Studies of carbohydrate derivatives having the -CH2F function

The following primary sulphonates have been converted into the corresponding deoxyfluoro derivatives by reaction with potassium fluoride in ethylene glycol:1,2:3,4-di-O-isopropylidene-6-O-tosyl α-D-galactopyranose (1), methyl 2,3-O2-isopropyliden-5-O-tosyl-α,β-D-ribofuranoside (2), 1,2:3,4-di-O-methylene-6-O-tosyl-α-D-glucofuranose (3), 3,5-di-O-benzylidene-1,2-O-isopropylidene-6-O-tosyl-α-D-glucofuranose (4), and 1,2:3,5-di-O-isopropylidene-6-O-tosyl-α-D-glucofuranose (5). The yields were generally poor; in the reaction of 1, a major by-product was 6-O-(2-hydroxyethyl)-1,2:3,4-di-O-isopropylidene-α-D-galactopyranose (11). The reaction of the primary hydroxyl precursor of each of the above tosylates with N2-(2-chloro- 1,1,2-trifluoroethyl)-N,N-diethylamine generally yielded the O-chlorofluoroacetyl derivative; however, 1,2:3,5-di-O-methylene-α-D-glucofuranose (12) was converted into the 6-deoxy-6-fluoro derivative (8). The ¹⁹F resonances of compounds containing the CH₂F moiety fall between φ_C +213 and φ_C +235 p.p.m. The differences between the vicinal¹⁹F-¹H couplings of compounds having the D-gluco and D-galacto configurations clearly reflect the influence of the C-4O-4 substitutents on the populations of the C-5C-6 rotamers. A novel type of noise-modulated, heteronuclear decoupling experiment is described.     

The influence of hydrogen bonding on the rate of thiolate alkylation in tripod-zinc thiolate complexes

A series of new thioimidazolylborate zinc thiolate complexes Tti^xylZnSR (2)-(5) (where R = C₆H₄-o-OH, C₆H₄-o-CH₂OH, C₆H₄-o-NH₂, and C₆H₄-p-OH, respectively) have been synthesized and characterized as structural and functional models of the active site of the Ada repair protein. Structural determination of complexes 2-4 reveals intramolecular N/O-H?S hydrogen-bonding interactions. The influence of these hydrogen bonding interactions on the methylation of the thiolate ligands is evident from the fact that the rate of methylation for these complexes is reduced ca. 2 orders of magnitude compared to that found in the case of the non-hydrogen bonding-containing complex, Tti^xylZnSC₆H₅ (1).     

Pyrogallol derivatives from Leucanthemopsis pallida subsp.flaveola

from Leucanthemopsis pallida subsp.flaveo three new pyrogallol derivatives were isolated: 4-hydroxy-5-propionyl-1,3-di-O-methylpyrogallol, 4-hydroxy-5-propionyl-1,3-di-O-methyl-2-O-isopentenylpyrogallol and 5-(1′-isovalerianoyloxy)-ethyl-1,3-di-O-methyl-2-O-isopentenylpyrogallol.     

O-Methylation of phenylphenalenone phytoalexins in Musa acuminata and Wachendorfia thyrsiflora

Biosynthetic O-methylation at various sites along the backbone of inducible phenylphenalenones in Musa acuminata var. “Williams” (Musaceae) and Wachendorfia thyrsiflora (Haemodoraceae) was investigated using ¹³C-labelled precursors. The inducibility of O-methylated metabolites was demonstrated in both species and the origin of methoxyl group from [methyl-¹³C]l-methionine was confirmed. In addition to known phenylphenalenones, a methoxylated metabolite, 4-(4-hydroxy-3-methoxy-phenyl)-benzo[de]isochromene-1,3-dione, was detected and its structure elucidated mainly by NMR spectroscopic techniques. The experiments were used to discriminate methionine-derived and artificial methoxy groups formed during methanolic extraction. Finally, demethylation of 4′-methoxycinnamic acid and subsequent conversion to 3′,4′-methylenedioxycinnamic acid was demonstrated in M. acuminata.     

A chemo-biocatalytic approach in the synthesis of β-O-naphtylmethyl-N-peracetylated lactosamine

A chemo-enzymatic approach combining an enzymatic regioselective hydrolysis of peracetylated N-acetyl-α-d-glucosamine (1) with a mild controlled acyl migration led to 2-acetamido-2-deoxy-1,3,6-tri-O-acetyl-α-d-glucopyranose, which was further used in a glycosylation reaction in the synthesis of β-O-naphtylmethyl-N-peracetylated lactosamine.Candida rugose lipase (CRL) immobilized on octyl-agarose and modified by covering it with polyethyleneimine was the best catalyst in terms of activity, stability and regioselectivity in the hydrolysis of 1, producing the deacetylation in C-6 in 95% overall yield. Other immobilized lipases were not specific or with a very low activity towards the hydrolysis of 1.An acyl chemical migration by incubation of the deacetylated C-6 derivative at pH 8.5, 4 °C, and 10–20% acetonitrile permitted to obtain up to 75% overall yield of the 4-OH derivative product. This molecule was successfully applied in a glycosylation reaction to get the peracetylated α-d-lactosamine and finally, the peracetyl-β-O-naphtylmethyl-lactosamine derivative in 20% overall yield.     

Hydrogenolysis of benzylidene acetals: synthesis of benzyl 2,3,6,2′,3′,4′-hexa-O-benzyl-β-cellobioside, -maltoside,and -lactoside,benzyl 2,3,4,2′,3′,4′-hexa-O-benzyl-β-allolactiside,and benzyl 2,3,6,2′,3′,6′-hexa-O-benzyl-β-lactoside

Hydrogenolysis of benzyl penta-O-benzyl-4′,6′-O-benzylidene-β-cellobioside (4), -maltoside (5), and -allolactoside (16) with LiAlH₄-AlCl₃ gave only the corresponding derivatives having HO-6′ free, in yields of 55, 78, and 90%, respectively. The main product of the hydrogenolysis of benzyl penta-O-benzyl-4′,6′-O-benzylidene-β-lactoside (6) also had HO-6′ free, but the isomer having HO-4′ free was also isolated. The role of the C-1 substituent in the galactose moiety in the direction of benzylidene ring-cleavage is discussed.     

Nitrous acid deamination of methylated amino-oligosaccharide glycosides

G.l.c.-mass spectrometry has been used to characterize the products of N-deacetylation-nitrous acid deamination of per-O-methylated derivatives (8–11) of methyl 2-acetamido-2-deoxy-3-O-β-D-galactopyranosyl-α-D-glucopyranoside(1), methyl (2) and benzyl (3) 2-acetamido-2-deoxy-4-O-β-D-galactopyranosyl-β-D-glucopyranosides, and methyl 2-acetamido-2-deoxy-6-O-β-D-galactopyranosyl-α-D-glucopyranoside (4). 2,5-Anhydrohexoses have been converted into alditol trideuteriomethyl ethers, alditol acetates, and aldononitriles. The importance of side reactions that lead to the formation of 2-deoxy-2-C-formylpentofuranosides is discussed.     

Discovery of potent α-glucosidase inhibitor flavonols: Insights into mechanism of action through inhibition kinetics and docking simulations

Beside other pharmaceutical benefits, flavonoids are known for their potent α-glucosidase inhibition. In the present study, we investigated α-glucosidase inhibitory effects of structurally related 11 flavonols, among which quercetin-3-O-(3″-O-galloyl)-β-galactopyranoside (8) and quercetin 3-O-(6″-O-galloyl)-β-glucopyranoside (9) showed significant inhibition compared to the positive control, acarbose, with IC₅₀ values of 0.97 ± 0.02 and 1.35 ± 0.06 µM, respectively. It was found that while sugar substitution to C3-OH of C ring reduced the α-glucosidase inhibitory effect, galloyl substitution to these sugar units increased it. An enzyme kinetics analysis revealed that 7 was competitive, whereas 1, 2, 8, and 9 were uncompetitive inhibitors. In the light of these findings, we performed molecular docking studies to predict their inhibition mechanisms at atomic level.     

Chain elongation of sugars with ethyl isocyanoacetate

Addition of ethyl isocyanoacetate to 3-O-benzyl-1,2-O-isopropylidene-α-D-ribo-pentodialdo-1,4-furanose in ethanolic sodium cyanide gave two oxazolines that were hydrolysed during chromatography to two isomeric ethyl 3-O-benzyl-6-deoxy-6-formamido-1,2-O-isopropylidene-heptofuranuronates. Similarly, 1,2-O-isopropyl-idene-3-O-methyl-α-D-xylo-pentodialdo-1,4-furanose gave the 3-O-methyl-heptofuranuronates 7 and 11. Reduction of 7 and 11 gave N-methylamino esters that exhibited Cotton effects from which the configurations at C-6 of 7 and 11 were deduced. The chiralities at C-5 of 7 and 11 were established by tetrahydropyranlation of 7 and 11, followed by consecutive treatment with bis(2-methoxyethoxy)aluminium hydride, periodate, sodium borohydride, and dilute acid, to give 1,2-O-isopropylidene-3-O-methyl-α-D-glucofuranose and its β-L-ido epimer, respectively. Attempts to methylate HO-5 of 7 and 11 resulted in elimination. On formylaminomethylenation (ethyl isocyanoacetate and potassium hydride in tetrahydrofuran), 3-O-benzyl-1,2-O-isopropylidene-α-D-ribo-pentodialdo-1,4-furanose and its 3-O-methyl-α-D-xylo epimer each gave (E)- and (Z)-mixtures of alkenes that were hydrogenated to give mixtures of 5,6-dideoxy-6-formamido-heptofuranuronates.     

Acetylated allose-containing flavonoid glucosides from Stachys anisochila

In continuation of our chemosystematic study of Stachys (Labiatae) we have isolated the previously reported isoscutellarein 7-O-[6″'-O-acetyl-β-D-allopyranosyl-(1 → 2)-β-D-glucopyranoside] (1) and 3′-hydroxy-4′-O-methylisoscutellarein 7-O-[6″'-O-acetyl-β-D-allopyranosyl-(1 → 2)-β-D-glucopyranoside] (4) and four new allose-containing flavonoid glycosides from S. anisochila. The new glycosides are hypolaetin 7-O-[6″'-O-acetyl-β-D-allopyranosyl-(1 → 2)-β-D-glucopyranside] (6) as well as the three corresponding diacetyl analogues of 1, 4 and 6, isoscutellarein 7-O-[6″'-O-acetyl-β-D-allopyranosyl-(1 → 2)-6″-O-acetyl-β-D-glucopyranoside], 3′-hydroxy-4′-O-methylisoscutellarein 7-O-[6″'-O-acetyl-β-D-allopyranosyl-(1 → 2)-6″-O-acetyl-β-D-glucopyranoside] and hypolaetin 7-O-[6″'-O-acetyl-β-D-allopyranosyl-(1 → 2)-6″-O-acetyl-β-D-glucopyranoside]. Extensive two-dimensional NMR studies (proton-carbon correlations, COSY experiments) allowed assignment of all ¹H NMR sugar signals and a correction of the ¹³C NMR signal assignments for C-2 and C-3 of the allose.     

Cytotoxic triterpenoid saponins from Aesculus glabra Willd.

Twenty-four acylated polyhydroxyoleanene saponins were isolated from the seeds of Aesculus glabra. Sixteen of them, namely aesculiosides G1–G16 (1–16), were determined as compounds by spectroscopic and chemical analysis. The structural features of all 24 saponins are: (1) arabinofuranosyl units affixed to C-3 of the glucuronopyranosyl unit in the trisaccharide chain; (2) no 24-OH substitution; (3) C-2 sugar moiety substitution of the 3-O-glucuronopyranosyl unit is either glucopyranosyl or galactopyranosyl. The features of these isolated saponin structures provide more evidence for chemical taxonomy within the genus Aesculus. The cytotoxicity of the aesculiosides (1–16) were tested against A549 and PC-3 cancer cell lines with GI₅₀ from 5.4 to >25 μM.     

Acyclic-sugar purine nucleosides derived from d-glucose: stereochemical correlations in acyclic-sugar derivatives unequally substituted at c-1

Condensation of 2,3,4,5,6-penta-O-acetyl-l-bromo-1-s-methyl-l-thio-d-glucito (1) with 6-chloro-9-(chloromercuri)purine gave 49% of crystalline, levorotatory (1s)-2,3,4,5,6-penta-O-acetyl-1-(6-chloropurin-9-yl)-1-s-methyl-1-thio-d-glucitol (3), together with a smaller proportion of the syrupy, dextrorotatory (1R) isomer. Thiourea converted 3 into its 6-mercaptopurine analog, whose O-deacetylated derivative could be s-methylated to the corresponding 6-(methylthio)purin-9-yl analog; all compounds in this sequence were crystalline and were the pure (1s) isomers, as were the corresponding 1′-s-ethyl derivatives prepared by a similar route. Crystal-structure analysis of the O-deacetylated derivative of the 1$\text{-}\text{?}$s-ethyl analog of 3 established the relative stereochemistry of the ethylthio group, permitting assignment of the (1s) absolute stereochemistry to this compound and thus to all compounds in the sequence starting from 1, including the previously described, crystalline, levorotatory 1-(1,6-dihydro-6-thioxopurin-9-yl)-1-s-ethyl-1-thio-d-glucitol, whose chirality at C-1 had not hitherto been established. The close similarity of the chiroptical properties of the crystalline 1′-s-methyl derivatives to those of their 1′-s-ethyl counterparts permitted firm attribution of (1s) chirality to the former series also. Conformational studies showed that all of the derivatives have the sugar chain in a non-extended (sickle) conformation.     

Deamination of 2-amino-2-deoxyhexitols and of their per-O-methylated derivatives with nitrous acid

The products of nitrous acid deamination of per-O-methylated 2-amino-2-deoxy-d-glucitol and $\text{2-}\text{amino}\text{-2-}\text{deoxy}\text{-3-O-β-}\text{d}\text{-galactopyranosyl-}\text{d}\text{-glucitol}$ and its per-O-methylated derivative have been characterized by g.l.c.—mass spectrometry after treatment with sodium borodeuteride and further substitution by acetylation, methylation, or (trideuteriomethyl)ation. The results confirm that the most important reaction pathway (1) involves a 1 → 2-hydride shift to give $\text{2-}\text{deoxy-}\text{d}\text{-arabino-}\text{hexoses}$, but that significant side-reactions include (2) solvolytic displacement at C-2, (3) a 3 → 2-hydride shift, to give $\text{2-}\text{deoxy-}\text{d}\text{-erythro-3-}\text{hexuloses}$, and (4) a C-4→C-2 migration to give $\text{2-}\text{deoxy}\text{-2-C-}\text{(hydroxymethyl)-}\text{d}\text{-ribose}$ and -d-arabinose. Reactions (3) and (4) result in elimination of the original 3-O-substituents, with the exposure of new reducing groups, from oligosaccharides terminated by 3-O-substituted 2-amino-2-deoxyhexitols.     

The synthesis and N.M.R. spectroscopy of derivatives of 6-amino-6-deoxy-D-galactose-6-15N

Derivatives of 6-amino-6-deoxy-D-galactose-6-¹⁵N have been synthesized by reaction of the 6-deoxy-6-iodo (1) or 6-O-p-tolylsulfonyl derivative of 1,2:3,4-di-O-isopropylidene-α-D-galactopyranose with potassium phthalimide-¹⁵N. The reaction of 1 also yielded an elimination product, 6-deoxy-1,2:3,4-di-O-isopropylidene-β-L-arabino-hex-5-enopyranose. The structures of the 6-amino-6-deoxy-D-galactose derivatives and their precursors were characterized by proton- and ¹³C-n.m.r. spectroscopy, with confirmation of the ¹³C assignments by selective proton decoupling. Selective broadening of the C-1, C-4, C-5, and C-6 resonances of 6-amino-6-deoxy-1,2:3,4-di-O-isopropylidene-α-D-galactopyranose by low concentrations of cupric ion was observed, and studied by computerized measurements of the ¹³C linewidths. The application of this broadening to ¹³C-spectral assignments of amino sugar derivatives is indicated.     

A simple method of the preparation of 2′-O-Methyladenosine Methylation of adenosine with methyl iodide in anhydrous alkaline medium

A simple and effective method of the methylation on the 2′-O position of adenosine is described. Adenosine is treated with CH₃I in an anhydrous alkaline medium at 0°C for 4 h. The major products of this reaction are monomethylated adenosine at either the 2′-O or 3′-O position (total of 64%) and the side products are dimethylated adenosine (2′,3′-O-dimethyladenosi, 21%, and N⁶-2′-O-dimethyladenosine, 11%). The ratio of 2′-O- and 3′-O-methyladenosine has been found to be 8 to 1. Therefore, this reaction preferentially favors the synthesis of 2′-O-methyladenosine. The monomethylated adenosine is isolated from reaction mixture by a silica gel column chromatography. Then the pure 2′-O-methyladenosine can be separated by crystallization in ethanol from the mixture of 2′-O and 3′-O-methylated isomers. The overall yield of 2′-O-methyladenosine is 42%.     

Synthesis of an intensely sweet chlorodeoxysucrose: Mechanism of 4′-chlorination of sucrose by sulphuryl chloride

Reaction of 6-O-acetylsucrose¹ with sulphuryl chloride in chloroform-pyridine affords, after dechlorosulphation and acetylation, a mixture of two isomeric 2,3,6-tri-O-acetyl-4-chloro-4-deoxy-α-d-galactopyranosyl 3-O-acetyl-1,4,6-trichloro-1,4,6-trideoxy-β-d-hexulofuranosides (6 and 7) and 2,3,6-tri-O-acetyl-4-chloro-4-deoxy-α-d-galactopyranosyl 3,4-di-O-acetyl-1,6-dichloro-1,6-dideoxy-β-d-fructofuranoside (4). Chlorination of C-4, C-1′, and C-6′ occurs by direct displacement of the initially formed chlorosulphonyloxy groups by chloride ions, but displacement of the 4′-chlorosulphate is sterically hindered. The introduction of a 4′-chloro substituent involves ring opening of intermediate 3′,4′-epoxides by chloride ions, the ribo-epoxide producing the sorbo-isomer 6 and the lyxo-epoxide giving the fructo-isomer 7. The proposed mechanism is supported by the formation of 4-chloro-4-deoxyfructofuranosides when 3′,4′-lyxo-hexulofuranosides are treated with sulphuryl chloride under the same conditions.     

Nephroprotective,cytotoxic and antioxidant activities of Euphorbia paralias

ObjectiveTo investigate the effect of the ethyl acetate fraction of the aerial parts of E. paralias L. F. Euphorbiaceae on nephroprotective, cytotoxic, and antioxidant.Methodsdifferent spectroscopic and spectrophotometric methods were applied to identify phytoconstituents. The nephroprotective potential of E. paralias ethyl acetate fraction (Ep EtOAc) was evaluated in male rats with thioacetamide-induced kidney injury, as wll as cytotoxic activity was evaluated using a viability assay, and the antioxidant activity was evaluated using the DPPH method. Results: quantitative estimation of total phenolics and flavonoids of E. paralias was performed using unique spectrophotometric methods. The polyphenolic compounds gallic acid (1), ellagic acid (2), kaempferol-3-O-(6″-O-galloyl-β-D-glucopyranoside) (3), quercetin-3-O-β-D-glucopyranoside (4) and quercetin-3-O-β-D-arabinoside (5) were isolated from the ethyl acetate fraction of the aerial parts of E. paralias. The thioacetamide administration resulted in marked nephrotoxicity, but pretreatment with Ep EtOAc significantly attenuated the nephrotoxicity through alteration of kidney biomarkers, thereby improving the redox status of the tissue and restoring serum biochemical parameters nearly to normal levels. This study revealed a significant cytotoxic and strong antioxidant effect. Conclusion: we conclude that the Ep EtOAc may be used in the future as nephroprotective, cytotoxic, and antioxidant agent derived from a natural source.     

Chemical constituents from the aerial parts of Impatiens hypophylla Makino var. hypophylla

Seven flavonoids such as luteolin (1), luteolin 7-O-β-glucopyranoside (2), luteolin 3'-O-β-glucopyranoside (3), chryseriol (4), apigenin (5), apigenin 7-O-β-glucopyranoside (6) and astragalin (7) and one coumarin, scopoletin (8) were isolated from the aerial parts of Impatiens hypophylla Makino var. hypophylla (Family: Balsaminaceae). Structures of these compounds were elucidated on the basis of spectroscopic methods. All these compounds were isolated for the first time from I. hypophylla var. hypophylla.     

Synthesis of the 6-methyl and 3,6- and 4,6-dimethyl ethers of methyl 2-acetamido-2-deoxy-α-D-mannopyranoside

The 6-mono- (6) and 4,6- (16) and 3,6-di-methyl (25) ethers of methyl 2-acetamido-2-deoxy-α-D-mannopyranoside have been synthesized from 6-O-trityl, 4,6-O-benzylidene, and 3-O-methyl derivatives, respectively, by way of O-benzoyl and of O-allyl derivatives. The yields were respectively 37 and 43% for 6, 34 and 50% for 16, and 14 and 25% for 25. These ethers are used as standard compounds for the structure elucidation, by methylation, of polymers containing 2-amino-2-deoxy-D-mannose.     

Location of O-acetyl groups in the acidic d-xylan of mimosa scabrella (bracatinga). A study of O-acetyl group migration

Extraction with dimethyl sulfoxide of wood-meal of the stem of bracatinga (Mimosa scabrella), a south Brazilian hardwood, that was defatted and delignified by treatment with aqueous chlorine at 0–5° followed by extraction with cold ethanol, gave a soluble O-acetylated 4-O-methyl-d-glucurono-d-xylan having (1→4)-linked β-d-xylopyranosyl residues that were unsubstituted (65%) and 2-O-(14%), 3-O- (16%), and 2,3-di-O-acetylated (5%), as determined by methylation analysis. Another preparation obtained by use of refluxing ethanol in the delignification process showed neither removal nor migration of acetyl groups. By comparison with synthetic, partly O-acetylated d-xylans of known composition, ¹³C-n.m.r. spectroscopy indicated that O-acetyl group migration does not occur during treatment with cold aqueous chlorine, refluxing ethanol, or water at 70°. Methyl 2-O-acetyl-4-O-methyl-β-d-xylopyranoside (6) was also unaffected by aqueous chlorine. O-Acetyl group migration took place more readily in aqueous and dimethyl sulfoxide solutions of 6 than of O-acetyl-d-xylans. The lowest temperatures at which migration was observed in monosaccharides was at 50 and 70° for solutions in D₂O and (CD₃)₂SO, respectively.