J.N. BeMiller

beta-elimination in uronic acids: evidence for an ElcB mechanism

Abstract Methyl esters of methyl pyranosides of 2,3,4-tri- O -methyl-α- D -mannuronic acid ( 3 ), -α- D -glucuronic acid ( 2 ), and -β- D -galacturonic acid ( 1 ) undergo rapid beta -elimination of the 4-methoxyl group in 0.50, 0.20, and 0.02 M sodium methoxide in methanol at room temperature to give 4,5-unsaturated esters via cis , cis and trans elimination, respectively. The ease of cis elimination in methyl (methyl 2,3,4-tri- O -methyl-α- D -glucopyranosid)uronate ( 2 ) and methyl (methyl 2,3,4-tri- O -methyl-α- D -mannopyranosid)uronate ( 3 ) to form the 4,5-unsaturated glycoside is explained by ring flexibility which allows a change in conformation. Only the methyl (methyl 2,3,4-tri- O -methyl-α- D -mannopyranosid)uronate ( 3 ) yields a 2,3:4,5-di-unsaturated ester ( 7 ) ( trans elimination), and this occurs in 0.50 M methoxide, in a much slower reaction. The favoring of trans elimination over the cis elimination that would have been needed in the other two compounds in order to form the second double bond is explained by the rigidity of the half-chair conformation of the 4,5-unsaturated esters. It is suggested that both eliminations proceed via an ElcB mechanism. The results of treatment of hydroxypropyl alginate with potassium hydroxide confirmed that its depolymerization is much slower, and more dependent on the concentration of alkali, than that of pectin.

Synthesis of 2,3-dideoxy-d-hex-2-enopyranosyl cyanides

Abstract Treatment of d -glycals with trimethylsilyl cyanide in the presence of a catalytic amount of a Lewis acid gives 2,3-dideoxy- d -hex-2-enopyranosyl cyanides. 3,4,6-Tri- O -acetyl-1,5-anhydro-2-deoxy- d - arabino -hex-1-enitol rapidly gives, exclusively and almost quantitatively, the product having the α- d configuration. 2,3,4,6-Tetra- O -acetyl-1,5-anhydro- d - arabino - and - d - lyxo -hex-1-enitol give anomeric mixtures of cyanides.

Use of Unsaturated Sugars as Alkylating Agents. Addition of Enol Esters and Ethers to Glycals

Abstract Addition of enol esters to acetylated 1,5-anhydro-D-hex-1-enitols (acetylated-D-glycals) in the presence of a Lewis acid catalyst yields acetylated 3-deoxy-α-D-hex-2-enopyranosyl compounds which can serve as starting materials for the synthesis of other C-(α-D-hexopyranosyl) compounds.

Aromatic and heterocyclic 1-C-substituted derivatives of 1,5-anhydro-d-glucitol

Reaction of anomeric 1-O-acyl and 1-halide derivatives of 2,3,4,6-tetra-O-benzyl-D-glucose with anisole, ferrocene, thiophene, furan, and 1,3,5-trimethoxybenzene in the presence of a Lewis acid gives the corresponding C-beta-D-glucopyranosyl derivatives.

Mechanism of corn indole-3-acetic acid oxidase in vitro

Abstract When indole-3-acetic acid (IAA) was oxidized in the presence of Mn 2+ and 2,4-dichlorophenol by a crude corn extract shown to contain IAA oxidase and by non-enzymic oxidation with Mn 3+ , 10 products of the reaction could be extracted by CH 2 Cl 2 and separated by TLC. Four of these products, 3-hydroxy-methyloxindole, 3-methyleneoxindole, indole-3-aldehyde, and the 3-indolylmethyl ester of indole-3-acetic acid had been previously identified as reaction products. In addition, 3,3′-di-indolylmethane and 3-methyleneindolenine were found. 3-Methyleneindolenine was readily and reversibly formed from 3-hydroxymethylindole. A reaction pathway involving a two-electron oxidation catalyzed by Mn 3+ and 3-hydroperoxymethylindole as a key intermediate in oxindole formation is proposed.

Preparation of Alkyl α-D-glucopyranosides

Abstract An improved preparation of alkyl α- D -glucopyranosides involves ( a ) reaction of β- D -glucopyranose pentaacetate or a similar ester with an alcohol in the presence of an acid catalyst until equilibrium is attained, ( b ) hydrolysis of the alkyl β- D -glucopyranoside present in the reaction mixture with a β- D -glucosidase, and ( c ) removal of the D -glucose and the alcohol formed by this hydrolysis. This sequence gave twelve pure alkyl α- D -glucopyranosides, each in high yield. The following alkyl α- D -glucopyranosides are reported for the first time (in unacetylated form): 2-propyl, 2-butyl, 2-methylpropyl, 1-pentyl, and 2,2-dimethylpropyl.

Methyl terminal-4-O-methylmalto-oligosaccharides

Abstract Malto-oligosaccharides substituted at only one hydroxyl group of the non-reducing end were prepared by the following sequence of reactions; tri- O -benzyl-amylose was prepared by treating amylose with benzyl chloride and sodium hydroxide in methyl sulfoxide, and was methanolyzed to give perbenzylated methyl malto-oligosaccharides having only the hydroxyl group at C-4 of thenonreducing end unsubstituted. Methylation with methyl iodide and sodium hydride in N , N -dimethylformamide yielded perbenzylated methyl terminal-4- O -methylmalto-oligosaccharides; debenzylation was effected by hydrogenolysis with the use of large amounts of Raney nickel catalyst, to yield methyl terminal-4- O -methylmalto-oligosaccharides having D.P. 1–16. Separation by carbon—Celite column chromatography gave individual components having degrees of polymerization of 1 to 3 which were characterized, by thin-layer and gas—liquid chromatography before and after hydrolysis.

Acid-catalyzed hydrolysis of alkyl α-d-glucopyranosides

Abstract Acid-catalyzed hydrolysis of a series of eleven alkyl α- d -glucopyranosides has been effected and compared with that of the corresponding series of alkyl β- d -glucopyranosides. The former were hydrolyzed at a lower rate than the latter, and, as a group, the d -glucopyranosides of primary alcohols were hydrolyzed at a lower rate than those of secondary alcohols. No relationship between rate of hydrolysis and steric or electronic effects of the aglycons was found. The activation parameters partially compensated each other. It is suggested that the rate of hydrolysis is primarily a function of the extent of protonation of the glycosidic oxygen atom, and that heterolysis leads, in each case, to a similar, product-like transition-state. The lower rate of hydrolysis (protonation) of alkyl α- d -glucopyranosides is attributed to the reverse anomeric effect.

Nuclear area changes in senescing human diploid fibroblasts

The pattern of mean nuclear area changes was determined in human fibroblast cell strains from male donors of three different ages (8,40 and 84 years) during their in vitro lifespan. There was a statistically significant increase in mean nuclear area of cells of all three strains during their aging in vitro. A gradual increase of the subpopulation of cells with larger nuclei was also observed. Evidence for a positive correlation between aging in vitro, as reflected by mean nuclear areas at the tenth doubling from the end of in vitro doubling activity, and donor age is presented.

Derivatives of S-α- and -β-d-hexopyranosyl thiophosphates

Abstract Di- tert -butyl esters of the tetra- O -acetyl and tetra- O -benzyl derivatives or S -α- and -β- D -glucopyranosyl thiophosphates were prepared by reaction of di- tert -butyl triethylammonium phosphorothioate with tetra- O -acetyl- or tetra- O -benzyl-hexopyranosyl halides.