Wigger Heerma

Identification of Oxidized Methionine in Peptides

The positive- and negative-ion collision-induced dissociation spectra of peptides containing methionine, methionine sulphoxide and methionine sulphone have been studied. Characteristic fragmentations were identified and evaluated as possible indicators for the presence of oxidized methionine residues in peptides. It was found that the elimination of CH3SOH (-64 u) from [M + H]+ is unique for peptides that contain methionine sulphoxide. Sequence ions containing the oxidized methionine undergo the same elimination, allowing unambiguous sequence determination. Methionine sulphone exhibits an analogous elimination of CH3SO2H (-80 u) from the protonated molecule, but not from sequence ions.

Solid-phase syntheses of peptoids using Fmoc-ProtectedN-substituted glycines: the synthesis of (retro)peptoids of leu-enkephalin and substance P

Solid-phase synthesis of oligomeric peptoids can be conveniently achieved by a repetitive cycle consisting of 1) the removal of the Fmoc group and 2) coupling of a N-substituted glycine derivative (a peptoid monomer). This “monomer” method allows the monitored synthesis of relatively large quantities of pure peptoids as well as the translation of in principle any peptide into the corresponding peptoid, illustrated here (below) by the solid-phase synthesis on a peptide synthesizer of the peptoid of substance P.

The structure of the lantibiotic lacticin 481 produced by Lactococcus lactis : location of the thioether bridges

The lantibiotic lacticin 481 is a bacteriocin produced by Lactococcus lactis ssp. lactis. This polypeptide contains 27 amino acids, including the unusual residues dehydrobutyrine and the thioether‐bridging lanthionine and 3‐methyllanthionine. Lacticin 481 belongs to a structurally distinct group of lantibiotics, which also include streptococcin A‐FF22, salivaricin A and variacin. Here we report the first complete structure of this type of lantibiotic. The exact location of the thioether bridges in lacticin 481 was determined by a combination of peptide chemistry, mass spectrometry and NMR spectroscopy, showing connections between residues 9 and 14, 11 and 25, and 18 and 26.

Cannabis—VIII : Pyrolysis of Cannabidiol. Structure elucidation of the main pyrolytic product

Abstract GLC analysis of the products obtained by pyrolysis of cannabidiol in air at 700° revealed the formation of several components, which are not only the result of a mere cracking process. A peak with a retention time corresponding to the one of Δ1(2)tetrahydrocannabinol has been analysed by mass spectrometry. Next to at least two components with a molecular weight of 314 (C21H30O2), possibly including a small amount of Δ1(2)tetrahydrocannabinol, the major component was shown to have the molecular formula C21H30O3. The structure of this oxidation product of cannabidiol has been established as the decarboxylated product of the naturally occurring cannabielsoic acid A by the identity of its mass spectrometrical fragmentation pattern to that of one of the two decarboxylated cannabielsoic acid A C1-stereoisomers, obtained by photochemical oxidation of cannabidiolic acid.

Mass spectrometric analysis of oxidized tryptophan

Oxindolylalanine and oxindolylalanine-containing peptides were prepared by treatment of tryptophan and tryptophan-containing peptides with mixtures of dimethyl sulfoxide and hydrochloric acid in acetic acid (DMSO–HCl–HAc). The reaction between tryptophan and DMSO–HCl–HAc was monitored by fast atom bombardment mass spectrometry (FAB-MS) and the proposed chlorotryptophan intermediate in the reaction was observed. Almost complete conversion of tryptophan to oxindolylalanine was obtained in reaction mixtures containing 3.75 M HCl when the reaction was performed in an open tube. A higher HCl concentration (5.5 M) and a closed reaction tube promoted the formation of by-products, such as dioxindolylalanine and 3-chlorooxindolylalanine. Extensive hydrolysis C-terminal of tryptophan was observed when tryptophan-containing peptides were treated with DMSO–HCl–HAc containing 5.5 M HCl, during which the tryptophan residue was modified to dioxindolylalanine lactone. Hydrolysis was not observed in mixtures containing 3.75 M HCl. The presence of oxindolylalanine in peptides could be demonstrated by characteristic peaks in FAB collision-induced dissociation tandem mass spectra.

Cannabispirone and cannabispirenone, two naturally occurring spiro-compounds

Abstract Structure elucidation of two naturally occurring acidic compounds from Cannabis gave two spiro-compounds. The spectroscopic properties ( 1 H-NMR, 13 C-NMR, MS, IR and UV) and interpretation of these spectra are given.

Comparing mass spectrometric characteristics of peptides and peptoids-2

The high-energy collision-induced dissociation (CID) spectra of the [M+H]+ and [M-H]- ions of substance P fragment 6–11, the retropeptide and the corresponding peptoid and retropeptoid were compared. The CID spectra of the [M+H]+ ion of the corresponding (retro)peptide and (retro)peptoid exhibit both B- and Y″-type sequence ions at identicalm/z-values. The differences in the relative abundances of these sequence ions, however, can be related to structural characteristics of the compounds. The fragmentation behaviour of theN-substituted immonium ions differs from that of the immonium ions derived from common amino acids by showing a preferential loss of a CH2=NH imine molecule. This dominant fragmentation reaction is suppressed in the CID spectrum of theN-substituted glutamine immonium ion in favour of a less energy demanding cyclization reaction involving the loss of NH3. The CID spectra of the [M-H]- ions of both peptides and peptoids show C-type ions, which appeared to be more abundant in the spectra of the peptides than in those of the peptoids.C-Terminal ″Z- and Y-type ions are characteristic of the peptides, whereas the peptoid spectra show relatively abundantN-terminal ″B-type ions. Both [M+H]+ and [M-H]- ion CID spectra show loss of amino acid-specific side-chains, which occurs as radical loss in the case of peptides and as molecular loss in peptoids.

The use of metastable ion characteristics for the determination of ion structures of some isomeric cannabinoids

The mechanism of formation of the prominent C15H19O2 ion at m/e 231 in the mass spectra of Δ1(6)-tetrahydrocannabinol and five isomeric cannabinoids has been investigated. Except via a well-documented two step process, involving an RDA mechanism, a sizeable percentage of these ions is formed by a novel one-step route from the molecular ion. This was deduced from the spectra of deuterium-labelled compounds and measurements of the kinetic energy release of metastable ions. The latter value for the one step process varies from 25–44 meV for the six compounds investigated, attributed to two interdependent effects, different transition state geometries and common transition states differing in the time elapsing before their formation.

Ring-A fissioned 3,4-seco-3-nor-triterpene-2-aldehydes and related pentacyclic triterpenoids from the leaf wax of Hoya australis

Abstract The leaf wax of Hoya australis has been shown to contain a series of new 3,4- seco -3- nor -triterpene-2-aldehydes (proposed names australinals A–D), the related 3,4- seco -3- nor -2-ol derivatives (australinols A–D) and their precursors, the non-fissioned pentacyclic triterpenols δ-amyrin, β-amyrin, lupeol and α-amyrin. Minor amounts of ψ-taraxasterol and taraxasterol-derived compounds were also present (australinals E and F, and australinols E and F) as well as traces of methylated 3,4- seco -3-acid derivatives of β- and δ-amyrin (methyl dihydronyctanthate and methyl dihydroaustralinoate. From the present data, it follows that the structures of the seco-nor -triterpenols, of which australinol B was published before as the 1-ol derivative, must be revised to a 2-ol derivative. To our knowledge, compounds australinals A–F, australinols A, C–F and methyldihydroaustralinoate have not been described from living plants before.

Phosphatidylcholine transfer protein from bovine liver contains highly unsaturated phosphatidylcholine species

The phosphatidylcholine transfer protein (PC‐TP) from bovine liver contains one molecule of non‐covalently bound PC. In order to gain more insight into the physiological function of PC‐TP, PC was extracted from bovine liver PC‐TP and its molecular species composition identified by fast atom bombardment mass spectrometry. The prevailing molecular species were C18:0/C18:1‐, C18:0/C18:2‐, C18:OIC20:4‐, C18:0120:5‐ and C18:OIC22:5‐PC accounting for 85% of the PC species present. This molecular species composition is not representative for what is present in bovine liver where these species account for 43% of the total PC content [Montfoort et al. (1971) Biochim. Biophys. Acta 231, 335–342]. Another striking observation is that PC species carrying a palmitoyl chain at the sn‐1 position are nearly absent, despite these species being abundantly present in bovine liver. This study suggests that PC‐TP could play a role in the metabolism of highly unsaturated, stearoyl‐containing PC species.