Trimethylsilylated Methyl Esters Research Articles

Acylglycerols (=Glycerides) from the Glandular Trichome Exudate on the Leaves of Paulownia tomentosa

AbstractChemical investigations of the glandular trichome exudates on the leaves of Paulownia tomentosa (Scrophulariaceae) led to the identification of the thirty acylglycerols (=glycerides) 1–30, including five known ones (2, 3, 6, 9, and 15) (Fig. 1). Spectroscopic analysis combined with GC/MS studies of the glycerides and the liberated fatty acids, in the form of trimethylsilyl ether derivatives and trimethylsilylated methyl esters, respectively, established that the constituents belonged to 1,3‐di‐O‐acetyl‐2‐O‐(fatty acyl)glycerols, 1‐O‐acetyl‐2‐O‐(fatty acyl)‐sn‐glycerols, and 2‐O‐(fatty acyl)glycerols, wherein the fatty acyl moiety was either an eicosanoyl or an octadecanoyl group bearing OH and/or AcO groups at the 3‐, 3,6‐, 3,7‐, 3,8‐, or 3,9‐positions. The 1‐O‐acetyl‐2‐O‐[(3R,6S)‐3‐(acetyloxy)‐6‐hydroxyeicosanoyl]‐sn‐glycerol (12; 20% of the total glycerides), 2‐O‐[(3R,8R)‐3,8‐bis(acetyloxy)eicosanoyl]glycerol (17; 14%), 2‐O‐[(3R,9R)‐3,9‐bis(acetyloxy)eicosanoyl]glycerol (18; 12%), and 2‐O‐[(3R)‐3‐(acetyloxy)eicosanoyl]glycerol (10; 12%) were relatively abundant constituents. The configurations of the stereogenic centers of the fatty acyl moieties were determined by 1H‐NMR analysis of the monoesters obtained from (R)‐ and (S)‐2‐(naphthalen‐2‐yl)‐2‐methoxyacetic acid ((R)‐ and (S)‐2NMAOH and the hydroxy‐substituted fatty acid methyl esters (Fig. 2). The configuration at C(2) of the glycerol moiety of the 1‐O‐acetyl‐2‐O‐(fatty acyl)glycerols was determined to be (2S) by chemical conversion of, e.g., G‐2 (=2/3 1 : 10) to (+)‐3‐O‐[tert‐butyl)diphenylsilyl]‐sn glycerol of known absolute configuration.

Trimethylsilyldiazomethane in the preparation of diazoketones via mixed anhydride and coupling reagent methods: a new approach to the Arndt–Eistert synthesis

Reaction of trimethylsilyldiazomethane with a mixed anhydride derived from a carboxylic acid by the action of ethyl chloroformate, yields the corresponding diazoketone in high yield. Subsequent Wolff rearrangement of the diazoketone leads to the homologated ester. Reaction of trimethylsilyldiazomethane with carboxylic acid–dicyclohexylcarbodiimide mixtures leads to the formation of diazoketone and trimethylsilylmethyl ester in equimolar ratio via an acid anhydride intermediate. The N-hydroxysuccinimide ester of the acid does not react with trimethylsilyldiazomethane or with its more reactive lithiated derivative.

Identification of three C 20-gibberellins: GA 97 (2β-hydroxy-GA 53), GA 98 (2β-hydroxy-GA 44) and GA 99 (2β-hydroxy-GA 19)

Three new C 20-gibberellins, GA 97 (2β-hydroxy-GA 53), GA 98 (2β-hydroxy-GA 44) and GA 99 (2β-hydroxy-GA 19), have all been isolated from spinach, GA 97 also from tomato root cultures and pea pods, and GA 98 from maize pollen. The structures of these compounds were established by GC-mass spectrometric comparisons of the trimethylsilylated methyl esters with authentic samples prepared from gibberellic acid (GA 3).

Gas chromatography-mass spectrometry of lipopolysaccharide 3-hydroxy fatty acids: comparison of pentafluorobenzoyl and trimethylsilyl methyl ester derivatives

3-Hydroxytetradecanoic and 3-hydroxyhexadecanoic acids were used as chemical markers for the determination of lipopolysaccharides by gas chromatography-mass spectrometry of their pentafluorobenzoyl and trimethylsilyl methyl ester derivatives. The latter derivatives were simpler to prepare than the former, although both were chemically stable. Analysis of pentafluorobenzoyl derivatives (chemical ionization mode with negative ion detection) provided somewhat better sensitivity than analysis of trimethylsilyl derivatives (electron impact mode): 1 pg (injected amount) of pentafluorobenzoyl derivatives was detectable under routine conditions. Both types of derivative gave similar values when used to measure lipopolysaccharides in a bacteria-contaminated pharmacological product. The described methods are useful for the determination and characterization of lipopolysaccharides in various environments.

Synthesis and study of the thermal stability of siliconcontaining esters of phosphorus acids. 4. Thermal rearrangement of trimethylsilylmethyl esters of phosphorus acids

NMR spectroscopy has been used to study the thermal rearrangement of siliconeopentyl esters of phosphorus acids Me3SiCH2OP(O)R2 (I, R=CF3CH2O, PhO, t-BuCH2O, Bu). It has been established that in all cases the products of the rearrangement are the respective silyl esters Me2EtSiOP(O)R2 (II). The thermal rearrangement of (Me3SiCH2O)2P(O)OR′ (III, R'=Ph, t-BuCH2, Me3SiCH2) is similar. It has been shown that electronic and steric attributes of the substituents R and R′ on the phosphorus atom are practically without effect on the extent of the thermal rearrangement. The presence of acidic additives, and initiators and inhibitors of radical reactions did not significantly influence the course of the rearrangement. It was concluded that this rearrangement apparently takes place as a result of heterolysis of the C-OP bond and simultaneous nucleophilic attack on the silicon atom by the phosphoryl part of the molecule.

Structure of the majorO-glycosidic oligosaccharide of monkey erythrocyte glycophorin

Sialic acids and the major O-glycosidic oligosaccharide of glycophorin MK from monkey (Japanese monkey, Macaca fuscata) erythrocyte membranes were characterized. N-Glycolylneuraminic acid (Neu5Gc) was found as the major sialic acid, which was confirmed by gas-liquid chromatography-mass spectrometry as the trimethylsilyl methyl ester. Three O-glycosidic oligosaccharide units were obtained from a tryptic glycopeptide that contained all of the carbohydrate units in glycophorin MK by mild alkaline borohydride/borotritide treatment. Carbohydrate analyses of the oligosaccharides revealed that they were composed of Neu5Gc, galactose and N-acetylgalactosaminitol in the molar ratios of 1:1:1 (trisaccharide), 2:1:1 (tetrasaccharide) and 3:1:1 (pentasaccharide). The content of oligosaccharide units was estimated to be 1:12:5 for penta-, tetra- and trisaccharide, respectively, based on the yields, the molecular weight, and the number of oligosaccharide attachment sites in the amino-acid sequence. The tetrasaccharide was the major oligosaccharide and its structure was proposed to be Neu5Gc alpha 2-3Gal beta 1-3[Neu5Gc alpha 2-6]GalNAcol.

Determination of double bond positions of unsaturated fatty acids by a chemical ionization mass spectrometry computer system

After stereospecific oxidation, trimethylsilylated methyl esters of mono- and diunsaturated fatty acids were analyzed by combined gas-liquid chromatography-chemical ionization mass spectrometry. The positions of original double bonds were deduced from the fragment ions produced by the cleavage of the carbon-carbon bond between two trimethylsilyl ethers. These fragment ions were recorded at m/e 187 and 259 in the case of 16:1(n-7), at m/e 187 and 287 in the case of 18:1(n-7), at m/e 215 and 259 in the case of 18:1(n-9), and at m/e 172 and 259 in the case of 18:2(n-6), respectively. The diastereoisomers of monounsaturated fatty acids can be discriminated by comparing the intensities of the fragment ions at m/e 253 and 285 in the case of 16:1 and at m/e 281 and 313 in the case of 18:1. The diastereosiomers of diunsaturated fatty acids may also be distinguished from each other by comparing the intensities of the fragment ions formed by the loss of trimethylsilyl function from the characteristic ions. Mono- and diunsaturated fatty acids in liver may be dominantly in cis- 18:1(n-1) and cis-cis-18:2(n-6) as determined by a mass chromatographic technique.

Determination of double bond positions in polyunsaturated fatty acid methyl esters by combined gas chromatography-chemical ionization mass spectrometry

Trimethylsilylated methyl esters of octadecadienoic, eicosadienoic, and octadecatrienoic acids, after stereospecific oxidation, were investigated by combined gas chromatography-chemical ionization mass spectrometry. Molecular weight could be determined by the ions at m e (M −11) + and ( M + 73) + and the characteristic ions derived from the sequential elimination of trimethylsilanols from a protonated molecule MH +. The position of original double bonds could be deduced from the recognizable ions which were produced by the cleavage of carbon-carbon bonds between the two trimethylsilyl ethers. The mode of fragmentation was confirmed by the mass spectra of deuteriomethyl derivatives of linoleic acid.

Synthesis and characterization of glucuronides of Cannabinol, cannabidiol, delta9-tetrahydrocannabinol and delta8-tetrahydrocannabinol.

Partially purified glucuronyltransferase immobilized on beaded sepharose has been used to synthesize the glucuronide conjugates of cannabinol, cannabidol, delta9-tetrahydrocannabinol and delta8-tetrahydrocannabinol. Trimethylsilylated methyl esters and per(trimethylsilyl) derivatives of these conjugates have been characterized by their gas chromatographic retention times and their electron impact and ammonia chemical ionization mass spectra.

Determination of geometrical and positional isomers in octadecenoic acids by chemical ionization mass spectrometry

Chemical ionization mass spectra of trimethylsilylated methyl esters of octadecenoic acids were investigated. The position of the original double bond could be deduced from the recognizable fragment ions produced by cleavage of the carbon-carbon bond between the two trimethylsilyl alcohols. The cis- and trans-isomers could be also distinguished from each other by comparing the abundance of the fragment ions given by subsequent loss of the trimethylsilyl residue and/or methoxy group from the characteristic peaks.

The identification of 3,3', 5,5',-tetraiodothyroformic acid within the rat liver.

Homogenized rat livers were extracted with organic solvents and the extracts converted into more readily volatile derivatives (trimethylsilylmethyl esters and permethyl esters). Combined g.l.c.-mass-spectrometric analysis identified the presence of tetraiodothyroformate. It is postulated that mitochondrial beta-oxidation of tetraiodothyropyruvate results in the formation of this apparently undescribed metabolite.

Determination of prostaglandin F 1α and F 2α by gas-liquid chromatography

A quantitative gas-liquid chromatographi method has been developed for the determination of prostaglandin F 1α and F 2α (PGF 1α and PGF 2α). The method involves the conversion of PGF 1α and PGF 2α into their trimethylsilyl methyl esters or heptafluorobutyryl methyl esters and their chromatography using 3% OV-1 on Gas-Chrom Z; their structures were established by combined gas chromatography-mass spectrometry. The method can be applied to human semen plasmas with prostagladin F 2β (PGF 2β) as an internal standard.