr~ffonia sirnplicifolia are interpreted in terms of the X-ray crystal structure at 2.5 A resolution of the GS-IV . L , e b -O~e complex. Both kinds of derivatives maintain high potencies when the hydroxyl groups involved appear, in the crystal structure, to be in contact with the aqueous phase. Hydroxyl groups situated at the periphery of the combining site and hydrogen bonded to the protein can also be deoxygenated without important loss in potency. However, their methylation leads to a strong decrease in the stability of the complex, because the steric bulk of the introduced methyl group causes loss of complementarity. In contrast, the hydroxyl groups that form hydrogen bonds with the protein along the base of the shallow amphiphilic cleft of the combining site can neither be deoxygenated nor methylated without virtually complete loss of binding activity. Thus, the procedure can provide an appreciation of the various kinds of hydrogen bonds that are present in a protein. oligosaccharide complex. Hard-sphere calculations supported these contentions since an energetically favorable orientation was indicated for a methoxy group at any one of the five positions that were expected to remain in contact with the aqueous phase. However, the calculations, as expected, showed the introduction of strong destabilizing nonbonded interactions when the methylation involved hydroxyl groups that are hydrogen bonded to the protein in the complex. The results are in accord with the previously made rationalization of the near linear enthalpy-entropy compensation found for the active deoxy congeners.Key words: molecular recognition, lectin IV of Griffonia simplicifolia, 0-methyl derivatives of the Lewis b-OMe tetrasaccharide, detection of intermolecular hydrogen bonds, hard-sphere calculations. On a determine les efficacitks relatives des dCrivCs monodksoxy-et mono-0-mCthyle du tetrasaccharide Leb-OM^ (a-]-P-D-GICNAC-OM~) comme inhibiteurs de la complexation d'un antigene artificiel du Leb par la lectine IV du Grlffonia simnplicifolia; on interprete les rCsultats en fonction de la structure cristalline d'un complexe GS-IV . Leb-OM^, dCterminCe par diffraction des rayons-X, ti une rCsolution de 2,5 A. Les deux types de dCrivks maintiennent des efficacitks ClevCes lorsqu'il semble que, dans la structure cristalline, les groupes hydroxyles sont en contact avec la phase aqueuse. Lorsqu'on dksoxygkne les groupes hydroxyles qui sont situCs 2 la pCriphCrie du site qui se combine et qui sont lies a la protCine par des liaisons hydrogknes, il n'y a pas de perte importante de I'efficacitC. Toutefois, leur mkthylation conduit a une perte de complCmentaritC et a une baisse importante de la stabilitC du complexe qu...

The periodate-permanganate oxidation of a terminal methylene (CH-C:) group can be made to produce formaldehyde in high although not quantitative yield. Since the yields compare favorably with those obtained by ozonolysis, the reagent can serve as the basis for a convenient micromethod for the estimation of terminal methylene groups. The less than theoretical yields of formaldehyde are believed mainly due to the conversion of the olefin in part to a-hydrosyaldehyde in the initial stage of the reaction. INTRODUCTIONResults were reported in our first communication in this series (12) which indicated that the periodate-permanganate oxidatioil of a terminal methylene group (I) produces, simultaneously, in the first stage of the reaction, glycol (II), ketol (111), and hydroxyaldehyde (IV). Subsequent periodate oxidation of these substances produces formaldehyde from I1 and I11 but not from IV. Glycol formation did not appear extensive in wealtly alkaline media since the oxidation of ethylene gave very nearly one mole of formaldehyde. However, oxidation of 10-undecenoic acid gave a 73% yield of formaldehyde (12). I t was therefore evident that the ltetol formation can be the preferred route and since the oxidant attaclted formaldehyde only very slowly, it was apparent that the reagent deserved attention as a means for the semiquailtitative estimation of terminal methylene groups.We now wish t o report on evidence that any attempt t o obtain a ~naximum yield of formaldehyde in the periodate-permanganate oxidation of a terminal methylene group should consider: (a) the effect of pH on the reaction route, (b) the effect of pH on the rate of the periodate oxidation of glycols and acyloins, (c) the effect of pH on the rate of the permanganate oxidatioll of formaldehyde, and (d) the solubility of the compound in aqueous media.Evidence has been obtained (12) that hydroxylatioil of the olefin is favored a t a pH of 9-10 with acyloiil formation predominating a t a slightly lower pH. On this basis, it would appear desirable t o operate a t a high pH. However, the periodate-permangallate reagent does not operate above about pH 10 (12).Also, even a t pH 10, the periodate oxidation of glycols is relatively slow (3, 14). For personal use only.