Biosynthesis of oxygen and nitrogen-containing heterocycles in polyketides

• Franziska Hemmerling and
• Frank Hahn

Beilstein J. Org. Chem. 2016, 12, 1512–1550, doi:10.3762/bjoc.12.148

• ]. Altering of synthase specificity and thus interconversion into each other has been demonstrated [173]. 2.1.2 Michael addition–lactamisation: Glutarimides. The biosynthesis of the glutarimides proceeds similar to δ-lactone biosynthesis and has been described in chapter 1.6. 2.1.3 Dieckmann condensation

Stereodynamic tetrahydrobiisoindole “NU-BIPHEP(O)”s: functionalization, rotational barriers and non-covalent interactions

• Golo Storch,
• Sebastian Pallmann,
• Frank Rominger and
• Oliver Trapp

Beilstein J. Org. Chem. 2016, 12, 1453–1458, doi:10.3762/bjoc.12.141

• enantiomerization as well as the half-life of isolated enantiomers. The latter are of particular importance if chiral co-ligands are cleaved off prior to catalysis and if the remaining stereochemically aligned BIPHEP complex fragment serves as the active species. Therefore, detailed knowledge of the interconversion

• crucial. In contrast to 1a and 1b, three coexisting isomeric species were observed with NMR spectroscopy in CDCl3 for tetrahydrobiisoindole “NU-BIPHEP(O)” 1c. This behaviour originates from an increased interconversion barrier between the E/Z isomers of the carbamate N–C(O) unit that is derived from a

• the corresponding author upon request. A rotational barrier of = 99.5 ± 0.1 kJ mol−1 was determined for the interconversion of 3. This is a significant increase compared to unsubstituted BIPHEP(O) ( = 88.6 kJ mol−1). Eyring plot analysis allowed the determination of the activation parameters ΔH

On the mechanism of imine elimination from Fischer tungsten carbene complexes

• Philipp Veit,
• Christoph Förster and
• Katja Heinze

Beilstein J. Org. Chem. 2016, 12, 1322–1333, doi:10.3762/bjoc.12.125

• , the 1,2-H shift in the free carbenes has been calculated as well (Scheme 3). The carbene E-2 is 23 kJ mol−1 more stable than the Z-2 isomer (Supporting Information File 1, Figure S17). The interconversion between these isomers E-2 → Z-2 (ΔG‡ = 130 kJ mol−1) proceeds via a bending vibration of the Cp–C

A modular approach to neutral P,N-ligands: synthesis and coordination chemistry

• Vladislav Vasilenko,
• Torsten Roth,
• Clemens K. Blasius,
• Sebastian N. Intorp,
• Hubert Wadepohl and
• Lutz H. Gade

Beilstein J. Org. Chem. 2016, 12, 846–853, doi:10.3762/bjoc.12.83

• temperature, indicating that a relatively fast interconversion of the different conformers occurs at ambient conditions. However, with increasing steric bulk of the aromatic nitrogen substituents, a substantial line broadening is observed, indicating the rise of the isomerization barrier through steric

A convenient route to symmetrically and unsymmetrically substituted 3,5-diaryl-2,4,6-trimethylpyridines via Suzuki–Miyaura cross-coupling reaction

• Dariusz Błachut,
• Joanna Szawkało and
• Zbigniew Czarnocki

Beilstein J. Org. Chem. 2016, 12, 835–845, doi:10.3762/bjoc.12.82

• the phenyl rings (or naphthalene ring for 26) with three methyl groups of the pyridine ring. Consequently, the inhibited rotation of the phenyl rings led to the formation of stable diastereomeric atropisomers which could be detected in NMR spectroscopy. The interconversion barrier is probably

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

• . This strategy resulted in the bioactive analogues 95–98 (Figure 12). Analogue 95 with an interconversion of the lipid side chain and the guanidine group had a slightly reduced activity compared to lipidated analogue 92g. Analogue 96 showed an increased antibacterial activity towards some of the tested

Strecker degradation of amino acids promoted by a camphor-derived sulfonamide

• M. Fernanda N. N. Carvalho,
• M. João Ferreira,
• Ana S. O. Knittel,
• Maria da Conceição Oliveira,
• João Costa Pessoa,
• Rudolf Herrmann and
• Gabriele Wagner

Beilstein J. Org. Chem. 2016, 12, 732–744, doi:10.3762/bjoc.12.73

• ). We therefore expected that kinetic effects during the tautomerizations might be responsible for the observed selectivity and checked the interconversion pathways between the tautomers 7–11 which differ only in the position of one proton. Such a proton migration must of course be catalyzed, and water

• ) for possible reactions. Thus we can draw the following conclusions from the results: 1. A direct interconversion of 7a and 7b (the azomethine ylides) by rotation around the bond which connects the bicyclic ring system with the nitrogen atom appears possible (barrier of medium height). No interference

• from 7b to 8 directly, but only via isomer 7a which is formed according to 1). 3. Barriers of medium height are observed for the tautomerizations 7b → 9 + 10 + 11 and 8 → 9 + 10 + 11. No direct reaction to these products is possible from 7a, but only after interconversion to 7b according to 1. From 8

(Thio)urea-mediated synthesis of functionalized six-membered rings with multiple chiral centers

• Giorgos Koutoulogenis,
• Nikolaos Kaplaneris and
• Christoforos G. Kokotos

Beilstein J. Org. Chem. 2016, 12, 462–495, doi:10.3762/bjoc.12.48

• resulted in three diastereoisomers (Scheme 62) [83]. With this in hand, they envisioned the interconversion of the kinetic products to the most stable product. In order to achieve that, they designed an one-pot two-step process, where upon completion of the tandem Henry–Michael reaction, TMG catalyzed the

Dynamic behavior of rearranging carbocations – implications for terpene biosynthesis

• Stephanie R. Hare and
• Dean J. Tantillo

Beilstein J. Org. Chem. 2016, 12, 377–390, doi:10.3762/bjoc.12.41

• in the pimar-15-en-8-yl cation can lead to a PTSB – one branch of which leads to the carbocation precursor to abietadiene (Figure 9, green), but the other branch of which leads to a rearranged skeleton, not yet reported for any diterpenes/diterpenoids from Nature (Figure 9, red). Interconversion of

Tandem processes promoted by a hydrogen shift in 6-arylfulvenes bearing acetalic units at ortho position: a combined experimental and computational study

• Mateo Alajarin,
• Marta Marin-Luna,
• Pilar Sanchez-Andrada and
• Angel Vidal

Beilstein J. Org. Chem. 2016, 12, 260–270, doi:10.3762/bjoc.12.28

• being lower than that of 10a into 12a (13.9 and 17.0 kcal·mol−1, respectively). 4) The overall processes 3a → 5a and 3a → 6a are exothermic by 31.3 and 30.7 kcal·mol−1, respectively. The interconversion between 5a and 6a is predicted to take place via two consecutive [1,5]-H shifts at the pentagonal

• . The interconversion between the isomeric benzindenes 5a and 6a could also occur by means of two consecutive [1,5]-H shifts through an unstable benzisoindene intermediate. Conclusion The ability of benzofulvenes bearing 1,3-dioxolane or -dioxane units in ortho position for undergoing cascade processes

Versatile deprotonated NHC: C,N-bridged dinuclear iridium and rhodium complexes

• Albert Poater

Beilstein J. Org. Chem. 2016, 12, 117–124, doi:10.3762/bjoc.12.13

• 3H-H and 3H-T (where H-H = head-to-head and H-T = head-to-tail). By DFT calculations here we contribute in the understanding of the thermodynamics of the subsequent C,N-bridged dinuclear iridium and rhodium complexes [59], and the facility for the interconversion between these latter dimeric species

• NHC here have been studied in detail by DFT calculations. This is a contribution in the understanding of the thermodynamics of the subsequent C,N-bridged dinuclear iridium and rhodium complexes defined by Braunstein et al. [59] and the facility for the interconversion between these latter dimeric

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

• agreement with the detection of (ring-2H5)benzoic acid in culture extracts from labeling experiments with (ring-2H5)Phe. This interconversion of two proteinogenic amino acids in the biosynthesis of an NRPS compound from secondary metabolism is unprecedented and its discovery was strongly supported by the

Biocatalysis for the application of CO₂ as a chemical feedstock

• Apostolos Alissandratos and
• Christopher J. Easton

Beilstein J. Org. Chem. 2015, 11, 2370–2387, doi:10.3762/bjoc.11.259

• Pyrococcus furiosus does not interfere. Decarboxylases A number of enzymes are capable of catalysing the reversible interconversion of lipophilic aromatics and the more polar respective carboxylates [12]. It is thought these reactions may proceed in the carboxylation direction as a detoxification mechanism

• formate and CO2 interconversion is broadly distributed in nature, irrespective of metabolic directionality, however, catalytic properties vary greatly depending on the source organism. As expected, the enzymes that naturally catalyse CO2 reduction and highly homologous FDHs from formate oxidation pathways

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

• the initial addition of 10 μL of 1 M HCl. Interconversion kinetics of compounds 2 (blue), 3 (orange) and 4 (grey). Modelling-derived structure of 3 showing key nOe interactions (calculated distances in Å). Modelling-derived structure of compound 4 showing key nOe interactions (calculated distances in

Why base-catalyzed isomerization of N-propargyl amides yields mostly allenamides rather than ynamides

• Armando Navarro-Vázquez

Beilstein J. Org. Chem. 2015, 11, 1441–1446, doi:10.3762/bjoc.11.156

• due to thermodynamic rather than kinetic reasons, and it is not necessarily the case that ynamides are more stable than the parent allenamides. Here it is hypothesized that N-propargylamide ↔ allenamide ↔ ynamide interconversion takes place reversibly and the outcome of the reaction is related to the

Further exploration of the heterocyclic diversity accessible from the allylation chemistry of indigo

• Alireza Shakoori,
• John B. Bremner,
• Mohammed K. Abdel-Hamid,
• Anthony C. Willis,
• Rachada Haritakun and
• Paul A. Keller

Beilstein J. Org. Chem. 2015, 11, 481–492, doi:10.3762/bjoc.11.54

• -membered ring [8]. However, analysis of the 13C NMR spectra of these products indicated only a single set of peaks in each case and no evidence for a diastereomeric mixture. Presumably, the atropisomeric rotation barrier is sufficiently low at room temperature to allow for interconversion. While

A comparative study of the interactions of cationic hetarenes with quadruplex-DNA forming oligonucleotide sequences of the insulin-linked polymorphic region (ILPR)

• Darinka Dzubiel,
• Heiko Ihmels,
• Mohamed M. A. Mahmoud and
• Laura Thomas

Beilstein J. Org. Chem. 2014, 10, 2963–2974, doi:10.3762/bjoc.10.314

• demonstrate a delicate equilibrium between the different quadruplex forms and some kinetic barriers that result in rather slow interconversion processes. Nevertheless, to provide comparable data, in this study we used slowly cooled ILPR-quadruplex a2 to ensure that we have the same relative population of

Microsolvation and sp²-stereoinversion of monomeric α-(2,6-di-tert-butylphenyl)vinyllithium as measured by NMR

• Rudolf Knorr,
• Monika Knittl and
• Eva C. Rossmann

Beilstein J. Org. Chem. 2014, 10, 2521–2530, doi:10.3762/bjoc.10.263

• averaged resonance position of (δcis + δtrans)/2 [24]. The temperature-dependent pseudo-first-order rate constants kψ of this interconversion were determined with a computer program [25][26][27][28] that can simulate and plot AB line shapes for visual comparison with the experimental spectra. This

Pyrrolidine nucleotide analogs with a tunable conformation

• Lenka Poštová Slavětínská,
• Dominik Rejman and
• Radek Pohl

Beilstein J. Org. Chem. 2014, 10, 1967–1980, doi:10.3762/bjoc.10.205

• existence of the two rotamers prompted us to estimate the energy barrier of their interconversion. We therefore performed variable 31P NMR measurements of 14 at different temperatures (starting at 25 °C with a 10 °C step, with the last measurement taken at 100 °C) and a line-shape analysis of an uncoupled

• , exchanging two-site 31P system (Figure 9). This enabled us to obtain the rate constants of the exchange at different temperatures and estimate the activation parameters of the interconversion such as the Gibbs free energy of activation ΔG‡298 = 80.7 kJ/mol; the enthalpy of activation ΔH‡ = 23.8 kJ/mol; and

Use of activated enol ethers in the synthesis of pyrazoles: reactions with hydrazine and a study of pyrazole tautomerism

• Denisa Tarabová,
• Stanislava Šoralová,
• Martin Breza,
• Marek Fronc,
• Wolfgang Holzer and
• Viktor Milata

Beilstein J. Org. Chem. 2014, 10, 752–760, doi:10.3762/bjoc.10.70

• a rapid exchange between tautomeric forms was expected – and in DMSO-d6 solution – where we assumed slower interconversion rates due to the acceptor properties of this solvent. However, the solubility in CDCl3 turned out to be very low for the studied compounds, so that only 1H NMR spectra could be

Thermodynamically stable [4 + 2] cycloadducts of lanthanum-encapsulated endohedral metallofullerenes

• Yuta Takano,
• Yuki Nagashima,
• M. Ángeles Herranz,
• Nazario Martín and
• Takeshi Akasaka

Beilstein J. Org. Chem. 2014, 10, 714–721, doi:10.3762/bjoc.10.65

• of the cycloadducts of EMFs has not been well-studied to date; the investigation of this interconversion serves to demonstrate the existence of a dynamic process in the molecules and is regarded as one index of the bonding energy of the addition position of the fullerene and the addend. Among various

• slow or fast to allow their observation in an NMR time scale. The signals from the AB-quartet of 4a coalesce at 290 K (= Tc) indicate a dynamic process, which is attributed to the boat-to-boat interconversion of the cyclohexane ring of the addend similarly to the related carbocyclic analogues of C60

Chromatographically separable rotamers of an unhindered amide

• Mario Geffe,
• Lars Andernach,
• Oliver Trapp and
• Till Opatz

Beilstein J. Org. Chem. 2014, 10, 701–706, doi:10.3762/bjoc.10.63

• .10.63 Abstract Surprisingly stable formamide rotamers were encountered in the tetrahydroisoquinoline and morphinan series of alkaloids. We investigated the hindered rotation around the amide bond by dynamic high-performance liquid chromatography (DHPLC) and kinetic measurements of the interconversion of

• the second development immediately followed the air-drying of the plate. If one hour at room temperature lay between the first and the second development, two weak off-diagonal spots indicated that interconversion of both species had taken place to a small extent. When the temperature was increased to

• 75 °C during a 15 min drying period, four spots with roughly equal intensity resulted from the second 2D-TLC run and indicated complete interconversion. A look into the literature revealed that the occurrence of separable amide rotamers of 1-benzyl-N-formyl-1,2,3,4-tetrahydroisoquinolines had been

Recent applications of the divinylcyclopropane–cycloheptadiene rearrangement in organic synthesis

• Sebastian Krüger and
• Tanja Gaich

Beilstein J. Org. Chem. 2014, 10, 163–193, doi:10.3762/bjoc.10.14

• desired DVCPR in almost quantitative yield at elevated temperature, followed by removal of the silyl-protecting group under acidic conditions to furnish cycloheptenone 70. Standard functional group interconversion furnished diolefin 71. Subjection of this compound to Heck coupling conditions resulted in

• 96, for which the yield and enantioselectivity was determined starting from 93. Standard functional group interconversion first provided exo-methylene 97, followed by ruthenium-catalyzed oxidative cleavage of the installed exo-methylene moiety [94] to give tricyclic ketone 98, which can be converted

The difluoromethylene (CF₂) group in aliphatic chains: Synthesis and conformational preference of palmitic acids and nonadecane containing CF₂ groups

• Yi Wang,
• Ricardo Callejo,
• Alexandra M. Z. Slawin and
• David O’Hagan

Beilstein J. Org. Chem. 2014, 10, 18–25, doi:10.3762/bjoc.10.4

• -tetrafluorohexadecanoic acid (6c). The X-ray structure of 8,8,11,11-tetrafluorononadecane (27). Conformational interconversion of 1,4-di-CF2 motif. Synthesis route to 8,8-difluorohexadecanoic acid (6a). The synthesis of palmitic acid analogues 6b and 6c. Synthesis route to the tetrafluorinated alkane 27. Supporting

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

• extend the application of NMR-derived interproton distances to a highly flexible molecular system with simultaneous assignment of four non-contiguous stereocenters. Chemical derivatization and quantum mechanical calculations of 13C on plakilactone G along with a plausible biogenetic interconversion

• consistent with anti-1,2-diol type C. Therefore the 7R,8S configuration is assigned. Notably, considering the plausible biogenetic interconversion of an epoxide and a diol, the above absolute configuration at C-7 and C-8 of plakilactone G is in full agreement with the trans-epoxide 2b. Having assigned the

• probability of 62.9% (Table 5), whereas for 1b–d we found a probability of 1.9%, 5.4% and 29.7% (Table 5), respectively. Isomers 1a and 1d differ only in the configuration at C-4, and considering a putative interconversion between diol 1 and epoxide 2 and a common biogenetic pathway in combination with the