Facile synthesis of plasmalogens via Barbier-type reactions of vinyl dioxanes and vinyl dioxolanes with alkyl halides in LiDBB solution

Plasmalogens (i.e. plasmenylcholines or plasmenylethanolamines) are a biologically important class of glycerophospholipids that have been difficult to synthesize due to the presence of an acid and oxidatively labile (Z)-vinyl ether substituent at the sn-1 position and a base-labile sn-2 acyl substituent that easily migrates during silica gel purification. We report two facile synthetic methods for the preparation of racemic plasmenylcholines via a tandem reductive vinyl dioxane/dioxolane ring opening and alkyliodide coupling process that proceeds in a single pot reaction. The key step in the formation of (Z)-vinyl ether precursors for the production of plasmenylcholines is accomplished using LiDBB under Barbier-type conditions to give the corresponding TBDMS-protected 1-O-Z'-vinylglycerol intermediate in moderate yields. This pathway is the most direct synthetic route for the formation of plasmenylcholines to date, requiring a total of six transformations from acrolein and glycerol or solketal as inexpensive starting materials, to generate glycerophosphocholine-type plasmalogens in 4% overall yield.     

Structural determination of hexadecanoic lysophosphatidylcholine regioisomers by fast atom bombardment tandem mass spectrometry

The structural determination of sn-1 and sn-2 hexadecanoic lysophosphatidylcholine (LPC) regioisomers was carried out using fast atom bombardment tandem mass spectrometry (FAB-MS/MS). The collision-induced dissociation (CID) of protonated and sodiated molecules produced diverse product ions due mainly to charge remote fragmentations. Based on the information obtained from the CID spectra of protonated and sodiated molecules, sn-1 and sn-2 hexadecanoic LPC isomers could be discriminated. Especially, the abundance ratio of the diagnostic ion pair [m/z 224/226] in the CID spectra of [M + H](+) ions was shown to be greatly different. Moreover, the CID-MS/MS spectra of sodium-adducted molecules for hexadecanoic LPC isomers showed characteristic product ions such as [M + Na - 103](+), [M + Na - 85](+), and [M + Na - 59](+), by which their regio-specificity can be differentiated.     

Density functional theory and the correlation consistent basis sets: the tight d effect on HSO and HOS

The HSO and HOS isomers have been revisited using the DFT functionals, B3LYP, B3PW91, and PBE, in combination with tight d-augmented correlation consistent basis sets, cc-pV(x+d)Z and aug-cc-pV(x+d)Z for second-row atoms. Structures, vibrationally averaged structures, relative energies, harmonic and anharmonic frequencies, enthalpies of formation of HSO and HOS, and the barrier for the HSO/HOS isomerization have been determined. These results were compared with results from previous DFT and ab initio studies in which the standard correlation consistent basis sets were used. The relative energies of the two isomers converge more rapidly and smoothly with respect to increasing basis set size for the tight d-augmented sets than for the standard basis sets. Our best calculations, B3PW91/aug-cc-pV(5+d)Z, for the relative energy of the isomers are in excellent agreement with previous CCSD(T) results given by Wilson and Dunning.     

Microwave spectra and barriers to internal rotation of z- and e-1-propenyl isocyanide

A synthetic procedure yielding a mixture of Z- and E-1-propenyl isocyanide (CH(3)CH═CHNC) is described. The microwave spectrum of this mixture has been recorded in the 12-100 GHz spectral range, and the spectra of the Z and E isomers have been assigned for the first time. Most transitions of the Z form were split into two components of equal intensity due to tunneling of the methyl group, which allowed the barrier to internal rotation of this group to be determined as 4.0124(12) kJ/mol by fitting 568 transitions with a maximum value of J = 46 using the computer program Xiam. This fit had a root-mean-square deviation as large as 4.325. The same transitions were therefore fitted anew using the more sophisticated program Erham. This fit has a rms deviation marginally better (4.136) than the Xiam fit. No split MW lines were found for E-1-propenyl isocyanide. The absence of splittings is ascribed to a barrier to internal rotation of the methyl group that is significantly higher than the barrier of the Z isomer. It is concluded that the barrier must be larger than 6 kJ/mol for the E form. The experimental work was augmented by quantum chemical calculations at CCSD/cc-pVTZ, B3LYP/cc-pVTZ, and MP2/cc-pVTZ levels of theory. The CCSD method predicts rotational constants of the Z and E forms well. The B3LYP barriers to internal rotation of a series of substituted propenes were calculated and found to be in good agreement with experiments. Calculations of the quartic centrifugal distortion constants of the two 1-propenyl isocyanides by the B3LYP and MP2 methods were less successful.     

Basis set effects on the stability of the Cl2O3 isomers using B3P86 and B3LYP methods of density functional theory

Four Cl₂O₃ isomers have been calculated using density functional theory with B3P86 and B3LYP functionals and various basis sets. The energy hypersurfaces of Cl₂O₃ are very flat and the relative energies of the isomers which have hypervalent characters such as ClOCl(O)O and ClClO₃ are strongly dependent on the basis sets. The stability for Cl₂O₃ isomers are in the order of (1)ClOOOCl(C_s), (2)ClOOOCl(C₂), (3)ClClO₃ and (4)ClOCl(O)O with ClOCl(O)O being most stable. We suggest that at least the cc-pV6Z(-ghi) basis set for Cl and the cc-pVTZ basis set for O are required to obtain reliable relative stabilities of Cl₂O₃ isomers with hypervalent characters.     

Determination of RS,E/Z-tocotrienols by HPLC

Synthetic alpha-tocotrienol was separated into four geometrical E/Z side chain isomers by preparative HPLC (permethylated beta-cyclodextrin phase). The isolated isomers were resolved in ethylene glycol dimethyl ether, converted into the corresponding methyl ether using dimethyl sulfate, and the tocotrienol methyl ethers were extracted with n-hexane. A subsequent HPLC separation on a chiral phase (adsorbent cellulose derivated with 3,5-dimethyl phenyl carbamate) discriminates between the enantiomers of each E/Z side chain isomer, achieving the complete resolution of the eight occurring synthetic RS,E/Z-alpha-tocotrienols. The method can be shortened by omitting the preparative separation of the E/Z tocotrienol isomers prior to the chromatography on the chiral dimethyl phenyl carbamate phase. The simplified method achieved the following separation: RS,E/Z-alpha-tocotrienol separated into five peaks, RS,E/Z-beta-tocotrienol into eight, RS,E/Z-gamma-tocotrienol into six and RS,E/Z-delta-tocotrienol into eight peaks. The naturally occurring R,E-E-tocotrienol isomer could be identified within the synthetic RS,E/Z-isomers by co-chromatography with tocotrienol methyl ethers derived from natural sources, respectively.     

A novel structural analysis of glycerophosphocholines as TFA/K(+) adducts by electrospray ionization ion trap tandem mass spectrometry

When collisionally activated dissociation (CAD) of glycerophosphocholine (GPC) species is examined using quadrupole ion trap mass spectrometry (QITMS), the spectral patterns differ from those obtained using sector or quadrupole mass spectrometry. Methods employed in the structural analysis of GPCs using a sector or quadrupole mass spectrometers are not necessarily useful for an ion trap mass spectrometer. A novel method is presented for structurally analyzing GPCs that involves the CAD of trifluoroacetic acid (TFA) adducts of kaliated GPCs. Solutions of GPCs in 0.1% TFA/methanol were electrosprayed to produce precursor ions by attaching a trifluoroacetic acid (TFA) molecule to a kaliated GPC molecule. The CAD-MS/MS spectra obtained by QITMS revealed a dramatic increase in the abundance of fragment ions, corresponding to the losses of sn-1 and sn-2 fatty acyl substituents. A preferential loss of the sn-1 fatty acyl group over the loss of the sn-2 fatty acyl group was observed among the GPC standards examined. A GPC extract from egg yolk was directly analyzed by this method without prior separation. The identities and positions of fatty acyl substituents of over 20 GPC species were identified. Some isomers present in very low relative abundance, which could not be analyzed by QITMS/MS using other ions as precursors, were identified by the TFA attachment method.     

Characterization of cardiolipin as the sodiated ions by positive-ion electrospray ionization with multiple stage quadrupole ion-trap mass spectrometry

The application of multiple-stage ion-trap (IT) mass spectrometric methods for the structural characterization of cardiolipin (CL), a 1,3-bisphosphatidyl-sn-glycerol that consists of four fatty acyl chains and three glycerol backbones (designated as A, B, and central glycerol, respectively), as the sodiated adduct ions in the positive-ion mode was evaluated. Following collisionally activated dissociation (CAD), the [M - 2H + 3Na]+ ions of CL yield two prominent fragment ion pairs that consist of the phosphatidyl moieties attached to the 1'- and 3'-position of the central glycerol, respectively, resulting from the differential losses of the diacylglycerol moieties containing A and B glycerol, respectively. The results are consistent with those previously described for the [M - H]- and [M - 2H + Na]- ions in the negative-ion mode, thus permitting assignment of the two phosphatidyl moieties attached to the 1'- or 3'-position of the central glycerol. The identities of the fatty acyl substituents and their positions on the glycerol backbones (glycerol A and B) are deduced from further degradation of the above ion pairs that give the fragment ions reflecting the fatty acid substituents at the sn-1 (or sn-1') and sn-2 (or sn-2') positions. The ions that arise from losses of the fatty acid substituents at sn-1 and sn-1', respectively, are prominent, but the analogous ions from losses of the fatty acid substituents at sn-2 and sn-2', respectively, are of low abundance in the MS2 product-ion spectra. This feature further confirms the assignment of the positions of the fatty acid substituents. The similar IT multiple-stage mass spectrometric approaches including MS2 and MS3 for structural characterization of CL using its [M + Na]+ and the [M - H + 2Na]+ ions are also readily applicable. However, their uses for structural characterization are less desirable because formation of the [M + Na]+ and the [M - H + 2Na]+ ions for CL is not predictable.     

Regiospecific analysis of neutral ether lipids by liquid chromatography/electrospray ionization/single quadrupole mass spectrometry: validation with synthetic compounds.

A reversed-phase high-performance liquid chromatography (HPLC) method with on-line electrospray ionization/collision-induced dissociation/mass spectrometry (ESI/CID/MS) is presented for the regiospecific analysis of synthetic reference compounds of neutral ether lipids. The reference compounds were characterized by chromatographic retention times, full mass spectra, and fragmentation patterns as an aid to clarify the regiospecificity of ether lipids from natural sources. The results clearly show that single quadrupole mass spectroscopic analysis may elucidate the regiospecific structure of neutral ether lipids. Ether lipid reference compounds were characterized by five to six major ions in the positive ion mode. The 1-O-alkyl-sn-glycerols were analyzed as the diacetoyl derivative, and showed the [M - acetoyl](+) ion as an important diagnostic ion. The diagnostic ions of directly analyzed 1-O-alkyl-2-acyl-sn-glycerols and 1-O-alkyl-3-acyl-sn-glycerols were the [M - alkyl](+), [M + H - H(2)O](+) and [M + H](+) ions. Regiospecific characterization of the fatty acid position was evident from the relative ion intensities, as the sn-2 species had relatively high [M + H](+) ion intensities compared with [M + H - H(2)O](+), whereas the reverse situation characterized the sn-3 species. Furthermore, corresponding sn-2 and sn-3 species were separated by the chromatographic system. However, loss of water was promoted as fatty acid unsaturation was raised, which may complicate interpretation of the mass spectra. The diagnostic ions of directly analyzed 1-O-alkyl-2,3-diacyl-sn-glycerols were the [M - alkyl](+), [M - sn-2-acyl](+) and [M - sn-3-acyl](+) ions. Regiospecific characterization of the fatty acid identity and position was evident from the relative ion intensities, as fragmentation of the sn-2 fatty acids was preferred to the sn-3 fatty acids; however, loss of fatty acids was also promoted by higher degrees of unsaturation. Therefore, both structural and positional effects of the fatty acids affect the spectra of the neutral ether lipids. Fragmentation patterns and optimal capillary exit voltages are suggested for each neutral ether lipid class. The present study demonstrates that reversed-phase HPLC and positive ion ESI/CID/MS provide direct and unambiguous information about the configuration and identity of molecular species in neutral 1-O-alkyl-sn-glycerol classes.     

Computational study on the structures of the [H, Si, N, C, O] isomers: possible species of interstellar interest

Ab initio methods have been used to study the lowest lying [H, Si, N, C, O] isomers, which are of astrochemical interest. Over 20 [H, Si, N, C, O] isomers in the 1A' electronic state have been investigated at the MP2/aug-cc-pVTZ level of theory. Of these, the seven lowest isomers have been further investigated using different levels of theory, including B3LYP and QCISD(T). It has been found that the relative energies of the isomers in their ground electronic state (1A') are very dependent on the level of theory used with either the cis-HOSiCN or cis-HOSiNC isomers being the lowest in energy. Overall, the four lowest isomers are within 6 kcal/mol of each other, and a further three isomers are less than 15 kcal/mol higher in energy than the lowest lying isomer, including HSiNCO, which has recently been detected spectroscopically. Natural bond analysis has been carried out on the ground electronic states of the seven lowest lying isomers to examine their electronic structure. The enthalpies of formation of the seven lowest isomers have also been evaluated using the G3MP2 and G3B3 multilevel methods and show that the isomers are relatively thermodynamically stable. The structures and energies of lowest lying 1A' and 3A' electronic states of these isomers have also been investigated and show that for most of the isomers the optimized structures in these excited electronic states correspond to a transition state structure.     

Diastereoselective synthesis of cyclopropane amino acids using diazo compounds generated in situ

A simple and high-yielding method for the preparation of cyclopropane amino acids is described. The novel method involves the one-pot cyclopropanation of readily available dehydroamino acids using aryl and unsaturated diazo compounds generated in situ from the corresponding tosylhydrazone salts. It was found that thermal 1,3-dipolar cycloaddition followed by nitrogen extrusion gave the cyclopropane amino acid derivatives with good E selectivity, while reactions in the presence of meso-tetraphenylporphyrin iron chloride gave predominantly the corresponding Z isomers. The synthetic utility of this process was demonstrated in the synthesis of (+/-)-(Z)-2,3-methanophenylalanine [(+/-)-(Z)-1], the anti-Parkinson (+/-)-(E)-2,3-methano-m-tyrosine [(+/-)-(E)-2], and the natural product (+/-)-coronamic acid [(+/-)-3].     

A new synthesis of lysophosphatidylcholines and related derivatives. Use of p-toluenesulfonate for hydroxyl group protection

A new stereoselective synthesis of lysophosphatidylcholines is reported. The synthesis is based upon (1) the use of 3-p-toluenesulfonyl-sn-glycerol to provide the stereocenter for construction of the optically active lysophospholipid molecule, (2) tetrahydropyranylation of the secondary alcohol function to achieve orthogonal protection of the sn-2- and sn-3-glycerol positions, and (3) elaboration of the phosphodiester headgroup using a 2-chloro-1,3,2-dioxaphospholane/trimethylamine sequence. In the course of developing the synthesis it has been discovered that methoxyacetate displacement of the sn-3-p-toluenesulfonate yields a reactive methoxyacetyl ester, which in turn can be selectively cleaved with methanol/tert-butylamine, while the ester group at the sn-1-position remains unaffected. The sequence has been shown to be suitable for preparation of spectroscopically labeled lysophosphatidylcholines. One of these compounds was readily converted to a double-labeled mixed-chain phosphatidylcholine applicable for real-time fluorescence resonance energy transfer (FRET) assay of lipolytic enzymes. In addition, the work led to new synthetic strategies based on chemoselective manipulation of the tosyl group in the presence of other base-labile groups such as FMOC derivatives that are often used for the protection of amino and hydroxyl groups in syntheses.     

Direct separation of regio- and enantiomeric isomers of diacylglycerols by a tandem column high-performance liquid chromatography

A novel HPLC-based method for direct separation of the three isomers of mono-acid diacylglycerols (DAGs), i.e., 1,2-DAG, 2,3-DAG and 1,3-DAG, has been established. The method employs a tandem column system, in which two different columns (a conventional silica gel column and a chiral stationary phase column) are connected in series. Two isomeric mixtures of DAGs (i.e., dicapryloylglycerol and dioleoylglycerol) and lipase-catalyzed reaction mixtures were successfully resolved on the tandem column HPLC system without any derivatization prior to the analysis. According to the established analytical method, stereoselectivity of two lipases toward mono-acid triacylglycerols in ethanolysis reaction was investigated. The tested enzymes were immobilized Candida antarctica lipase B (CALB) and Rhizomucor miehei lipase (RML). Analyses of the enantiomeric purity of 1,2-DAG and 2,3-DAG, generated as intermediates during the reaction, revealed that CALB and RML have sn-3 and sn-1 stereopreference, respectively.     

Structure of small TiCn clusters: A theoretical study

A theoretical study of the TiC_n (n = 1–8) clusters has been carried out at the B3LYP/6-311+G(d) level. Molecular properties for three different isomers, namely linear, cyclic, and fan species, have been determined. The fan isomers, where the titanium atom is essentially side-bonded to the entire C_n unit, are predicted to be more stable than both linear and cyclic isomers. Only for the largest studied species, TiC₈, the cyclic isomer is located lower in energy. An even–odd parity effect in the incremental binding energies is observed for the three isomers, n-even species being in general more stable for linear and fan isomers, whereas for the cyclic species n-odd clusters are favoured. A topological analysis of the electronic charge density shows that all cyclic isomers correspond to true monocyclic rings, whereas for the fan species a variety of different connectivities has been observed.     

Preparative thin-layer chromatographic separation and subsequent gas chromatographic-mass spectrometric analysis of monoacylglycerols derived from butter oil by fungal degradation.

A semi-micro method has been developed using preparative thin-layer chromatography (TLC) to separate acylglycerols for the subsequent analysis by gas chromatography-mass spectrometry (GC-MS). Monoacylglycerols (MAGs) were formed from butter oil by fungal degradation with Penicillium roquefortii. Total lipids were extracted with hexane-2-propanol (3:2, v/v) and separated on silica gel preparative TLC plates with fluorescence indicator (Merck). The plates were developed in hexane-diethyl ether-formic acid (80:20:2, v/v). Lipid bands were detected under UV light or with iodine vapour, removed and then extracted with hexane-2-propanol (3:2, v/v). The MAG band (RF 0.03) was silylated into trimethylsilyl (TMS) ethers. Structures and composition of MAG-TMS ethers were analysed by GC and GC-MS. Formation of characteristic ions for the identification of sn-1(3)- and sn-2-MAG isomers was discussed. The method is simple, inexpensive and powerful for the separation and analysis of relatively small amounts of MAGs (0.2-5.0 mg) formed from fungal degradation.     

Temperature investigations of E/Z isomers in ketimines based of p-dibenzoylobenzene with aniline and 2,6-dimethylaniline by infrared spectroscopy

The reaction of aniline with p-dibenzoylobenzene (K1) can lead to Z/Z, Z/E and E/E isomers however the only Z/Z and E/E were formed. At room temperature these isomers may be separated, thus the corresponding FTIR spectra could be recorded. The observed bands were assigned and temperature investigations were lead to monitor the structural changes during heating Z and E forms of K1 from 20 to 240 degrees C. FTIR spectroscopy showed that the bigger changes of the Z form was observed with an increase of temperature. Similar experience was lead with the ketimine synthesized from 2,6-dimethylaniline and p-dibenzoylobenzene (K2) investigated as a mixture of isomers.     

Stereospecific synthesis and biological evaluation of farnesyl diphosphate isomers

[formula: see text] A unified, stereospecific synthetic route to the three geometric isomers of (E,E)-farnesyl diphosphate (E,E-FPP) (1, 2, and 3) has been developed. The key feature of this synthesis is the ability to control the stereochemistry of triflation of the beta-ketoester 10 to give either 11 or 14. Preliminary evaluation of these compounds with protein-farnesyl transferase indicates that 1 and 2 are surprisingly effective substrates; however, Z,Z-FPP (3) is a poor substrate and a sub-micromolar inhibitor.     

Experimental and Computational Studies of the Isomerization between Z and E Isomers of Benzaldoximes

The isomerization between Z and E isomers of benzaldoximes in different solvents were measured by TLC method. The experimental results show that acid solvents catalyze this inter‐conversion process dramatically. Solution state NMR measurements also show very different spectra for Z and E isomers of benzaldoximes in different solvents. All this suggests that the acidity of solvent is a very important factor to affect the inter‐conversion process. Theoretical investigations of Z to E inter‐conversion of benzaldoximes in different solvents were carried out by DFT calculations at B3LYP/6–3 11+G** level. The calculations show that the barrier from Z to E in the presence of acid is much lower than that without acid. This agrees with the experimental data very well. The calculated structure in the transition state is helpful for the understanding of the inter‐conversion mechanism.     

Scorpion digestive lipase: kinetic study using monomolecular film technique

Using the classical emulsified system and the monomolecular film technique, we compared the interfacial properties of the scorpion digestive lipase (SDL) with those of higher animals'. In the absence of bile slats, SDL does not hydrolyse efficiently pure tributyrin, as well as dicaprin films maintained at low surface pressure. The preincubation of bile salts with tributyrin seems to be a better substrate for SDL than the pure tributyrin. A kinetic study on the surface pressure dependency, stereospecificity and regioselectivity of SDL was performed using monomolecular films of either three dicaprin isomers or three pairs of didecanoyl-deoxyamino-O-methyl glycerol enantiomers (DDG) containing a single hydrolysable decanoyl ester bond. With all diacylglycerol isomers, SDL has a surface pressure threshold of about 15 m Nm(-1), below which enzymatic activity is undetectable. SDL seems to prefer vicinal ester groups of the diacylglycerol isomers, with preference for sn-1 position at both 15 and 23 m Nm(-1). Furthermore, the maximum SDL activity is measured with DDG having a primary ester bond (1,3DDG, SII). This shows that SDL has a preference for the sn-1 position of this diacylglycerol analogue. Moreover, this was in line with the fact that SDL is inactive on sn-2 position of both DDG isomers and a triacylglycerol. With diacylglycerol analogue isomers, SDL shows a preference for distal isomers contrary to what has been observed with diacylglycerol isomers. SDL interacts with egg-phosphatidyl choline (egg-PC) monomolecular films. The critical surface pressure value (13 m Nm(-1)) is comparable to those of pancreatic lipases.     

Ph3P/CF3CCl3作为一个新的羰基烯烃化试剂的研究—一锅法合成烯烃RCH=CClCF3

Ph3P/CF3CCl3与醛在室温下一锅反应生成三氟甲基取代的烯烃RCH=CClCF3(3). 芳香醛及α,β-不饱和醛的反应显示高度立体选择性, 给出Z式异构体. 而饱和脂肪醛的反应立体选择性较低, Z与E式异构体的比例为2:1至3:1. 反应可能是经由叶立德Ph3P-CClCF3的Wittig型反应. 本工作表明, Ph3P/CF3CCl3可以作为在十分温和的条件下向有机分子中引入=CClCF3结构单元的方便试剂.