A facile approach to anhydrogalactosucrose derivatives from chlorinated sucrose

Three new anhydrosucrose derivatives: 1,4:3,6-dianhydro-beta-D-fructofuranosyl 4-chloro-4-deoxy-alpha-D-galactopyranoside (4), 1,4:3,6-dianhydro-beta-D-fructofuranosyl 3,6-anhydro-4-chloro-4-deoxy-alpha-D-galactopyranoside (6) and 1,6-dichloro-1,6-dideoxy-beta-D-fructofuranosyl-3,6-anhydro-4-chloro-4-deoxy-alpha-D-galactopyranoside (8) were prepared from chlorinated sucrose. The structures of these anhydrides were confirmed by their (1)H and (13)C NMR spectra, ESIMS and elemental analysis. The crystal structures of 6 and the acetate of 4 (5) are presented. The relative reactivity of the chloromethyl groups towards S(N)2 reactions in 1,6-dichloro-1,6-dideoxy-beta-d-fructofuranosyl 4,6-dichloro-4,6-dideoxy-alpha-D-galactopyranoside was found to be in order 6>6'>1'.     

Synthesis of the alpha-L-Araf-(1-->2)-beta-D-Galp-(1-->6)-beta-D-Galp-(1-->6)-[alpha-L-Araf-(1-->2)]-beta-D-Galp-(1-->6)-D-Gal hexasaccharide as a possible repeating unit of the cell-cultured exudates of Echinacea purpurea arabinogalactan.

For the characterization of the supposed epitope of an arabinogalactan, isolated from the extract of the cell-cultured Echinacea purpurea, the title hexasaccharide was synthesized. The whole synthetic route was based on the 6-O-(methoxydimethyl)methyl ether (MIP) protecting group strategy. 2-O-Benzyl-3,4-O-isopropylidene-6-O-(methoxydimethyl)methyl-beta-D-galactopyranosyl-(1-->6)-1,2:3,4-di-O-isopropylidene-alpha-D-galactopyranose was used to prepare the desired glycosyl donor and glycosyl acceptor both carrying a persistent O-benzyl group at position 2'. Reaction of the digalactose donor and the digalactose acceptor resulted in a beta-(1-->6)-linked galactose-containing tetrasaccharide in which OH-2' and OH-2"' were substituted with benzyl groups. Hydrogenolytic removal of the benzyl groups of the tetragalactose compound gave the diol aglycon which was diarabinosylated in one step to furnish the protected target compound, whose deprotection led to the title hexasaccharide. All of the synthesized compounds were characterized by 1H and 13C NMR spectra, as well as by MALDI-TOF mass-spectrometry measurements.     

Synthesis of modified tetrasaccharide sequences of N-glycoproteins

The tetrasaccharides O-alpha-D-mannopyranosyl-(1----3)-O-[alpha-D- mannopyranosyl-(1----6)]-O-(4-deoxy-beta-D-lyxo-hexopyranosyl)-(1- ---4)-2- acetamido-2-deoxy-alpha, beta-D-glycopyranose (22) and O-alpha-D-mannopyranosyl-(1----3)-O-[alpha-D-mannopyranosyl-(1----6)]-O- beta-D-talopyranosyl-(1----4)-2-acetamido-2-deoxy-alpha, beta-D- glucopyranose (37), closely related to the tetrasaccharide core structure of N-glycoproteins, were synthesized. Starting with 1,6-anhydro-2,3-di-O-isopropylidene-beta-D-mannopyranose, the glycosyl donors 3,6-di-O-acetyl-2-O-benzyl-2,4-dideoxy-alpha-D-lyxo- hexopyranosyl bromide (10) and 3,6-di-O-acetyl-2,4-di-O-benzyl-alpha-D-talopyranosyl bromide (30), were obtained in good yield. Coupling of 10 or 30 with 1,6-anhydro-2-azido-3-O-benzyl-beta-D-glucopyranose to give, respectively, the disaccharides 1,6-anhydro-2-azido-3-O-benzyl-2-deoxy-4-O-(3,6-di-O-acetyl-2-O-benzyl-4 -deoxy- beta-D-lyxo-hexopyranosyl)-beta-D-glucopyranose and 1,6-anhydro-2-azido-3-O-benzyl-2-deoxy-4-O-(3,6-di-O-acetyl-2,4-di-O-ben zyl- beta-D-talopyranosyl)-beta-D-glucopyranose was achieved with good selectivity by catalysis with silver silicate. Simultaneous glycosylation of OH-3' and OH-6' of the respective disaccharides with 2-O-acetyl-3,4,6-tri-O-benzyl-alpha-D-mannopyranosyl chloride yielded tetrasaccharide derivatives, which were deblocked into the desired tetrasaccharides 22 and 37.     

Synthesis of protected fragments of the capsular polysaccharide of Streptococcus pneumoniae, type 8]

Oxidation of acetates of allyl and 2-(benzyloxycarbonylamino)ethyl beta-cellobiosides (with OH-4' and OH-6' unprotected) with the Jones reagent followed by esterification (with diazomethane or phenyldiazomethane) gave corresponding uronates with OH-4' unsubstituted. Condensation of these glycosyl acceptors and benzylated derivatives of D-galactose or 4-O-(alpha-D-glucopyranosyl)-D-galactose led to the protected tri- and tetrasaccharide fragments of the capsular polysaccharide from Streptococcus pneumoniae type 8.     

Cyclic acetals of 4,1',6'-trichloro-4,1',6'-trideoxy-galacto-sucrose and their conversion into methyl ether derivatives

The acid-catalysed reaction of 4,1',6'-trichloro-4,1',6'-trideoxy-galacto- sucrose (1) with 5.5 equiv. of 2-methoxypropene in N,N-dimethylformamide followed by acetylation gave 3',4'-di-O-acetyl-4,1',6'-trichloro-4,1',6'-trideoxy-2,3-O- isopropylidene-6-O-(1-methoxy-1-methylethyl)-galacto-sucrose (2, 2%), 6,3',4'- tri- O-acetyl-4,1',6'-trichloro-4,1',6'-trideoxy-2,3-O-isopropylidene-galacto -sucrose (3, 31%), 3',4'-di-O-acetyl-4,1',6'-trichloro-4,1',6'-trideoxy-2,3-O- isopropylidene- galacto-sucrose (4, 38%), 3'-O-acetyl-4,1',6'-trichloro-4,1',6'-trideoxy-2,3-O- isopropylidene- galacto-sucrose (5, 13%), and 2,3',4'-tri-O-acetyl-4,1',6'-trichloro- 4,1',6'-trideoxy-galacto-sucrose (6, 13%). Methylation of 4 followed by removal of the protecting groups gave 4,1',6'-trichloro-4,1',6'-trideoxy-6-O-methyl- galacto- sucrose (8). 4,1',6'-Trichloro-4,1',6'-trideoxy-3-O-methyl-galacto-sucrose (11) was synthesised from 6 by preferential tert-butyldiphenylsilylation of HO-6 followed by methylation and removal of the protecting groups. Likewise, 4,1',6'-trichloro- 4,1',6'-trideoxy-4'-O-methyl-galacto-sucrose (14) was synthesised from 5. Treatment of 3 with aqueous acetic acid followed by methylation and removal of the protecting groups afforded 4,1',6'-trichloro-4,1'6'-trideoxy-2,3-di-O-methyl- galacto-sucrose (17).     

Acetylated flavonol diglucosides from Meconopsis quintuplinervia

Four acetylated flavonol diglucosides, quercetin 3-O-[2'-O-acetyl-beta-d-glucopyranosyl-(1-->6)-beta-d-glucopyranoside], quercetin 3-O-[2',6'-O-diacetyl-beta-d-glucopyranosyl-(1-->6)-beta-d-glucopyranoside], isorhamnetin 3-O-[2'-O-acetyl-beta-d-glucopyranosyl-(1-->6)-beta-d-glucopyranoside], and quercetin 3-O-[2'-O-acetyl-alpha-l-arabinopyranosyl-(1-->6)-beta-d-glucopyranoside], together with five known flavonol glycosides quercetin 3-O-beta-d-glucopyranoside, kaempferol 3-O-beta-d-glucopyranoside, quercetin 3-O-[beta-d-galactopyranosyl-(1-->6)-glucopyranoside], isorhamnetin 3-O-[beta-d-galactopyranosyl-(1-->6)-beta-d-glucopyranoside], and kaempferol 3-O-[beta-d-glucopyranosyl-(1-->2)-beta-d-glucopyranoside] have been isolated from Meconopsis quintuplinervia. Their structures were determined using chemical and spectroscopic methods including HRFABMS, (1)H-(1)H COSY, HSQC and HMBC experiments.     

Acylated flavonoids and phenol glycosides from Veronica thymoides subsp. pseudocinerea

A new acylated flavone glucoside, 3'-hydroxyscutellarein 7-O-(6'-O-protocatechuoyl)-beta-glucopyranoside (1), and a new phenol glucoside, 3,5-dihydroxyphenethyl alcohol 3-O-beta-glucopyranoside (6) were isolated from Veronica thymoides subsp. pseudocinerea together with seven known flavone, phenol and lignan glycosides; 3'-hydroxyscutellarein 7-O-(6'-O-trans-feruloyl)-beta-glucopyranoside (2), 3'-hydroxy, 6-O-methylscutellarein 7-O-beta-glucopyranoside (3), luteolin 7-O-beta-glucopyranoside (4), isoscutellarein 7-O-(6'-O-acetyl)-beta-allopyranosyl (1' --> 2')-beta-glucopyranoside (5), 3,4-dihydroxyphenethyl alcohol 8-O-beta-glucopyranoside (7), benzyl alcohol 7-O-beta-xylopyranosyl (1" --> 2')-beta-glucopyranoside (8), and (+)-syringaresinol 4'-O-beta-glucopyranoside (9). Compounds 2, 3 and 7-9 were reported for the first time in the genus Veronica. The structures of the isolates were determined by means of spectroscopic (UV, IR, 1D and 2D NMR, HR ESI-MS) methods. Isolated compounds (1-7) exhibited potent radical scavenging activity against the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical.     

Bioactive sucrose esters from Bidens parviflora

An investigation on Bidens parviflora led to the isolation of three sucrose esters and a substituted truxillate. Their structures were elucidated as (6-O-(E)-p-coumaroyl)-beta-D-fructofuranosyl-(2-->1)-alpha-D-glucopyranoside, (6-O-(E)-p-coumaroyl)-beta-D-fructofuranosyl-(2-->1)-(6-O-(E)-p-coumaroyl)-alpha-D-glucopyranoside II, 6,6'-sucrose ester of (1alpha,2alpha,3beta,4beta)-3,4-bis(4-hydroxyphenyl)-1,2-cyclobutanedicarboxylic acid, dimethyl ester of (1alpha,2alpha,3alpha,4alpha)-2,4-bis(3,4-dihydroxyphenyl)-1,3-cyclobutanedicarboxylic acid on the basis of spectral and chemical evidence. These compounds were subjected to the following bioassays: the histamine release inhibition of rat mast cells induced by antigen-antibody reaction and the inhibitory activity of PGE(2) production by macrophages.     

Coumarin glucosides from Cruciata taurica

Two new coumarin glycosides (1 and 2) along with two known coumarin glucosides, daphnin (3) and daphnetin glucoside (4) were isolated from the aerial parts of Cruciata taurica. The structures of the new compounds were elucidated by spectral methods and chemical means as 7-O-(6' -acetoxy-beta-D-glucopyranosyl)-8-hydroxycoumarin (1) and 7-O-[6 '-O-(3',4'-dihydroxycinnamoyl)-beta-D-glucopyranosyl]-8-hydroxycoumarin (2). The phylogenetic significance of coumarins in C. taurica was discussed.     

Alkaloids from Galanthus nivalis

Phytochemical studies on Galanthus nivalis of Bulgarian origin resulted in the isolation of five compounds: 11-O-(3'-hydroxybutanoyl)hamayne, 3,11-O-(3',3'-dihydroxybutanoyl)hamayne, 3-O-(2'-butenoyl)-11-O-(3'-hydroxybutanoyl)hamayne, 3,11,3'-O-(3',3',3'-trihydroxybutanoyl)hamayne, and 2-O-(3'-acetoxybutanoyl)lycorine, together with five known alkaloids: ungeremine, lycorine, tazettine, hamayne, and ismine. Their structures were determined by (1)H and (13)C NMR spectroscopy and two-dimensional (1)H-(1)H and (1)H-(13)C chemical shift correlation experiments.     

Molecular cytotoxic mechanisms of catecholic polychlorinated biphenyl metabolites in isolated rat hepatocytes

Polychlorinated biphenyl (PCB) and PCB metabolites are highly lipophilic and accumulate easily in the lipid bilayer and fat deposits of the body. The molecular cytotoxic mechanisms of these metabolites are still not understood. The aim of the present study was to compare the cytotoxicity and toxicological properties of six dihydroxylated metabolites using isolated rat hepatocytes. All of the metabolites were more cytotoxic than 4-chlorobiphenyl (4-ClBP) and less cytotoxic than phenyl hydroquinone (PHQ). The order of cytotoxic effectiveness of catecholic metabolites expressed as LC(50) (2h) was 3',4'-diCl-2,3-diOH-biphenyl>PHQ>4'-Cl-2,5-diOH-biphenyl, 4'-Cl-2,3-diOH-biphenyl>2',5'-diCl-3,4-diOH-biphenyl>2',3'-diCl-3,4-diOH-biphenyl>3',4'-diCl-3,4-diOH-biphenyl>4'Cl-3,4-diOH-biphenyl>4'-Cl-biphenyl; showing that the positions of hydroxyl and chlorine groups were important for their hepatotoxicity and that the two 2,3-diOH congeners were the most cytotoxic. Cytotoxicity for 3,4-diOH metabolites correlated with the number and position of chlorine atoms with the more chlorine atoms being more cytotoxic. The cytotoxic order of metabolites with two chlorine atoms being 2',5'>2',3'>3',4'. Borneol, an uridine diphosphate glucuronosyltransferases (UGT) inhibitor, increased the cytotoxicity of all tested metabolites; suggesting that glucuronidation was a major mechanism of elimination of these compounds. On the other hand entacapone, a catechol-O-methyl transferase (COMT) inhibitor, only increased the cytotoxicity of 3',4'-diCl-3,4-diOH-biphenyl, 3',4'-diCl-2,3-diOH-biphenyl and 4'-Cl-2,3-diOH-biphenyl. Hepatocyte GSH was depleted (oxidized and conjugated) by these metabolites before cytotoxicity ensued in a similar order of effectiveness to their cytotoxicity with PHQ being the most effective. Hepatocyte mitochondrial membrane potential also decreased before cytotoxicity ensued with a similar order of effectiveness as their cytotoxicity. These results suggest that catecholic cytotoxicity can be attributed to mitochondrial toxicity and oxidative stress. Semiquinone or benzoquinone species were also important in the cytotoxicity of catecholic metabolites.     

Determination of substituents distribution in carboxymethylpullulans by NMR spectroscopy

The distribution of carboxymethyl substituents in the alpha-(1 --> 6)-linked maltotriosyl repeating units of a carboxymethylpullulan (CMP) series was investigated by high resolution NMR spectroscopy on very short oligomers (DPn = 1.2-1.5) obtained by acid hydrolysis. A series of 2D NMR experiments on parent pullulan, hydrolysed pullulan and CMP was used to assign the proton and carbon chemical shifts of CMP acid hydrolysates. The degree of substitution (DS) and the relative distribution of -CH2COONa groups at OH-2, OH-3, OH-4 and OH-6 of glucose residues (DSi) were determined from 1H NMR measurements. From a set of CMP samples, widely different in degree of substitution, it was observed that the substitution at C-2 is predominant and decreases according to the order C-2 > C-3 > C-6 > C-4. Taking into account the availability of each OH group in the parent pullulan, an order of relative reactivity of hydroxyl groups is defined according to the relation: Ri = DSi/ni, where ni is the number of free OH groups in a maltotriose unit (MTU) for a given site C-i, the reactivity order was found to be OH-2 > OH-4 > OH-6 > OH-3.     

Reactivity of melezitose and raffinose under Mitsunobu reaction conditions

The reactivity of melezitose and raffinose under Mitsunobu conditions was studied within the scope of the use of trisaccharides for the synthesis of fatty acid esters. Melezitose led to esters with preferential substitution at primary positions following the order of reactivity 6'>6>6'. Raffinose proved to be very reluctant toward ester formation in these conditions, leading mainly to the new 3',6'-anhydroraffinose.     

Formation and structure of a complex of sucrose with cobalt(III)bis(phenanthroline).

Sucrose forms a dicationic complex with cobalt(III)bis(phenanthroline) which can be isolated as the sparingly water-soluble triiodide salt or the water-soluble chloride. The circular dichroism (CD) spectrum demonstrates the Delta configuration at Co(III) and the presence of two phenanthroline and one sucrose residues in the complex. The O-2(g)--O-1(f) distance in crystalline sucrose permits strain-free coordination of these centers with Co(III) and in the complex the H-1,1'(f) singlet of sucrose separates into a pair of doublets. The 1H NMR spectrum in DMSO-d(6) shows that OH-2(g) is deprotonated and the signal of OH-1(f) is shifted strongly downfield by complexation with Co(III). Coordination involving glucose and fructose residues is consistent with neither alpha-methyl glucoside nor fructofuranose forming mixed complexes with phenanthroline. Structure simulation with the semi-empirical PM3(tm) basis set indicates that complexation by O-2(g) and OH-1(f) can give a Delta-complex with little structural distortion, whereas in hypothetical Lambda-complexes there is distortion of the sucrose residue. Observation of an NOE involving the sucrose and phenanthroline residues supports the postulated structure of the Delta-complex.     

Acylated flavone glycosides from Veronica

A survey of the flavonoid glycosides of selected taxa in the genus Veronica yielded two new acylated 5,6,7,3',4'-pentahydroxyflavone (6-hydroxyluteolin) glycosides and two unusual allose-containing acylated 5,7,8,4'-tetrahydroxyflavone (isoscutellarein) glycosides. The new compounds were isolated from V. liwanensis and V. longifolia and identified using NMR spectroscopy as 6-hydroxyluteolin 4'-methyl ether 7-O-alpha-rhamnopyranosyl(1"'-->2")[6"-O-acetyl-beta-glucopyranoside] and 6-hydroxyluteolin 7-O-(6"-O-(E)-caffeoyl)-beta-glucopyranoside, respectively. Isoscutellarein 7-O-(6"'-O-acetyl)-beta-allopyranosyl(1"'-->2")-beta-glucopyranoside was obtained from both V. intercedens and V. orientalis and its 4'-methyl ether from V. orientalis only. Complete 1H and 13C NMR spectral assignments are presented for both isoscutellarein glycosides. Two iridoid glucosides new to the genus Veronica (melittoside and globularifolin) were also isolated from V. intercedens.     

Iridoid glycosides from Gmelina arborea

Three iridoid glycosides 6-O-(3'-O-benzoyl)-alpha-l-rhamnopyranosylcatalpol (1a), 6-O-(3'-O-trans-cinnamoyl)-alpha-l-rhamnopyranosylcatalpol (2a) and 6-O-(3'-O-cis-cinnamoyl)-alpha-l-rhamnopyranosylcatalpol (3a) were isolated from aerial parts of Gmelina arborea and structures were elucidated by spectral analysis. Additionally a known iridoid 6-O-(3', 4'-O-dibenzoyl)-alpha-l-rhamnopyranosylcatalpol (4) was also isolated and identified.     

Antioxidant flavonoids from leaves of Polygonum hydropiper L

Ten flavonoid compounds were isolated from the dried leaves of Polygonum hydropiper L. (Laksa leaves), and identified as 3-O-alpha-L-rhamnopyranosyloxy-3',4',5,7-tetrahydroxyflavone; 3-O-beta-D-glucopyranosyloxy-4',5,7-trihydroxyflavone; 6-hydroxyapigenin; 6"-O-(3,4,5-trihydroxybenzoyl) 3-O-beta-D-glucopyranosyloxy-3', 4', 5, 7-tetrahydroxyflavone; scutillarein; 6-hydroxyluteolin; 3',4',5,6,7-pentahydroxyflavone; 6-hydroxyluteolin-7-O-beta-D-glucopyranoside; quercetin 3-O-beta-D-glucuronide; 2"-O-(3,4,5-trihydroxybenzoyl) quercitrin; quercetin. Evaluation of the antioxidative activity, conducted in vitro, by using electron spin resonance (ESR) and ultraviolet visible (UV-vis) spectrophotometric assays, showed that these isolated flavonoids possess strong antioxidative capabilities. Measurement of the Trolox equivalent antioxidant capacity (TEAC) values, against ABTS (2,2'-azinobis(3-ethyl-benzo-thiazoline-6-sulphonic acid) radicals and phenyl-tert-butyl nitrone (PBN) azo initiator (AI) also showed strong anti-oxidative activity. The most powerful of the antioxidants was 2"-O-(3,4,5-trihydroxybenzoyl) quercitrin (galloyl quercitrin). A combination of two flavonoid compounds was tested for synergistic anti-oxidative capacity, but no significant improvement was observed.     

Phenylpropanoid glucosides from leaves of Coussarea hydrangeifolia (Rubiaceae)

Phenylpropanoid glycosides, 1'-O-benzyl-alpha-L-rhamnopyranosyl-(1'-->6')-beta-D-glucopyranoside (1) and alpha-L-xylopyranosyl-(4'-->2')-(3-O-beta-D-glucopyranosyl)-1'-O-E-caffeoyl-beta-D-glucopyranoside (2), together with the known derivatives, 1,6-di-O-caffeoyl-beta-D-glucopyranoside (3), 1-O-(E)-caffeoyl-beta-D-glucopyranoside (4) and 1-O-(E)-feruloyl-beta-D-glucopyranoside (5), were isolated from leaves of Coussarea hydrangeifolia. Their structures were determined by IR, HRESIMS, and 1D and 2D NMR experiments, and their antioxidant activities, evaluated by assaying the free radical scavenging capacity using the DPPH (1,1-diphenyl-2-picrylhydrazyl) radical as substrate. The antioxidant activities of 3 and 4 (IC50 values of 15.0 and 19.2 microM, respectively) were comparable to that of the standard positive control caffeic acid, whilst 2 and 5 were only weakly active and 1 was inactive.     

Preparation of sucrose heptaesters unsubstituted at the C-1 hydroxy group of the fructose moiety via selective O-desilylation

Selective O-desilylation of 6,1',6'-tri-O-tert-butyldiphenylsilyl-2,3,4,3',4'-penta-O-benzo ylsucrose with hydrofluoric acid in acetonitrile led to the 1'-O-tert-butyldiphenylsilyl derivative (96% yield), which was further perbenzoylated and deprotected at OH-1' with tetrabutylammonium fluoride (86%). An analogous sequence with the corresponding O-acetylated sucrose derivative and tetrabutylammonium fluoride as desilylating agent resulted in a lower yield of the C-1' hydroxy derivative.     

Further saponins from Meryta lanceolata

Five new oleanane-type saponins along with 11 known ones were isolated from the leaves and stems of Meryta lanceolata. The new saponins were characterised by spectroscopic analysis including FAMS, 1 and 2D NMR experiments and the results of hydrolysis as 3-O-[beta-d-glucopyranosyl-(1-->2)-beta-d-glucuronopyranosyl] hederagenin 28-O-[alpha-l-rhamnopyranosyl-(1-->4)-beta-d-glucopyranosyl-(1-->6)-beta-d-glucopyranosyl] ester, 3-O-[beta-d-glucopyranosyl-(1-->2)-beta-d-glucuronopyranosyl] oleanolic acid 28-O-[alpha-l-rhamnopyranosyl-(1-->4)-beta-d-glucopyranosyl-(1-->6)-beta-d-glucopyranosyl]ester, 3-O-[beta-d-glucopyranosyl-(1-->2)-beta-d-glucuronopyranosyl] oleanolic acid 28-O-[alpha-l-rhamnopyranosyl-(1-->4)-beta-d-6-O-acetyl glucopyranosyl-(1-->6)-beta-d-glucopyranosyl]ester, 3-O-[beta-d-glucopyranosyl-(1-->3)-beta-d-glucopyranosyl-(1-->3)-alpha-l-arabinopyranosyl] oleanolic acid 28-O-[alpha-l-rhamnopyranosyl-(1-->4)-beta-d-glucopyranosyl-(1-->6)-beta-d-glucopyranosyl] ester and 3-O-[beta-d-glucopyranosyl-(1-->2)-beta-d-glucuronopyranosyl] hederagenin, respectively.