Walter Meister

Fragmentation of Bosentan ® (Ro 47-0203) in ionspray mass spectrometry after collision-induced dissociation at low energy: a case of radical fragmentation of an even-electron ion

For metabolic studies the fragmentation of a novel endothelin receptor antagonist, Bosentan, was investigated using ionspray tandem mass spectrometry. Bosentan belongs to the sulphonamide class and a complicated and unexpected fragmentation at low energy, involving a radical fragmentation of an even-electron ion at the sulphonamide bond, is reported.

Determination of tenoxicam, and the isolation, identification and determination of Ro 17-6661, its major metabolite, in human urine

A high-performance liquid chromatographic method for the determination of tenoxicam (Ro 12-0068, I) and the hydroxy metabolite Ro 17-6661 (II) in human urine has been developed. The parent drug and metabolite were extracted from acidified urine by means of an Extrelut column with chloroform. The evaporated eluate was analysed on a C18 reversed-phase column with methanol-phosphate buffer as the mobile phase and UV detection at 371 nm. The detection limit for both compounds in a 1-ml sample was 50 ng/ml (C.V. 7%). The inter- and intra-assay precision up to 20 micrograms/ml was 3-6%. The method was applied to the analysis of I and II in the urine of a human subject who had received a 40-mg oral dose of the drug. Approximately 36% of the dose was eliminated in the urine as II, and less than 0.5% as unchanged I. After enzymatic hydrolysis of the urine, an extra 2% of the dose was found as II. Compound II was isolated from human urine by preparative thin-layer chromatography and identified by comparison of its mass and proton resonance spectra with those of an authentic specimen.

New C30-Carotenoic Acid Glucosyl Esters from Pseudomonas rhodos

Abstract The carotenoid pigments of the Gram-negative bacterium Pseudomonas rhodos were identified as 4,4′-diapocarotene-4-oic acid, di (β,ᴅ-glucosyl) 4,4′-diaptocarotene-4,4′-dioate, and β,ᴅ-glucosyl-4,4′-diapocarotene-4-oate-4′-oic acid. One hydroxy group of the glucose moieties, probably at C (6), was esterified with one of several fatty acids (12:0, 14:0, 14:1, 16:0, 1 6 :1).

2‐Alkylimidazoline derivative to control fatty acid fragmentation upon electron impact and electrospray ionization

A new derivative of the carboxyl group, N-methyl-2-alkylimidazoline, was introduced with the aim of improving the control of fatty acid fragmentation. Owing to the strongly basic character and the cyclic structure of this derivative, strong stabilization of the charge on the ionized group is obtained so that extensive radical and charge-remote fragmentation of the chain can be achieved with electron impact and electrospray ionization.

The influence of strongly acidic groups on the protonation of peptides in electrospray MS

In order to obtain experimental data on the question of compensation of positive charges by anionic groups in multiply charged ions of polyfunctional molecules in electrospray MS, several pairs of peptides with the same basic structure but differentiated by one or two strongly acidic groups (phosphate or sulfonate) were investigated. It was found that depending on the density of basic centers and the strength of acidic groups present, the observed changes upon introduction of acidic groups ranged from complete elimination of the most highly charged state to absence of any difference.

Carotenoids of Rhizobia

With increasing concentrations in the growth medium of the cyclization inhibitors nicotine or 2-(4-chlorophenylthio)-triethylamine hydrochloride (CPTA) the previously identified bicyclic carotenoids of Rhizobium lupini (2,3,2′,3′-tetrahydroxy-β,β-caroten-4-one and 2,3,2′,3′-tetrahydroxy-β,β-carotene) were successively replaced by hitherto unknown monocyclic carotenoids. By application of mass and nuclear magnetic resonance spectroscopy 3 carotenoids were identified as 2,3-trans-dihydroxy-β,ψ-caroten-4-one, 2,3-trans-dihydroxy-β,ψ-carotene, and 3-hydroxy-β,ψ-caroten-4-one. A further compound was tentatively established as (2- or 3-)monohydroxy-β,ψ-carotene. It was found that other inhibitors such as diphenylamine or 4-chloro-5-(dimethylamino)-2-α,α,α(trifluoro-m-tolyl)-3-(2H)-pyridazinone (San 6706) did not affect the pigment pattern. The results are discussed in relation to carotenoid biosynthesis in Rhizobium lupini.

Tools for the Identification of Receptor Dimmers: Synthesis and Biological Evaluation of On-Resin Dimerized, Photosensitive Analogues of Angiotensin II

Molecular tools for the identification of homodimers of G protein coupled receptors are not available yet. We intended to investigate the possibility of functional dimerization of the known angiotensin II (AngII, DRVYIHPF) receptors AT1 and AT2; either as homo-dimers of AT1 or AT2 or as heterodimers of AT1–AT2. For this purpose, we synthesized AngII dimer ligands with a photosensitive residue (p-benzoylphenylalanine, B) in the C-terminal position. The dimers were held together with linkers anchored either to the Nα-terminus (I), or to Ne of Lys in position 1 (II), or to Ne of Lys in position 3 (III), or to p-NH2-Phe replacing Y in position 4 (VI). The linker was of the general structure (CO(CH2)nNH)2 X, where n = 10 and X is either CO or CO(CH2) m CO with m = 1–10. Fmoc peptide synthesis was carried out on Tentagel resin (0.06 meq/g) or Wang resin (0.7 meq/g). Orthogonality for linker introduction was achieved with Nα-Boc-Ne-Fmoc-Lys for group II, with Nα-Fmoc-Ne-Dde-Lys for III, and Nα-Fmoc-Nar-Dde-p-NH2-Phe for VI. Couplings were performed with TPTU. On-resin dimerization was achieved after Fmoc deprotection of the first linker moiety, by coupling for 2 h with either carbonyl-diimidazole or the respective diacid disuccinimide in half-equivalent amount, followed by a five-fold excess of dimerization reagent until a negative ninhydrine test. Peptide resins were cleaved with 95% TFA & 2% triisopropylsilane; crude peptides were purified by prep RP-HPLC, lyophilized and analyzed by electrospray MS.

Carotenoids of Rhizobia. III. 2',3'-trans-Dihydroxy-2-nor-β, β-carotene-3,4-dione, a Novel Carotenoid from a Mutant of Rhizobium lupini

Abstract Nor-Carotenoid, Rhizobium lupini The mutant strain 1-289 of Rhizobium lupini containes in addition to the normal carotenoid pattern a violet carotenoid whose structure was derived by MS and 270 1H-NMR as 2′,3′-trans-dihydroxy-2-nor-β,β-carotene-3,4-dione. The possible biochemical origin of this compound is dis cussed.