Role of the methoxy group in product formation via TiCl4 promoted 4-phenyldioxolane isomerizations

The product distribution obtained from the TiCl4 initiated intramolecular isomerizations of 4- methoxyphenyl- and trimethoxyphenyldioxolanes at -78 oC, -30 oC and 0 oC provided insights into the important regiochemical role played by these groups in such Mukaiyama- type rearrangements through their resonance effects on the aryl ring of the dioxolanes.Our interest in naphthopyranquinones as potential antimicrobial and antibiotic agents has extended over two decades1-6 as a result of their well documented importance.7,8 Additionally, the synthesis of benzopyrans as model systems has received attention by ourselves6,9-13 and others.14- 16 Of particular interest to us was our earlier discovery of a TiCl4 - induced intramolecular isomerization in which phenyl- and naphthyldioxolanes were stereoselectively transformed into their corresponding benzo- and naphthopyrans.1

2-Arylnaphthoquinone analogues: Potential anti-TB and pro-apoptotic agents

A useful library of substituted 2-arylnaphthoquinones prepared by reaction between the corresponding bromonaphthoquinones and arylboronic acids via Suzuki-Miyaura protocols has been established. Conversion of some of the products into new analogues was effected. The bisnaphthoquinone disospyrin 1 comprises two 7-methyljuglone units linked between C2 and C6. 1,2 Antimycobacterial activity studies performed on diospyrin 1 alerted the scientific community to the potential importance of this natural product3 which was soon followed by its first published synthesis by Yoshida and Mori in the same year.4 Subsequent studies, which included the synthesis and evaluation of related analogues of diospyrin 1 demonstrated the potential of this basic scaffold to be considered as an integral aspect for good antimycrobacterial activity

Regulation of Translesion Synthesis DNA Polymerase η by Monoubiquitination

DNA polymerase eta is a Y family polymerase involved in translesion synthesis (TLS). Its action is initiated by simultaneous interaction between the PIP box in pol eta and PCNA and between the UBZ in pol eta and monoubiquitin attached to PCNA. Whereas monoubiquitination of PCNA is required for its interaction with pol eta during TLS, we now show that monoubiquitination of pol eta inhibits this interaction, preventing its functions in undamaged cells. Identification of monoubiquitination sites within pol eta nuclear localization signal (NLS) led to the discovery that pol eta NLS directly contacts PCNA, forming an extended pol eta-PCNA interaction surface. We name this the PCNA-interacting region (PIR) and show that its monoubiquitination is downregulated by various DNA-damaging agents. We propose that this mechanism ensures optimal availability of nonubiquitinated, TLS-competent pol eta after DNA damage. Our work shows how monoubiquitination can either positively or negatively regulate the assembly of a protein complex, depending on which substrates are targeted by ubiquitin

5-epi-Incensole: synthesis, X-ray crystal structure and absolute configuration by means of ECD and VCD studies in solution and solid state

Incensole 1 and its acetate 2, found in incense, demonstrate interesting biological activities. Incensole acetate 2 was prepared on a large scale by employing the Paul and Jauch protocol from the crude extracts of Boswellia papyrifera Hochst. 5-epi-Incensole 3, obtained as colorless crystals, was prepared from incensole acetate via three steps; deacetylation, oxidation and reduction. The structure of 5-epi-incensole 3 was elucidated by means of spectroscopic data analysis, and the absolute configuration was established by single crystal X-ray analysis in combination with electronic and vibrational circular dichroism. In particular, the applicability of the solid-state ECD/TDDFT protocol to a compound with only two non-conjugated alkene chromophores was verified

Planet Hunters. VIII. Characterization of 41 Long-Period Exoplanet Candidates from Kepler Archival Data

The census of exoplanets is incomplete for orbital distances larger than 1 AU. Here, we present 41 long-period planet candidates in 38 systems identified by Planet Hunters based on Kepler archival data (Q0-Q17). Among them, 17 exhibit only one transit, 14 have two visible transits and 10 have more than three visible transits. For planet candidates with only one visible transit, we estimate their orbital periods based on transit duration and host star properties. The majority of the planet candidates in this work (75%) have orbital periods that correspond to distances of 1-3 AU from their host stars. We conduct follow-up imaging and spectroscopic observations to validate and characterize planet host stars. In total, we obtain adaptive optics images for 33 stars to search for possible blending sources. Six stars have stellar companions within 4". We obtain high-resolution spectra for 6 stars to determine their physical properties. Stellar properties for other stars are obtained from the NASA Exoplanet Archive and the Kepler Stellar Catalog by Huber et al. (2014). We validate 7 planet candidates that have planet confidence over 0.997 (3-{\sigma} level). These validated planets include 3 single-transit planets (KIC-3558849b, KIC-5951458b, and KIC-8540376c), 3 planets with double transits (KIC-8540376b, KIC-9663113b, and KIC-10525077b), and 1 planet with 4 transits (KIC-5437945b). This work provides assessment regarding the existence of planets at wide separations and the associated false positive rate for transiting observation (17%-33%). More than half of the long-period planets with at least three transits in this paper exhibit transit timing variations up to 41 hours, which suggest additional components that dynamically interact with the transiting planet candidates. The nature of these components can be determined by follow-up radial velocity and transit observations.Comment: Published on ApJ, 815, 127 Notations of validated planets are changed in accordance with naming convention of NASA Exoplanet Archiv

Enzymatic modification of 2,6-dimethoxyphenol for the synthesis of dimers with high antioxidant capacity

2,6-Dimethoxyphenol is a phenolic compound that is extensively used for the measurement of laccase activity, but is often not exploited for its potential as an antioxidant compound. Since laccase can be used to modify phenolic antioxidants as a way of improving their activities, the present study investigated the laccase-mediated oxidation of 2,6-dimethoxyphenol in biphasic or homogenous aqueous-organic media for the production of compounds with higher antioxidant capacity than the starting substrate. The main product was a dimer (m/z 305.0672), which was further characterized as a symmetrical C-C linked 3,3’,5,5’-tetramethoxy biphenyl-4,4’-diol. In the monophasic system, the dimer was preferentially formed when acetone was used as co34 solvent, while in the biphasic system, formation of the dimer increased as the concentration of ethyl acetate was increased from 50 to 90 %. The dimer showed higher antioxidant capacity than the substrate (≈ 2×) as demonstrated by standard antioxidant assays (DPPH and FRAP). These results demonstrate that a product of the laccase-catalysed oxidation of 2,6-dimethoxyphenol can find useful application as a bioactive compound.National Research Foundation (South Africa)http://www .elsevier.com/locate/procbiohb2013ai201

Synthesis of pyrrolocarbazoles with N-substituted alkynyl-, alkylcyano- and alkylhydroxyl-groups

CITATION: Van der Westhuyzen, A. E. et al. 2020. Synthesis of pyrrolocarbazoles with N-substituted alkynyl-, alkylcyano- and alkylhydroxyl-groups. Arkivoc, v:129-147, doi:10.24820/ark.5550190.p011.412.The original publication is available at https://www.arkat-usa.orgDue to their involvement in almost all stages of cellular life, kinase biomolecular catalysts have been linked to cancer development and, thus, remain attractive drug targets for cancer therapeutics. 6-(3ꞌ-Hydroxypropyl)-, 6-(2ꞌ-hydroxyethyl)-, 6-(2ꞌ-propynyl)- and 6-(3ꞌ-propanenitrile)-pyrrolo[3,4-c]carbazole-1,3(2H,6H)-diones were synthesized as potential small molecule EGFR kinase inhibitors. The pyrrolocarbazole compounds were synthesized by way of a Diels-Alder approach involving N-alkylated 2-vinyl-1H-indole and maleimide as starting materials followed by aromatization with MnO2.Publisher's versio

Meroterpenoids: A Comprehensive Update Insight on Structural Diversity and Biology.

Funder: This research was funded by the Deanship of Scientific Research at Princess Nourah bint Abdulrahman University through the Fast-track Research Funding ProgramMeroterpenoids are secondary metabolites formed due to mixed biosynthetic pathways which are produced in part from a terpenoid co-substrate. These mixed biosynthetically hybrid compounds are widely produced by bacteria, algae, plants, and animals. Notably amazing chemical diversity is generated among meroterpenoids via a combination of terpenoid scaffolds with polyketides, alkaloids, phenols, and amino acids. This review deals with the isolation, chemical diversity, and biological effects of 452 new meroterpenoids reported from natural sources from January 2016 to December 2020. Most of the meroterpenoids possess antimicrobial, cytotoxic, antioxidant, anti-inflammatory, antiviral, enzyme inhibitory, and immunosupressive effects