Highly glycosylated flavonoids from the pods of Bobgunnia madagascariensis

Methanolic extracts of the pods of Bobgunnia madagascariensis (Leguminosae) yielded four pentaglycosylated flavonoids, including the 3-O-α-l-rhamnopyranosyl(1→3)-α-l-rhamnopyranosyl(1→2)[α-l-rhamnopyranosyl(1→6)]-β-d-glucopyranoside-7-O-α-l-rhamnopyranosides of 3,5,7-trihydroxy-2-(4-hydroxyphenyl)-4H-benzopyran-4-one (kaempferol) and 3,5,7-trihydroxy-2-(3,4-dihydroxyphenyl)-4H-benzopyran-4-one (quercetin), which were characterized by a novel O-linked branched tetrasaccharide. Spectroscopic and chemical methods were used to determine the structures of the latter, which co-occurred with the corresponding β-d-galactopyranosyl isomers, and two saponins. Conformational isomerism of quercetin 3-O-α-l-rhamnopyranosyl(1→3)-α-l-rhamnopyranosyl(1→2)[α-l-rhamnopyranosyl(1→6)]-β-d-glucopyranoside-7-O-α-l-rhamnopyranoside was detected in solution by NMR, a phenomenon previously associated only with C-glycosylflavonoids.     

New constituents from Mikania laevigata Shultz Bip. ex Baker

A new phenylpropanoid and two new diterpenes were isolated from the leaves of the plant Mikania laevigata Shultz Bip. ex Baker. The structures of these compounds were established by 1D- and 2D-nuclear magnetic resonance spectroscopic techniques and mass spectrometry data. Taraxerol, lupeol, coumarin, syringaldehyde, trans-melilotoside, cis-melilotoside, adenosine, patuletin 3-O-β-d-glucopyranoside, kaempferol 3-O-β-d-glucopyranoside, quercetin 3-O-β-d-glucopyranoside, methyl 3,5-di-O-caffeoyl quinate, and 3,3′,5-trihydroxy-4′,6,7-trimethoxyflavone were isolated too. In addition, the compounds dihydrocoumarin, spathulenol, caryophyllene oxide, kaurenoic acid, beyerenoic acid, and lupeol acetate were identified by GC-MS.     

A novel acylated quercetin tetraglycoside from oolong tea (Camelia sinensis) extracts

A novel acylated quercetin tetraglycoside, namely quercetin 3-O-(2^G-p-coumaroyl-3^G-O-β-l-arabinosyl-3^R-O-β-d-glucosylrutinoside) was isolated from oolong tea (Camelia sinensis) extracts. Structural analysis of this compound was achieved by NMR, TOF-MS and high-resolution FAB-MS. Triglycosyl flavonols have previously been reported from tea leaves and tea seeds however this is the first report of an aromatic acylated and tetraglycosyl flavonol.     

Structural revision of shatavarins I and IV, the major components from the roots of Asparagus racemosus

The two major steroidal saponins from the roots of Asparagus racemosus were isolated by RP-HPLC and their structure determined by extensive NMR studies. Their structures did not match those reported previously for shatavarins I and IV and were found to be 3-O-{[β-d-glucopyranosyl(1→2)][α-l-rhamnopyranosyl(1→4)]-β-d-glucopyranosyl}-26-O-(β-d-glucopyranosyl)-(25S)-5β-furostan-3β,22α,26-triol and 3-O-{[β-d-glucopyranosyl(1→2)][α-l-rhamnopyranosyl(1→4)]-β-d-glucopyranosyl}-(25S)-5β-spirostan-3β-ol.     

C-Glycopyranosyl-1,4-benzoquinones and -hydroquinones opening access to C-glycosylated analogs of vitamin E

2-(Per-O-acetyl-β-d-glycopyranosyl)-1,4-dimethoxybenzenes led to C-glycosyl-hydroquinones suitable for preparing C-glycosylated analogs of vitamin E, having the sugar moiety free or acetylated.     

Structure of tecophilin,a tri-caffeoylanthocyanin from the blue petals of Tecophilaea cyanocrocus, and the mechanism of blue color development

The pigment, tecophilin, in blue flowers of Tecophilaea cyanocrocus was isolated and the structure was determined to be 3-O-(6-O-α-l-rhamnopyranosyl-β-d-glucopyranosyl)-7-O-(6-O-(4-O-(2-O-(4-O-β-d-glucopyranosyl-(E)-caffeoyl)-6-O-(4-O-β-d-glucopyranosyl-(E)-caffeoyl)-β-d-glucopyranosyl)-(E)-caffeoyl)-β-d-glucopyranosyl)delphinidin. The reproduction experiment of the same color as petals according to the results of chemical analysis and measurement of vacuolar pH of blue cells clarified that the blue color solely develops by tecophilin without interaction of metal ions nor co-pigments. ¹H NMR analysis and CD spectrum indicate the co-existence of clockwise intermolecular self-association of the delphinidin nuclei and intramolecular π–π stacking between the chromophore and caffeoyl residues to derive bathochromic shift of the absorption spectrum and stabilize the color by preventing hydration reaction.     

Thyonosides A and B, two new saponins isolated from the holothurian Thyone aurea

The structures of two saponins, thyonosides A and B, isolated from the holothurian Thyone aurea collected in Namibia, were elucidated by 1D and 2D NMR (¹H, ¹³C, ¹H-¹H COSY, ¹H-¹H J-resolved, TOCSY, HMQC, HMBC and NOESY). The two compounds have the same aglycon but different oligosaccharidic chains. Thyonoside A has a 3-O-methyl-β-d-xylopyranosyl-(1→3)-6-O-sodium sulphate-β-d-glucopyranosyl-(1→4)-β-d-quinovopyranosyl-(1→2)-4-O-sodium sulphate-β-d-xylopyranosyl chain, and thyonoside B a 3-O-methyl-β-d-xylopyranosyl-(1→4)-β-d-xylopyranosyl-(1→4)-β-d-quinovopyranosyl-(1→2)-4-O-sodium sulphate-β-d-xylopyranosyl chain. The holostane-type aglycon features an endocyclic double bond at position 7-8, a double bond at position 25-26 and a β-acetoxy group at C16.     

Two novel carbonic acid esters conjugated with oligophenyl glucosides from Rhamnus nakaharai

Two novel carbonic acid esters conjugated with oligomeric phenyl glycosides have been isolated and characterized from the wood of Rhamnus nakaharai. The structures are characterized as 5,7-dihydroxyphthalide 5-O-β-[6-O-{3″-methoxy-4″-O-β-[6?-O-(4?-O-carboxy-3?,5?-dimethoxy)phenyl]glucopyranosyl}phenyl]glucopyranoside (1) and 6-O-{3′-methoxy-4′-O-β-[6″-O-(3?-mercapto-5?-methoxy-4?-O-methylcarboxy)phenyl]glucopyranosyl}phenyl β-glucopyranose (2), namely, rhamnakoside A (1) and B (2), all by NMR and other spectral methods, respectively. They could be a novel case of phase II detoxification products and biogenetic diversity in plant kingdom.     

Synthesis of 4,8-anhydro-d-glycero-d-ido-nonanitol 1,6,7-trisphosphate as a novel IP3 receptor ligand using a stereoselective radical cyclization reaction based on a conformational restriction strategy

4,8-Anhydro-d-glycero-d-ido-nonanitol 1,6,7-trisphosphate (9), designed as a novel IP₃ receptor ligand having an α-C-glycosidic structure, was synthesized via a radical cyclization reaction with a temporary connecting allylsilyl group as the key-step. Phenyl 2-O-allyldimethylsilyl-3,4-bis-O-TBS-1-seleno-β-d-glucopyranoside (10a), conformationally restricted in the unusual ¹C₄-conformation, was treated with Bu₃SnH/AIBN to form the desired α-cyclization product 16a almost quantitatively. On the other hand, when a conformationally unrestricted O-benzyl-protected 2-O-allyldimethylsilyl -1-selenoglucoside 15 was used as the substrate, the radical reaction was not stereoselective and gave a mixture of the α-and β-products. From 16a, the target C-glucoside trisphosphate 9 was synthesized via phosphorylation of the hydroxyls by the phosphoramidite method. During the synthetic study, an efficient procedure for the oxidative C-Si bond cleavage, via a nucleophilic substitution at the silicon with p-MeOPhLi followed by Fleming oxidation, was developed. The C-glycoside 9 was found to be a full agonist for Ca²⁺ mobilization, although its activity was weaker than that of the natural ligand IP₃. Thus, the α-C-glucosidic structure was shown to be a useful mimic of the myo-inositol backbone of IP₃.     

Design and synthesis of a novel water-soluble Aβ1-42 isopeptide: an efficient strategy for the preparation of Alzheimer's disease-related peptide, Aβ1-42, via O-N intramolecular acyl migration reaction

A novel water-soluble isopeptide of Alzheimer's disease-related peptide Aβ1-42, `26-O-acyl isoAβ1-42', which could efficiently convert to intact Aβ1-42 under physiological conditions via O-N intramolecular acyl migration, was synthesized providing a new system useful for investigation of biological function of Aβ1-42.     

Intramolecular C-glycosylation of 2-O-benzylated pentenyl mannopyranosides: remarkable 1,2-trans stereoselectivity

The IDCP-promoted intramolecular C-glycosylation of pentenyl α-mannopyranosides carrying, at O-2, an activated benzyl group gave, unexpectedly, the 1,2-trans-fused bicyclic product which corresponds to an α-C-aryl mannopyranose derivative. This remarkable, strained C-glycosyl compound was rapidly epimerized to the more stable 1,2-cis product on treatment with BF₃·Et₂O. The IDCP-reaction product could be elaborated into a 2-(α-C-mannopyranosyl)-3,4,5-trimethoxybenzyl alcohol derivative.     

Justiciosides E-G, triterpenoidal glycosides with an unusual skeleton from Justicia betonica

Three new triterpenoidal glucosides, justiciosides E, F and G, were isolated from the aerial portion of Justicia betonica. Their structures were established through chemical and spectroscopic analyses, and showed an unusual A-nor-B-homo oleanan-12-ene skeleton type for the aglycone moiety as A-nor-B-homo-oleanan-10,12-diene-3β,11α,28-triol 28-O-β-d-glucopyranosyl-(1→2)-β-d-glucopyranoside, A-nor-B-homo-oleanan-10,12-diene-3β,11α,28-triol 28-O-β-d-glucopyranosyl-(1→2)-β-d-glucopyranosyl-(1→2)-β-d-glucopyranoside, and 11α-methoxy-A-nor-B-homo-oleanan-10,12-diene-3β,11α,28-triol 28-O-β-d-glucopyranosyl-(1→2)-β-d-glucopyranosyl-(1→2)-β-d-glucopyranoside, respectively.     

Separation and identification of three epimeric pairs of new C-glucosyl anthrones from Rumex dentatus by on-line high performance liquid chromatography–circular dichroism analysis

Six C-glucosyl anthrones were characterized as three pairs of epimers by on-line high performance liquid chromatography–circular dichroism (HPLC–CD) analysis and isolated from the roots of Rumex dentatus by column chromatography. Their structures were elucidated by mass spectrometry, nuclear magnetic spectroscopy and HPLC–CD analysis. They are 10R-C-β-d-glucosyl-10-hydroxyemodin-9-anthrone (rumejaposide E, 1) and 10S-C-β-d-glucosyl-10-hydroxyemodin-9-anthrone (rumejaposide F, 2), 10R-C-β-d-glucosylemodin-9-anthrone (rumejaposide G, 3) and 10S-C-β-d-glucosylemodin-9-anthrone (rumejaposide H, 4), 10S-C-β-d-glucosyl-10-hydroxychrysophanol-9-anthrone (cassialoin, 5) and 10R-C-β-d-glucosyl-10-hydroxychrysophanol-9-anthrone (rumejaposide I, 6). Rumejaposides F–I (2–4 and 6) were new C-glucosyl anthrones. Rumejaposide E (1) and cassialoin (5) were isolated for the first time in Rumex plants. On-line HPLC–UV–CD analysis was a useful tool for structure elucidating epimeric C-glycosides anthrones 3–6 because of the poor stability of the pure isomers (3 and 4) and the minute quantity of 5 and 6 in the mixture.     

A novel labdane diterpene from Acritopappus longifolius

A novel labdane diterpene was isolated from the plant Acritopappus longifolius. The structure of this compound was established by 1D- and 2D-nuclear magnetic resonance spectroscopic techniques and mass spectrometry data. N-Methyl-4-hydroxy-trans-proline, stigmasterol-3-O-β-d-glycoside, and the flavonoids quercetin, luteolin, kaempferol, and rutin were also isolated.     

Two additional 1,9-diarylnonanoid 3-glucosides from Erica cinerea among which an unusual α-dione in conformational equilibrium

Continuation of the phytochemical analysis of Erica cinerea fresh aerial parts resulted in the isolation of two new compounds with a very close chromatographic behavior. On the basis of spectroscopic evidence (UV, MS and NMR), the structures were established as (−)-(3S,6E)-1,9-bis(p-hydroxyphenyl)-3-hydroxynon-6-en-5-one 3-O-β-d-glucoside named 6,7-anhydroericaone 3-O-β-d-glucoside and (−)-(3S)-1,9-bis(p-hydroxyphenyl)-3-hydroxynonan-5,6-dione 3-O-β-d-glucoside named α-ericadione 3-O-β-d-glucoside. Unanticipated by its α-alkadione type structure —a very unusual feature in the plant kingdom— the latter metabolite was found as a mixture of the minor s-cis and the major s-trans conformers. Moreover, the GC-MS analysis of the aglycone moieties of such glucosides, pointed out the permanent absence of the molecular ion and the constant hydroxybenzylium base peak, as well as the conversion of the α-dione into the major α-keto-enol tautomer.     

Synthesis of PI-88 analogue using novel O-glycosidation of exo-methylenesugars

Acid-promoted α-stereoselective O-glycosidation of 1-exo-methylenesugars was successfully applied to the synthesis of a PI-88 analogue. By using methanesulfonic acid as a promoter, 1′-C-methyl-α-disaccharides with p-methoxybenzyl protection were obtained in high yield. The sequence of selective deprotection and glycosidation provided 1-C-methyl-pentasaccharide efficiently.     

The microbiological transformation of steroidal saponins by Curvularia lunata

The microbiological transformation of polyphyllin I (compound I), polyphyllin III (compound II), polyphyllin V (compound III) and polyphyllin VI (compound IV) by Curvularia lunata into their corresponding subsaponins, for example, diosgenin-3-O-α-l-arabinofuranosyl (1→4)-β-d-glucopyranoside (compound V), diosgenin-3-O-α-l-rhamnopyranosyl (1→4)-β-d-glucopyranoside (compound VI), diosgenin-3-O-β-d-glucopyranoside (compound VII) and pennogenin-3-O-β-d-glucopyranoside (compound VIII), were studied in this paper. Curvularia lunata is able to hydrolyze terminal rhamnosyls that are linked by 1→2 C- bond to sugar residues of steroidal saponins at C-3 position with high activity and regioselectivity.     

Synthetic studies of erythromycin derivatives: 6-O-methylation of (9S)-12,21-anhydro-9-dihydroerythromycin A derivatives

Synthetic studies on methylation of erythromycin derivatives were conducted. Methylation of 6 resulted in the formation of the C-3′ quaternary ammonium salts with a rate faster than 6-O-methylation. In dipolar aprotic solvent and under strong base conditions, 6-O-methylation, C-3′ quaternary ammonium salts formation and 2-C-methylation proceeded simultaneously to yield a mixture of three different products 7, 8 and 9. The quaternary ammonium salts were converted back to the corresponding tertiary amines 2, 10 and starting material 6 by employing sodium 4-pyridinethiolate as a N-demethylation reagent. The 6-O-methylation was eventually achieved in a good yield when a carbobenzyloxy (Cbz) group was utilized to protect the C-3′-dimethylamino group of 4. In this report, we will discuss the details of different reaction courses in the methylation of (9S)-12, 21-anhydro-9-dihydroerythromycin A derivatives.     

Neoverataline A and B, two antifungal alkaloids with a novel carbon skeleton from Veratrum taliense

Bioassay-guided fractionation of the ethanol extract of the roots and rhizomes of Veratrum taliense yielded two new and thirteen known steroidal alkaloids. The structures of the two new compounds, neoverataline A and B, were established by extensive spectroscopic analyses to be 3,4-secocevane-4,9-olid-14,15,16,20-tetra-ol-3-oic acid and 3,4-secocevane-4,9-olid-7,14,15,16,20-penta-ol-3-oic acid, respectively, and are a novel carbon skelton. All of the fifteen alkaloids were subjected to in vitro antifungal assays, which showed that the verazine- (veramitaline, stenophylline B, stenophylline B-3-O-β-d-glucopyranoside, veramiline-3-O-β-d-glucopyranoside) and jerveratrum-type (jervine, jervine-3-O-β-d-glucopyranoside) alkaloids exhibited strong antifungal activities against the phytopathogenic fungus Phytophthora capisis with MICs of 160, 120, 160, 80, 80 and 120 μg·L⁻¹, respectively. Furthermore, the verazine-type alkaloids stenophylline B, stenophylline B 3-O-β-d-glucopyranoside and veramiline 3-O-β-d-glucopyranoside were shown to also inhibit the growth of another fungal phytopathogen Rhizoctonia cerealis with MICs of 160, 120 and 120 μg mL⁻¹. The MICs of triadimefon (an antifungal agrochemical used herein as a positive control) against P. capisis and R. cerealis were 120 and 80 μg mL⁻¹, respectively. A preliminary structure-activity relationship regarding these alkaloids has been formulated.