Streptococcus pneumoniae type XIV polysaccharide: synthesis of a repeating branched tetrasaccharide with dioxa-type spacer-arms

β-Glycosides of 2-acetamido-2-deoxy- -glucopyranose were synthesized, using either 7-methoxycarbonyl-3,6-dioxa-1-heptanol or 8-azido-3,6-dioxa-1-octanol. Selective β-lactosylation of 7-methoxycarbonyl-3,6-dioxaheptyl 2-acetamido-3-O-benzyl-2-deoxy-β- -glucopyranoside with hepta-O-acetyl-lactosyl-trichloroacetimidate, followed by β-galactosylation of the secondary hydroxyl group with O-(2,3,4,6-tetra-O-acetyl-- -galactopyranosyl)trichloroacetimidate, catalytic hydrogenolysis, and O-deacetylation, gave 7-methoxycarbonyl-3,6-dioxaheptyl 2-acetamido-2-deoxy-4-O-β- -galactopyranosyl-6-O-(4-O-β- -galactopyranosyl-β- -glucopyranosyl)β- -glucopyranoside. Selective β-lactosylation of 8-azido-3,6-dioxaocytl 2-acetamido-3-O-benzyl-2-deoxy-β- -glucopyranoside with hepta-O-acetyl-lactosyl bromide in the presence of silver triflate, followed by condensation with 2,3,4,6-tetra-O-acetyl-- -galactopyranosyl bromide in the presence of silver triflate, catalytic hdyrogenolysis, and O-deacetylation, gave 8-azido-3,6-dioxaoctyl 2-acetamido-2-deoxy-4-O-β- -galactopyranosyl-6-O-(4-O-β- -galactopyranosyl-β- -glucopyranosyl)-β- glucopyranoside.     

Iridoid glucosides from Thunbergia laurifolia

Two iridoid glucosides, 8-epi-grandifloric acid and 3′-O-β-glucopyranosyl-stilbericoside, were isolated from the aerial part of Thunbergia laurifolia along with seven known compounds, benzyl β-glucopyranoside, benzyl β-(2′-O-β-glucopyranosyl) glucopyranoside, grandifloric acid, (E)-2-hexenyl β-glucopyranoside, hexanol β-glucopyranoside, 6-C-glucopyranosylapigenin and 6,8-di-C-glucopyranosylapigenin. Strucural elucidation was based on the analyses of spectroscopic data.     

Cycloartane triterpene glycosides from Astragalus trigonus

Three new cycloartane glycosides, trigonoside I, II and III, and the known astragalosides I and II were isolated from the roots of Astragalus trigonus. The structures of the new glycosides were totally elucidated by high field (600 MHz) NMR analyses as cycloastragenol-6-O-β-xylopyranoside, cycloastragenol-3-O-[-l-arabinopyranosyl(1 → 2)-β-d-xylopyranosyl]-6-O-β- d-xylopyranoside and cycloastragenol-3-O-[-l-arabinopyranosyl(1 → 2)-β-d-(3-O-acetyl)-xylopyranosyl]-6-O-β-d-xylopyranoside.     

Anthocyanins with an unusual acylation pattern from stem of Allium victorialis

Two novel anthocyanins have been isolated from the stem of Allium victorialis. By means of chemical degradation and spectroscopy, especially homo- and hetero-nuclear two-dimensional NMR techniques, the structures were determined to be cyanidin 3-O-(3″,6″-O-dimalonyl-β-glucopyranoside) (76.6%) and cyanidin 3-O-(3″,O-malonyl-β-glucopyranoside) (13.8%). This is the first report of acylation of the 3-position in the sugar moiety of any anthocyanin. The stability of malonyl substitution in the 3″-position on glucose is higher than the corresponding 6″-malonylation.     

Isolation and characterization of a tetrasialoganglioside from mouse brain, containing 9-O-acetyl,N-acetylneuraminic acid

A new ganglioside, containing an alkali-labile linkage, was extracted from mouse brain and purified. It represents 3.6% of total lipid-bound sialic acid in the tissue and was obtained in pure form with a yield of about 35%. It contains sphingosine, glucose, galactose, N-acetylgalactosamine and sialic acid in the molar ratio 1:1:2:1:4 and, upon exhaustive sialidase treatment gives the monosialoganglioside GM1. Partial acid hydrolysis, methylation analysis, gas-liquid chromatography-mass spectrometry and chromium trioxide oxidation studies showed its basic neutral glycosphingolipid core to be ganglio-N-tetraose-ceramide. Three of the four sialic acid residues are N-acetylneuraminic acid and one, as shown by gas-liquid chromatography-mass spectrometry, is 9-O-acetyl,N-acetylneuraminic acid, which contains the alkali labile linkage. 9-O-acetyl,N-acetylneuraminic acid is -ketosidically linked to position 8 of the N-acetylneuraminic acid residue bound to position 3 of the internal galactose. The other two N-acetylneuraminic acid residues form a disialosyl residue linked to position 3 of external galactose. The complete structure of the studied ganglioside is as follows: NeuAc2–8NeuAc2–3Galβ1–3GalNAcβ1–4(9-O-Ac-NeuAca2–8NeuAc2-1′-N-acylsphingosine, and it can be considered as a derivative of the tetrasialoganglioside GQ1b.     

Chalconoid and stilbenoid glycosides from Guibourtia tessmanii

Phytochemical studies on the stem bark of Guibourtia tessmanii yielded a dihydrochalcone glucoside, 2′,4-dihydroxy-4′-methoxy-6′-O-β-glucopyranoside dihydrochalcone and a new stilbene glycoside, 3,5-dimethoxy-4′-O-(β-rhamnopyranosyl-(1→6)-β- glucopyranoside) stilbene besides the known pterostilbene. Their structures were established on the basis of one and two dimensional NMR spectroscopic techniques, FABMS and chemical evidence.     

A triterpenoid glucoside from Barringtonia acutangula

The structure of a new triterpenoid glucoside from Barringtonia acutangula was deduced as 2,3β,19-trihydroxy-olean-12-ene-23,28-dioic acid 28-O-β- -glucopyranoside from chemical reactions and spectral data.     

Synthesis of a series of ganglioside GM3 analogs containing a deoxy-N-acetylneuraminic acid residue.

Ganglioside GM₃ analogs containing 4-, 7-, 8-, and 9-deoxy-N-acetylneuraminic acids in the place of N-acetylneuraminic acid (Neu5Ac) have been synthesized. Glycosylation of 2-(trimethylsilyl)ethyl O-(6-O-benzoyl-β- - galactopyranosyl)-(1 → 4)-2,6-di-O-benzoyl-β- -glucopyranoside with the methyl 2-thioglycoside derivatives of the respective deoxy-N-acetylneuraminic acids, using dimethyl(methylthio)sulfonium triflate as a promoter, gave the four required 2-(trimethylsilyl)ethyl -sialosyl-(2 → 3b)-β-lactosides. These were converted via O-acetylation, selective removal of the 2-(trimethylsilyl)ethyl group, and subsequent imidate formation, into the corresponding -sialosyl-(2 → 3b)--lactose trichloroacetimidates 15, 17, 19, and 21. Glycosylation of (2S,3R,4E)-2-azido-3-O-benzoyl-4-octadecene-1,3-diol with 15, 17, 19, and 21 in the presence of boron trifluoride etherate afforded the expected β glycosides, which were transformed in good yields, via selective reduction of the azido group, coupling with octadecanoic acid, O-deacylation, and de-esterification, into the target compounds.     

Chemotaxonomic significance of flavonoids and phenolic acids in the Hieracium rohacsense group (Hieracium sect. Alpina; Lactuceae, Compositae)

Five apomictic taxa from the Hieracium rohacsense group were studied for their phenolic constituent composition. The following substances represent dominant compounds in the leaves: chlorogenic acid, 3,5-dicaffeoylquinic acid, luteolin 7-O-β- -glucopyranoside, luteolin 4′-O-β- -glucuronopyranoside and apigenin 4′-O-β- -glucuronopyranoside. Within the group only quantitative differences were found, luteolin 7-O-glucoside being the most important chemotaxonomic marker. Each taxon has its own specific quantitative pattern, invariable within the taxon. Based on these characteristic profiles, H. rohacsense can be distinguished from a closely related and still undescribed taxon from Mt. Pip Ivan. The proportion of luteolin 7-O-glucoside to apigenin 4′-O-glucuronoside also clearly separates the individuals of two morphologically close species—H. ratezaticum and H. pseudocaesium, which corresponds to a few slight but recognisable morphological and phenological characteristics. The ontogenetic stage of leaf development and seasonal variation are also important factors, which must be taken into consideration, as the quantity of the substances changes during leaf ontogeny and with season.     

Saponins from Albizzia lucida.

Three main saponins were isolated from the seeds of Albizzia lucida. Their structures were established by spectral analyses and chemical and enzymatic transformations as 3-O-[β- -xylopyranosyl(1→2)-- -arabinopyranosyl (1→6)] [β- -glucopyranosyl (1→2)] β- -glucopyranosyl echinocystic acid; 3-O-[- -arabinopyranosyl (1→6)][β- -glucopyranosyl (1→2)]-β- -glucopyranosyl echinocystic acid and 3-O-[β- -xylopyranosyl (1→2)-β- -fucopyranosyl (1→6)-2-acetamido-2-deoxy-β- -glucopyranosyl echinocystic acid, characterized as its methyl ester.     

Catalytic properties of the endoxylanase I from Thermoascus aurantiacus

Endo-β-1,4-xylanase I previously purified from Thermoascus aurantiacus solid state culture was further characterized. The enzyme had a molecular weight of 33 kDa by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and 31 kDa by gel filtration. Thin layer chromatography (TLC) analysis showed that endoxylanase liberates aldotetrauronic acid MeGlcA-1,2-Xylβ-1,4-Xylβ-1,4-Xyl as the shortest acidic fragment from glucuronoxylan and an isomeric xylotriose (Xyl₃) of the structure Xylβ1-3Xylβ1-4Xyl from rhodymenan. The enzyme performed ideally on O-acetyl-4-O-methylglucuronoxylan, liberating large amounts of short acetylated and non-acetylated fragments. Also, the enzyme was capable to hydrolyse arabinoxylan to arabinose (Arab), xylose (Xyl) and xylobiose (Xyl₂). The enzyme degraded pNPX (4-nitrophenyl β- -xylopyranoside) by a complex reaction pathway that involved both hydrolysis and glycosyl transfer reactions. The enzyme tolerates the replacement of β-xylopyranosyl units in several artificial substrates by β-glucopyranosyl, - -arabinopyranosyl and - -arabinofuranosyl units and was active on pNPC (4-nitrophenyl β- -cellobioside), pNP-Arap (4-nitrophenyl - -arabinopyranoside) and pNPAraf (4-nitrophenyl - -arabinofuranoside). The enzyme also hydrolysed the 4-methylumbelliferyl glycosides of β- -xylobiose and β- -xylotriose at the agluconic linkage. The results suggested that the xylanase I from T. aurantiacus has catalytic properties similar to those belonging to family 10.     

Polysaccharides from the seeds of Senna multijuga

The seeds of Senna multijuga were extracted with water or 1% acetic acid and treated with ethanol, resulting in two insoluble fractions. After purification, the major one (FIA, 23%) was shown to be a galactomannan (Man:Gal 2.3:1;[] = + 54.6;[η]=1340mlg⁻¹). It consists of a main chain of (1 → 4)-linked β-d-mannopyranosyl residues substituted at 06 by single-unit -d-galactopyranosyl side chains. The second fraction (FIB, 2.5%) was an O-acetyl-glucuronoarabinoxylan from the seed coats (O-acetyl 8.3 mol%; glucuronic acid 11.7%, Xyl:Ara ratio 20:1), which showed a predominance of 4-O-substituted Xylp units (84.4%), branched at 03 with non-reducing end units of Xylp, Araf and glucuronic acid. The O-acetyl positions in d-xylosyl units are at 02 (4.8%), 03 (4.4%) and 02,3 (0.9%). The ratio between 03 and 02 determined by ¹³C-nuclear magnetic resonance spectroscopy is 1.5:1.     

An approach to address Candida rugosa lipase regioselectivity in the acylation reactions of trytilated glucosides

Candida rugosa lipase crude preparations (CRL) catalyse the regioselective acylation of methyl 6-O-trytil beta-d-glucopyranoside in organic solvents, using vinyl acetate as acyl donor. The ratio of the two products formed, namely methyl 2-O acetyl 6-O-trytil beta-d-glucopyranoside and methyl 3-O acetyl 6-O-trytil beta-d-glucopyranoside was found to be markedly affected by the nature of the reaction medium. In hydrophobic solvents values up to 80% of the monoacetylated product in position C-3 were obtained compared to less than 30% in solvents with low hydrophobicity. Computational studies were carried out to simulate the interactions between methyl 6-O-trytil beta-d-glucopyranoside and both CRL and the solvents, in order to rationalize the experimental results.     

Kinetically controlled synthesis of ampicillin with immobilized penicillin acylase in the presence of organic cosolvents

Penicillin acylase (PA) is used in the industrial production of 6-amino penicillanic acid (6-APA). However, by proper control of reaction medium, the enzyme can be used in the reverse synthesis of β-lactam antibiotics from the corresponding β-lactam nuclei and suitable acyl donors. Under thermodynamically controlled strategy, the use of organic cosolvents can favor synthesis over hydrolysis by lowering water activity and favoring the non-ionic reactive species. Under kinetically controlled strategy using activated acyl donors, organic solvents can favor synthesis by depressing hydrolytic reactions. Results are presented on the synthesis of ampicillin from phenylglycine methyl ester and 6-APA with immobilized Escherichia coli PA in the presence of organic cosolvents. Several solvents were tested in terms of enzyme stability and solubility of substrates. Ethylene glycol, glycerol, 1–2 propanediol and 1–3 butanediol were selected accordingly and ampicillin synthesis was performed in all of them. Best results in terms of yield and productivity were obtained with ethylene glycol, with which further studies were conducted. Variables studied were enzyme to limiting substrate ratio, acyl acceptor to acyl donor ratio, organic solvent concentration, pH and temperature. Experimental design based on a two-level fractional factorial design was conducted. pH was determined as the most sensitive variable and was further optimized. The best conditions for ampicillin synthesis in terms of productivity, within the range of values studied for those variables, were pH 7.4, 28°C, 36 U_S PA/mmol 6-APA, 3 mol PGME/mol 6-APA and 45 % (v/v) ethylene glycol concentration. Productivity was 7.66 mM ampicillin/h, which corresponds to a specific productivity of 7.02 μmol ampicillin/h U_S at 55 % yield. Productivity was lower than in buffer but product yield was higher because of the much lower relative hydrolysis rates.     

Synthesis of a di- and a tri-saccharide related to the K-antigen of Klebsiella type 10 and a study of their inhibition in the precipitin reaction

Syntheses of methyl 3-O-- -galactopyranosyl-- -mannopyranoside (10) and methyl 3-O-- -galactopyranosyl-2-O-(β- -glucopyranosyluronic acid)-- -mannopyranoside (11) in good yield are described. Both 10 and 11 significantly inhibit antigen-antibody precipitation in the Klebsiella Type 10 immune system. The results provide more evidence for the structure (1) of the antigen from Klebsiella K-10 and its immunodominant grouping.     

Pentacyclic triterpenes from Myrianthus liberecus

From the methylated trunk wood extracts of Myrianthus liberecus, six pentacyclic triterpenes have been isolated as their methyl esters. These included the known methyl benthamate, methyl euscaphate, methyl tormentate, methyl arjunolate, methyl 3-isoarjunolate and methyl 3β-O-(4″-O-methyl-E-coumaroyl)-arjunolate, a new triterpene derivative.     

Acylated flavonol diglucosides from Lotus polyphyllos

Three acylated flavonol diglucosides, kaempferol 3-O-β-(6″-O-E-p-coumaroylglucoside)-7-O-β-glucoside; quercetin 3-O-β-(6″-O-E-p-coumaroylglucoside)-7-O-β-glucoside; isorhamnetin 3-O-β-(6″-O-E-p-coumaroylglucoside)-7-O-β-glucoside were isolated from the whole plant aqueous alcohol extract of Lotus polyphyllos. The known 3,7-di-O-glucosides of the aglycones kaempferol, quercetin and isorhamnetin were also characterized. All structures were established on the basis of chemical and spectral evidence.     

Laccase-catalyzed oxidation of 1-(3,4-dimethoxyphenyl)-1-propene using ABTS as mediator

The fungal laccases catalyzed oxidation of 1-(3,4-dimethoxyphenyl)-1-propene (2) with dioxygen in acetate buffer (pH 4.5) producing 1-(3,4-dimethoxyphenyl)propane-1,2-diol (4) and its 1-O-acetyl and 2-O-acetyl derivatives 5 and 6, and 3,4-dimethoxybenzaldehyde (7). However, in phosphate buffer (pH 5.9), the same reaction produced only 4 and 7. When 4 was treated in the same fashion in the phosphate buffer, it was converted into 7 with more than 95 mol% yield. This, together with the formation of 5 and 6 in the acetate buffer, showed that 2 is converted into 3–5 via 1-(3,4-dimethoxyphenyl)propane-1,2-epoxide (3) in the acetate buffer in the presence of ABTS. The major reaction of fungal laccase-catalyzed oxidation of 2 with dioxygen in the presence of ABTS is epoxidation of the double bond conjugated to the aromatic ring.     

Chiral macrocyclic compounds from lactose derivatives

The reaction of benzyl 2,6,6′-tri-O-benzyl-3′,4′-O-isopropylidene-β-lactoside with 1,11-ditosyloxy-3,6,9-trioxaundecane gave benzyl 2,6,6′-tri-O-benzyl-3′,4′-O-isopropylidene-3,2′-O--(3,6,9-trioxaundecane-1,11-diyl)-β-lactoside (2, 47%). Acid hydrolysis of 2 and condensation of the product with 1,14-ditosyloxy-3,6,9,12-tetra-oxatetradecane afforded benzyl 2,6,6′-tri-O-benzyl-3′,4′-O-(3,6,9,12-tetraoxa-tetradecane-1,14-diyl)-3,2′-O-(3,6,9-trioxaundecane-1,11-diyl)-β-lactoside (29%). Similarly, the reaction of benzyl 2,6,2′,4′,6′-penta-O-benzyl-β-lactoside with Ts[OCH₂CH₂]₄OTs gave benzyl 2,6,2′,4′,6′-penta-O-benzyl-3,3′-O-(3,6,9-trioxaundecane-1,11-diyl)-β-lactoside (78%). ¹H-N.m.r. spectroscopy has been used to study the formation of host-guest complexes with some of these macrocyclic compounds and benzyl ammonium thiocyanate.     

A triterpenoid and its saponin from Phytolacca esculenta.

A new triterpenoid, esculentagenin, and its glycoside, esculentoside M, were isolated from the roots of Phytolacca esculenta and characterized as 11-oxo-3-O-methyloleanata-12-en-2β,3β,23-trihydroxy-28-oic acid and 3-O-[β - -glucopyranosyl (1→4)-β- -Xylopyranosyl]-28-O-β- -glucopyranosyl-11-oxo-30-methyloleanate-12-en-2β,3β,23-trihydroxy-28-oic acid by spectral and chemical evidence.