Mass spectral fragmentation esters

Further work on the free and ester-bound triterpenoid alcohols in cellular subtractions of Calendula officinalis flowers has appeared. An investigation of the mass spectral fragmentation of pentacyclic hydrocarbons in petroleum has been published. ... 

The mass spectral fragmentation reactions of a number of derivatives used in GC-MS have been reported including a series of esters of the JV-trifluoroacetates [152] and the pertrimethylsilyl derivatives [153-155] and their carbon-13- [156] and deuterium-containing analogues [157]. General reviews of the mass spectra of the common amino acids and their derivatives are also available [151,158]. 

Routine, but useful, interpretations of the mass spectral fragmentation patterns under electron impact have been reported for esters of the menthane and camphane series,39-40 for thioketones with the thujane, pinane, camphane, and fenchane skeleta,41 for [2H]limonene,42 for cannabinoids,43-46 and for the volatile components from Pinus seedlings.47... 

Dimers 39 and 40, issued from grass samples, reveal the linkage type of p-cou-maric and ferulic esters and show that some ester bonds survive thioacidolysis. Dimer 39 confirms thatp-coumaric acid is ester-linked at Cy of S lignin units [60,61]. Compound 40, tentatively assigned from its mass spectral fragmentation pattern, may originate from ferulic units ester-linked to pentose units [85]. 

The structure and absolute configuration (45 R1 = Me, R2 = H) previously deduced for deoxynupharidine by chemical degradation67 has now been confirmed by X-ray analysis.68 The mass spectral fragmentation patterns of pedicularine (56) and its methyl ester have been determined and compared with... 

A recent communication by Kumar and co-workers reported the isolation of a new binary tetrahydrocarbazole-indole alkaloid, methyl 2-methyl-4-(iV-2")8-methyl-l",2",3",4"-tetrahydrocarbazol-l"a-ylindol-3 -yl butanoate (77), C27H30N2O2 from the root timber of Murraya gleniei (67). It exhibited spectral data characteristic of an indole with an ester function. The mass spectral fragments having m/z 231 and 184 indicated that it was a binary alkaloid consisting of C14H17N02 and Q3H14N units. The structure and stereochemistry of 77 were established by the application of 1H, 13C, DEPT,... 

Isoxazoline Derivatives. Reductive and oxidative cleavages of 5-phenyl-A -isoxazoline-3-carboxyIic acid derivatives (450) have been reported. In the reductive cleavage (Scheme 36) a single crystalline isomer, presumed to be c -(451), is formed. The oxidative fragmentation of the peroxy-esters parallels the mass spectral fragmentation pattern giving, inter alia, benzal-dehyde, 3-hydroxy-3-phenypropionitrile, and 3-oxo-3-phenylpropionitrile (Scheme 36). 

A further means for ready identification of a galloyl ester is by mass spectroscopy of the methylated (diazomethane) ester. The mass spectral fragmentation pattern usually displays the ion 16 as base peak, m/e 195 (37, 112). 

FIG. 4. Mass spectral fragmentations of iopronic acid and its methyl ester. 

By gas chromatography-mass spectrometry N-acetyl-p-aryloxy-alanine was identified as a metabolic product of 3-aryloxy-1,2-propanediol in rats. Although we have not yet obtained authentic N-acetyl-g-(2 -tolyloxy) alanine and N-acetyl-g-phenoxyalanine, the proposed structure was supported by following data 1. The gas chromatographic properties such as heat instability and retention time were very similar to that of N-acetyl-6-(o -tolyloxy)alanine TMS ester. 2. The mass spectra of mono-trimethylsilylated N-acetyl-3 ( 7tolyloxy)alanine and N-acetyl-3 phenoxyalanine closely resembled that of N-acetyl-g-(o-tolyloxy)alanine, the structure of which was confirmed by high resolution mass measurement, acid hydrolysis and TLC, 3. These two metabolites showed very similar properties to N-acetylphenyl alanine on trimethyls ilyl at ion and similar mass spectral fragmentations. 

FIG. 5. Cl mass spectral fragmentations of penicillin and penicilloic acid methyl esters. 

A comparison of the mass spectral fragmentation patterns of the dimethyl ester of caperatic acid (41) and the corresponding di(trideutero-methyl) ester located the position of the ester function in this molecule and established the structure as methyl 3,4-dicarboxy-3-hydroxyoctadecanoate (41) (25). In a corroborative chemical degradation (41) was oxidized by treatment with sodium bismuthate, whereupon methyl 3-oxo-octadecano-ate (42), the decarboxylation product of the initially formed P-keto-carboxylic acid, was detected (25). 

The mass spectral behavior of tropane alkaloids is well documented (53,63,142,166-171), and only the most characteristic points will be noted here. The general fragmentation pattern of the 3-hydroxytropane esters can be described in terms of the following five routes (Routes A-E) (Scheme 29) (55). 

The seventh new alkaloid of K. strobilina is the cinnamoyl 3cr-ester of 3cr,6/ -dihydroxytropane (8), the assignment being based mostly on mass-spectral evidence (M+ 287 C17H21N03) the radical ions of m/z 156 (PhCH=CH—COOt) and m/z 140 (PhCH=CH—COt) are crucial, in addition to the typical8 6/ff-tropanol fragments. 

Although the fragmentation reactions of the molecular ions of sul-phones and sulphoxides varied, the first step in rationalizing their behaviour was initial isomerization to sulphinate (64) and sulphenate esters (65). A variety of reactions of this type has been collated by Fields and Meyerson (1968), who pointed out that isomerization of sulphoxides to sulphenate esters was a known thermal reaction (see also, Kutz and Weininger, 1968, Kinstle et al., 1968b). In experiments designed to compare the mass-spectral and thermal behaviour of a series of sulphoxides, it was observed that the thermal isomerization appeared to proceed, but no comparable behaviour was observed in the mass spectra (Entwistle et al., 1967). 

Gas chromatographic mass spectral analysis of the methyl esters showed three major compounds. Table II lists the retention times, mass spectra of compotinds and the struct ares assigned to the parent compound or the largest fragment observed on the mass spectrum. Compounds eluting from the column at temperatures above 300 C yielded poor mass spectra as the transfer lines including the jet... 

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