Pairs Of Positional Isomers Research Articles

Comprehensive exploration of a traditional Chinese medicinal plant of Magnolia officinalis based on high-coverage mass spectrometry and multidimensional chemical-biological analysis

Magnolia bark is a traditional Chinese medicine used for hypoglycaemia. With the widespread use of Magnolia bark, its resources are facing a serious shortage. To address this issue, a strategy based on high-coverage mass spectrometry (HCMS) and multidimensional chemical-biological analysis (MCBA) was proposed for the comprehensive exploration of Magnolia officinalis which is the main source of Magnolia bark. The strategy is divided into three main steps. In the first step, the stem bark, stem xylem, root bark, root xylem, leaf and rootlet of Magnolia officinalis were comprehensively analyzed using high-coverage mass spectrometry. In the second step, multivariate statistical analysis was used to explore the heterogeneity of the six parts and detect differential chemical components. In the third step, a combination of experimental screening and molecular docking was used to explore α-glucosidase inhibitors from Magnolia officinalis. Multidimensional chemical-biological analysis (MCBA) of Magnolia officinalis was achieved by combining the last two steps. Finally, a total of 103 compounds were identified from the whole plant of Magnolia officinalis. Differential components of stem bark, stem xylem, leaf, root bark, root xylem and rootlet were systematically revealed. A pair of positional isomers, namely magnolol and honokiol, were found to be α-glucosidase inhibitors. The activity of their combination is superior to that of each single compound, indicating that magnolol and honokiol are in a synergistic relationship. This strategy contributes to comprehensive exploitation of functional plants and effective alleviation of resource shortage. This study also provides a research paradigm for other similar traditional Chinese medicinal plants.

Impact of Positional Isomerism on Melting Point and Stability in New Energetic Melt-Castable Materials

For an energetic material with a definite composition, the substituent position is the most crucial factor to influence its physicochemical properties. Thus, it is becoming increasingly important to understand the impact of positional isomerism on multidimensional properties differences. Herein, we reported two new potential energetic melt-castable molecules, a pair of positional isomers (4-MMDNP and 5-MMDNP). These two explosives exhibit obviously different properties, including densities (Δρ = 0.03 g cm–3), melting point (ΔTm = 47.2 °C), decomposition temperature (ΔTd = 27.3 °C), stability (IS = 20 J, FS = 160 N vs IS = 10 J, FS = 40 N), etc., even though they share similar compositions and structures. Simultaneously, by analyzing crystal packing, intermolecular interactions, and monomolecular parameters, we were able to uncover the roots of property differences. Altogether, our results provide comprehensive molecular and crystal level insight into the effect of positional isomerism, which may be useful for new molecular design.

Design of highly stable thermally activated delayed fluorescence emitters via the overlap degree of HOMO-LUMO distributions

Two questions including the judgement of thermally activated delayed fluorescence (TADF) property and high stability are crucial for designing TADF emitters. In this work, based on the experimental TADF emitters, we investigated the essential reason of improving the stability of TADF device by introducing tert-butyl and phenyl into the peripheral position of carbazole, and suggested to judge the TADF property via the concrete HOMO-LUMO overlap calculation. To design highly stable TADF emitters, several pairs of positional isomers combining tert-Butyl-substituted carbazole as donor with different acceptors are designed by connecting the donor and acceptor groups through the orth-, meta- and para-position. Via the HOMO-LUMO overlap calculation, the potential TADF emitters have been point out. Our results find that the HOMO-LUMO overlap values are dependent on the linkage styles and acceptor species. For example, the designed molecules m-Cz-BF/BF-Cz/NOBF2-DTCz/CPS, o-CNImPy-Cz/PQM-Cz, and m-, p-Cz-NAI have the potential to perform better TADF performance than other isomers. These results indicate that the HOMO-LUMO overlap could be used to identify synthetic motifs for promising TADF candidates among structural isomers.

Achieving Molecular Fluorescent Conversion from Aggregation-Caused Quenching to Aggregation-Induced Emission by Positional Isomerization.

In this work, we synthesized a pair of positional isomers by attaching a small electron-donating pyrrolidinyl group at ortho- and para-positions of a conjugated core. These isomers exhibited totally different fluorescent properties. PDB2 exhibited obvious aggregation-induced emission properties. In contrast, PDB4 showed the traditional aggregation-caused quenching effect. Their different fluorescent properties were investigated by absorption spectroscopy, fluorescence spectroscopy, density functional theory calculations and single-crystal structural analysis. These results indicated that the substituent position of the pyrrolidinyl groups affects the twisted degree of the isomers, which further induces different molecular packing modes, thus resulting in different fluorescent properties of these two isomers. This molecular design concept provided a new accurate strategy for designing new aggregation-induced emission luminogens.

Synthesis and characterization of a series of N,N′‐substituted urea derivatives by using electrospray ionization tandem mass spectrometry: Differentiation of positional isomers

Characterization of N,N'-substituted ureas was found to be challenging by nuclear magnetic resonance (NMR) spectroscopy, particularly N-di- and tri-alkylated ureas because of the absence of adjacent protons. In the present study, electrospray ionization tandem mass spectrometry has been used to differentiate positional isomeric pairs and to characterize a series of N,N'-substituted ureas, as these compounds have significant importance for drug discovery. Additionally, urea is an essential functionality in several bioactive compounds as well as a variety of clinically approved therapies. High-resolution electrospray ionization tandem mass spectrometry (ESI-HR-MS/MS) has been used to characterize a series of N,N'-substituted urea derivatives and differentiate two pairs of positional isomers. The data was acquired by Xcaliber application in positive ionization mode. ESI-HR-MS/MS spectra of [M + H]+ ions of the positional isomeric urea derivatives 8a and 8b show distinct fragmentation patterns. For example, the MS/MS spectrum of the [M + H]+ ion of isomer 8a displays the abundant fragment ion at m/z 285.1595, which was totally absent in isomer 8b. This would be plausibly formed by the cleavage of the C-N bond of the urea group with the elimination of the isocyanate moiety. In contrast, the MS/MS spectrum of the [M + H]+ ion of isomer 8b shows an intense ion at m/z 311.1389 which is completely absent in isomer 8a which would be formed by the cleavage of the C-N bond attached to the ring nitrogen. Similarly, another pair of positional isomers, 8c and 8d, have been clearly distinguished by their fragmentation behaviour. In addition, a series of N,N'-substituted urea derivatives were studied to investigate the impact of different substitution on the fragmentation behaviour. The present study demonstrates that ESI-HR-MS/MS can be used to differentiate pairs of N,N'-substituted urea positional isomers and characterize a series of derivatives. It was observed that a characteristic fragment ion was formed by the C-N bond cleavage with the elimination of an isocyanate moiety. The proposed mechanism of fragmentation was supported by the change in the fragmentation pathway upon alkylation of the NH. In order to generalize this fragmentation pattern, a series of N-alkylated ureas was synthesized and studied by MS/MS.

Proton conduction and luminescent sensing property of two newly constructed positional isomer-dependent redox-active Mn(II)-organic frameworks

Recently, investigation of proton conduction and luminescent sensing property of crystalline MOFs-based materials have attracted intensive attention. Herein, two luminescent and redox-active Mn(II)-organic frameworks (MOFs) based on the multi-functional 5-iodoisophthalic acid (H2iip) and a pair of positional isomers N,N′-bis(3-pyridylmethyl)oxalamide (3bpmo) and N,N′-bis(4-pyridylmethyl)oxalamide (4bpmo), {[Mn(iip)(3bpmo)0.5·(H2O)]·0.5(3bpmo)}n (1) and {[Mn(iip)(4bpmo)·(H2O)]·(H2O)}n (2), were obtained at ambient conditions. 1 is a 2D (4, 4) topological framework which further extends into a 3D supramolecular architecture pillared by the interstitial 3bpmo molecule via 1D hydrogen-bonded tape between the coordinated 3bpmo ligand and lattice 3bpmo molecule. 2 shows a 2D centro-symmetric double-layer structure. The R22(8) hydrogen-bonded ring further holds the adjacent 2D layers into a 3D supramolecular network. The wide indirect band gap exists in both 1 and 2, which is further illustrated by the calculation based on the Density Functional Theory using Materials studio software. The electrochemical studies suggest that the positional isomers 3bpmo and 4bpmo have great influence on the redox characteristics of 1 and 2. The proton-conductive properties of 1 and 2 in both the solid state and the composite Nafion-MOFs membranes were studied by AC impedance spectroscopy. The proton conductivities of 2 are higher than those of 1 in both cases. 1 and 2 show greatly solvent-dependent luminescent emissions and the strongest emission occurs in water. 1 and 2 exhibit efficient and selective turn off sensing towards Fe3+. Moreover, 1 and 2 show quite different sensing behavior to the Cr(VI) anions. 1 has nearly no fluorescence response to Cr2O72− and CrO42−, while 2 demonstrates sensitive sensing toward both Cr2O72− and CrO42−. The sensing for the Fe3+ cation and the Cr(VI) anions is quite recyclable. The limits of detection (LOD) for these analytes are in ppm order.

Chemometrically assisted RP-HPLC method development for efficient separation of ivabradine and its eleven impurities

The aim of this study was to develop a novel reversed-phase high-performance liquid chromatography (RP-HPLC) method for efficient separation of ivabradine and its 11 impurities. Similar polarity of impurities in the sample mixture made method optimization challenging and accomplishable only when different chemometric tools, such as principal component analysis (PCA), Box–Behnken design (BBD), and desirability function as a multicriteria approach, were employed. The presence of 3 positional isomers (impurities III, V, and VI), keto–enol tautomerism of impurity VII, and diastereoisomers of impurity X made separation of this complex mixture even more challenging. Chromatographic retention parameters obtained with the mobile phase consisting of 30 mM phosphate buffer and acetonitrile (80:20, v/v) on four different RP-HPLC columns at varying pH values (3.0, 4.0, and 5.0) were subjected to the PCA analysis to select the column with the most appropriate selectivity. Then the column temperature, pH of the aqueous component of mobile phase, phosphate buffer molarity and the organic solvent content in the mobile phase were estimated employing BBD. Valid and reliable mathematical models towards resolution of twelve critical peak pairs were obtained. After determination of the desirability making criteria for all responses, desirability functions were established and used in optimization. The proposed optimal chromatographic conditions included the Zorbax Eclipse Plus C18 chromatographic column (100 × 4.6 mm, 3.5 μm), the column temperature of 34 °C, the mobile phase flow rate of 1.6 mL min−1 and the UV detection at 220 nm. The mobile phase consisted of the 28 mM phosphate buffer at pH 6.0 and acetonitrile (85:15, v/v). Separation of one pair of positional isomers was not achieved, so methanol was added to the organic part of mobile phase in small increments with the optimal ratio of methanol to acetonitrile 59:41, v/v. The overall organic component of the mobile phase also increased to 18%, accelerating the chromatographic analysis.

Improved synthesis of natural isomeric naphthoxanthenones

5-methoxy-1H-naphtho[2,1,8-mna]xanthen-1-one (1) and 5-methoxy-3H-naphtho[2,1,8-mna]xanthen-3-one (musafluorone 2), a pair of positional isomers isolated from Wachendorfia thyrsiflora and Musa acuminata, were synthesized in six steps in an overall yield of 53% and 59% starting from the corresponding methoxyphenalenones and employing an acid mediated cyclocondensation strategy. Preliminary assays demonstrated the intercalation ability of compounds 1 and 2 into DNA.

Silver perchlorate in the mobile phase for rapid separation and determination of a pair of positional isomers in Inula racemosa Hook.f. with RP-HPLC.

Alantolactone and isoalantolactone isolated from many species of plants are a pair of positional isomers of CC bond. Previously, alantolactone and isoalantolactone have been proved to be good lead compounds for future anticancer agent development. Similarity of their molecular structures increases the separation difficulty for these two isomers on a conventional C18 column. Silver perchlorate (AgClO4) as mobile phase additives with RP-HPLC for improving the separation was developed for rapid determination of the positional isomers in Inula racemosa Hook.f. The effects of the concentration of silver perchlorate on the separation of the analytes were investigated. The composition of acetonitrile and water containing 5.0% silver perchlorate in a 65:35 (v/v) ratio was used as mobile phase, in which they were well separated within a short period of time on the C18 column. The method was successfully applied to determine them in an extract of Inula racemosa Hook.f. root. Silver perchlorate in mobile phase can efficiently improve the separation of the positional isomers and could be applied to rapidly determinate their content in this plant.

Mechanochromic and acidochromic response of 4H-pyran derivatives with aggregation-induced emission properties

Several 1- and 2-position naphthylethylene-substituted 4H-pyran derivatives comprising two different end groups were synthesized. These two pairs of positional isomers with aggregation-induced emission properties exhibit different stimuli-responsive solid-state fluorescent properties. Both the linking position of the naphthylethylene and the electron-withdrawing end group have a significant impact on the mechanochromic properties of the compounds, whereas, the acidochromic properties are only related to the latter. The transformation between amorphous and crystalline states accounts for the mechanochromic properties and is attributed to loose molecular packing with weak intermolecular interactions, as revealed by crystallographic data. The reversible acidochromic properties are mainly ascribed to protonation/deprotonation of the carbonyl group, which is confirmed by 1H NMR experiments. Additionally, because the emission of these 4H-pyran derivatives in solid state can be tuned by external stimuli, several molecular logic gates were established by using appropriate stimuli operations as the inputs and fluorescent colors as the outputs.

Identification of molecular species of monoalkyldiacylglycerol from the squid Berryteuthis magister using liquid chromatography–APCI high-resolution mass spectrometry

Monoalkyldiacylglycerol (MADAG) is an important lipid class in mollusks, corals, starfishes, and some species of zooplankton. Up to 80% of liver oils of squids and sharks are comprised of MADAG. Except for one fish species, there are no data on the composition of MADAG molecular species of marine organisms. The molecular species of MADAG obtained from digestive glands of the deep-sea squid Berryteuthis magister were identified. High-performance liquid chromatography (HPLC) and tandem high-resolution mass spectrometry (HRMS) with atmospheric pressure chemical ionization (APCI) were applied. The mass spectra of each molecular species contained positive quasi-molecular ion [M+H]+ with fragment ions [M–R′CO2]+, [M–R′′CO2]+, and [M–OR′′′]+, as well as negative cluster ion [M+2H2OH]− without fragments. The exact masses of the negative ions allowed determination of the molecular formulas and the number of double bonds; the positive fragment ions were used to determine the location of acyl and alkyl groups in MADAG molecules. Ninety molecular species of MADAG were revealed. The regiospecific composition was identified for 72 individual molecular species. Eleven pairs of positional isomers of acyl groups were found. Four molecular ions were produced by a mixture of acyl/alkyl isomers. Most of molecular species contained 16:0e or 18:1e alkyl groups in the sn-1 position, whereas polyunsaturated fatty acids mainly esterified the sn-2 position of MADAG from B. magister. These structural features are supposed to be characteristic for biologically active MADAG.

Examining the Influence of Phosphorylation on Peptide Ion Structure by Ion Mobility Spectrometry-Mass Spectrometry.

Ion mobility spectrometry-mass spectrometry (IMS-MS) techniques are used to study the general effects of phosphorylation on peptide structure. Cross sections for a library of 66 singly phosphorylated peptide ions from 33 pairs of positional isomers, and unmodified analogues were measured. Intrinsic size parameters (ISPs) derived from these measurements yield calculated collision cross sections for 85% of these phosphopeptide sequences that are within ±2.5% of experimental values. The average ISP for the phosphoryl group (0.64 ± 0.05) suggests that in general this moiety forms intramolecular interactions with the neighboring residues and peptide backbone, resulting in relatively compact structures. We assess the capability of ion mobility to separate positional isomers (i.e., peptide sequences that differ only in the location of the modification) and find that more than half of the isomeric pairs have >1% difference in collision cross section. Phosphorylation is also found to influence populations of structures that differ in the cis/trans orientation of Xaa-Pro peptide bonds. Several sequences with phosphorylated Ser or Thr residues located N-terminally adjacent to Pro residues show fewer conformations compared to the unmodified sequences.

Use of isomeric, aromatic dialdehydes in the synthesis of photoactive, positional isomers of higher analogs of o-bromo(hetero)acenaldehydes

A series of photoresistant, positional isomers of o-bromo(hetero)acenaldehydes containing RO-Ar and bifunctional ortho-CHO/Br structural motifs, is available in the peculiar Friedel–Crafts modification, using isomeric aromatic o,o-dibromodialdehydes.

Isolation and Characterization of Batatasin III and 3,4’- Dihydroxy-5-methoxybibenzyl: A Pair of Positional Isomers from <i>Sunipia scariosa</i>

Purpose : To isolate and characterize chemical compounds of biological importance from the whole plant of Sunipia scariosa. Methods : The whole plant of Sunipia scariosa was extracted with methanol (MeOH) and chromatographed on silica gel and sephadex LH-20 to afford the pure isolates. High perfomance liquild chromatography (HPLC) was used for further purification of the isolated compounds. Characterization of the isolated compounds was achieved by 1H and 13C nuclear magnetic resonance spectroscopy (NMR) and mass spectrometry (MS). Results : Batatasin III (3,3’-dihydroxy-5-methoxybibenzyl) and 3,4’-dihydroxy-5-methoxybibenzyl, a pair of positional isomers, were isolated from the whole plant of Sunipia scariosa. The yields of the two isomers were 60 and 40 %, respectively, from the mixture of two compounds. Conclusion : Batatasin III and 3,4’-dihydroxy-5-methoxybibenzyl, a pair of positional isomers were successfully isolated from the whole plant of Sunipia scariosa for the first time. Keywords : Sunipia scariosa, Batatasin III, 3,4’-Dihydroxy-5-methoxybibenzyl, Isomers

The influence of positional isomerism on G-quadruplex binding and anti-proliferative activity of tetra-substituted naphthalene diimide compounds

The synthesis together with biophysical and biological evaluation of a series of tetra-substituted naphthalene diimide (ND) compounds, are presented. These compounds are positional isomers of a recently-described series of quadruplex-binding ND derivatives, in which the two N-methyl-piperidine-alkyl side-chains have now been interchanged with the positions of side-chains bearing a range of end-groups. Molecular dynamics simulations of a pair of positional isomers are in accord with the quadruplex stabilization and biological data for these compounds. Analysis of structure–activity data indicates that for compounds where the side-chains are not of equivalent length then the positional isomers described here tend to have improved cell proliferation potency and in some instances, superior quadruplex stabilization ability.

Electrospray ionization tandem mass spectrometry of protonated and alkali‐cationized Boc‐N‐protected hybrid peptides containing repeats of D‐Ala‐APyC and APyC‐D‐Ala: Formation of [bn–1 + OCH3 + Na]+ and [bn–1 + OH + Na]+ ions

Differentiation and structural characterization of positional isomers of non-natural amino acid hybrid peptides by using electrospray ionization tandem mass spectrometry (ESI-MS(n) ) is desirable because of their fundamental importance from the view point of peptide mass spectrometry and also of their increasing importance in the area of research towards biomedical and material applications; hence, the present study is undertaken. Electrospray ionization ion-trap tandem mass spectrometry (ESI-MS(n)) was used to characterize and differentiate three pairs of positional isomers of Boc-N-protected hybrid peptides containing repeats of D-Ala-APyC and APyC-D-Ala (D-Ala = D-alanine and APyC = trans-3-aminopyran-2-carboxylic acid). ESI-MS(n) spectra of protonated and alkali-cationized positional isomeric peptides display characteristic fragmentation involving the peptide backbone, the Boc group, and the side chain. It is observed that abundant rearrangement ions [b(n-1) + OCH(3) + Na](+) or [b(n-1) + OH + Na](+) are formed when D-Ala is present at C-terminus and the presence of APyC at the C-terminus inhibits the formation of rearrangement ions. In addition, abundant b(n-1)(+) ions are formed, presumably with stable oxazolone structures, when the C-terminus of b(n-1) (+) ions possessed D-Ala. The present study demonstrates that ESI tandem mass spectrometry is very useful for differentiating positional isomers of hybrid peptides containing D-Ala and APyC amino acids. While the protonated peptides give rise to characteristic sequencing ions, the cationized peptides produce additional rearrangement ions ([b(n-1) + OCH(3) + Na](+) and [b(n-1) + OH + Na](+)) which helps distinguish between the presence of D-Ala and APyC amino acids at the C-terminus.

The use of boronate derivatives in the characterization of cathecholamines and related beta-hydroxy-amines by gas liquid chromatography-mass spectrometry.

Abstract The gas chromatographic separation of various β-hydroxy-amines in the form of derived 1, 3, 2-oxazaborolidines is complemented by a mass-spectrometric study of cyclic boronates of natural catecholamines. These derivatives and their synthetic analogues yield characteristic mass spectra. Closely similar compounds, such as the n-butylboronates of the diastereoisomers (—)-ephedrine and (+)-ψ-ephedrine, give almost identical spectra but can be readily distinguished by their glc retention times. The same can be said for the positional isomer pairs synephrine and phenylephrine, and for octopamine and 4-deoxynoradrenaline. Mass-spectrometric fragmentation modes are postulated from a comparison of the shifts in the masses of fragment ions corresponding to various substituents in the group of biological amines studied. Additional correlations are derived from studies of methyl-, cyclohexyl- and phenyl-boronates.

Actual ratios of triacylglycerol positional isomers consisting of saturated and highly unsaturated fatty acids in fishes and marine mammals

The distribution of fatty acid species at the (sn-1, 3) position or the (sn-2) position of triacylglycerol (TAG) in natural fats and oils has already been analysed by many researchers and several interesting results have been reported. However, most of these reports only focused on the distribution of fatty acids at the or positions in TAG, and did not take account of the combination of fatty acids in the TAG, i.e., the TAG positional isomers. In this study, the actual ratios of TAG positional isomer pairs, consisting of palmitic acid and highly unsaturated fatty acid (HUFA) such as DHA or EPA, in fish and marine mammals were investigated using a high-performance liquid chromatography/atmospheric pressure chemical ionisation-mass spectrometry (HPLC/APCI-MS) system equipped with tandem jointed non-endcapped polymeric ODS columns. The results show that for combinations of DHA or EPA with two palmitic acids in the TAG of marine mammals, binding was almost all at the α position. In contrast, binding of DHA or EPA was mainly at the β position in fish. The preferred DHA and EPA positions in TAG were the same in the same marine mammal or fish. The binding position tendency of HUFA in TAG positional isomers consisting of two HUFAs and one palmitic acid was the same as that for combinations of one HUFA and two palmitic acids. These results were interpreted as showing that the preferred fatty acid species of sn-glycerol-3-phosphate acyltransferase and 1-acyl-sn-glycerol-3-phosphate acyltransferase in marine mammals are different to those in fish and other animals, or that diacylglycerol acyltransferase in marine mammals favours 1,2-dipalmitoyl-sn-glycerol formed from 1,2-dipalmitoyl-sn-glycerol-3-phosphatidate if HUFA is the reaction substrate.

Characterization of Nα‐Fmoc‐protected ureidopeptides by electrospray ionization tandem mass spectrometry (ESI‐MS/MS): differentiation of positional isomers

Four pairs of positional isomers of ureidopeptides, FmocNH-CH(R(1))-ϕ(NH-CO-NH)-CH(R(2))-OY and FmocNH-CH(R(2))-ϕ(NH-CO-NH)-CH(R(1))-OY (Fmoc = [(9-fluorenyl methyl)oxy]carbonyl; R(1) = H, alkyl; R(2) = alkyl, H and Y = CH(3)/H), have been characterized and differentiated by both positive and negative ion electrospray ionization (ESI) ion-trap tandem mass spectrometry (MS/MS). The major fragmentation noticed in MS/MS of all these compounds is due to --N--CH(R)--N--bond cleavage to form the characteristic N- and C-terminus fragment ions. The protonated ureidopeptide acids derived from glycine at the N-terminus form protonated (9H-fluoren-9-yl)methyl carbamate ion at m/z 240 which is absent for the corresponding esters. Another interesting fragmentation noticed in ureidopeptides derived from glycine at the N-terminus is an unusual loss of 61 units from an intermediate fragment ion FmocNH = CH(2) (+) (m/z 252). A mechanism involving an ion-neutral complex and a direct loss of NH(3) and CO(2) is proposed for this process. Whereas ureidopeptides derived from alanine, leucine and phenylalanine at the N-terminus eliminate CO(2) followed by corresponding imine to form (9H-fluoren-9-yl)methyl cation (C(14)H(11) (+)) from FmocNH = CHR(+). In addition, characteristic immonium ions are also observed. The deprotonated ureidopeptide acids dissociate differently from the protonated ureidopeptides. The [M - H](-) ions of ureidopeptide acids undergo a McLafferty-type rearrangement followed by the loss of CO(2) to form an abundant [M - H - Fmoc + H](-) which is absent for protonated ureidopeptides. Thus, the present study provides information on mass spectral characterization of ureidopeptides and distinguishes the positional isomers.

Rapid differentiation of isobaric and positional isomers of structurally related glycosides from Phytolacca bogotensis

Through the action of glycosyltransferases, a plant can biosynthetically assemble small different aglycons or 'templates' to various polysaccharides to produce numerous glycoconjugates differing in the type of the attached aglycon, the anomeric configuration of C-1 of the glycosylating sugar, the type of sugar and the different position of attachments of the sugar unit present in the polysaccharide chain. The position of attachments and the anomeric configuration of the different sugar present in the polysaccharide create the opportunity to generate molecules with either the same or very close molecular weights, which have relative structural similarity--forming isobaric and positional isomers. Although isomeric differentiation was once considered outside of the domain of mass spectrometry, this task can now be resolved using tandem mass spectrometry. In a standardized purified glycoconjugate fraction (SPT01) from Phytolacca bogotensis, we report conventional electrospray ionization mass spectrometry and collision-induced dissociation (CID) MS/MS parameters which favored the formation of characteristic product ions. This allowed us to suggest the type of sugar linkages present in a specific glycoconjugate. Ten new glycoconjugate are described from this plant and another twelve known saponins were structurally characterized using the automatic MSn acquisition mode. The differentiation of two pairs of positional isomers and four isobaric glycosides and the production of a library of 30 glycosides present in P. bogotensis were accomplished.