Gerhard Englert

TETRAHYMANOL FROM THE PHOTOTROPHIC BACTERIUM RHODOPSEUDOMONAS PALUSTRIS : FIRST REPORT OF A GAMMACERANE TRITERPENE FROM A PROKARYOTE

Summary: Tetrahymanol, a rare triterpene from the gammacerane series, previously detected only in a few scattered eukaryotic taxa, has been isolated for the first time from the phototrophic bacterium Rhodopseudomonas palustris. This extends the significance of geochemical markers from this series, which are abundant in marine sediments and palaeohypersaline environments.

Proton Magnetic Resonance Spectra of Oriented Molecules: Acetylenic Compounds, Acetonitrile and Methanol

Abstract The proton magnetic resonance spectra of some acetylenic compounds, acetonitrile and methanol, oriented in the nematic phase of 4, 4-di-n-hexyloxy-azoxy benzene or 4-n-octyloxy-benzoic acid have been investigated. From the chemical shift difference of the signals of the acetylenic proton in the isotropic and nematic phase a value of 12± 1.5 ppm is obtained for the anisotropy of the chemical shift. From the spectra of oriented acetontrile-2−13C and methanol−13C accurate values for the H-C-H bond angle of the methyl groups are derived. The absolute sign of the indirect spin coupling constant J13 CH in acetonitrile-2-13C has been found to be positive.

Isolation and structural elucidation of the predominant geometrical isomers of α-carotene

Abstract The recent development and application of a polymeric C30 stationary phase have given unique separations of cis-trans carotenoid isomers in reversed-phase (RP) liquid chromatography (LC) owing to the exceptional shape selectivity of this stationary phase. In the present research, several geometrical isomers of α-carotene were at least partially resolved from a photo-isomerized mixture when chromatographed on μm polymeric C30 column. Double bond configurations of the five predominant α-carotene peaks, as isolated on a semi-preparative C30 column, were unambiguously assigned using 1H nuclear magnetic resonance (NMR) spectroscopy, giving the following order of elution: 13-cis, 13′-cis, all-trans, 9-cis, and 9′-cis geometrical forms. Electronic absorption spectra for these isomers were in agreement with the identification of peaks. The α-carotene isomers separated and identified herein had not been previously resolved in RPLC. Confirmation of the structures of geometrical α-carotene isomers will aid further studies on the possible physiological roles of these compounds in biological tissues.

CAROTENOIDS OF Erwinia herbicola AND AN Escherichia coli HB101 STRAIN CARRYING THE Erwinia herbicola CAROTENOID GENE CLUSTER

Carotenoid pigments of Erwinia herbicola and a transformed strain of Escherichia coli carrying the carotenoid biosynthesis gene cluster of E. herbicola have been analyzed. Both organisms are capable of making essentially the same carotenoids, indicating that all of the genes required for the biosynthesis of the wild type E. herbicola carotenoids have been transformed intact into E. coli. The major products in both species of bacteria are p‐cryptoxanthin glucoside, zeaxanthin monoglucoside and zeaxanthin diglucoside. These compounds are the first example of secondary, non‐allylic carotenoid glucosides. The absolute configuration 3R,3′R for zeaxanthin diglucoside was determined from its circular dichroism spectrum. Both species of bacteria also accumulate small amounts of hydrocarbon carotenes with similar cisltrans isomerization states.

N.M.R. OF CAROTENOIDS

Abstract The advantages and some applications of high-field p.m.r. spectroscopy especially for the elucidation of the structures of cis -isomeric carotenoids are discussed. Examples are presented of the high sensitivity of modern instruments enabling p.m.r. spectra to be run from sample quantities below 1 μg and 13 C-n.m.r. spectra from quantities of less than 1 mg. The characteristic p.m.r. data of a great number of typical end groups are given. Some applications of the homonuclear Overhauser effect and of the two-dimensional J-resolved p.m.r. spectroscopy are presented. The potential use of 17 O-n.m.r. spectroscopy in the field of carotenoids is discussed.

Molecular Geometry of Acetonitrile, Determined by Proton Magnetic Resonance in Nematic Solutions

Abstract The PMR spectra of carbon-13 and nitrogen-15 substituted acetonitrile have been investigated in 3 different nematic solutions. From the direct magnetic spin-spin interactions values for the H—G—H—bond angle of the methyl group and for the other relative internuclear distances ware calculated under the assumption that the anisotropic part of the indirect spin-spin interactions can be neglected. Small differences in the molecular geometry were observed in the three nematic solvents and also between the latter and the gas phage (microwave data). Approximate nuclear positions can be calculated if the PMR data are combined with microwave data, e.g. the moment of inertia of the molecule in the gas phase. It is shown that the nuclear positions calculated by this method are in approximate agreement with pure microwave data. Under the assumption that acetonitrile is aligned preferentially parallel to the magnetic field, the absolute signs of the indirect spin couplings 1J13C-H 2J13C-C-H and 3J15N-CCH are ...

An apocynaceae-alkaloid of a novel type

Bei thermischer oder solvolytischer Decarbonylierung eines neuen Alkaloids ausMelodinus scandens Forst. entsteht eine Verbindung II, die ihrerseits in die Derivate III–VI umgewandelt werden kann. Auf Grund eingehender NMR- und MS-Untersuchungen können für die Verbindungen II–VII die angegebenen Strukturen vorgeschlagen werden. Alkaloide mit dem Skelett der Verbindung II entstehen biosynthetisch wahrscheinlich aus Alkaloiden des Aspidospermin-Typs durch Oxidation an C-2 und nachfolgende Umlagerung.

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).

Topochemical photoreactions of aromatic retinoids

Abstract The aromatic retinoid 1a exists in three crystal modifications. The centric α- 1a yields the centrosymmetric photocycloadduct 2 , whereas the γ-modification of 1a does not react photochemically. Deviations from this commonly accepted pattern are the occurrence of a second centric modification α1- 1a instead of the usual β-type and of two different photocycloadducts 3 and 4 derived therefrom in a ratio of 5 : 1. This ratio results from the probability of the excited molecule to react with its neighbours which are shifted against each other in the crystal lattice. Substitution of the ethyl ester group in 1a by a di-ethylamide ( 1 d) leads to E/Z-isomerization only, though the shortest distance of 3.66 A between two molecules is suitable for a [2+2]-photocycloaddition across the centre of symmetry. The packing diagrams of α- 1a , α1- 1a , and of 1d as well as the structures of 1a , 1d , and 2 have been determined by X-ray analyses, whereas the structures of 3 , 4 , and 5 could be deduced from 1H- and 13C-NMR data including homo- and heteronuclear 2D and inter-proton Overhauser experiments.

High-performance liquid chromatographic separation and proton nuclear magnetic resonance identification of the 6-mono-cis and 6,6′-di-cis isomers o rhodoxanthin

Abstract The separation by high-performance liquid chromatography of the all- trans , the 6-mono- cis and the 6,6′-di- cis -isomers from synthetic samples o rhodoxanthin is described. The structures of the cis isomers are deduced by 1 H nuclear magnetic resonance (NMR) at 400 MHz, including several homonuclear Overhauser 1 H NMR experiments and, in part, by 13 C NMR at 100 MHz.