Biomimetic synthesis and HPLC–ECD analysis of the isomers of dracocephins A and B

• Viktor Ilkei,
• András Spaits,
• Anita Prechl,
• Áron Szigetvári,
• Zoltán Béni,
• Miklós Dékány,
• Csaba Szántay Jr,
• Judit Müller,
• Árpád Könczöl,
• Ádám Szappanos,
• Attila Mándi,
• Sándor Antus,
• Ana Martins,
• Attila Hunyadi,
• György Tibor Balogh,
• György Kalaus (†),
• Hedvig Bölcskei,
• László Hazai and
• Tibor Kurtán

Beilstein J. Org. Chem. 2016, 12, 2523–2534, doi:10.3762/bjoc.12.247

• Dracocephalum rupestre, have been synthesized in a one-pot reaction. The separation of 2a–d and 3a–d was achieved by preparative HPLC. The four stereoisomers of each natural product were separated by analytical chiral HPLC and their absolute configuration was studied by the combination of HPLC–ECD measurements

• and TDDFT–ECD calculations. The synthesized flavonoid alkaloids were further characterized by physicochemical and in vitro pharmacological studies. Keywords: absolute configuration; Dracocephalum rupestre; dracocephins A–B; ECD calculation; flavonoid alkaloids; HPLC–ECD; Introduction Flavonoid

• racemates (2a, 2c/2b, 2d; 3a, 3c/3b, 3d) by HPLC–ECD analysis (Figure 1). The planar structure and absolute configuration of the first-eluted stereoisomer of dracocephins A (±)-2a–d was determined by single-crystal X-ray diffraction analysis as (2R,5”S)-2a [2]. The biosynthesis of these flavonoid

Determination of the absolute stereostructure of a cyclic azobenzene from the crystal structure of the precursor containing a heavy element

• Reji Thomas and
• Nobuyuki Tamaoki

Beilstein J. Org. Chem. 2016, 12, 2211–2215, doi:10.3762/bjoc.12.212

• enantiomer formed by the reductive debromination. In the previous study with the combination of density functional theoretical calculations (DFT) and electronic circular dichroism (ECD), we have assigned the first and second eluted enantiomers of (E)-2 as R-(−)-(E)-2 and S-(+)-(E)-2, respectively, on a

New furoisocoumarins and isocoumarins from the mangrove endophytic fungus Aspergillus sp. 085242

• Ze’en Xiao,
• Senhua Chen,
• Runlin Cai,
• Shao’e Lin,
• Kui Hong and
• Zhigang She

Beilstein J. Org. Chem. 2016, 12, 2077–2085, doi:10.3762/bjoc.12.196

• configuration of compound 2 was unambiguously determined by X-ray structure analysis and ECD calculation. Moreover, the absolute configurations of compounds 3–5 were assigned by comparison of their ECD spectra with isocoumarins described in the literature. Asperisocoumarins C and D (3 and 4) were fully

• ) [16][17], which allowed the assignment of the absolute configuration of 2 as (2R,3R,7R) (Figure 3). Moreover, the predicted ECD curves of 2 and its relevant enantiomer were computed at the [B3LYP/6-31 G(2d,p)] level, and the experimental ECD curve of 2 agreed well with the predicted one (Figure 4), in

• at δC 167.2 were observed, whereas two oxygenated methine carbons at δC 94.5 and 71.0 were absent in the spectrum of compound 3. These differences were further supported by the HMBC correlations of olefinic proton H-3 to C-2, C-3a and C-9b (Figure 2). By comparison of the ECD spectrum (Figure 5) and

Varioloid A, a new indolyl-6,10b-dihydro-5aH-[1]benzofuro[2,3-b]indole derivative from the marine alga-derived endophytic fungus Paecilomyces variotii EN-291

• Peng Zhang,
• Xiao-Ming Li,
• Xin-Xin Mao,
• Attila Mándi,
• Tibor Kurtán and
• Bin-Gui Wang

Beilstein J. Org. Chem. 2016, 12, 2012–2018, doi:10.3762/bjoc.12.188

• time-dependent density functional theory-electronic circular dichroism (TDDFT-ECD) calculations. A similar compound, whose planar structure was previously described but the relative and absolute configurations and 13C NMR data were not reported, was also identified and was tentatively named as

• varioloid B (2). Both compounds 1 and 2 exhibited cytotoxicity against A549, HCT116, and HepG2 cell lines, with IC50 values ranging from 2.6 to 8.2 µg/mL. Keywords: bisindolyl benzenoid derivatives; cytotoxicity; marine alga-derived fungus; Paecilomyces variotii; TDDFT-ECD calculation; Introduction The

• NOE correlation between H-2 and 3-OMe led to recognition that these protons adopt cis orientation. In order to elucidate the absolute configuration of 1, solution TDDFT-ECD protocol [14][15] was carried out on the arbitrarily chosen (2R,3R) enantiomer. The preliminary conformational search at MMFF

Three new trixane glycosides obtained from the leaves of Jungia sellowii Less. using centrifugal partition chromatography

• Luíse Azevedo,
• Larissa Faqueti,
• Marina Kritsanida,
• Antonia Efstathiou,
• Despina Smirlis,
• Gilberto C. Franchi Jr,
• Grégory Genta-Jouve,
• Sylvie Michel,
• Louis P. Sandjo,
• Raphaël Grougnet and
• Maique W. Biavatti

Beilstein J. Org. Chem. 2016, 12, 674–683, doi:10.3762/bjoc.12.68

• . Similarly, H-13 unveiled the same interactions with H-1 and H-9 while H-14 correlated with H-8 (Figure 4). In order to determine the absolute configuration of the compounds 1–3, ECD spectra prediction was used [36][37]. The absolute configuration of 1 was assigned as 2R, 6S, 7R, 10R, and 11S by ECD analysis

• similar interactions with H-1 (δ 1.72) and H-9 (δ 1.56, 1.67). The absolute configuration of 2 was determined to be 2R, 3S, 6S, 7R, and 10S by ECD analysis. As compound 1, two Cotton Effects (CE) from the n→π* transition of the α,β-unsaturated lactone were revealed at 225 and 275 nm with alternative signs

• aglycone [39]. The absolute configuration of 3 was assigned as 1R, 6R, 7S, and 10S. Three CE's were observed on the experimental ECD spectrum at 240, 305 and 350 nm due to the n→π* transition of the α,β-unsaturated ketone. The foregoing data led to identify 3 as 6-hydroxyguaiane congener (Figure 2) and the

Unconventional application of the Mitsunobu reaction: Selective flavonolignan dehydration yielding hydnocarpins

• Guozheng Huang,
• Simon Schramm,
• Jörg Heilmann,
• David Biedermann,
• Vladimír Křen and
• Michael Decker

Beilstein J. Org. Chem. 2016, 12, 662–669, doi:10.3762/bjoc.12.66

• yielded the individual enantiomers (10R,11R)- and (10S,11S)-hydnocarpin D (2a, 2b). We measured optical rotations and ECD and confirmed the proposed structures (see Figures S3 and S4 in Supporting Information File 1). To our knowledge, this is the second case only [22] that these two enantiomers were

Chiroptical properties of 1,3-diphenylallene-anchored tetrathiafulvalene and its polymer synthesis

• Masashi Hasegawa,
• Junta Endo,
• Seiya Iwata,
• Toshiaki Shimasaki and
• Yasuhiro Mazaki

Beilstein J. Org. Chem. 2015, 11, 972–979, doi:10.3762/bjoc.11.109

• undergoes slow photoracemization even in daylight, the present allene is totally configurationally stable under ordinary conditions. Each isomer possesses pronounced chiroptical properties in its ECD spectra reflecting the chiral allene framework. Moreover, the elongation of the chiral main chain was also

• systems having strong chiroptical properties because they have great potential for use in optical devices involving polarized light [1][2][3]. Chiral response, in electronic circular dichroism (ECD) based on an exciton coupling between two adequate π-chromophores, can express a pronounced chiroptical

• orientation of the chromophores [8][9]. We recently introduced 1,3-bis(tetrathiafulvalenyl)allene derivatives 1, as a new class of chiral electrochromic (EC) materials consisting of redox-active chromophores and a non-centrochiral framework (Figure 1) [10]. The intensive Cotton effect on the ECD spectra is

Preparation of neuroprotective condensed 1,4-benzoxazepines by regio- and diastereoselective domino Knoevenagel–[1,5]-hydride shift cyclization reaction

• László Tóth,
• Yan Fu,
• Hai Yan Zhang,
• Attila Mándi,
• Katalin E. Kövér,
• Tünde-Zita Illyés,
• Attila Kiss-Szikszai,
• Balázs Balogh,
• Tibor Kurtán,
• Sándor Antus and
• Péter Mátyus

Beilstein J. Org. Chem. 2014, 10, 2594–2602, doi:10.3762/bjoc.10.272

• . Separated enantiomers of the products were characterized by HPLC-ECD data, which allowed their configurational assignment on the basis of TDDFT-ECD calculation of the solution conformers. Two compounds showed neuroprotective activities against hydrogen peroxide (H2O2) or β-amyloid25–35 (Aβ25–35)-induced

• cellular injuries in human neuroblastoma SH-SY5Y cells in the range of those of positive controls. Keywords: 1,4-benzoxazepine; diastereoselective domino Knoevenagel–[1,5]-hydride shift cyclization; neuroprotective; tert-amino effect; TDDFT-ECD calculation; Introduction The 1,4-benzoxazepine structural

• ,b were separated on a Chiralpak IA column using hexane/dichloromethane as eluent and online HPLC-ECD spectra of the separated enantiomers were recorded. Due to their similar chromophoric system, the HPLC-ECD spectra of 7a and 7b were quite similar. The first-eluting enantiomer of 7a had an intense

Effect of cyclodextrin complexation on phenylpropanoids’ solubility and antioxidant activity

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

Beilstein J. Org. Chem. 2014, 10, 2322–2331, doi:10.3762/bjoc.10.241

• ) leading to two different orientations of the aromatic ring inside the host cavity. The total energy difference (ΔE, kJ/mol) between inclusion complexes and the sum of their individual components in their optimized fundamental states was calculated (ΔE = ECD/PP – (ECD + EPP)) and used as the theoretical

Human dendritic cell activation induced by a permannosylated dendron containing an antigenic GM₃-lactone mimetic

• Renato Ribeiro-Viana,
• Elena Bonechi,
• Javier Rojo,
• Clara Ballerini,
• Giuseppina Comito,
• Barbara Richichi and
• Cristina Nativi

Beilstein J. Org. Chem. 2014, 10, 1317–1324, doi:10.3762/bjoc.10.133

• (Immunotech) directed against the following antigens (the tags are given in parentheses): CD80 (FITC), CD86 (PE), HLA-DR (ECD), CD83 (PC5). Cell vitality was tested with propidium iodide (PI, molecular probes). The cells were labelled in PBS with 1% FCS for 15 min at room temperature (rt), washed twice and

• panels: percentage of expression of dendritic cell markers (HLA-DR ECD, CD80 FITC, CD86 PE and CD83 PC5). Cell phenotypes, expressed as the percentage of positive cells for CD80, CD86 and HLA-DR, did not change when activation took place in the presence of compound 5 (left) at 10 or 50 µg/mL compared to

Synthesis of a sucrose dimer with enone tether; a study on its functionalization

• Zbigniew Pakulski,
• Norbert Gajda,
• Magdalena Jawiczuk,
• Jadwiga Frelek,
• Piotr Cmoch and
• Sławomir Jarosz

Beilstein J. Org. Chem. 2014, 10, 1246–1254, doi:10.3762/bjoc.10.124

• dimolybdenum methodology offers the hard proof of the absolute configuration of the vic-diols [27][28][29]. In this methodology, dimolybdenum tetraacetate acts as auxiliary chromophore allowing the application of electronic circular dichroism (ECD) to (otherwise in ECD non-observable) vic-diols. Mo2(OAc)4 when

• mixed with a chiral diol ligand forms complexes active in ECD in which a transfer of ligand chirality to the in situ-formed complex occurs in solution. Thus, stereochemistry of vic-diols can be easily assigned based on the helicity rule developed for this class of compounds. This rule correlates the

• positive/negative signs of Cotton effects (CE) occurring in the 300–400 nm spectral range in the ECD spectra with the positive/negative sign of the O–C–C–O torsion angle of the diol unit of resultant complexes with the Mo2-core. The basic assumption leading to the assignment of the absolute configuration

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

• -cis-10,11-trans-isomer 12 and a minor 23-O-acetyl-2,3-trans-10,11-cis-isomer 13 (Scheme 3). Surprisingly, the absolute configuration at C-2, C-3 of compound 13 was the opposite of 1a (2S,3S vs 2R,3R), which was confirmed by a comparison of their electronic circular dichroism (ECD) data. Formation of

• ) and B (1b) was determined indirectly on the basis of a comparison of their physicochemical data (NMR, ECD, OR). Later, these data were matched to those of their 10,11-regioisomer, isosilybin A (5) [11]. The same approach was used to determine the absolute configuration of isosilybin B (6). The only

• analogue that yielded suitable crystals, and hence an unequivocal determination of its absolute configuration, was 7-(4-bromobenzoyl)isosilybin A [15]. In this study the determination of the absolute configuration was based on NMR and ECD spectroscopy. Their relative configurations, i.e., the determination

Theoretical study on β-cyclodextrin inclusion complexes with propiconazole and protonated propiconazole

• Adrian Fifere,
• Narcisa Marangoci,
• Stelian Maier,
• Adina Coroaba,
• Dan Maftei and
• Mariana Pinteala

Beilstein J. Org. Chem. 2012, 8, 2191–2201, doi:10.3762/bjoc.8.247

• + inclusion compounds were selected by considering the binding energy as being the difference between the heat of formation of the complex and the heat of formation of the involved free molecules: where ECD/PP, EPP and ECD represent the heat of formation of the complex, of the free β-CD, and of the free guest