Anna Laura Segre

Syringopeptins, new phytotoxic lipodepsipeptides of Pseudomonas syringae pv. syringae

The primary structure of some new lipodepsipeptides named syringopeptins, produced by plant pathogenic strains of Pseudopmonas syringae pv. syringae has been determined by a combination of chemical methods, 1H and 13C NMR spectroscopy and FAB mass spectrometry. Two syringomycin‐producing strains afforded 3‐hydroxydecanoyl‐Dhb‐Pro‐Val‐Val‐Ala‐Ala‐Val‐Val‐Dhb‐Ala‐Val‐Ala‐Ala‐Dhb‐aThr‐Ser‐Ala‐Dhb‐Ala‐Dab‐Dab‐Tyr, with Tyr acylating a Thr to form a macrolactone ring, and smaller amounts of the 3‐hydroxydodecanoyl homologue. Evidence was obtained that a third syringomycin‐producing strain and a syringotoxin‐producing strain synthesize 3‐hydroxydecanoyl‐Dhb‐Pro‐Val‐Ala‐Ala‐Val‐Leu‐Ala‐Ala‐Dhb‐Val‐Dhb‐Ala‐Val‐Ala‐Ala‐Dhb‐aThr‐Ser‐Ala‐Val‐Ala‐Dab‐Dab‐Tyr, with Tyr and aThr forming again the macrolactone ring, and smaller amounts of the 3‐hydroxydodecanoyl homologue.

The structure of syringomycins A1, E and G

By a combination of 1D and 2D 1H‐ and 13C‐NMR, FAB‐MS, and chemical and enzymatic reactions carried out at the milligram level, it has been demonstrated that syringomycin E, the major phytotoxic antibiotic produced by Pseudomonas syringae pv. syringae, is a new lipodepsipeptide. Its amino acid sequence is Ser‐Ser‐Dab‐Dab‐Arg‐Phe‐Dhb‐4(Cl)Thr‐3(OH)Asp with the β‐carboxy group of the C‐terminal residue closing a macrocyclic ring on the OH group of the N‐terminal Ser, which in turn is N‐acylated by 3‐hydroxydodecanoic acid. Syringomycins A1 and G, two other metabolites of the same bacterium, differ from syringomycin E only in their fatty acid moieties corresponding, respectively, to 3‐hydroxydecanoic and 3‐hydroxytetradecanoic acid.

Structure of syringotoxin, a bioactive metabolite of Pseudomonas syringae pv. syringae

The covalent structure of syringotoxin, a bioactive metabolite of Pseudomonas syringae pv. syringae isolates, pathogenic on various species of citrus trees, has been deduced from ID and 2D 1H‐ and 13C‐NMR spectra combined with extensive FAB‐MS data and results of some chemical reactions. Similarly to syringomicins and syringostatins, produced by other plant pathogenic strains of P. syringae pv. syringae, syringotoxin is a lipodep‐sinonapeptide. Its peptide moiety corresponds to Ser‐Dab‐Gly‐Hse‐Om‐aThr‐Dhb‐(3‐OH)Asp‐(4‐Cl)Thr with the terminal carboxy group closing a macrocyclic ring on the OH group of the N‐terminal Ser, which in turn is N‐acetylated by 3‐hydroxytetradecanoic acid.

Novel bioactive lipodepsipeptides from Pseudomonas syringae: The pseudomycins

The covalent structure and most of the stereochemistry of the pseudomycins, bioactive metabolites of a transposon‐generated mutant of a Pseudomonas syringae wild‐type strain proposed for the biological control of Dutch elm disease, have been determined. While two pseudomycins are identical to the known syringopeptins 25‐A and 25‐B, pseudomycins A, B, C, C′ are new lipodepsinonapeptides. For all of these the peptide moiety corresponds to l‐Ser‐d‐Dab‐l‐Asp‐l‐Lys‐l‐Dab‐l‐aThr‐Z‐Dhb‐l‐Asp(3‐OH) ‐l‐Thr(4‐Cl) with the terminal carboxyl group closing a macrocyclic ring on the OH group of the N‐terminal Ser. This is in turn N‐acylated by 3,4‐dihydroxytetradecanoate in pseudomycin A, by 3‐hydroxytetradecanoate in pseudomycin B, by 3,4‐dihydroxyhexadecanoate in pseudomycin C, and by 3‐hydroxyhexadecanoate in pseudomycin C′. Some preliminary data on the biological activity of pseudomycin A are reported.

Reasons for the nonequivalence of the exo-exo and endo-endo vicinal NMR coupling constants in norbornanes

Abstract In a series of norbornanes, benzonorbornenes, and norbornenes, the vicinal cis couplings 3Jexo,exo and 3Jendo,endo are determined. A trend is recognized in which Jexo,exo steadily decreases in this series while Jendo,endo remains relatively constant; in norbornenes Jexo,exo and Jendo,endo are about the same. These observations are understood by means of theoretical calculations performed for representative compounds of the series. This study indicates that interactions of the C7-methylene bridge with the bonds of the C2C3 ethylene bridge are responsible for the nonequivalence of Jexo,exo and Jendo,endo in norbornanes, and that in norbornenes interaction of the olefin functionality with bonds of the ethylene bridge is responsible for bridging Jexo,exo back fortuitously close to Jendo,endo.

Corceptins, new bioactive lipodepsipeptides from cultures of Pseudomonas corrugata

© 1998 Federation of European Biochemical Societies.

NMR study of paper

Abstract High quality antique sheets of paper have been characterized by 1 H NMR relaxations and 13 C CP MAS spectra. Paper can be regarded as a bicomponent material made of cellulose and water plus a small amount of organic and inorganic impurities. Semicrystalline fibrous cellulose, rich in water, is present in the I α and I β forms. The amorphous cellulose, with a low water content, contains a higher amount of paramagnetic impurities and it is characterized by quite short 1 H spin-lattice relaxations and by 113 C resonances with noticeable chemical shifts. Ad hoc tailored pulse sequences are able to produce 13 C CP MAS spectra in which only the amorphous content of paper is clearly observed. It is shown that water is fully bound to the cellulose lattice. It also seems reasonable to formulate the hypothesis that a larger concentration of paramagnetic ions is located in the amorphous fraction of highly degraded paper compared with paper in good condition.

Proliferin, a new sesterterpene from Fusarium proliferatum

Abstract A new bicyclic sestertepene, named proliferin, has been characterized from Fusarium proliferatum . The pure compound exhibit toxic activity. The structure elucidation of the molecula was accomplished using data from 2D-NMR strategies. Proliferin was shown to have a novel ring skeleton and molecular formula C27H40O5.

Advances in the 13C NMR characterization of ethene/propene copolymers, 1

The microstructure of a number of ethene/propene copolymers prepared with three representative C2-symmetric ansa-metallocene catalysts was investigated by means of high-field (150 MHz) 13C NMR. Thanks to the exceedingly high resolution of the spectra, an unprecedented experimental basis for the constitutional sequence analysis was achieved, which enabled us to test complex statistical models of chain propagation in a significant manner. In particular, the need for a 2nd-order Markov model, previously suggested by some authors on the basis of triad data, was confirmed by our study at pentad/heptad level. Some correlations between metallocene structure and copolymerization statistics were also identified. Expansion of the methyl region of the 13C NMR spectrum of an E/P copolymer obtained at 30 °C with catalyst system I/MAO (150 MHz).

A new fungal growth inhibitor from Trichoderma viride

Abstract A new tetracyclic diterpene having molecular formula C 20 H 28 O 2 and molecular mass of 300 a.m.u., has been isolated from culture filtrate of a strain of Trichoderma viride. The pure compound shows antifungal activity; its structure elucidation was accomplished using 2D-NMR strategies and chemical derivatization.