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

• mechanism is reminiscent of the formation of a tetrahydropyridine ring by the berberine bridge enzyme in plant alkaloid biosynthesis. It starts with S-adenosyl-L-methionine (SAM)-dependent methylation of the secondary hydroxy group in 81 by the O-methyltransferase Leu14 (Scheme 14a) [71][72][73][74

• lactone that is decarboxylated towards the xanthone [103]. Studies with recombinant AflM and a lack of isolatable intermediates however made it clear that the order of steps in demethylsterigmatocystin (107) formation needs to be carefully re-evaluated [100]. Methylation by an O-methyltransferase and

Synthesis of highly functionalized 2,2'-bipyridines by cyclocondensation of β-ketoenamides – scope and limitations

• Paul Hommes and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2016, 12, 1170–1177, doi:10.3762/bjoc.12.112

• or O-nonaflation led to functionalized pyridine derivatives. Scheme 1 illustrates this sequence with the synthesis of two 2,2´-bipyridine derivatives 4a or 5b that were obtained by employing picolinic acid chloride for the N-acylations followed by O-methylation with methyl iodide or by O-nonaflation

Synthesis of 2-oxindoles via 'transition-metal-free' intramolecular dehydrogenative coupling (IDC) of sp² C–H and sp³ C–H bonds

• Nivesh Kumar,
• Santanu Ghosh,
• Subhajit Bhunia and
• Alakesh Bisai

Beilstein J. Org. Chem. 2016, 12, 1153–1169, doi:10.3762/bjoc.12.111

• methylation can be done in the presence of 1.2 equivalents of KOt-Bu and 1.1 equivalents of methyl iodide. This was accompanied with an oxidative coupling using 1.2 equivalents of KOt-Bu and iodine to afford the desired product in 65% yield (Table 1, entries 1 and 2). Optimization studies in search of

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

• miuraenamide A (31) the absolute configuration was determined. Marfey´s method was employed to show that L-alanine and N-methyl-D-tyrosine are present. Furthermore, after acid hydrolysis, methylation and application of modified Mosher´s method the absolute configuration at the oxygen bearing C-9 was deduced as

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

• followed by an azide reduction, Boc protection, saponification of the ester, peptide coupling with the amino acid 17, oxidative cleavage of the double bond to give 18 and an intramolecular reductive amination in order to construct the seven-membered ring. Methylation with subsequent acidic global

Opportunities and challenges for direct C–H functionalization of piperazines

• Zhishi Ye,
• Kristen E. Gettys and
• Mingji Dai

Beilstein J. Org. Chem. 2016, 12, 702–715, doi:10.3762/bjoc.12.70

• and properties, as the so-called as the “magic methyl effect” [44]. Direct enantioselective α-methylation of piperazines however, has been a great synthetic challenge and an effective method still needs to be developed. O’Brien and co-workers also reported their work towards a solution to this problem

• . As shown in Figure 11, they have tried various reaction conditions to achieve an enantioselective methylation of the α-lithiation intermediate of N-Boc-N’-alkylpiperazines by using different diamines (TMEDA, 21, and 28) as well as the “chiral auxiliary” strategy. While the result is not yet optimal

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

• hydrolysis of the lipopolysaccharide isolated by the phenol–water extraction from the halotolerant soil bacteria Azospirillum halopraeferens type strain Au4. The polysaccharide was studied by sugar and methylation analyses, selective cleavages by Smith degradation and solvolysis with trifluoroacetic acid

• -methylglucose, 2,4-di-O-methylrhamnose, 2,4-di-O-methylfucose, 2-O-methylfucose, and 3,4-di-O-methylxylose were identified by GLC–MS of partially methylated alditol acetates derived after methylation of the OPS with MeI followed by hydrolysis and acetylation [14]. Therefore, the OPS contains 3-substituted Rha

• 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

Biosynthesis of α-pyrones

• Till F. Schäberle

Beilstein J. Org. Chem. 2016, 12, 571–588, doi:10.3762/bjoc.12.56

• biosynthesis was investigated using various 13C-labeled precursors [55]. Hence, it was concluded that beside four acetate units also two propionate units and one butyrate unit form the backbone, while the O-methylation is S-adenosyl-methionine dependent. Also cyclooxygenase-2 (COX-2) inhibitors are an

• . Cyclization between C-2, C-7 and C-8, C-13, as well as lactonization takes place, resulting in alternariol (17). Subsequently, a methylation and a hydroxylation reaction occur, catalyzed by the respective enzymes. Structures of phenylnannolones and of enterocin, both biosynthesized via polyketide synthase

Interactions between 4-thiothymidine and water-soluble cyclodextrins: Evidence for supramolecular structures in aqueous solutions

• Vito Rizzi,
• Sergio Matera,
• Paola Semeraro,
• Paola Fini and
• Pinalysa Cosma

Beilstein J. Org. Chem. 2016, 12, 549–563, doi:10.3762/bjoc.12.54

• appeared only weakly in DIMEB CD (Figure 5D). This is due to the methylation of the OH moieties. As described in [42], weak absorption bands were detected also in the region of 1100–650 cm−1 and can be related to vibrations of the С–Н bonds and to the glucopyranose rind. Further, in the region of 1400–1150

Regiodefined synthesis of brominated hydroxyanthraquinones related to proisocrinins

• Joyeeta Roy,
• Tanushree Mal,
• Supriti Jana and
• Dipakranjan Mal

Beilstein J. Org. Chem. 2016, 12, 531–536, doi:10.3762/bjoc.12.52

• ][25][26][27][28][29][30]. It was then treated with bromine in AcOH to afford 3,5-dibromoorsellinate 20 in 81% yield [31][32][33]. Subsequent O-methylation of 20 (using CH3I, K2CO3), and benzylic bromination of 21 with NBS followed by lactonization of 22 in a refluxing mixture of dioxane and water

Interactions of cyclodextrins and their derivatives with toxic organophosphorus compounds

• Sophie Letort,
• Sébastien Balieu,
• William Erb,
• Géraldine Gouhier and
• François Estour

Beilstein J. Org. Chem. 2016, 12, 204–228, doi:10.3762/bjoc.12.23

• trend was disclosed by theoretical semi-empirical calculations of parathion-, methyl parathion- and fenitrothion-β-CD complexes [55]. It was shown that the methyl group, adjacent to the nitro function slightly impairs both deep and axial inclusion of fenitrothion into the cavity. The methylation degree

• decrease of the hydrolysis rate of fenitrothion is observed with methylation of β-CD. These unpredictable results revealed that much more complex parameters than the easiness of the guest entry into the (methylated)CD are involved in the hydrolysis. Indeed, the methylation degree could also affect the

• steric hindrance of the secondary rim, resulting in CD geometrical changes with modifications of the complex stability, the orientation and inclusion depth of the pesticide within the cavity. However, the two main parameters to take into account remain the methylation degree and the pesticide inclusion

Determination of formation constants and structural characterization of cyclodextrin inclusion complexes with two phenolic isomers: carvacrol and thymol

• Miriana Kfoury,
• David Landy,
• Steven Ruellan,
• Lizette Auezova,
• Hélène Greige-Gerges and
• Sophie Fourmentin

Beilstein J. Org. Chem. 2016, 12, 29–42, doi:10.3762/bjoc.12.5

• inclusion of 1 inside the cavity. RAMEB gave the most stable inclusion complexes with both 1 and 2. This is due to that the methoxy groups of RAMEB are small and do not lead to a significant steric hindrance and that the methylation of β-CD hydroxy groups increases the hydrophobic character of the cavity

Physical properties and biological activities of hesperetin and naringenin in complex with methylated β-cyclodextrin

• Waratchada Sangpheak,
• Jintawee Kicuntod,
• Roswitha Schuster,
• Thanyada Rungrotmongkol,
• Peter Wolschann,
• Nawee Kungwan,
• Helmut Viernstein,
• Monika Mueller and
• Piamsook Pongsawasdi

Beilstein J. Org. Chem. 2015, 11, 2763–2773, doi:10.3762/bjoc.11.297

• )-glycosidic bonds. It contains a highly hydrophobic central cavity and the hydrophilic outer surface. The 2,6-di-O-methyl-β-cyclodextrin (DM-β-CD), a commercially available β-CD derivative, is obtained by methylation of the hydroxy groups at C2 and C6 of all glucose units, thus having the degree of

• give much difference to these properties. However, in the third part whereby biological activities were examined, the two flavanones complexing with β-CD and DM-β-CD were used since the different degree of methylation might exert significant effect on the result as previously reported [28]. Binding

• . The methyl substitution plays an important role in balancing the CD water solubility and its complexing ability [44]. It was previously reported that increasing the degree of methylation up to an optimum level improves the CD aqueous solubility, and the binding of guests to CDs is increased by

Inclusion complexes of 2-methoxyestradiol with dimethylated and permethylated β-cyclodextrins: models for cyclodextrin–steroid interaction

• Mino R. Caira,
• Susan A. Bourne,
• Halima Samsodien and
• Vincent J. Smith

Beilstein J. Org. Chem. 2015, 11, 2616–2630, doi:10.3762/bjoc.11.281

• . The unique layering that results in the extended crystal structure is shown in Figure 2f, a view along the [010] direction. Methylation of the DIMEB molecule at the 3-position results in fully methylated β-CD (TRIMEB), the second crystalline derivatised CD investigated here for its potential to

• thermal motion that was not amenable to standard anisotropic treatment while the disordered water oxygen atoms did not warrant anisotropic treatment. A minor, but unexpected feature of the DIMEB inclusion complex, was partial methylation of the O3-H hydroxy group of the host glucose ring G1 (s.o.f. = 0.5

• host molecule. This necessitated reduction of the s.o.f. of the latter methyl group from 1.0 to 0.5. The net effect was that despite partial methylation of O3–H on G1, appropriate modelling of disordered residues resulted in retention of the nominal formula for the DIMEB molecule, namely C56H98O35. The

Synthesis of Xenia diterpenoids and related metabolites isolated from marine organisms

• Tatjana Huber,
• Lara Weisheit and
• Thomas Magauer

Beilstein J. Org. Chem. 2015, 11, 2521–2539, doi:10.3762/bjoc.11.273

• isobutene (36), an isomeric mixture of trans- and cis-fused [4.2.0]octanone was obtained (trans-38/cis-39 = 4:1). The more stable cis-bicycle 39 could be obtained by isomerization of trans-38 with base. Acylation with sodium hydride and dimethyl carbonate followed by methylation furnished β-keto ester 40

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

• branched polyketides at the α-position of the growing chain include the usage of different elongation units such as methylmalonyl-CoA, or methylation of the nucleophilic α-position by S-adenosyl methionine (SAM) [21]. Branching in the β-position is less common and proceeds through a β-aldol attack of an

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

• described for nagelamide B (8) [15]. The structure of citrinamine C (3) was elucidated to be the 2,2´-didebromo derivative of nagelamide B (8) with an additional methylation of the hydroxy group at C-9 (80.8 ppm) and an oxidation of the imidazole ring at position C-13 (154.6 ppm) (an urea instead of a

• (130.2 ppm), and H-17 to C-5 (121.6 ppm) indicated a methylation of the pyrrole nitrogen (Figure 6) which was proven by the 1H,15N-HMBC correlations H-2 to N-1 (159 ppm), H-4 (6.91 ppm) to N-1, and H-17 to N-1. The correlation between the methyl group H-17 and C-6 (158.6 ppm) suggested a linkage with the

Total synthesis of panicein A₂

• Lili Yeung,
• Lisa I. Pilkington,
• Melissa M. Cadelis,
• Brent R. Copp and
• David Barker

Beilstein J. Org. Chem. 2015, 11, 1991–1996, doi:10.3762/bjoc.11.215

• of panicein A2 Firstly, aldehyde 10 was required; it was prepared through methylation followed by Vilsmeier–Haack reaction of 2,3,5-trimethylphenol (11), giving 10 in 51% yield over two steps (Scheme 1) [7]. Aldehyde 10 then underwent an aldol reaction according to the procedures of Samokhvalov et al

Fates of imine intermediates in radical cyclizations of N-sulfonylindoles and ene-sulfonamides

• Hanmo Zhang,
• E. Ben Hay,
• Stephen J. Geib and
• Dennis P. Curran

Beilstein J. Org. Chem. 2015, 11, 1649–1655, doi:10.3762/bjoc.11.181

• amination of N-tosylindole aldehyde 6 with 2-iodoaniline (66%), followed by methylation of the aniline nitrogen atom (91%). Substrate 10 with the ester on C2 of the indole was chosen to learn if a more stabilized radical intermediate would still eliminate the N-tosyl group. Reductive amination of 9, 2

Synthesis of icariin from kaempferol through regioselective methylation and para-Claisen–Cope rearrangement

• Qinggang Mei,
• Chun Wang,
• Zhigang Zhao,
• Weicheng Yuan and
• Guolin Zhang

Beilstein J. Org. Chem. 2015, 11, 1220–1225, doi:10.3762/bjoc.11.135

• , Southwest University for Nationalities, Chengdu 610041, China 10.3762/bjoc.11.135 Abstract The hemisynthesis of the naturally occurring bioactive flavonoid glycoside icariin (1) has been accomplished in eleven steps with 7% overall yield from kaempferol. The 4′-OH methylation of kaempferol, the 8

• a continuation of this program, herein we report a new approach to icaritin and then icariin through semi-synthesis from the commercially available natural product kaempferol. Our previously developed regioselective methylation of kaempferol [19], Europium(III)-catalyzed para-Claisen–Cope

• rearrangement and the bis-glycosylation are the key features of this linear synthesis. Previously, we succeeded in the selective methylation of 4′-OH in kaempferol. In this work, we focus on developing an efficient procedure for the selective prenylation of flavonols for facile access to icariin (1). Results

The synthesis of active pharmaceutical ingredients (APIs) using continuous flow chemistry

• Marcus Baumann and
• Ian R. Baxendale

Beilstein J. Org. Chem. 2015, 11, 1194–1219, doi:10.3762/bjoc.11.134

• which although commercially available was expensive and could be generated from 1,3-cyclohexadione (104). The sequence consisted of O-acetylation, a Steglich rearrangement, oxidation and a final methylation reaction. As the use of flow chemistry had already improved the O-acetylation during scale-up

• an iodine mediated aromatisation, followed by high temperature mono-methylation using dimethyl carbonate/dimethylimidazole as a more benign alternative to methyl iodide at scale. The subsequent Claisen condensation step between ketone 112 and diethyl oxalate (113) was reportedly hampered by product

Advances in the synthesis of functionalised pyrrolotetrathiafulvalenes

• Luke J. O’Driscoll,
• Sissel S. Andersen,
• Marta V. Solano,
• Dan Bendixen,
• Morten Jensen,
• Troels Duedal,
• Jess Lycoops,
• Cornelia van der Pol,
• Rebecca E. Sørensen,
• Karina R. Larsen,
• Kenneth Myntman,
• Christian Henriksen,
• Stinne W. Hansen and
• Jan O. Jeppesen

Beilstein J. Org. Chem. 2015, 11, 1112–1122, doi:10.3762/bjoc.11.125

• ) (EtO)3P, 120–135 °C, 1–4 h, 70–87%. Deprotection and methylation of cyanoethyl-protected thiol moieties on MPTTFs as reported by Jeppesen et al. [25]. Reagents and conditions: a) (i) 1 equiv CsOH·H2O, MeOH, THF, rt, 1 h, (ii) MeI, THF, rt, 30 min; b) (i) 1 equiv CsOH·H2O, MeOH, THF, rt, 1 h, (ii) MeI

Quarternization of 3-azido-1-propyne oligomers obtained by copper(I)-catalyzed azide–alkyne cycloaddition polymerization

• Shun Nakano,
• Akihito Hashidzume and
• Takahiro Sato

Beilstein J. Org. Chem. 2015, 11, 1037–1042, doi:10.3762/bjoc.11.116

• region of the 13C NMR spectrum, the signals at 141.4, 135.2, 133.5, and 124.3 ppm are ascribable to the carbons in the 1,2,3-triazole ring. This observation indicates that the methylation occurred on both the 2- and 3-positions in 1,2,3-triazole under the present conditions, although the quarternization

• indicated that the methylation occurred on both the 2- and 3-positions in 1,2,3-triazole under the present conditions. The hydrodynamic radius RH of oligoAPMe of n = 11 and xq = 0.96 in DMSO-d6 dilute solutions was determined to be 0.95 nm by PGSE NMR to study the conformation of the quarternized oligomer

An intramolecular C–N cross-coupling of β-enaminones: a simple and efficient way to precursors of some alkaloids of Galipea officinalis

• Hana Doušová,
• Radim Horák,
• Zdeňka Růžičková and
• Petr Šimůnek

Beilstein J. Org. Chem. 2015, 11, 884–892, doi:10.3762/bjoc.11.99

• ]. As part of our ongoing interest in the preparation of polarized ethylenes and their application in organic synthesis, we have been attracted by the procedure published by Zhou [30]. Here, the authors used heterocyclic enaminone 1b as the reactant for an asymmetric reduction followed by N-methylation

Ruthenium-catalyzed C–H activation of thioxanthones

• Danny Wagner and
• Stefan Bräse

Beilstein J. Org. Chem. 2015, 11, 431–436, doi:10.3762/bjoc.11.49

• cleavage catalyzed by hot sulfuric acid. In this case, methylation (Me2SO4, K2CO3) of the hydroxythioxanthones 1c, 1e and 1g provided the required methyl ethers 1d, 1f and 1h, respectively in good yields (80, 85 and 95%), Scheme 1. Ru-catalyzed C–H activation Following the precedence for other carbonyl