A novel,stereospecific synthesis of β-D-glucopyranosyl phosphate

In alkaline solution, periodate ions form complexes with three consecutive hydroxyl groups in an axial-equatorial-axial arrangement but not with three syn-axial hydroxyl groups. Borate ions form complexes with three syn-axial hydroxyl groups but not with the axeqax sequence. Accordingly, cis-inositol gives a 1,2,3-periodate and a 1,3,5-borate complex. Cations form complexes with either type of conformation, but complex formation provides little energy towards achieving it by ring inversion. Lanthanide ions have been used to establish the sites of complex formation.     

Free and bound hydroxyl and carboxyl groups in the cutin of Quercus suber leaves

The number of free and bound hydroxyl and carboxyl groups of the cutin of Quercus suber leaves was investigated by the lithium borohydride hydrogenolysis of mesyl-cutin compared with the lithium borohydride hydrogenolysis of untreated cutin. Fifty per cent of the vic-diol groups of the trihydroxy C₁₈ acid component and twenty five per cent of the secondary hydroxyl groups of the dihydroxy C₁₆ acid component are free. The rest of the secondary and all of the primary hydroxyl groups are esterified; all carboxyl groups are esterified.     

Anion-exchange chromatography of monocarboxylic hydroxy-acids in borate medium

The formation of borate complexes contributes significantly to the distribution coefficients obtained in the separation of polyhydroxy acids in borate medium. A study of a large number of straight-chain hydroxy acids shows that these contributions tend to increase with the number of vicinal hydroxyl groups and with their distance from the carboxylate group. Vicinal hydroxyl groups in gauche conformation have the ability to form strong complexes, provided that the steric conditions are favourable in other respects. The contributions of vicinal hydroxyl groups in anti conformation are much less.     

A rigid-rod dihydroxy poly(p-phenylene benzobisoxazole) fiber with improved compressive strength

A series of dihydroxy poly(p-phenylene benzobisoxazole) (DHPBO) were prepared by introducing binary hydroxyl groups, that is 2,5-dihydroxyterephthalic acid (DHTA) into poly(p-phenylene benzoxazole) (PBO) macromolecular chains and then DHPBO fibers were prepared by dry-jet wet-spinning method. As indicated by Fourier transform infrared spectrum (FTIR), hydroxyl groups were incorporated into DHPBO polymer chains successfully and intermolecular hydrogen-bonds had been formed. The effects of hydroxyl groups on the compressive property of PBO fibers were investigated by elastic loop test method. The test results showed that the compressive strength of DHPBO fibers with 10 mol% DHTA content were obviously higher than that of PBO fibers.     

Détermination des sites d'oxydation des dérivés du α-D-glucofuranose utilisés comme donneurs

The sites of oxidation, by catalytic transfer of H, of derivatives of 1,2-O-isopropylidene-α-D-glucofuranose suggest a regiospecific reaction. Compounds having vicinal hydroxyl groups at C-5 and C-6, or at C-3 and C-5, are oxidized at OH-5, whereas compounds having two hydroxyl groups at C-3 and C-6 or three hydroxyl groups give first aldehydes and then lactones.     

Catalytic action of comicelles containing imidazolyl and hydroxyl groups in the hydrolysis of enantiomeric esters

The rate constants for hydrolysis of the enantiomers of amino acid p-nitrophenyl esters catalyzed by bifunctional comicellar catalysts containing the imidazolyl and hydroxyl groups have been determined at pH 7.30, 0.02 m phosphate buffer, and 25°C. The kinetic analysis suggests a reaction scheme which involves acylation followed by deacylation at the imidazolyl group. Although no appreciable cooperative catalytic efficiencies are observed between the bifunctional groups in the acylation step, it is found that the deacylation rates are thus accelerated by surfactant hydroxyl groups, and some of the stereoselective acyl transfer reaction occurs from the imidazolyl to the hydroxyl group in optically active comicellar systems.     

L-Xylo-3-hexulose,a new rare sugar produced by the action of acetic acid bacteria on galactitol,an exception to Bertrand Hudson's rule

BackgroundIn acetic acid bacteria such as Gluconobacter oxydans or Gluconobacter cerinus, pyrroloquinoline quinone (PQQ) in the periplasm serves as the redox cofactor for several membrane-bound dehydrogenases that oxidize polyhydric alcohols to rare sugars, which can be used as a healthy alternative for traditional sugars and sweeteners. These oxidation reactions obey the generally accepted Bertrand Hudson's rule, in which only the polyhydric alcohols that possess cis d-erythro hydroxyl groups can be oxidized to 2-ketoses using PQQ as a cofactor, while the polyhydric alcohols excluding cis d-erythro hydroxyl groups ruled out oxidation by PQQ-dependent membrane-bound dehydrogenases.MethodsMembrane fractions of G. oxydans were prepared and used as a cell-free catalyst to oxidize galactitol, with or without PQQ as a cofactor.ResultsIn this study, we reported an interesting oxidation reaction that the polyhydric alcohols galactitol (dulcitol), which do not possess cis d-erythro hydroxyl groups, can be oxidized by PQQ-dependent membrane-bound dehydrogenase(s) of acetic acid bacteria at the C-3 and C-5 hydroxyl groups to produce rare sugars l-xylo-3-hexulose and d-tagatose.ConclusionsThis reaction may represent an exception to Bertrand Hudson's rule.General significanceBertrand Hudson's rule is a well-known theory in polyhydric alcohols oxidation by PQQ-dependent membrane-bound dehydrogenase in acetic acid bacteria. In this study, galactitol oxidation by a PQQ-dependent membrane-bound dehydrogenase represents an exception to the Bertrand Hudson's rule. Further identification of the associated enzymes and deciphering the explicit enzymatic mechanism will prove this theory.     

Enzymatic synthesis of sulphated flavonols in Flaveria

Cell-free extracts of Flaveria bidentis and F. chloraefolia catalysed the transfer of sulphate groups from 3′-phosphoadenosine-5′-phosphosulphate to the hydroxyl groups of a variety of hydroxylated and O-methylated flavonols, but not to flavones or phenylpropanoids. Enzymatic sulphation was more predominant at the 3-hydroxyl group, but not to the exclusion of other hydroxyl substituents on the flavonoid ring. Quercetin was sulphated to yield its mono-, di-, tri- and tetrasulphate esters. This, together with the differences observed in the sulphation of different flavonols by extracts of both Flaveria species, suggests the existence of a number of distinct, position-specific sulphotransferases (EC 2.8.2.-). The sulphation reaction was catalysed at an optimum pH of 7.5 in Tris-HCl buffer, required SH groups for activity and was stimulated in the presence of divalent cations.     

Enzymatic regioselective deprotection of peracetylated mono- and disaccharides

Selective enzymatic hydrolysis of the peracetylated disaccharides, namely cellobiose, lactose, maltose and melibiose, with lipase from Asperilligus niger in aqueous buffer and organic solvent for 30 min afforded exclusively the corresponding heptaacetates with a free hydroxyl group at C-1 in high yield. Prolonged reaction of the β-1,4 linked cellobiose and lactose peracetates afforded selectively their hexaacetates with free hydroxyl groups at C-1,2, whereas the α-1,4 linked disaccharides maltose and melibiose peracetate gave a complex mixture of products. The reaction of 2-acetamido-2-deoxy-1,3,4,6-tetra-O-acetylglucopyranose (11) for 22 h afforded as the major product the diacetate 12 with free hydroxyl groups at C-1,4.     

Bacterial Conversion of Hydroxylamino Aromatic Compounds by both Lyase and Mutase Enzymes Involves Intramolecular Transfer of Hydroxyl Groups

Hydroxylamino aromatic compounds are converted to either the corresponding aminophenols or protocatechuate during the bacterial degradation of nitroaromatic compounds. The origin of the hydroxyl group of the products could be the substrate itself (intramolecular transfer mechanism) or the solvent water (intermolecular transfer mechanism). The conversion of hydroxylaminobenzene to 2-aminophenol catalyzed by a mutase from Pseudomonas pseudoalcaligenes JS45 proceeds by an intramolecular hydroxyl transfer. The conversions of hydroxylaminobenzene to 2- and 4-aminophenol by a mutase from Ralstonia eutropha JMP134 and to 4-hydroxylaminobenzoate to protocatechuate by a lyase from Comamonas acidovorans NBA-10 and Pseudomonas sp. strain 4NT were proposed, but not experimentally proved, to proceed by the intermolecular transfer mechanism. GC-MS analysis of the reaction products formed in H₂¹⁸O did not indicate any ¹⁸O-label incorporation during the conversion of hydroxylaminobenzene to 2- and 4-aminophenols catalyzed by the mutase from R. eutropha JMP134. During the conversion of 4-hydroxylaminobenzoate catalyzed by the hydroxylaminolyase from Pseudomonas sp. strain 4NT, only one of the two hydroxyl groups in the product, protocatechuate, was ¹⁸O labeled. The other hydroxyl group in the product must have come from the substrate. The mutase in strain JS45 converted 4-hydroxylaminobenzoate to 4-amino-3-hydroxybenzoate, and the lyase in Pseudomonas strain 4NT converted hydroxylaminobenzene to aniline and 2-aminophenol but not to catechol. The results indicate that all three types of enzyme-catalyzed rearrangements of hydroxylamino aromatic compounds proceed via intramolecular transfer of hydroxyl groups.     

Synthesis and antiplasmodial activity of lycorine derivatives

Twenty seven lycorine derivatives were prepared and evaluated for their in vitro antimalarial activity against chloroquine-sensitive strains of Plasmodium falciparum. The best antiplasmodial activities were achieved with lycorine derivatives that present free hydroxyl groups at C-1 and C-2 or esterified as acetates or isobutyrates. The double bond C-2–C-3 is also important for the activity. Concerning to the antiplasmodial activity of the secolycorines, the higher values were obtained with the replacement of the methylenedioxy moiety by hydroxyl or acetate groups and with methyl substituent attached to the nitrogen atom.     

Influence of the orientation of hydroxyl groups on the puckering modes of furanoid rings

The influence of the orientations of HO-2 and HO-3 on the puckering of the ring in (2S,3R)-tetrahydrofuran-2,3-diol (1) and (3R)-tetrahydrofuran-3-ol (2) has been investigated by consistent force-field methods. In the E or W regions of the pseudorotation cycle, there are no local energy minima. The local minima in the N and S regions are affected by different orientations of the hydroxyl groups, with up to 12.2 kJ.mol^?1 for 1 and 6.9 kJ.mol^?1 for 2. If statistical weights of different rotamers are used to calculate N/S equilibrium constants, both conformational states are equally populated. However, if the orientations of the hydroxyl groups are restricted to simulate behaviour of these molecular fragments in DNA double-helices, the equilibrium shifts towards N. The results indicate that, in the vapor state, a unique one-dimensional N-S energy-barrier does not exist and that there is a spectrum of barriers depending on the orientation of the hydroxyl groups.     

Blocksynthese von O-glycopeptiden und anderen T-antigen strukturen

Under the conditions of in situ anomerisation, the 2-azido-4,6-di-O-benzoyl-2-deoxy-3-O-(2,3,4,6-tetra-O-acetyl-β-d-galactopyranosyl)-α-d-galactopyranosyl bromide reacted directly and with high selectivity with the reactive hydroxyl groups of l-serine and l-threonine derivatives to form α-glycosidically-linked products. Thus, the glycopeptides containing l-serine and l-threonine are more accessible. The disaccharide block could also be coupled with other reactive hydroxyl compounds to give compounds that contain the T-receptor.     

Flavone Derivatives as Inhibitors of Insulin Amyloid-Like Fibril Formation

Several natural and synthetic flavone derivatives have been reported to inhibit formation of amyloid fibrils or to remodel existing fibrils. These studies suggest that the numbers and positions of hydroxyl groups on the flavone rings determine their effectiveness as amyloid inhibitors. In many studies the primary method for determining the effectiveness of inhibition is measuring Thioflavin T (ThT) fluorescence. This method demonstrably results in a number of false positives for inhibition. We studied the effects of 265 commercially available flavone derivatives on insulin fibril formation. We enhanced the effectiveness of ThT fluorescence measurements by fitting kinetic curves to obtain halftime of aggregation (t ₅₀). Maximal values of ThT fluorescence varied two fold or more in one third of all cases, but this did not correlate with changes in t ₅₀. Changes in t ₅₀ values were more accurate measures of inhibition of amyloid formation. We showed that without a change in an assay, but just by observing complete kinetic curves it is possible to eliminate numbers of false positive and sometimes even false negative results. Examining the data from all 265 flavones we confirmed previous observations that identified the importance of hydroxyl groups for inhibition. Our evidence suggests the importance of hydroxyl groups at locations 5, 6, 7, and 4’, and the absence of a hydroxyl group at location 3, for inhibiting amyloid formation. However, the main conclusion is that the positions are not additive. The structures and their effects must be thought of in the context of the whole molecule.     

Relative reactivity of hydroxyl groups in inositol derivatives: role of metal ion chelation

O-Alkylation of myo-inositol derivatives containing more than one hydroxyl group via their alkali metal alkoxides (sodium or lithium) preferentially occurs at a hydroxyl group having a vicinal cis-oxygen atom. In general the observed selectivity is relatively higher for lithium alkoxides than for the corresponding sodium alkoxide. The observed regioselectivity is also dependent on other factors such as the solvent and reaction temperature. A perusal of the results presented in this article as well as those available in the literature suggests that chelation of metal ions by inositol derivatives plays a significant role in the observed regioselectivity. Steric factors associated with the axial or equatorial disposition of the reacting hydroxyl groups do not contribute much to the outcome of these O-alkylation reactions. These results could serve as guidelines in planning synthetic strategies involving other carbohydrates and their derivatives.     

Structure–activity relationships of diverse xanthones against multidrug resistant human tumor cells

Thirteen xanthones were isolated naturally from the stem of Securidaca inappendiculata Hassk, and structure-activity relationships (SARs) of these compounds were comparatively predicted for their cytotoxic activity against three human multidrug resistant (MDR) cell lines MCF-7/ADR, SMMC-7721/Taxol, and A549/Taxol cells. The results showed that the selected xanthones exhibited different potent cytotoxic activity against the growth of different human tumor cell lines, and most of the xanthones exhibited selective cytotoxicity against SMMC-7721/Taxol cells. Furthermore, some tested xanthones showed stronger cytotoxicity than Cisplatin, which has been used in clinical application extensively. The SARs analysis revealed that the cytotoxic activities of diverse xanthones were affected mostly by the number and position of methoxyl and hydroxyl groups. Xanthones with more free hydroxyl and methoxyl groups increased the cytotoxic activity significantly, especially for those with the presence of C-3 hydroxyl and C-4 methoxyl groups.     

Chemical identification and enzymatic synthesis of a newly discovered lipid class--hydroxyalkylglycerols

We have isolated and identified a new class of alkyl glycerolipids in lipid extracts prepared from the pink portion of the harderian glands of rabbits. After LiAlH₄ reduction, the esterified lipid yields a hydroxyalkylglycerol. Identification was based on chromatography, infrared spectroscopy, and mass spectra of various derivatives of this lipid and of standards prepared chemically. The isomers of the hydroxyalkylglycerols isolated consisted of O-hexadecyl moieties with hydroxyl groups at C-10 and C-11 and of O-octadecyl moieties with hydroxyl groups at C-11 and C-12. In the natural state all of the hydroxyl groups are thought to be esterified with aliphatic moieties, and this lipid class accounts for approximately 80% of the total lipids of the pink harderian gland of rabbits. Enzymatic experiments demonstrated that [1-³H]octadecane-1,12-diol was readily incorporated into the hydroxyalkylglycerols when dihydroxyacetone-P, CoA, ATP, Mg²⁺, and the microsomal fraction of the pink harderian gland were included in the incubations. Thus, it appears that the ether linkage of hydroxyalkylglycerols is biosynthesized in a manner analogous to that previously described for glycerolipids containing unsubstituted O-alkyl moieties.     

Isopropylidenation with 2,2-dimethoxypropane-N,N-dimethylformamide-p-toluenesulfonic acid selective substitution in certain aminocyclitols

The behavior of a variety of N-acetyl- and N-(benzyloxycarbonyl)-aminocyclitols with 2,2-dimethoxypropane-N,N-dimethylformamide-p-toluenesulfonic acid has been examined. Both cis- and trans-vicinal hydroxyl groups are readily bridged to give 1,3-dioxolanes. In one (sterically favorable) case, the reagent linked the nitrogen atom of an acetamido group with a vicinal hydroxyl group to give an N-acetyl-2,2- dimethyloxazolidine; this heterocyclic system is less labile to acid than are the 1,3-dioxolanes.     

Modification of polysaccharides containing uronic acid residues

Klebsiella Type 47 capsular polysaccharide has side chains attached to the main chain viaD-glucuronic acid residues. The side chains have been removed to yield an essentially linear polysaccharide by the following sequence of reactions: (1) substitution of hydroxyl and car?yl groups with methyl vinyl ether; (2) β-elimination by treatment with base; (3) removal of modified uronic acid residues and protecting groups by mild acid hydrolysis. The possibility of modifying other uronic acid-containing polysaccharides by this method is discussed.     

Synthetic routes to higher-carbon sugars. 1-C-Formylation of a 2-deoxyaldose via the anion of its diethyl dithioacetal

Diphenylmethylation of carbohydrate hydroxyl groups may be effected by the thermal reaction with diazo(diphenyl)methane in the absence of catalysts. Migration of the labile ester groups of methyl 2,3,4-tri-O-acetyl-α-d-glucopyranoside and 3-O-benzoyl-1,2-O-isopropylidene-α-d-glucofuranose does not occur during diphenylmethylation by this procedure. The diphenylmethyl group may be readily removed by catalytic hydrogenolysis, and is sufficiently acid-stable to enable the selective hydrolysis of acetal groups. Its use as an O-4 protecting-group and as a non-participating O-2 protecting-group in α-glycoside synthesis has been demonstrated in syntheses of methyl 2,3,6-tri-O-methyl-α-d-glucopyranoside and kojibiose octa-acetate, respectively.