E. W. Hagaman

Bio: E. W. Hagaman is an academic researcher from Rice University. The author has contributed to research in topics: Carbon-13 NMR & Nuclear magnetic resonance spectroscopy. The author has an hindex of 7, co-authored 14 publications receiving 317 citations.

Pattern recognition of geminal proton nonequivalence and second-order coupling in 13C single-frequency off-resonance decoupled spectra. Assignment criteria and structure elucidation

Abstract: 13C n.m.r. single-frequency off-resonance decoupled (sford) CH multiplet resonance which deviate from normally assumed, isolated AnX spin descriptions have been characterized. Methylene carbons whose appended protons are nonequivalent generate doublets of doublets in sford spectra provided the proton chemical shift difference exceeds c. 3 × (Jgem). The isolated moiety–CHH′–closely approximates an AMX spin system. The strong chemical shift nonequivalence of geminal aminomethylene protons induced by the nitrogen lone pair in some N-substituted piperidine derivatives is accompanied by preferential modification of the one-bond CH coupling constants of the α-amino protons. In N-methyl-4-t-butylpiperidine the natural coupling constants were shown to differ by 6–12 Hz. The 13C sford resonances of protonated carbons display varying degrees of second-order coupling depending on the coupling strength of a carbon's appended protons with a strongly coupled spin set, the number of nuclei in the spin set, and the magnitude of the carbon's residual one-bond splitting. Qualitative criteria that allow the classification of degrees of second-order coupling have been established and utilized in signal assignment and structure analysis.

13C-NMR. Spectroscopy of Naturally Occuring Substances. XLII. Conformational analysis of quebrachamine-like indole alkaloids and related substances†

Abstract: The 13C shifts of 16α- and 16β-substituted derivatives of quebrachamine, 14,15-dehydroquebrachamine, cleavamine, 15,20α-dihydrocleavamine and 15,20β-dihydrocleavamine are determined and correlated with possible conformations of these tetracycles. The method of analysis of the C(16) configuration of these compounds, which emanated from this study, is used for the determination of the configuration of the site of coupling of vindoline and cleavamine β-chloroindolenine.

13C-NMR. Spectroscopy of naturally occurring substances. XXXII. Vincaleucoblastine and related alkaloids.

Abstract: The total assignment of the 13C-shifts of the complex Vinica rosea L. alkaloids vincaleucoblastine, leurosidine and leurosine and of a synthetic isomer of the latter is presented. The structure of leurosidine is corrected and a tentative structure for the acid-catalyzed product of isomerization of leurosine is proposed.

13C n.m.r. spectra of steroids —a survey and commentary†

Abstract: The literature on 13C n.m.r. examinations of steroids has been reviewed and the shielding data for over 400 examples are tubulated. The assignments for each compound have been considered and, where necessary, revised in the light of more recent evidence and for consistency throughout each series. The methods available for assignments are reviewed and, in many cases, illustrated with specific examples. The major practical features concerning 13C studies of steroids are discussed as a guide to the use of the technique. From the main body of shielding data, an extensive set of substituent effects has been generated to aid the examination of new systems. The utility and the limitations of these effects are described.

Natural products with antifungal activity from Pseudomonas biocontrol bacteria

Abstract: It is now well established that some bacteria and fungi are aggressive colonizers of soil and the roots of plants, and are able to protect plants from infection by soil-borne fungal pathogens. In most cases that have been well studied, the biological mechanisms underlying this phenomenon, known as biocontrol, include the production of antifungal compounds, involving both metabolites and enzymes. Bacteria of the genus Pseudomonas comprise a large group of the active biocontrol strains as a result of their general ability to produce a diverse array of potent antifungal metabolites. These include simple metabolites such as 2,4-diacetylphloroglucinol, phenazine-1-carboxylic acid and pyrrolnitrin [3-chloro-4-(2'- nitro-3'-chlorophenyl)-pyrrole], as well as the complex macrocyclic lactone, 2,3-de-epoxy-2,3-didehydro-rhizoxin. Study of the biochemistry and mechanism of formation of these metabolites has proved useful in several ways. Pyrrolnitrin is active against Rhizoctonia spp, Fusarium spp, and other plant pathogenic fungi, and it has been used as a lead structure in the development of a new phenylpyrrole agricultural fungicide. In addition, pyrrolnitrin has been used for years as a model for the study of the mechanisms involved in the chlorination of organic molecules. We have cloned a four-gene cluster from a P fluorescens biocontrol strain that encodes the enzymes required for the production of pyrrolnitrin. Using these genes and strains mutated in the individual genes, we have elucidated the biochemical pathway by which pyrrolnitrin is synthesized. Studies of the genes involved in pyrrolnitrin biosynthesis have demonstrated that a new class of halogenase enzyme is involved in the chlorination reactions in pyrrolnitrin biosynthesis. The P fluorescens mutants that do not produce pyrrolnitrin have been used to demonstrate clearly the important role of pyrrolnitrin in the overall biocontrol activity shown by the strain. In addition, we have modified the pyrrolnitrin genes within the P fluorescens strain, which has resulted in significant increases in the production of this metabolite. The strains which overproduce pyrrolnitrin are also significantly more active than the wild-type strain in biocontrol. These studies suggest that the biocontrol activity of bacteria can be dramatically increased to rival the activity of commercial chemical fungicides through directed genetic modification. Bacteria remain important sources of natural products with diverse activities. In order to capture the full potential of these compounds, it will be necessary in the future to take a multidisciplinary approach to their study and development.

Functions Encoded by Pyrrolnitrin Biosynthetic Genes from Pseudomonas fluorescens

Abstract: Pyrrolnitrin is a secondary metabolite derived from tryptophan and has strong antifungal activity. Recently we described four genes, prnABCD, from Pseudomonas fluorescens that encode the biosynthesis of pyrrolnitrin. In the work presented here, we describe the function of each prn gene product. The four genes encode proteins identical in size and serology to proteins present in wild-type Pseudomonas fluorescens, but absent from a mutant from which the entire prn gene region had been deleted. The prnA gene product catalyzes the chlorination of l-tryptophan to form 7-chloro-l-tryptophan. The prnB gene product catalyzes a ring rearrangement and decarboxylation to convert 7-chloro-l-tryptophan to monodechloroaminopyrrolnitrin. The prnC gene product chlorinates monodechloroaminopyrrolnitrin at the 3 position to form aminopyrrolnitrin. The prnD gene product catalyzes the oxidation of the amino group of aminopyrrolnitrin to a nitro group to form pyrrolnitrin. The organization of the prn genes in the operon is identical to the order of the reactions in the biosynthetic pathway.