Gas-liquid chromatography-mass spectrometry of acetates of partially methylated methyl glycosides. VII. Tri- and tetramethylheptoses

Nine tri- and five tetramethyl ethers have been obtained by the partial methylation of methyl - and -glucoheptopyranosides and methyl 2,3,4,6,7-penta-O-acetyl1-- and--glucoheptopyranosides. The retention indices of both types of methyl ethers on the liquid phase NPGS have been measured and the main directions of the fragmentation of these compounds under electron impact have been determined. The laws of the mass spectra of the position isomers that have been found will permit their use in GLC-MS analysis for determining the structure of a polysaccharide by the methylation method.Pacific Ocean Institute of Bioorganic Chemistry, Far Eastern Scientific Center, Academy of Sciences of the USSR, Vladivostok. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 492–498, July–August, 1982.     

Gas-liquid chromatography-mass spectrometry of acetates of partially methylated methyl glycosides. VII. Mono- and dimethylheptoses

The partial methylation of methyl β-glucoheptopyranoside has given a complex mixture of methyl ethers, from which five monomethyl ethers have been isolated by preparative GLC. Methylation of the latter gave a mixture in which ten dimethyl ethers were detected. The retention indices on the phase NPGS of the mono- and dimethyl ethers of methyl β-glucoheptopyranoside have been measured, and their mass spectra have been recorded and discussed. The mass spectra of these position isomers unambiguously characterize the pattern of methylation.     

Polyfluoro-1,2-epoxy-alkanes and -cycloalkanes. Part I. Preparation of some polyfluoro-1,2-epoxycyclohexanes

Polyfluorocyclohexenes with hydrogen, bromine, and methoxy substituents yielded the corresponding 1,2-epoxides when treated with aqueous sodium hypochlorite containing some acetonitrile. 4,5-Dibromooctafluoro-1,2-epoxycyclohexane was debrominated with zinc dust to give a mixture of octafluoro- and 4H-heptafluoro-1,2-epoxycyolohex- 4-ene. Decafluoro- and 4,5-dibromo-octafluoro-1,2-epoxycyolohexane gave with potassium fluoride in acetonitrile the corresponding potassium perhalogenocyclohexyloxides; heating these gave the analogous cyclohexanones, and treatment with methyl iodide the methyl ethers. The unsaturated 1,2-epoxides also gave methyl ethers on treatment with KF, followed by methylation.     

Gas-liquid chromatography and mass spectrometry of methyl ethers of methyl N-acetyl-N-methyl-β-d-neuraminate methyl glycoside

Partial methylation of methyl N-acetyl-β-d-neuraminate methyl glycoside using methyl iodide and silver oxide gives a mixture of methyl ethers of methyl N-acetyl-N-methyl-β-d-neuraminate methyl glycoside, which was fractionated by chloroform-water partition followed by preparative column chromatography on silica gel. After trimethylsilylation of the fractions, gas-liquid chromatography on OV-101 and mass spectrometry facilitated the identification of 13 methyl ethers.     

Synthesis of methyl ethers of methyl 2-acetamido-2-deoxy-α-D-glucopyranoside

A convenient method is proposed for the synthesis of all the individual methyl ethers of methyl 2-acetamido-2-deoxy-α-D-glucopyranoside based on the partial methylation of 2-acetamido-2-deoxy-α-D-glucopyranoside with dimethyl sulfate in an alkaline medium followed by preparative liquid column chromatography on silica gel of the resulting mixture of methyl ethers.     

Use of ethyl ethers, deuteriomethyl ethers and cyclic n-butylboronates of hydroxychlorobiphenyls in identification of metabolites of polychlorinated biphenyls.

The mass spectra and gas chromatographic properties of a number of chlorobiphenylols, chlorobiphenyldiols, chlorophenols and naphthols, as well as their methyl, deuteriomethyl and ethyl ethers and some cyclic n-butylboronates have been investigated. Metabolism experiments with 4'-chloro-4-biphenylol showed that the selective use of ethylation and methylation is most effective in both detection and structure elucidation of metabolites partly methylated by metabolic processes. The usefulness of deuteriomethylation in such studies seems to be limited. The formation of cyclic n-butylboronates provides specific information on o-dihydroxy derivatives of chlorobiphenyls.     

New syntheses and13C NMR spectra of the methyl ethers of methyl α-L-arabinopyranoside

A method is described for obtaining the methyl ethers of methyl -L-arabinopyranoside that is based on the partial methylation of methyl -L-arabinopyranoside followed by the liquid chromatography of the methyl ethers. The¹³C NMR spectra of the methyl ethers of methyl -L-arabinopyranoside have been studied.Pacific Ocean Institute of Bioorganic Chemistry, Far Eastern Scientific Center, Academy of Sciences of the USSR, Vladivostok. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 178–181, March–April, 1985.     

Partial methylation of methyl glycosides

Summary The partial methylation of methyl xylo-, arabino-, lyxo- and rhamnopyranosides by Purdie's method has been studied; it is possible to use the results obtained for the isolation of individual methyl ethers by micro-preparative GLC.Pacific Ocean Institute of Bioorganic Chemistry, Far Eastern Scientific Center of the Academy of Sciences of the USSR. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 682–686, November–December, 1975.     

Micropreparative gas-liquid chromatography of the products of the partial methylation of methyl α-L-rhamnopyranoside

Summary A method has been developed for obtaining acetates of the methyl ethers of methyl -L-rhamnopyranoside by the preparative gas-liquid chromatography of the products of the partial methylation of methyl -L-rhamnopyranoside, and the properties of the compounds isolated have been described.Pacific Ocean Institute of Bioorganic Chemistry, Far Eastern Center of the Academy of Sciences of the USSR, Vladivostok. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 142–144, March–April, 1979.     

Characterization of the Dissociation Behavior of Gas-Phase Protonated and Methylated Lactones

The dissociation behavior of gas-phase protonated and methylated four-, five-, six-, and seven-membered ring lactones, some with methyl substituents in various positions, has been characterized by using a quadrupole ion trap mass spectrometer and a triple quadrupole mass spectrometer. The energy dependence of collisionally activated dissociation pathways was determined by energy-resolved mass spectrometry, and the dissociation behavior of the various protonated lactones was compared to that observed for protonated cyclic ketones and ethers of analogous ring size. The protonated cyclic ethers and ketones predominantly dissociated via dehydration, whereas the protonated lactones dissociated via losses of an alkene, ketene, and water. The dissociation behavior of the gas-phase methylated lactones formed from ion/molecule reactions with dimethyl ether ions was compared to the collisionally activated dissociation behavior of isomeric protonated methyl-substituted lactones. The methylation experiments indicated that the gas-phase addition of a methyl group may dramatically alter the favored dissociation pathways when compared to the simple protonated ions.     

New inhalation anaesthetics: III. Fluorinated aliphatic ethers

A range of fluorinated methyl ethyl ethers, diethyl ethers and methyl butyl ethers has been synthesised as potential inhalation anaesthetics. Seven compounds produced anaesthesia with minimal side effects in mice, and their biological testing will be reported in more detail elsewhere [1].     

Synthesis and 13C-NMR spectroscopic investigations of rhamnobioses

A convenient method has been developed for the synthesis of all mono- and di-O-benzyl ethers of methyl α-L-rhamnopyranoside applying a new stereoselective method for the hydrogenolytic ring-cleavage of benzylidene acetals. Using the prepared dibenzyl ethers as aglycones, the (1→2)-, (1→3)- and (l→4)-linked rhamnosyl-rhamnose derivatives (13–15) were synthesised. Hydrogenolysis of the latter compounds and subsequent acetylation gave the pentaacetates (16–18) of methyl dirhamnosides, which on saponification furnished the free methyl dirhamnosides (19–21). Acetolysis of 16–18 gave the corresponding dirhamnose-hexaacetates which were transformed into the three disaccharides by saponification. The structure of each product was investigated by ¹³C-NMR spectroscopy, and for the purpose of ¹³C-NMR studies the mono-O-methyl ethers of methyl α-L-rhamnopyranoside, the diacetates and di-O-benzyl ethers of the latter compounds, and, also the diacetates of methyl α-L-rhamnopyranoside were synthesised.It has been established that, for ¹³C-NMR investigations of oligosaccharides, the benzyl ethers of monosaccharides are more suitable model compounds than the currently used monosaccharide methyl ethers.     

Distribution of Substituents in Methylcellulose

Abstract

The distribution of methyl groups in methylcelluloses (DS 1.7) has been determined. The partially methylated monosaccharides obtained on complete hydrolysis of methylcellulose were converted into alditols by reduction. They were identified as their acetates or trimethylsilyl ethers by gas-liquid chromatography-mass spectrometry and quantified by gas-liquid chromatography. In addition, ¹³C-nuclear magnetic resonance spectra of native and hydrolyzed methylcelluloses as well as the partially methylated alditols obtained by hydrolysis and reduction were analyzed. The main glucose methyl ethers obtained were in decreasing order 2,6-, 2,3,6-, 2-, 6-, and 2,3-. The 2-and 6-positions were occupied by methyl groups in 70.0 and 61.5%, respectively, while the 3-position contained only 37.4%. The GLC-MS method gave a more accurate determination of the distribution of methyl groups in methylcellulose compared to NMR spectroscopy.     

Ferrocene compounds XXIII. Synthesis and reactions of the new type of methyl ferrocyloxyalkanoates

The new types of ferrocenyloxaaliphatic acid ester, FcCHROCHR′COOMe (R = H, Me, Ph; R′ = H, Me) (7) have been prepared by the action of alkoxides derived from methyl glycolate or methyl lactate on the corresponding ferrocenylcarbinyl acetates (2) or N,N,N-trimethylferrocylammonium iodides (4). The esters obtained were accompanied by a small quantity of oligomeric esters, FcCHR(OCHR′CO)_n OMe (9), and with more or less ferrocyl methyl ethers (8). As opposed to the alkaline hydrolysis of the analogous methyl benzoxyacetate (6) into benzoxyacetic acid (5) the acidification of sodium alkanoates 10 obtained by saponification of esters 7 gave unexpectedly the corresponding ferrocenylcarbinols 1. In a similar way the esters 7 were converted into mixtures of the mentioned carbinols and diferrocyl ethers 11 under action of aqueous hydrochloric acid. The mechanisms of the reactions 10 → 1 and 7 → 1, 11 are discussed.     

Macroheterocycles. 34. Synthesis and enantiomeric selectivity of chiral azacrown

Chiral azacrown ethers were obtained by the condensation of (4S,5S)-4,5-ditosyl-oxymethyl-2,2-dimethyl-1,3-dioxolane with 6-benzyl-3,9-dioxa-6-azaundecane-1,11-diol. Their debenzylation and deacetalization were realized. The enantiomeric selectivity in the complex formation between the obtained crown ethers and the hydrochlorides of L- and D-valine methyl esters was determined by a potentiometric method. The chiral azacrown ethers exhibit higher enantioselectivity than their oxygen analogs.See [1] for Communication 33.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 687–691, May, 1988.     

Polar nematic methyl (E)-[trans-4-cyclohexyl-substituted]allyl ethers: Synthesis, liquid crystal transition temperatures and some physical properties

We have introduced an oxygen atom and a carbon-carbon double bond with a trans-configuration (E) into the terminal alkyl chain attached to the cyclohexyl ring of a variety of two- and three-ring nematic liquid crystals of positive dielectric anisotropy. The new polar two-ring methyl (E)-allyl ethers often possess low melting points, but are not mesomorphic in general. The related three-ring methyl (E)-allyl ethers exhibit high clearing points and wide nematic ranges. Comparisons with the corresponding derivatives incorporating either just an oxygen atom or just a carbon-carbon double bond in the same position indicate that synergetic effects lead to broader nematic phases than would otherwise have been expected. This is partially due to the low smectic transition temperatures observed for the methyl (E)-allyl ethers. Selected physical properties of three binary mixtures of a weakly polar standard nematic liquid crystal and three difluoro-substituted (polar) liquid crystals (including the new ethers) differing only in the nature of the terminal chain show that, although some of the methyl (E)-allyl ethers exhibit longer switch-off times in TN cells than those of analogous liquid crystals incorporating either a methyl propyl ether or a 1-(E)-propenyl chain instead of the methyl (E)-allyl ether chain, they are still useful components for nematic mixtures, especially where a wide temperature range is required.     

Chemistry of lichen constituents—VII: Mass spectra of some pulvic acid derivatives

The mass spectra of three methoxypulvic dilactones, four methyl esters of methoxypulvic acids and five methyl ethers of pulvic acid derivatives have been measured and rationalised employing accurate mass measurements and metastable peak assignments to substantiate the proposed fragmentations and rearrangements. In particular, the mass spectral differences and similarities between the isomeric methoxypulvic dilactones, between their methanolysis products and between the isomeric methyl ethers, are rationalised.     

Synthese et proprietes d'ethers β-monofluores

Two methods have been used for the synthesis of β-monofluorinated ethers. One is the methylation of α-fluorinated alcoholates obtained from corresponding 2-fluoroalcohols by action of NaH in T.H.F. The second method is the nucleophilic substitution of tosyl group by fluorine in 2-methoxy-tosylates. Spectral properties of these β-fluorinated ethers have been studied. Furthermore ¹⁹F N.M.R. spectrum of the E 2-methoxyfluorocyclohexane has been investigated at low temperatures.