Structural Characterization of Mono- and Dimethylphosphatidylethanolamines from Various Organisms Using a Complex Analytical Strategy Including Chiral Chromatography

Two minor phospholipids, i.e., mono- and/or dimethylphosphatidylethanolamines, are widespread in many organisms, from bacteria to higher plants and animals. A molecular mixture of methyl-PE and dimethyl-PE was obtained from total lipids by liquid chromatography and further identified by mass spectrometry. Total methyl-PE and dimethyl-PE were cleaved by phospholipase C, and the resulting diacylglycerols, in the form of acetyl derivatives, were separated into alkyl-acyl, alkenyl-acyl, and diacylglycerols. Reversed-phase LC/MS allowed dozens of molecular species to be identified and further analyzed. This was performed on a chiral column, and identification by tandem positive ESI revealed that diacyl derivatives from all four bacteria were mixtures of both R and S enantiomers. The same applied to alkenyl-acyl derivatives of anaerobic bacteria. Analysis thus confirmed that some bacteria biosynthesize phospholipids having both sn-glycerol-3-phosphate and sn-glycerol-1-phosphate as precursors. These findings were further supported by data already published in GenBank. The use of chiral chromatography made it possible to prove that both enantiomers of glycerol phosphate of some molecular species of mono- and dimethylphosphatidylethanolamines are present. The result of the analysis can be interpreted that the cultured bacteria do not have homochiral membranes but, on the contrary, have an asymmetric, i.e., heterochiral membranes.

Review: Derivatization in mass spectrometry--2. Acylation

The present review is devoted to acylation as a widely employed derivatization procedure for protection of OH (alcohols, polyols, phenols, enols), SH (thiols) and NH (amines, amides) groups in order to increase volatility, improve chromatographic properties and, if possible, improve mass spectral properties of derivatives. Chemical aspects of derivatization and various acylating agents are characterized. Mass spectral [electron ionization (EI), chemical ionization (CI) and negative-ion (NI) CI] properties of derivatives that are helpful in identification, structure elucidation and quantitative determination of the analyzed compounds are discussed. Some recent analytical applications of the procedure in synthetic organic chemistry, clinical chemistry, environmental chemistry etc. are summarized.

Characterization of novel long-chain 1,2-diols in Thermus species and demonstration that Thermus strains contain both glycerol-linked and diol-linked glycolipids

In this study, we purified and characterized tetra- and triglycosyl glycolipids (GL-1 and GL-2, respectively) from two different colonial forms of Thermus scotoductus X-1, from T. filiformis Tok4 A2, and from T. oshimai SPS-11. Acid hydrolysis of the purified glycolipids liberated, in addition to the expected long-chain fatty acids, two components which were identified by gas chromatography-mass spectrometry as 16-methylheptadecane-1,2-diol and 15-methylheptadecane-1,2-diol. Fast atom bombardment mass spectrometry of the intact glycolipids indicated that a major proportion consisted of components with glycan head groups linked to long-chain 1,2-diols rather than to glycerol, although in all cases glycerol-linked compounds containing similar glycan head groups were also present. As in other Thermus strains, the polar head group of GL-1 from T. filiformis Tok4 A2 and from T. scotoductus X-1 colony type t2 was a glucosylgalactosyl-(N-acyl)glucosaminylglucosyl moiety. However, GL-2 from T. scotoductus X-1 colony type t1 and from T. oshimai SPS-11 was a truncated analog which lacked the nonreducing terminal glucose. Long-chain 1,2-diols have been previously reported in the polar lipids of Thermomicrobium roseum and (possibly) Chloroflexus aurantiacus, but to our knowledge, this is the first report of their detection in other bacteria and the first account of the structural determination of long-chain diol-linked glycolipids.

Ram sexual pheromone: first approach of chemical identification

A series of experiments has been designed with the aim of identifying the pheromone of the ram responsible for the primer effect--induction of a LH peak and ovulation--in anoestrous ewes. In a first experiment, the pheromonal activity of various sources was tested, extract of ram fleece and ante orbital gland secretion induced characteristic changes in LH secretion, whereas urine was ineffective. A second experimental series showed that an accurate separation of the ram's fleece extract in acid and neutral fractions resulted in each case in a complete loss of activity whereas both together were efficient, indicating that the pheromonal action involves several components. From GC-MS analysis of both fractions, and after comparison of male and female wool extract, semi-synthetic formulations were tested. The association of synthetic 1,2-hexadecanediol and 1,2-octadecanediol with the natural acid fraction was efficient in stimulating LH release in anoestrous ewes. As the most frequent linear fatty acids have been shown not to be necessary, a role of branched and oxygenated fatty acids has been hypothesised.

Application of triple quadrupole tandem mass spectrometry to the analysis of pyridine-containing derivatives of long-chain acids and alcohols

An improved derivatization procedure for the preparation of nicotinate and 3-picolinyl esters from mixtures of fatty alcohols and acids has been developed. The derivatives can be analysed by capillary gas chromatography on an SE-54 type column, which affords separation of the acid and alcohol derivatives with the same carbon chain. Detection with tandem mass spectrometric techniques on a triple quadrupole instrument is feasible, and yields informative spectra devoid of coeluting interferences.

Identification and quantification of lipids from rabbit Harderian glands by gas chromatography/mass spectrometry

Lipids from hydrolysed extracts of Harderian glands from the rabbit were examined as trimethylsilyl, acetonide, nicotinate and picolinyl esters and shown to consist mainly of acylated glycerol ethers and acylated hydroxy-glycerol ethers. Constituents amounting to 98.8% of the recovered secretion were identified. Fatty acids were mainly normal, saturated compounds with chain lengths from 12 to 24 carbon atoms; n-16:0 and n-18:0 accounted for about 40% of the identified acids. Small concentrations of iso-17:0 and unsaturated acids with 18-carbon chains were also identified. Fatty alcohols were again mainly normal-unsaturated compounds; the chains varied from C18 to C25 with 20:0-OH and 22:0-OH being the most abundant. Three types of 1-alkyl glycerols were found. The major constituents had normal, saturated chains with from 14 to 23 carbon atoms with the even carbon chains predominating. These were accompanied by hydroxylated derivatives of the 16- and 18-carbon glycerol ethers with hydroxy groups in the 10, 11 and 12 positions. Branched-chain glycerol ethers were of low concentration and contained predominantly iso chains. Many of these compounds have not been reported before in this secretion. Low concentrations of the previously reported hydroxy acids with n-C14, -C15 and -C16 chains were also found. Nicotinate derivatives were applied to the structural determination of glycerol ethers for the first time and shown to reveal the position of methyl branch points in an analogous manner to that previously shown for mono- and di-hydric alcohols. Acids were identified as picolinyl esters.

Pyridine-Containing schiff base derivatives for the struxtural determination of long-chain aldehydes by gas chromatography combined with mass spectrometry

Long-chain aldehydes, encountered as insect pheromones, were converted into Schiff bases with 3-aminopyridine, 3-(aminomethyl)pyridine, or 2-aminopyrimidine to provide derivatives suitable for revealing the alkyl chain structure by mass spectrometry. The two pyridine-containing derivatives were satisfactory in initiating a radical-induced cleavage. of the chain to give a series of fragment ions, the masses and relative abundance of which revealed the chain structure. The derivatives were applied to aldehydes having straight, branched (iso and anteiso), and unsaturated (delta-7, delta-9, delta-ll, and delta-13) structures; these all gave the fragmentation patterns that have been seen earlier for similar pyridine-containing derivatives of fatty acids (picolinyl esters) and alcohols (nicotinates).Of the two derivatives, those from 3-aminopyridine gave slightly simpler spectra. Derivatives formed from 2-aminopyrimidine were less satisfactory in revealing chain structure.

Identification by gas chromatography and mass spectrometry of lipids from the rat Harderian gland

Lipids from rat Harderian glands were extracted with ethyl acetate, hydrolysed with base and examined by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) as trimethylsilyl (TMS), [2H9]TMS, methyl ester-TMS, picolinyl, nicotinate and nicotinylidene derivatives. The latter three derivatives were used to reveal the structures of the alkyl chains of fatty acids, alcohols and glycerol ethers, respectively. Forty-eight compounds were identified, representing about 97% of the total extracted lipids as measured by GC peak areas. The major constituents were fatty acids with chain lengths from 12 to 22 carbon atoms (mainly C18 and C20) and fatty alcohols (C16 to C26) derived from wax esters. Most of these acids and alcohols were unsaturated in the omega-7 position and were accompanied by smaller amounts of the saturated and omega-5 monounsaturated analogues. glycerol ethers were also identified for the first time in this secretion; the ether chains contained from 14 to 19 carbon atoms (mainly 16) and were straight-chain saturated, unsaturated (omega-5 and omega-7) and branched (iso). The only sterol found was cholesterol amounting to 1.24% of the total extract.

Lipids from the guinea pig Harderian gland: use of picolinyl and other pyridine-containing derivatives to investigate the structures of novel branched-chain fatty acids and glycerol ethers

The lipid extracted from guinea pig Harderian glands was hydrolysed and the constituents were examined as trimethylsilyl (TMS), (2H9)TMS, methyl ester/TMS, acetonide/TMS, nicotinate/TMS, picolinyl/TMS and nicotinylidene/TMS derivatives by capillary gas-liquid chromatography and gas chromatography/mass spectrometry. Over 70 compounds amounting to over 93% of the extract were identified. These consisted of 1-O-alkyl glycerols (glycerol ethers) with alkyl chains containing from 17 to 21 carbon atoms and fatty acids ranging from 14 to 26 carbon atoms. The alkyl chains in the glycerol ethers were straight, mono- and dimethyl-branched with the major site of branching being at C-14. All straight-chain acids from C14 to C26 were present, with the most abundant being n-24:0. Again mono- and dimethyl branched structures comprised the bulk of the remaining acids. Methyl groups tended to be towards the middle of the chain rather than in the more usual omega-1 (iso) and omega-2 (anteiso) positions, with C-14 again being a major site. The shorter-chain acids tended to have methyl groups closer to the acid group, with several of the short-chain compounds being substituted at C-2. Structural information on the acids was provided by the picolinyl derivatives and the sample provided an opportunity to evaluate these derivatives with branched acids other than the iso and anteiso compounds studied previously. They were found to be satisfactory for analysis of both mono- and dimethyl branched acids with the possible exception of compounds containing a methyl branch at C-4. However, in this case, structural information was provided by the methyl ester.(ABSTRACT TRUNCATED AT 250 WORDS)

Nicotinylidene derivatives for the structural elucidation of glycerol mono-ethers and mono-esters by gas chromatography/mass spectrometry

Nicotinylidene and methylnicotinylidene derivatives of representative glycerol ethers and glycerol esters were prepared by their reaction with pyridine-3-carboxaldehyde and 3-acetyl pyridine respectively. Each compound gave two sets of diastereoisomers which could be separated by gas-liquid chromatography. The extent of formation of the derivatives was nearly quantitative and chromatographic peak shape was good. The compounds producing both peaks gave similar spectra but with differences that were characteristic of the isomer. The derivatives fragmented in an analogous manner to that reported earlier for nicotinate derivatives of alcohols and picolinyl derivatives of carboxylic acids, with the production of a series of diagnostic ions formed by radical-induced cleavage of the chain following random hydrogen abstraction. Branched chain compounds, exemplified by glycerol ethers, gave spectra in which one of the ions diagnostic of the branch-point was missing. Unsaturated compounds, exemplified by the glycerol esters, gave characteristic mass spectra in which separation between ions representing formal cleavage at each side of the double bond enabled the position of this bond to be determined. In addition the spectra of unsaturated compounds contained two abundant ions whose formation could be rationalized by abstraction of the allylic hydrogen atoms. The nicotinylidene derivatives gave more diagnostic spectra than the methylnicotinylidene derivatives, whose spectra were complicated by the appearance of ions produced by loss of the methyl and pyridyl groups from the derivative. Both derivatives were superior to the nicotinate derivatives of these dihydroxy compounds in that only one pyridine residue was introduced on derivatization; this gave a lower molecular weight increment and allowed compounds with longer chains to be examined.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification by gas chromatography/mass spectrometry of long-chain fatty acids and alcohols from hamster meibomian glands using picolinyl and nicotinate derivatives

Meibomian secretions from the hamster were hydrolysed with base and examined as TMS, [2H9]TMS, methyl ester/TMS, picolinyl ester/TMS and nicotinate/TMS derivatives by capillary GC/MS. Over 90 compounds, representing over 89% of the hydrolysed fraction, were identified. Fatty acids with chain lengths from 10 to 32 carbon atoms were found, the most common of these were in the C15 to C18 and in the C25 to C30 regions. Chain types were predominantly iso or anteiso branched, mono-unsaturated (C16 and C18) and straight. Fatty alcohols were mainly from the iso or anteiso series and tended to have longer chain lengths; the major alcohols had anteiso-25 and 27 and iso-26-chains. In these respects the secretions were similar to those reported earlier from other species, although fewer mono-unsaturated compounds with longer chains (C20 to C30 region) were found than in the rat and human. The steroid fraction was characterized by a larger number of compounds than normally present in secretions of this type. The major compound was cholesterol, in common with that in all other examined species except the rabbit.

Long-chain fatty acids and alcohols from gerbil meibomian lipids

Capillary gas chromatography-mass spectrometry was used to identify constituent fatty acids, alcohols and steroids from gerbil meibomian glands. Over 80 compounds representing about 90% of the total fraction were identified. The major steroid was cholesterol accompanied by a lower concentration of 3 beta-hydroxy-5 alpha-cholestane. Fatty acids with chain lengths from 12 to 27 carbon atoms were present; they had predominantly straight, iso or anteiso chains with major concentrations in the C15-C18 and C25-C27 regions. Unsaturated acids had mainly 16 and 18 carbon atoms. The fatty alcohols were mainly branched-chain with the majority of compounds having chain lengths of 25-27 carbon atoms. Several alcohols, both branched and unsaturated, were found with chains of up to 33 carbon atoms long. The profile was similar to that found earlier in other species, but with lower concentrations of mono-unsaturated compounds than were found in rats and humans. Di-hydroxy compounds, on the other hand, tended to be more abundant although still of low relative concentration.

Identification of long-chain fatty acids and alcohols from human cerumen by the use of picolinyl and nicotinate esters

Human cerumen was hydrolysed with base and the constituents were examined as trimethylsilyl (TMS), methyl ester/TMS, picolinyl/TMS and nicotinate/TMS derivatives by gas chromatography and gas chromatography/mass spectrometry. A sample was also reacted with osmium tetroxide for double bond location. The major constituents were cholesterol, squalene and several series of long-chain fatty acids and alcohols. These latter compounds had chain lengths of 12-26 carbon atoms and were predominantly either straight-chain saturated or straight-chain unsaturated compounds. Saturated branched-chain acids with methyl groups predominantly on even-numbered carbon atoms were present but were less abundant. Unsaturated, branched-chain acids were also present. The major unsaturated acids contained unsaturation at the delta-6-position or were derived from these acids by chain elongation. The compounds were similar to those found in vernix caseosa. The mass spectra of picolinyl esters were, for the first time, shown to be capable of determining both the position of unsaturation and methyl branching in the same molecule.

Identification by combined gas chromatography-mass spectrometry of constituent long-chain fatty acids and alcohols from the meibomian glands of the rat and a comparison with human meibomian lipids

Constituent long-chain fatty acids and alcohols from the meibomian secretions of the rat were examined as trimethylsilyl (TMS) and methyl ester-TMS derivatives by capillary gas chromatography and by combined gas chromatography-mass spectrometry. The positions of double bonds and methyl branch points were determined by the mass spectra of picolinyl esters and nicotinates for long-chain fatty acids and alcohols, respectively. Fatty acids had chain lengths from C12 to C34 and were of the straight-chain iso, anteiso and monounsaturated types. The unsaturated acids had double bonds in the omega-7 and omega-9 positions. The alcohols had corresponding structures. In common with the constituent acids and alcohols of other meibomian secretions, the chain lengths of the constituents showed a biphasic distribution with maxima around C16-C18 and C25-C27. The profile was qualitatively similar to that obtained from human meibomian secretion but with some differences in the relative proportions of certain acids and alcohols.