The EIMS fragmentation mechanisms of the sesquiterpenes corvol ethers A and B, epi-cubebol and isodauc-8-en-11-ol

• Patrick Rabe and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2016, 12, 1380–1394, doi:10.3762/bjoc.12.132

• standard. Furthermore, various high quality databases containing the EI mass spectra and retention indices of thousands of compounds are available that assist in automated compound identification [2][3]. If unknown compounds are detected in natural extracts, their structure elucidation by GC–MS is more

Marine-derived myxobacteria of the suborder Nannocystineae: An underexplored source of structurally intriguing and biologically active metabolites

• Antonio Dávila-Céspedes,
• Peter Hufendiek,
• Max Crüsemann,
• Till F. Schäberle and
• Gabriele M. König

Beilstein J. Org. Chem. 2016, 12, 969–984, doi:10.3762/bjoc.12.96

• . Further investigation led to the isolation and structure elucidation of the bioactive polyketide haliangicin (24, Figure 10), which was the first myxobacterial metabolite of true marine origin. It was found that this molecule comprised a β-methoxyacrylate subunit including a conjugated tetraene moiety [52

• . Structure elucidation was achieved via extensive NMR measurements. The absolute configuration of the chiral centers could be resolved through comparison of the experimental CD spectrum with calculated data. This metabolite showed inhibitory activity towards the bacterium Arthrobacter crystallopoietes with

• production of secondary metabolites [65]. This work led to the isolation and structure elucidation of two compounds of peptidic nature called miuraenamide A (31) and B (32, Figure 13). Two years later, the same research group published the structures of four additional derivatives, named miuraenamides C–F

Muraymycin nucleoside-peptide antibiotics: uridine-derived natural products as lead structures for the development of novel antibacterial agents

• Daniel Wiegmann,
• Stefan Koppermann,
• Marius Wirth,
• Giuliana Niro,
• Kristin Leyerer and
• Christian Ducho

Beilstein J. Org. Chem. 2016, 12, 769–795, doi:10.3762/bjoc.12.77

• which have a uridine-derived core structure in common. Their antibiotic potency is based on the inhibition of MraY, thereby blocking a membrane-associated intracellular step of bacterial cell-wall biosynthesis. The structure elucidation was carried out using one- and two-dimensional NMR experiments as

Elucidation of a masked repeating structure of the O-specific polysaccharide of the halotolerant soil bacteria Azospirillum halopraeferens Au4

• Elena N. Sigida,
• Yuliya P. Fedonenko,
• Alexander S. Shashkov,
• Nikolay P. Arbatsky,
• Evelina L. Zdorovenko,
• Svetlana A. Konnova,
• Vladimir V. Ignatov and
• Yuriy A. Knirel

Beilstein J. Org. Chem. 2016, 12, 636–642, doi:10.3762/bjoc.12.62

• revealed that its reason is a non-stoichiometric side-chain glucosylation and methylation of the main polysaccharide chain but at this stage, a straightforward structure elucidation of the OPS by NMR spectroscopy [16] was complicated. In order to obtain oligosaccharide fragments of the OPS a Smith

• oligosaccharide, selective solvolysis with CF3CO2H was employed. Recently, this method has been successfully used for the structure elucidation of the O-specific polysaccharides of Escherichia coli (e.g. [20]). The reagent was found to cleave selectively the glycosidic linkage of 6-deoxyhexoses (Rha, Fuc

• afforded complementary oligosaccharides, which identification shed light on the nature of the OPS irregularity and, combined with chemical analysis and NMR spectroscopic analysis data, enabled the structure elucidation of the OPS. Chemical modifications of the OPS, such as O-methylation or O-acetylation

Natural products from microbes associated with insects

• Christine Beemelmanns,
• Huijuan Guo,
• Maja Rischer and
• Michael Poulsen

Beilstein J. Org. Chem. 2016, 12, 314–327, doi:10.3762/bjoc.12.34

• light on the ecology and evolution of defensive associations. Keywords: biosynthesis; chemical ecology; natural products; secondary metabolism; structure elucidation; symbiosis; Introduction Although natural products represent the most consistently successful drug leads [1][2], many pharmaceutical

Recent highlights in biosynthesis research using stable isotopes

• Jan Rinkel and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2015, 11, 2493–2508, doi:10.3762/bjoc.11.271

• in the structure elucidation of complex polyketide natural products will be discussed. Especially in combination with two-dimensional NMR spectroscopic techniques, several powerful tools are becoming more interesting to natural products research. Production of new compounds in a labeled medium and

• investigated by fermentation in a 15N-labeled medium and analysis of the resulting product with 13C,15N-HMQC [32]. These applications represent helpful additions to the repertoire for structure elucidation of complex natural products, which can be produced under laboratory conditions in sufficient amounts. Non

• high hopes in the treatment of resistant pathogens (Figure 3). Producing an isotopologue of the desired compound by feeding of labeled precursors or growing the producing organism in labeled medium can simplify structure elucidation by giving access to the sum formula by mass spectrometry, which is not

Bromotyrosine-derived alkaloids from the Caribbean sponge Aplysina lacunosa

• Qun Göthel,
• Thanchanok Sirirak and
• Matthias Köck

Beilstein J. Org. Chem. 2015, 11, 2334–2342, doi:10.3762/bjoc.11.254

• , Verongida), three new bromotyrosine-derived alkaloids: 14-debromo-11-deoxyfistularin-3 (1), aplysinin A (2), and aplysinin B (3) (Figure 1), together with 15 known compounds were obtained. In this report we describe the structure elucidation of 1 to 3 and the biological activities of all the isolated

The marine sponge Agelas citrina as a source of the new pyrrole–imidazole alkaloids citrinamines A–D and N-methylagelongine

• Christine Cychon,
• Ellen Lichte and
• Matthias Köck

Beilstein J. Org. Chem. 2015, 11, 2029–2037, doi:10.3762/bjoc.11.220

• (10) [8][9][10] (Figure 1). Additionally, five new compounds, four with a dimeric PIA structure (1–4) and the N-methyl analogue (5) of the bromopyrrole alkaloid agelongine (12) [11], were isolated. Herein, we describe the isolation and structure elucidation of citrinamines A (1), B (2), and N

• at carbon C-9 in citrinamines C (3) and D (4) may be attributed to the utilization of MeOH as solvent for the extraction of the sponge. To verify the structure elucidation of citrinamines C (3) and D (4), further extraction of sponge tissue of Agelas citrina is necessary to obtain pure material. The

• scheme. The MeOH/CH2Cl2 extract of the sample was partitioned between n-hexane, n-BuOH, and H2O. The n-BuOH soluble fraction was further purified by size exclusion chromatography (Sephadex LH-20) and preparative reversed-phase HPLC yielding five new compounds (1–5). The isolation and structure

Synthesis of constrained analogues of tryptophan

• Elisabetta Rossi,
• Valentina Pirovano,
• Marco Negrato,
• Giorgio Abbiati and
• Monica Dell’Acqua

Beilstein J. Org. Chem. 2015, 11, 1997–2006, doi:10.3762/bjoc.11.216

• compounds embodying constrained analogues of tryptophan. Structure elucidation of diastereoisomeric tetrahydrocarbazoles 3a and 3’a via NMR experiments. Planned Diels–Alder reactions for the synthesis of tetrahydrocarbazoles as constrained analogues of tryptophan. Synthesis of unprotected tryptophan

Pyridinoacridine alkaloids of marine origin: NMR and MS spectral data, synthesis, biosynthesis and biological activity

• Louis P. Sandjo,
• Victor Kuete and
• Maique W. Biavatti

Beilstein J. Org. Chem. 2015, 11, 1667–1699, doi:10.3762/bjoc.11.183

• also interact with DNA [41]. Review Chemistry Structure elucidation: 13C NMR data The difficulty of NMR data assignment could be related to the presence of a high number of quaternary carbons in tetra- to octaheterocycles of these alkaloids. For example, up to eleven quaternary carbons may be involved

• (compounds 12–15) if the CH3 group is bound to an uncharged nitrogen atom [50]. Rings A–C (Table 6) rarely contain functional groups and the hydrogen chemical shifts (compounds 12–14, 17, and 19) can be used as a starting point for structure elucidation. 2D Long range correlations maps (HMBC) can easily lead

• of the A ring when the B ring is not aromatic. The compilation of this NMR data could be used as a library for a database prediction and could also save time with respect to structure elucidation of related natural congeners. Earlier, successful synthetic figures have also been presented as well as

Structure and conformational analysis of spiroketals from 6-O-methyl-9(E)-hydroxyiminoerythronolide A

• Ana Čikoš,
• Irena Ćaleta,
• Dinko Žiher,
• Mark B. Vine,
• Ivaylo J. Elenkov,
• Marko Dukši,
• Dubravka Gembarovski,
• Marina Ilijaš,
• Snježana Dragojević,
• Ivica Malnar and
• Sulejman Alihodžić

Beilstein J. Org. Chem. 2015, 11, 1447–1457, doi:10.3762/bjoc.11.157

• to isolate and fully characterise the products. Structure elucidation of compound 2 Analysis of HMBC spectra, as well as chemical shift comparison with the parent compound 1 [39], showed that the 9-C-signal of 2 exhibits a large upfield shift to 107.1 ppm (168.1 ppm in 1), as well as intense HMBC

• unchanged. Structure elucidation of compound 3 The main feature of compound 3 is the appearance of a double bond between 10-C and 11-C, as evidenced by the signal in the 1H NMR spectrum at 5.65 ppm and relevant HMBC correlations. The initial 3D structure of the compound was generated from the previously

• , antiperiplanar and one weak, synclinal) suggest an axial orientation of 8-H and equatorial position of 8-Me. Similar to 2, the six-membered tetrahydropyran assumes an anomerically non-stabilised chair conformation with the larger 6-methoxy substituent in the axial position. Structure elucidation of compound 4

A novel and widespread class of ketosynthase is responsible for the head-to-head condensation of two acyl moieties in bacterial pyrone biosynthesis

• Darko Kresovic,
• Florence Schempp,
• Zakaria Cheikh-Ali and
• Helge B. Bode

Beilstein J. Org. Chem. 2015, 11, 1412–1417, doi:10.3762/bjoc.11.152

• their isolation followed by NMR-based structure elucidation (Table S5, Supporting Information File 1) we could confirm that Pseudomonas sp. GM30 is producing pseudopyronine A (9), B (10) and the new derivative C (11) all differing in the chain length of the eastern acyl moiety. As heterologous

New depsidones and isoindolinones from the mangrove endophytic fungus Meyerozyma guilliermondii (HZ-Y₂) isolated from the South China Sea

• Senhua Chen,
• Zhaoming Liu,
• Yayue Liu,
• Yongjun Lu,
• Lei He and
• Zhigang She

Beilstein J. Org. Chem. 2015, 11, 1187–1193, doi:10.3762/bjoc.11.133

• ). In the bioactivity assay, all depsidones showed strong α-glucosidase inhibitory activity with IC50 values ranging from 2.1 to 13.3 μM. Details of the isolation, structure elucidation, and biological activity of these compounds are reported herein. Results and Discussion Botryorhodine E (1) was

Synthesis of modified cyclic and acyclic dextrins and comparison of their complexation ability

• Kata Tuza,
• László Jicsinszky,
• Tamás Sohajda,
• István Puskás and
• Éva Fenyvesi

Beilstein J. Org. Chem. 2014, 10, 2836–2843, doi:10.3762/bjoc.10.301

• shows similarity to a typical CD-drug interaction. Based on the promising results of the preliminary complexation studies with some model drugs, modified cyclodextrins and the corresponding acyclodextrins were synthesized (Scheme 1) in order to compare their complexation behavior. The structure

• elucidation of the O-benzyl intermediary products and the final HP-maltooligomers was performed by NMR (see Supporting Information File 1). Both proton and carbon assignments are based on the DEPT-ed-HSQC spectra. The NMR spectra confirm the complete 1-O-benzylation at the glycosidic oxygen (Figures S1–S6

Specific DNA duplex formation at an artificial lipid bilayer: fluorescence microscopy after Sybr Green I staining

• Emma Werz and
• Helmut Rosemeyer

Beilstein J. Org. Chem. 2014, 10, 2307–2321, doi:10.3762/bjoc.10.240

• ], 2. for the development of analytical techniques for the detection of nucleic acids [15][16][17], 3. for structure elucidation of complex aggregates formed by such natural nanostructures [5][6] and 4. for cell-surface engineering [18]. In a preceding manuscript [19] we reported the lipid bilayer

A new charge-tagged proline-based organocatalyst for mechanistic studies using electrospray mass spectrometry

• J. Alexander Willms,
• Rita Beel,
• Martin L. Schmidt,
• Christian Mundt and
• Marianne Engeser

Beilstein J. Org. Chem. 2014, 10, 2027–2037, doi:10.3762/bjoc.10.211

• spectrometric means for structure elucidation, collision-induced dissociation (CID) experiments have been perfomed. The results for R = Et are shown in Figure 5. All four mass-selected ions [IIa]+/[IIb]+ and [IIIa]+/[IIIb]+ show a very strong propensity to expel CO2 which even happens during the ESI process via

A tandem Mannich addition–palladium catalyzed ring-closing route toward 4-substituted-3(2H)-furanones

• Jubi John,
• Eliza Târcoveanu,
• Peter G. Jones and
• Henning Hopf

Beilstein J. Org. Chem. 2014, 10, 1462–1470, doi:10.3762/bjoc.10.150

• obtained from these two substrates in good yields (Figure 2). We also tried a reaction with N-Boc protected imine under optimized conditions and the corresponding furanone was obtained in good yield (Figure 2, compound 14). The structure elucidation of the furanone products 3, and 5–14 was accomplished by

Heronapyrrole D: A case of co-inspiration of natural product biosynthesis, total synthesis and biodiscovery

• Jens Schmidt,
• Zeinab Khalil,
• Robert J. Capon and
• Christian B. W. Stark

Beilstein J. Org. Chem. 2014, 10, 1228–1232, doi:10.3762/bjoc.10.121

• quantity available was insufficient for in depth structure elucidation. Fortunately, analytical HPLC–DAD comparisons between natural and synthetic samples of heronapyrrole D (see the Supporting Information File 1), together with optical rotation measurements [natural [α]D22 +7.5 (c 0.003, MeOH); synthetic

cis–trans Isomerization of silybins A and B

• Michaela Novotná,
• Radek Gažák,
• David Biedermann,
• Florent Di Meo,
• Petr Marhol,
• Marek Kuzma,
• Lucie Bednárová,
• Kateřina Fuksová,
• Patrick Trouillas and
• Vladimír Křen

Beilstein J. Org. Chem. 2014, 10, 1047–1063, doi:10.3762/bjoc.10.105

• -glucopyranoside 6''-gallate, Figure 6) was subjected to both, basic and acidic hydrolysis during its structure elucidation. However, under these conditions four stereoisomers of the original aglycon (2R,3R)-taxifolin were formed. Base-catalyzed isomerization of another taxifolin glycoside, (2R,3R)-2,3

Structure elucidation of female-specific volatiles released by the parasitoid wasp Trichogramma turkestanica (Hymenoptera: Trichogrammatidae)

• Armin Tröger,
• Teris A. van Beek,
• Martinus E. Huigens,
• Isabel M. M. S. Silva,
• Maarten A. Posthumus and
• Wittko Francke

Beilstein J. Org. Chem. 2014, 10, 767–773, doi:10.3762/bjoc.10.72

• -diene and (2E,4E,6S,8S,10S)-4,6,8,10-tetramethyltrideca-2,4-dien-1-ol or their enantiomers as sex specific volatiles. The structures were assigned on the basis of GC–MS investigations using synthetic reference compounds. Keywords: natural products; structure elucidation; sex specific; Trichogramma

New sesquiterpene hydroquinones from the Caribbean sponge Aka coralliphagum

• Qun Göthel and
• Matthias Köck

Beilstein J. Org. Chem. 2014, 10, 613–621, doi:10.3762/bjoc.10.52

• ; natural products; NMR; sesquiterpene hydroquinone; structure elucidation; Introduction Aka coralliphagum (Siphonodictyon coralliphagum) is known to have four distinct morphological forms: forma typica, f. tubulosa, f. obruta, and f. incrustans [1]. This sponge has the ability to burrow into live coral

• compounds. Results and Discussion The aqueous n-BuOH extract from Aka coralliphagum was subjected to solvent partitioning, followed by gel chromatography and reversed phase (C18) HPLC to yield siphonodictyals E1–E4 (1–4) and cyclosiphonodictyol A (5) (Figure 1). The structure elucidation was based on 1D and

Total synthesis and cytotoxicity of the marine natural product malevamide D and a photoreactive analog

• Werner Telle,
• Gerhard Kelter,
• Heinz-Herbert Fiebig,
• Peter G. Jones and
• Thomas Lindel

Beilstein J. Org. Chem. 2014, 10, 316–322, doi:10.3762/bjoc.10.29

• , Scheme 2). However, after treatment of dipeptide 15 with secondary amine 16 (0.43 equiv) and DEPC (17, 2.5 equiv), the only isolable product was oxazolylphosphate 18 (35%) without any amide formation occurring. The structure elucidation of 18 required C–P coupling constant analysis, which showed doublet

Tanzawaic acids I–L: Four new polyketides from Penicillium sp. IBWF104-06

• Louis P. Sandjo,
• Eckhard Thines,
• Till Opatz and
• Anja Schüffler

Beilstein J. Org. Chem. 2014, 10, 251–258, doi:10.3762/bjoc.10.20

• same trans-decalinpentanoic acid skeleton as tanzawaic acids A–H. One of the new compounds was found to inhibit the conidial germination in the rice blast fungus Magnaporthe oryzae at concentrations of 25 μg/mL. Keywords: arohynapene; natural products; polyketides; structure elucidation; tanzawaic

• Discussion Structure elucidation. Compound 1 has the molecular formula C18H26O4 determined on the basis of NMR and HRMS-ESI data which gave a pseudo-molecular ion at m/z 329.1744 (calcd for [M + Na]+: 329.1729). This composition accounted for six double bond equivalents. The NMR spectra of 1 (Table 1 and

Plakilactones G and H from a marine sponge. Stereochemical determination of highly flexible systems by quantitative NMR-derived interproton distances combined with quantum mechanical calculations of ¹³C chemical shifts

• Simone Di Micco,
• Angela Zampella,
• Maria Valeria D’Auria,
• Carmen Festa,
• Simona De Marino,
• Raffaele Riccio,
• Craig P. Butts and
• Giuseppe Bifulco

Beilstein J. Org. Chem. 2013, 9, 2940–2949, doi:10.3762/bjoc.9.331

• the four diastereoisomers 2a,b,e,f endowed with the epoxide moiety in a trans-configuration, by comparing the experimental vs the calculated distances (Table 3). In Table 3 only a subset of all values was used for the stereochemical structure elucidation, more specifically, the values where DFT

Synthesis and determination of the absolute configuration of (−)-(5R,6Z)-dendrolasin-5-acetate from the nudibranch Hypselodoris jacksoni

• I. Wayan Mudianta,
• Victoria L. Challinor,
• Anne E. Winters,
• Karen L. Cheney,
• James J. De Voss and
• Mary J. Garson

Beilstein J. Org. Chem. 2013, 9, 2925–2933, doi:10.3762/bjoc.9.329

• methoxyphenylacetic acid (MPA) derivative. Results and Discussion Isolation and structure elucidation of natural product 1 Eight individuals of H. jacksoni were collected by SCUBA from two locations in SE Queensland. Owing to their small size (21–40 mm), the specimens were not examined individually. Extraction into