摘要:

The capsular polysaccharide fromStreptococcus pneumoniaetype 12F is composed ofD-glucosyl,D-galactosyl, 2-acetamido-2-deoxy-D-galactosyl, 2-acetamido-2,6-dideoxy-L-galactosyl, and 2-acetamido-2-deoxy-D-mannuronic acid residues in the proportions 2:1:1:1:1. The main structural evidence was adduced from nmr spectroscopy, methylation analysis, and specific degradations whereby it could be concluded that the polysaccharide is composed of hexasaccharide repeating-units having the structure:

ISSN:0008-4042    

DOI:10.1139/v81-303

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Guanosine diphosphate fucose (GDPFuc) has been synthesized chemically in an overall yield of 40% from fucose. This synthesis was made possible by increasing the yield of the key intermediate, β-L-fucopyranosyl phosphate, five-fold over that previously reported (Prihar and Behrman. Biochemistry,12, 997 (1973)), by utilizing guanosine 5′-phosphoric di-n-butylphosphinothioic anhydride (Furusawaet al. J. Chem. Soc. Perkin Trans I, 171 (1976)) or GMP morpholdate for the synthesis of GDPFuc, and by improving the method of isolating intermediates and the final product. At pH 3, GDPFuc is degraded to GDP with a half-life of 7 h at 37 °C and 52 h at 4 °C. At pH values between 5 and 8, less than 10% is degraded after 7 days. Neither 20 mM Mn2+nor Mg2+in 0.2 MPIPES buffer at pH 7.5 stimulate the hydrolysis of GDPFuc. Heteronuclear, C–P and H–P coupling constants indicate that the preferential position of the phosphate moiety in both β-L-fucopyranosyl phosphate and GDPFuc istransto C-2. In the ribose moiety of GDPFuc, the 5′-phosphate istransto C-4. The1Hand13C nmr parameters of intermediates and products are reported.

ISSN:0008-4042    

DOI:10.1139/v81-304

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Deamination of 2-amino-4,4-dideuterio-6,6-dimethylcyclohexanone, 2-exo-amino- and 2-endo-amino-norbornane-3-one, 2-diazo-norbornan-3-one, 2-exo-amino-5,6-exo-dideuterionorbornan-3-one and the corresponding 5,6-endo-dideuterio isomer has been studied. The nature of the products, the deuterium location in them, and the high retention of steric identity in the carbocations are interpreted in terms of σ-bond participation leading to corner- and edge-protonated cyclopropanes as reaction intermediates. Results with other destabilized carbocations are correlated.

ISSN:0008-4042    

DOI:10.1139/v81-305

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Excess acidity (X-function) scales for 0–40% w/w aqueous HCl and 0–60% w/w aqueous HBr solutions are derived, using ionization ratio data for 29 and 9 weak bases, respectively; in these media the resulting PKBH+values are quite similar to those obtained by standard acidity function treatments. A generalized derivation of the excess acidity enables the determination of pKR+values for protonation–dehydration processes, some of which are given, and the study of partially dissociated acids. An improved computer program was used, applicable to smaller data sets (up to 50 bases); this program permitted a determination of the inherent precision of the derived functions, and a more rigorous evaluation of previously derivedX-functions and the whole excess acidity method.

ISSN:0008-4042    

DOI:10.1139/v81-306

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

The chemical ionization mass spectra of eight C5alkanols and fourteen C6alkanols have been obtained using H3+, N2H+, CO2H+, N2OH+, and HCO+as reactant ions. This choice of reactant ions allows the exothermicity of the protonation reaction to be varied from ∼90 kcal mol−1(H3+) to ∼50 kcal mol−1(HCO+). The major fragmentation reaction in all cases was H2O elimination from the protonated alcohol forming the appropriate C5H11+or C6H13+alkyl ion. The extent of further fragmentation of the alkyl ions decreased with decreasing exothermicity of the protonation reaction and was greatest for alkyl ions derived from primary alcohols, less for alkyl ions derived from secondary alcohols, and very small for alkyl ions derived from tertiary alcohols. The results indicate that there is negligible rearrangement to more stable alkyl ions prior to attaining the critical configuration which determines the energy partitioning between R+and H2O in the fragmentation of ROH2+. Other less important reaction modes in the CI spectra involved formation of (M – H)+ions and formation of oxycarbonium ions by alkane elimination from protonated alcohols.

ISSN:0008-4042    

DOI:10.1139/v81-307

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

A series of formate (methyl through butyl) and acetate (methyl through pentyl) esters have been protonated in the gas phase by the Brønsted acids H3+, N2H+, CO2H+, N2OH+, and HCO+. Carbonyl oxygen protonation is 87–97 kcal mol−1exothermic for H3+and 47–57 kcal mol−1exothermic for the weakest acid HCO+, permitting a study of the effect of protonation exothermicity on the decomposition modes of the protonated esters. With the exception of protonated methyl formate, three decomposition modes, (a) to (c) are observed.Reaction (a) is unimportant for formates; for acetates it is the sole decomposition channel for the methyl ester, but is less important for higher acetates. The dependence of the relative importance of this reaction mode on the protonation exothermicity indicates an activation energy considerably in excess of ΔH0, presumably because the reaction involves a symmetry-forbidden 1,3-H shift for the carbonyl protonated ester. For the higher acetates where the difference in the proton affinities of the carbonyl and ether oxygens is less, acyl ion formation results, in part, from protonation at the ether oxygen. For protonated methyl formate the major fragmentation reaction yields CH3OH2+ + CO; this reaction also appears to have an activation energy considerably in excess of the ΔH0. For the remaining esters either reaction (b) or (c) is the major decomposition mode. The competition between these two channels depends strongly on the protonation exothermicity and the relative activation energies. From the reaction competition we conclude that 1,2-H shifts occur in the case of primary alkyl esters yielding more stable secondary or tertiary alkyl ions. This rearrangement appears to occur after the excess energy has been partitioned between the alkyl ion and the neutral acid since the extent of further fragmentation of the alkyl ion reflects the original structure of the alkyl group.

ISSN:0008-4042    

DOI:10.1139/v81-308

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

The oxidation ofE-5-decene by potassium permanganate in slightly acidic aqueous acetone solutions has been studied. An analysis of the reaction mixture at various time intervals indicates that the ketol, 5-hydroxy-6-decanone, is the initially formed product under these conditions. The other major product, 5,6-decanedione, is formed sequentially from oxidation of the ketol rather than directly from the alkene.

ISSN:0008-4042    

DOI:10.1139/v81-309

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

The isolation and structure determination of the "cybrodins", a new group of sesquiterpenoids produced by a new strain of the bird's nest fungusCyathus bulleri, is reported. Cybrodol (3), isocybrodol (4), cybrodal (5), trisnorcybrodolide (6), and cybrodic acid (7) may be classified asseco-illudalane sesquiterpenes. The evidence leading to the structural assignments is presented, along with chemical correlations among the cybrodins. The possible mode of biogenesis is discussed. Pterosin-C (13), a known norsesquiterpene, and 3-methyllumichrome (17) were also isolated. Small quantities of a new sesquiterpenoid, broderol, believed to possess structure21, were obtained on two occasions.

ISSN:0008-4042    

DOI:10.1139/v81-310

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

The total syntheses of cybrodol (1), isocybrodol (2), cybrodal (3), cybrodic acid (4), and trisnorcybrodolide (5), starting from 2-bromomesitylene (6) are described. The route involves oxidation of the 5-methyl group of6by means of chromyl acetate, addition of the β-hydroxyethyl chain by aryllithiation and reaction with ethylene oxide, and addition of the fifth carbon substituent by aryllithiation and treatment with ethyl chloroformate to give the key intermediate, methyl 3-(2-hydroxyethyl)-6-methoxymethyl-2,4-dimethylbenzoate (18d). The latter was transformed into trisnorcybrodolide (5), and further elaborated via the corresponding aldehyde21into the remaining cybrodins.

ISSN:0008-4042    

DOI:10.1139/v81-311

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

A correlation is proposed between the ratios:Y = πΔV≠/E(p)≠(where π is the internal pressure of a liquid, ΔV≠the volume of activationRT(∂ ln η/∂p)T, andE(p)≠the activation energy at constant pressure for viscous flow, or the corresponding quantities for diffusion) andX = E(ρ)≠/E(p)(whereE(ρ)is the "energy of thermal expansion", defined by:−R[∂ ln (ρ−1 − ρ0−1)/∂T−1]p). The first,Y, involves quantities measured at high pressures, whileXrequires only measurements at ordinary pressure. The correlation will permit estimation of viscosities and diffusion coefficients at high pressures from low-pressure measurements.

ISSN:0008-4042    

DOI:10.1139/v81-312

出版商:NRC Research Press    

年代:1981

数据来源: NRC