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  • 1
    Publication Date: 2014-10-11
    Description: Cycloaddition is an essential tool in chemical synthesis. Instead of using light or heat as a driving force, marine sponges promote cycloaddition with a more versatile but poorly understood mechanism in producing pyrrole-imidazole alkaloids sceptrin, massadine, and ageliferin. Through de novo synthesis of sceptrin and massadine, we show that sponges may use single-electron oxidation as a central mechanism to promote three different types of cycloaddition. Additionally, we provide surprising evidence that, in contrast to previous reports, sceptrin, massadine, and ageliferin have mismatched chirality. Therefore, massadine cannot be an oxidative rearrangement product of sceptrin or ageliferin, as is commonly believed. Taken together, our results demonstrate unconventional chemical approaches to achieving cycloaddition reactions in synthesis and uncover enantiodivergence as a new biosynthetic paradigm for natural products.〈br /〉〈br /〉〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4205478/" target="_blank"〉〈img src="https://static.pubmed.gov/portal/portal3rc.fcgi/4089621/img/3977009" border="0"〉〈/a〉   〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4205478/" target="_blank"〉This paper as free author manuscript - peer-reviewed and accepted for publication〈/a〉〈br /〉〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Ma, Zhiqiang -- Wang, Xiaolei -- Wang, Xiao -- Rodriguez, Rodrigo A -- Moore, Curtis E -- Gao, Shuanhu -- Tan, Xianghui -- Ma, Yuyong -- Rheingold, Arnold L -- Baran, Phil S -- Chen, Chuo -- R01 GM073949/GM/NIGMS NIH HHS/ -- R01 GM079554/GM/NIGMS NIH HHS/ -- R01-GM073949/GM/NIGMS NIH HHS/ -- R01-GM079554/GM/NIGMS NIH HHS/ -- New York, N.Y. -- Science. 2014 Oct 10;346(6206):219-24. doi: 10.1126/science.1255677.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Biochemistry, The University of Texas Southwestern Medical Center, Dallas, TX 75390, USA. ; Department of Chemistry, The Scripps Research Institute, La Jolla, CA 92037, USA. ; Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, CA 92093, USA. ; Department of Biochemistry, The University of Texas Southwestern Medical Center, Dallas, TX 75390, USA. chuo.chen@utsouthwestern.edu.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25301624" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Biosynthetic Pathways ; *Cycloaddition Reaction ; Molecular Structure ; Porifera/*metabolism ; Pyrroles/*chemical synthesis/chemistry/metabolism ; Stereoisomerism
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 2
    Publication Date: 2015-07-15
    Description: Sherman et al. commented on the precedence of enantiodivergence, listing a number of congeneric natural products with opposite chirality. However, these "congeners" are not derived from enantiodivergent biosyntheses. Instead, they are antipodes arising from separate enantiomeric biosyntheses. A distinct feature of the biosynthesis of the cyclic pyrrole-imidazole dimers is the production of antipodal congeners without the corresponding enantiomers.〈br /〉〈br /〉〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4536548/" target="_blank"〉〈img src="https://static.pubmed.gov/portal/portal3rc.fcgi/4089621/img/3977009" border="0"〉〈/a〉   〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4536548/" target="_blank"〉This paper as free author manuscript - peer-reviewed and accepted for publication〈/a〉〈br /〉〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Ma, Zhiqiang -- Wang, Xiaolei -- Wang, Xiao -- Rodriguez, Rodrigo A -- Moore, Curtis E -- Gao, Shuanhu -- Tan, Xianghui -- Ma, Yuyong -- Rheingold, Arnold L -- Baran, Phil S -- Chen, Chuo -- R01 GM073949/GM/NIGMS NIH HHS/ -- R01 GM079554/GM/NIGMS NIH HHS/ -- R01-GM073949/GM/NIGMS NIH HHS/ -- R01-GM079554/GM/NIGMS NIH HHS/ -- New York, N.Y. -- Science. 2015 Jul 10;349(6244):149. doi: 10.1126/science.aaa9626. Epub 2015 Jul 9.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Biochemistry, The University of Texas Southwestern Medical Center, Dallas, TX 75390, USA. chuo.chen@utsouthwestern.edu. ; Department of Biochemistry, The University of Texas Southwestern Medical Center, Dallas, TX 75390, USA. ; Department of Chemistry, The Scripps Research Institute, La Jolla, CA 92037, USA. ; Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, CA 92093, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26160939" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; *Cycloaddition Reaction ; Porifera/*metabolism ; Pyrroles/*chemical synthesis
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 3
    Publication Date: 2018-06-06
    Description: One of the major objectives of Laboratory Astrophysics is the optimization of data return from space missions by measuring spectra of atomic and molecular species in laboratory environments that mimic interstellar conditions (WhitePaper (2002, 2006)). Among interstellar species, PAHs are an important and ubiquitous component of carbon-bearing materials that represents a particularly difficult challenge for gas-phase laboratory studies. We present the absorption spectra of jet-cooled neutral and ionized PAHs and discuss the implications for astrophysics. The harsh physical conditions of the interstellar medium have been simulated in the laboratory. We are now, for the first time, in the position to directly compare laboratory spectra of PAHs and carbon nanoparticles with astronomical observations. This new phase offers tremendous opportunities for the data analysis of current and upcoming space missions geared toward the detection of large aromatic systems (HST/COS, FUSE, JWST, Spitzer).
    Keywords: Astrophysics
    Type: Proceedings of the NASA Laboratory Astrophysics Workshop; 243-247; NASA/CP-2006-214549
    Format: application/pdf
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  • 4
    Publication Date: 2019-07-18
    Description: We present the results of a dedicated search for the spectral signatures in the visible range of neutral polycyclic aromatic hydrocarbons (PAHs) in astronomical observations representing various astrophysical environments, probing a total column of line of sight material corresponding to Av=50. Laboratory measurements of PAHs in simulated astrophysical conditions are now available (see contribution of Salama et al.) which provide for the first time the exact wavelengths for the spectral features of these molecules, as well as detailed information on the intrinsic line profiles and oscillator strengths. These measurements therefore allow a direct comparison to astronomical observations and an estimate of, or upper limit to, the abundance of individual PAHs in space. As the column densities for individual PAHs in interstellar or circumstellar lines of sight are expected to be very low, such a comparison and analysis requires astronomical observations at very high signal to noise. We present such a data set here for lines of sight representing diffuse clouds and circumstellar environments of carbon stars, and their comparison with gas phase spectra of a representative set of free, cold PAHs.
    Keywords: Astrophysics
    Type: AAS 206th Meeting; May 29, 2005 - Jun 02, 2005; Minneapolis, MN; United States
    Format: text
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