Manfred Hesse

Spectroscopic methods in organic chemistry

Download Area for Lecturers: www.thieme.de/specials/hmz_en.html This book provides the necessary equipment for the application of spectroscopic methods in organic chemistry, as required as part of chemistry courses in all universities. The following methods are explained and examples given: * UV/Vis Spectroscopy, derivative Spectroscopy, chirooptical methods CD and ORD. * Aggregated molecules, charge transfer complexes, conjugated oligomers. * Infrared (IR) and Raman Spectroscopy, Fourier transform IR spectroscopy, and GC/IRcombination methods. * Nuclear Magnetic Resonance Spectroscopy (NMR), 1H-, 13C-, 19F-, 15N- und 31P-NMR, spin decoupling, triple resonance, INDOR difference spectroscopy, 2D- and 3D-NMR, COSY, TOCSY, ROESY and NOESY spectra, NOE, INEPT, and DEPT technique, DEPTQ, HETCOR, HRMAS, INADEQUATE and lanthanide shift reagents, simulation and calculation of spectra, and the combination of separation and NMR methods. The new 2D NMR techniques TOCSY, HMQC and HMBC, more examples and a guide to completely assign all 1H and 13C NMR signals of a given substrate. * Mass spectrometry (MS), electron impact and chemical ionization (EI and CI), fast atom bombardment (FAB), electrospray und thermospray ionization (ESI and TSI), MS/MS technique (MSn), field ionization and field desorption (FI and FD), atmospheric pressure chemical ionization (APCI), MALDI TOF technique, GC/MS, LC/MS, and HPLC-UV(DAD)-APCI combination MS/MS technique. Fourier transform ion cyclotron resonance MS (FT-ICR-MS). The layout and many tables help to introduce the reader to spectroscopy. The extensive and thorough approach makes the text the first choice both as a companion for the professional chemists and as a refresher course in practical spectroscopy. The second English edition is a translation of the 7th German edition, in which several major alterations and didactic improvements have been made. For further information on our chemistry products, please visit: Thieme Chemistry.

Tetrahedron report number 230 : Synthesis of macrocyclic compounds by ring enlargement

Abstract A summary of important ring expansion strategies, including recent references, is presented in Section 1. Subsequently the synthesis of macrocyclic ketones, lactams and lactones involving the heterolytic cleavage of the bridge bond in bicyclic intermediates is discussed. Typical applications in the field of natural product synthesis are shown. Finally the ring enlargement strategies are compared, pointing out the advantages and drawbacks of each method.

Benzoxazinoids-cyclic hydroxamic acids, lactams and their corresponding glucosides in the genus Aphelandra (Acanthaceae).

An improved method of sample preparation and simultaneous HPLC separation was developed that allowed the separation of 2,4-dihydroxy-1,4-benzoxazine-3(4H)-one (DIBOA), 2,4-dihydroxy-7-methoxy-1,4-benzoxazine-3(4H)-one (DIMBOA), 2-hydroxy-1,4-benzoxazine-3(2H)-one (HBOA), 2-hydroxy-7-methoxy-1,4-benzoxazine-3(2H)-one (HMBOA) and their corresponding glucosides as well as the benzoxazolinones BOA and MBOA. The amount and distribution of these compounds was determined in the roots of Aphelandra squarrosa and A. fuscopunctata plants. There is a significant difference in the amount and distribution of this substance class in the two species analyzed. The results are discussed in relation to their function as defence compounds and allelochemicals.

Antimicrobial activities of secondary metabolites produced by endophytic fungi from Spondias mombin.

We performed a search for bioactive compounds produced by fungal endophytes from Spondias mombin (Anacardiaceae). Culture broth extracts of Guignardia sp., Phomopsis sp. and Pestalotiopsis guepinii were separated by chromatographic methods and tested for biological activities. The crude extracts of these endophytes were tested against fourteen organisms, including actinomycetes, Gram‐negative and Gram‐positive bacteria, yeast, and filamentous fungi. All fungal extracts inhibited actinomycete growth. Guignardia sp. was also active against Escherichia coli, Staphylococcus aureus, Saccharomyces cerevisiae, Geotrichum sp., and Penicillium canadensis. Culture extracts ofP. guepinii were active against S. cerevisae, while strains of Phomopsis sp. showed a pronounced antifungal effect against Cladosporium elatum, Mycotypha sp. and S. cerevisae.

Signalling molecules and the synthesis of alkaloids in Catharanthus roseus seedlings

The Madagascar periwinkle, Catharanthus roseus, produces numerous alkaloids, several of which have important pharmaceutical uses. Catharanthus seedlings rapidly accumulate the monomeric alkaloids, vindoline, catharanthine and tabersonine, during germination. Various plant signalling molecules were tested for their ability to enhance alkaloid synthesis in Catharanthus seedlings. The compounds tested included plant hormones, fatty acid-derived messengers and agents that can induce systemic-acquired resistance in plants. Of these compounds, only methyl jasmonate (MeJa) enhanced the synthesis of monomeric alkaloids. However, feeding of a MeJa biosynthetic precursor, or inhibition of the lipoxygenase pathway, had no effect on alkaloid production in the seedlings. We conclude that, although MeJa is able to enhance alkaloid synthesis when supplied exogenously, the lipoxygenase pathway probably does not play a role in the regulation of alkaloid synthesis during normal germination of Catharanthus. Furthermore, it was found that Catharanthus seedlings accumulate small quantities of the dimeric alkaloid, vinblastine, a valuable antitumour drug. Contrary to its effect on the accumulation of monomeric alkaloids, MeJa did not influence the accumulation of vinblastine.

Macrocyclic spermidine and spermine alkaloids

In this short review of spermine and spermidine plant alkaloids, which are characterized by the presence of a macrocyclic Iactam ring, special consideration has been given to the alkaloids from Oncinotis species and to the spermine alkaloid, chaenorrhine.

Di-coumaroylspermidines and tri-coumaroylspermidines in anthers of different species of the genus Aphelandra

Abstract N 1 , N 5 -Di- p -coumaroylspermidine, N 5 , N 10 -di- p -coumaroylspermidine, and N 1 , N 5 , N 10 tri- p -coumaroylspermidine were isolated from anthers of Aphelandra tetragona and A. chamissoniana . The correct substitution pattern of the di-coumaroylspermidines could be identified by their specific photoisomerization to four isomers which can be separated by HPLC.

Efficient reduction of azides with samarium diiodide

Abstract Reduction of alkyl, aryl and aroyl azides to the parent primary amines or amides, respectively, occurs in good yield upon treatment with an excess of SmI2 in THF at room temperature. A radical mechanism is proposed.

Ring closure methods in the synthesis of macrocyclic natural products

Macrocyclization methods by means of ring closure from linear bifunctional precursors are critically reviewed. The scope of this article is limited to macrocyclic natural products and, to some extent, their model compounds. However, not only macrolides, but all kinds of macrocyclic natural products which have been synthesized by ring closure reactions are covered. The commonly used ring closure methods in recent literature include those involving lactonization, lactamization, C-C bond formation, C=C bond formation, ether formation, amine formation, and exo ring formation. The activation of one or both interacting sites of the bifunctional linear precursor is the central issue of some ring closure methods. Stereochemistry plays an important role in ring closure reactions. Only when the stereochemistry of the linear precursor allows its two interacting sites to reach each other occurs a successful ring closure. If the adopted conformation of a linear precursor sufficiently resembles that of the corresponding macrocycle a ring closure can be very facile.

Guignardic Acid, a Novel Type of Secondary Metabolite Produced by the Endophytic Fungus Guignardia sp.: Isolation, Structure Elucidation, and Asymmetric Synthesis

A UV-guided fractionation of the AcOEt extract of the fermentation broth of Guignardia sp., an endophytic fungus from the leaves of the tropical tree Spondias mombin, resulted in the identification of the new metabolite (−)-(2S,5Z)-2-(1-methylethyl)-4-oxo-5-(phenylmethylene)-1,3-dioxolane-2-carboxylic acid (1), isolated as NH salt 1a. The metabolite 1 was designated (−)-(S)-guignardic acid. This first member of a new class of natural compounds contains a dioxolanone moiety formed by fusion of 2-oxo-3-phenylpropanoic acid (phenylpyruvic acid) and 3-methyl-2-oxobutanoic acid (dimethylpyruvic acid), products of the oxidative deamination of phenylalanine and valine, respectively. The structure of 1a was deduced from spectral data (UV, IR, MS, 1H- and 13C-NMR) and confirmed by asymmetric synthesis.