Theoretical studies on the conformations of methyl glycopyranosides

The σ-charges on various atoms of methyl glycosides have been computed by using the MO-LCAO method of Del Re. The potential and free energies of methyl aldohexopyranosides and methyl aldopentopyranosides in their C1(d) and 1C(d) conformations have been calculated. Minimization of the energies of these conformations has been studied by suitably tilting the axial C-C and C-O bonds. Considerable release of strain is achieved when tilts of 4.5 and 3° are given to the axial hydroxymethyl and hydroxyl groups, respectively, that are involved in Hassel-Ottar effect. A tilt of 3° is also found necessary for the axial OMe group involved in the Hassel-Ottar effect. The calculated free-energy values are in accord with experimental ones, after adding a value of 0.8 kcal.mole^?1 for the anomeric effect of -OMe group. These studies predict that all of the methyl aldohexopyranosides, except methyl α-d- and methyl β-d-idopyranosides, favour the C1 conformation. On the other hand, the energy calculations also predict that, of the eight methyl aldopentopyranosides studied, only methyl α-d- and methyl β-d-xylopyranosides and methyl α-d -ribopyranoside favour the C1(d) conformation; for the other pentopyranosides, considerable amounts of both C1(d) and 1C(d) conformations are present in the equilibrium mixture. The calculated values of the percentage of α-anomer present in the equilibrium mixture agree fairly well with those obtained experimentally.     

Acetoxonium ions from acetoxyoxiranes and orthoesters: their conversion into ethylidene acetals,rearrangement, and solvolysis

The acid-catalysed ethylidenation of some methyl pentopyranosides has been studied and the configuration at the acetal carbon atom assigned by p.m.r. spectroscopy. There is a strong preference for the isomer in which the methyl group has the endo configuration. Several cyclic alkyl orthoacetates derived from methyl pentopyranosides have been prepared by orthoester exchange and the endo C-methyl isomer shown to preponderate. Treatment of vicinal acetoxyoxiranes and orthoacetates with boron trifluoride followed by lithium borohydride, or with diborane, yields ethylidene acetals in which the C-methyl group is endo. Rearrangements of the hexachloroantimonate salts of acetoxonium ions derived from methyl lyxo- and arabino-pyranosides, possessing trans-vicinal acetoxyl groups, have been studied. The ions having the arabino configuration are preferred in both the α and β series. The reaction of cyclic orthoacetates of methyl β-L-arabinopyranoside and some derivatives with dry acetic acid proceeds via an acyclic acetoxonium ion to yield only products having the L-arabino configuration.     

The oxidation of methyl α-D-glucopyranoside with methyl sulproxide and acetic anhydride

The relative proportions of carbonyl, O-acetyl, and O-(methylthio)methylsugars resulting from the partial oxidation of methyl α-D-glucopyranoside with methyl sulphoxide and acetic anhydride have been investigated@ the preparation of the 2- and 6-(methylthio)methyl ethers of methyl α-D-glucopyranoside is described.     

13C-n.m.r. spectra of xylo-oligosaccharides and their application to the elucidation of xylan structures

¹³C-N.m.r. spectra of thirteen xylo-oligosaccharides [a complete series of α- and β-d-xylopyranosyl derivatives of methyl α-d-xylopyranoside, β-d-xylopyranosyl derivatives of methyl 4-O-β-d-xylopyranosyl-d-xylopyranoside, methyl O-α-d-xylopyranosyl-(1→3)-O-β-d-xylopyranosyl-(1→4)-d-xylopyranoside, and a branched methyl β-xylotetraoside] have been interpreted. The data obtained have been used for the carbon signal assignment in the spectra of a number of red-algal xylans. ¹³C-N.m.r. spectroscopy is shown to be a rapid and convenient method for the structural analysis of xylose-rich polysaccharides.     

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.     

Odoriferous compounds from the flowers of the conifers Picea abies,pinus sylvestris and Larix sibirica

A GC/MS analysis of the volatile constituents from the flowers of Norway Spruce, Picea abies, has been carried out. The volatile constituents of the female flowers were distinctly different from those of the male flowers and the twigs. Characteristic constituents are methyl and ethyl benzoate, methyl and ethyl salicylate, methyl and ethyl butanoate, borneol and bornyl acetate. In the scent from the male flowers we could only detect the same monoterpenes as in the twigs. In Larix sibirica methyl benzoate, methyl salicylate, borneol and bornyl acetate were detected in the female flowers and, in the female flowers of Pinus sylvestris, methyl salicylate was found.     

Carbon-13 nuclear magnetic resonance spectra of carbohydrate oxirane derivatives

The ¹³C-chemical shifts and ¹J_C,H values of two series of carbohydrate oxirane derivatives, namely methyl 2,3-anhydro-ribo- and -lyxofuranosides and methyl 2,3-anhydro-4,6-O-benzylidene-manno- and -allopyranosides have been determined. The assignment of ¹³C resonances has been established mainly by the examination of the proton-coupled and the selective proton-decoupled spectra. The effect of the oxirane rings on the chemical shifts of β and γ carbon atoms (from the oxirane ring oxygen atom) has been observed. Large ¹J_C,H values associated with cis CH bonds adjacent to the oxirane rings relative to those of trans counterparts have been found.     

Phenolic constituents of Semecarpus anacardium

GLC-MS analysis of methylated bhilawanol from S. anacardium nuts and its oxidation product, the methyl ester of an aromatic carboxylic acid, conclusively proved that it contains more than seven closely related compounds. Two of them are major components which were isolated and shown to be 1-pentadec-Δ^5′-enyl-2,3-dimethoxybenzene (I) and 1-pent biflavanoids A, B and C have been also isolated from defatted nuts of S. anacardium. The first of these has been characterized as its methyl ethers. A₁ and A₂, for which biflavanone structures (VI) and (VII) are suggested on the basis of chemical and spectral evidence. The biflavanones B and C have been also characterized as their methyl ethers. Suggested structures are O-methyl derivatives of a IB-3′, IIA-8-binaringenin (XIV) for the former and IB-3′, IIA-8-biliquiritigenin (XV) for the latter.     

Margotianin,a new diterpenoid from Margotia gummifera

From the roots and aerial parts of Margotia gummifera a new natural diterpenic methyl ester, margotianin, has been isolated. Its structure was established as methyl ent-7α-angeloxy-15α-acetoxy-atis-16-en-19-oate almost exclusively by ¹³C NMR spectroscopy.     

Équilibres conformationnels de glucides au niveau de liaisons σ SP-SP: Partie V. Dérivés 2,3,-O-isopropylidène de pyranosides hybrides sp en C-4. Comparaison avec leurs analogues saturés

The conformation in solution of derivatives of methyl hexopyranosides has been studied by n.m.r. The esters of methyl 2,3-O-isopropylidene-α-D-manno- and -talopyranosides as well as their 4-deoxy-4-C-methyl analog having a manno configuration exist mainly in a flattened (^4,0F) chair conformation (⁴C₁). The presence in the talo epimer of the 4-deoxy-4-C-methyl analog of the bulky methyl group on the endo side of the bicyclic system results in a skew form (³S₁). The methyl 4-deoxy-2,3-O-isopropylidene-4-C-methylene-α-D-lyxo-hexopyranosides monosubstituted at C-4′ adopt, in solution, a conformation close to ³S₁, whichever their configuration (cis or trans) at the double bond, as indicated by their allylic coupling constants.     

Bioherbicidal ability and weed management of allelopathic methyl esters from Lantana camara

Allelochemicals are secondary metabolites which are not edible and can be used as growth regulators and bio-herbicides. The goal of current study was to assess allelopathic ability of Lantana camara (Sage-plant) flowers against weeds viz. Avena fatua (Wild oat), Euphorbia helioscopia (Sun-spurge), Chenopodium album (Goosefoot), Phalaris minor (Canary-grass), and Rumex dentatus (Knotweed). Bioassay analysis of three methanolic fractions of the Combiflash from L. camara was performed at 50%, 75% and 100% concentration using germination percentage parameters, inhibition of plumule and radicle size. The fraction II of Combiflash strongly suppressed all weeds with negligible effect on T. aestivum. Gas chromatography-mass spectroscopy was conducted for the fraction, and isolated compounds were used to perform bioassays. From fraction II GC–MS detected four methyl esters of allelopathic fatty acid viz. Methyl oleate, methyl palmitate, methyl stearate and methyl linoleate. The evaluation of physiological effects of the bioassay revealed substantial suppression of chlorophyll, antioxidant enzymes (superoxide, dismutase peroxidase) and protein material in all weeds by methyl palmitate. Bioassay activity and study of physiological parameters revealed that the effective bio-herbicidal compound in Lantana camara flowers is methyl palmitate. This is the first time that methyl palmitate (a fatty acid methyl ester) has been related to herbicidal activity in L. camara flowers. It is proposed that field studies based on hormesis research and the mechanism of action of this compound be carried out.     

Biotransformation of organic sulfides: Part. 10. Formation of chiral ortho- and meta-substituted benzyl methyl sulfoxides by biotransformation using Helminthosporium species NRRL 4671

Benzyl methyl sulfides substituted with methyl, chloro, cyano, bromo, methoxy, nitro and amino groups in the ortho or meta positions of the aromatic ring have been converted to (S) sulfoxides by biotransformation using the fungal biocatalyst Helminthosporium species NRRL 4671. The enantiomeric excesses for meta-substituted examples were high in those cases where the substituent was of a polar nature, and comparable to those observed for the corresponding para-substituted substrates. With one exception (o-amino), the ortho-substituted examples gave sulfoxides of lower enantiomeric purity. The role of a suitably located polar substituent on an aryl ring of the substrate in ensuring a high enantiomeric excess in sulfoxidation by Helminthosporium species has been confirmed by the biotransformations of 4-(methylthiomethyl)benzyl alcohol and 2-(4-nitrophenyl) ethyl methyl sulfide, which give sulfoxides of much higher optical purity than those obtained from the corresponding unsubstituted substrates.     

Formation,isolation and structure determination of methyl linolenate diperoxides

Autoxidation of methyl linolenate gives rise to isomeric mono-hydroperoxides by reaction with one mole of oxygen but further reaction with a second mole of oxygen readily occurs to produce an isomeric mixture of diperoxides. Autoxidation of individual pure methyl hydroperoxylinolenate isomers has been used as a method of obtaining less complex diperoxide mixtures which can be separated into their pure components by preparative high-pressure liquid chromatography (HPLC). The major diperoxide isomers arising from the autoxidation of pure 9R- and 13S- hydroperoxides of methyl linolenate have been isolated and characterised as isomeric epidioxyhydroperoxides of methyl linolenate. These same compounds have been identified as components of the more complex mixture of diperoxides produced during methyl linolenate autoxidation. The structures of the isolated diperoxides have been determined by physico-chemical methods and a mechanism for their formation is proposed.     

Terpenoid and biflavonoid constituents of Calophyllum calaba and Garcinia spicata from Sri Lanka

A new bark acid, isochapelieric acid (cis-chapelieric acid), chapelieric acid, friedelin, friedelan-3β-ol, canophyllal, canophyllol, friedelan-3β,28-diol, canophyllic acid and amentoflavone have been isolated and characterized from leaf extractives of Calophyllum calaba. ¹³CNMR spectra of methyl chapelierate and methyl isochapelierate have been recorded and interpreted. Leaf extractives of Garcinia spicata afforded an unidentified long chain carboxylic acid, friedelin, friedelan-3β-ol, sitosterol and the biflavanones GB-1, GB-1a, GB-2a and morelloflavone. Chemotaxonomic significance of the occurrence of some of the above foliar constituents in Calophyllum and Garcinia species is discussed.     

Minor lignans of Piper clusii

Further investigations on the petrol extract of Piper clusii have afforded four more new lignans.These are 2S,3R,4R,2-ethoxy-3-(3,4,5-trimethoxyphenyl)methyl 4-(1,3-benzodioxol-5-yl) methyl tetrahydrofuranol; 3R,4R,bis-3,4-(3,4,5-trimethoxyphenyl) methyl tetrahydrofuran-2-one; 2R,3R,2-(7-methoxy-1,3-benzodioxol-5-yl) methyl 3-(3,4,5-trimethoxyphenyl)methyl butan-1,4-diol and 2R,3R,2-(1,3-benzodioxol-5-yl)methyl 3-(3,4,5-trimethoxyphenyl) methyl butan-1,4-diol. This is the first report of these compounds from a natural source.     

Mass spectra of acetylated derivatives of sialic acids

The fragmentation pattern in electron-impact mass spectrometry has been established for the peracetylated methyl ester methyl glycoside derivative of N-acetylneuraminic acid. The resulting, data allow the interpretation of the mass spectrum of the corresponding derivative of a new sialic acid isolated from the starfish Distolasterias nipon which is shown to be 8-O-methyl-N-acetylneuraminic acid.     

Synthesis of acetylenic sugars and uronic acids via two-carbon chain extension of d-ribose

Treatment of methyl β-d-ribofuranoside with acetone gave methyl 2,3-O-isopropylidene-β-d-ribofuranoside (1, 90%), whereas methyl α-d-ribofuranoside gave a mixture (30%) of 1 and methyl 2,3-O-isopropylidene-α-d-ribofuranoside (1a). On oxidation, 1 gave methyl 2,3-O-isopropylidene-β-d-ribo-pentodialdo-1,4-furanoside (2), whereas no similar product was obtained on oxidation of 1a. Ethynylmagnesium bromide reacted with 2 in dry tetrahydrofuran to give a 1:1 mixture (95%) of methyl 6,7-dideoxy-2,3-O-isopropylidene-β-d-allo- (3) and -α-l-talo-hept-6-ynofuranoside (4). Ozonolysis of 3 and 4 in dichloromethane gave the corresponding d-allo- and l-talo-uronic acids, characterized as their methyl esters (5 and 6) and 5-O-formyl methyl esters (5a and 6a). Ozonolysis in methanol gave a mixture of the free uronic acid and the methyl ester, and only a small proportion of the 5-O-formyl methyl ester. Malonic acid reacted with 2 to give methyl 5,6-dideoxy-2,3-O-isopropylidene-β-d-ribo-trans-hept-5-enofuranosiduronic acid (7).     

Sialic acids in permethylation analysis: preperation and identification of partially O-methylated derivatives of methlyl N-acetyl-N-methyl-β-D-neuraminate methyl glycoside

A set of partially O-methylated derivatives of methyl N- acetyl-N-methyl-β-D-neuraminate methyl glycoside has been prepared as reference compounds for the Incorporation of acylneuraminic acids into methylation analysis. G.1.c.-m.s. data for the O-trimethylsilyl and O-acetyl derivatives of these compounds are described in detail. The various substances give rise to highly characteristic mass-spectrometric fragmentation-patterns.     

Synthesis of 2-acetamido-2-deoxy-5-thio-d-glucopyranose

2-Acetamido-2-deoxy-5-thio-d-glucopyranose (12) has been synthesized from methyl 2-acetamido-2-deoxy-5,6-O-isopropylidene-β-d-glucofuranoside (1). Benzoylation of 1, followed by O-deisopropylidenation, gave methyl 2-acetamido-3-O-benzoyl-2-deoxy-β-d-glucofuranoside, which was converted, via selective benzoylation and mesylation, into methyl 2-acetamido-3,6-di-O-benzoyl-2-deoxy-5-O-mesyl-β-d-glucofuranoside (5). Treatment of 6, formed by the action of sodium methoxide in chloroform on 5, with thiourea gave methyl 2-acetamido-2,5,6-trideoxy-5,6-epithio-β-d-glucofuranoside (7), which was converted into the 5-thio compound 9 by cleavage of the epithio ring in 7 with potassium acetate. Alkaline treatment of 10, derived from 9 by hydrolysis, afforded the title compound. Evidence in support of the structures assigned to the new derivatives is presented.     

Identification by gc-ms of 4-chloroindolylacetic acid and its methyl ester in immature Vicia faba seeds

4-Chloroindolylacetic acid and its methyl ester have been converted to the N′-heptafluorobutyryl methyl ester derivative. An extract of immature seeds of Vicia faba has been similarly derivatized. It gave in its mass spectrum the same fragmentation pattern as the synthetic heptafluorobutyryl derivative. The chlorine atom was assigned to the 4-position on the indole ring after comparison by GLC of the extract and of four monochlorinated IAA isomers.