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An expression is derived for the viscous drag of a spheroidal particle whose temperature differs from that of the carrier liquid. Calculations are performed for the case where the temperature dependence of the liquid viscosity may be represented by an exponential power series. 相似文献
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Noncanonical RNA Nucleosides as Molecular Fossils of an Early Earth—Generation by Prebiotic Methylations and Carbamoylations
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Christina Schneider Sidney Becker Dr. Hidenori Okamura Antony Crisp Dr. Tynchtyk Amatov Michael Stadlmeier Prof. Dr. Thomas Carell 《Angewandte Chemie (International ed. in English)》2018,57(20):5943-5946
The RNA‐world hypothesis assumes that life on Earth started with small RNA molecules that catalyzed their own formation. Vital to this hypothesis is the need for prebiotic routes towards RNA. Contemporary RNA, however, is not only constructed from the four canonical nucleobases (A, C, G, and U), it also contains many chemically modified (noncanonical) bases. A still open question is whether these noncanonical bases were formed in parallel to the canonical bases (chemical origin) or later, when life demanded higher functional diversity (biological origin). Here we show that isocyanates in combination with sodium nitrite establish methylating and carbamoylating reactivity compatible with early Earth conditions. These reactions lead to the formation of methylated and amino acid modified nucleosides that are still extant. Our data provide a plausible scenario for the chemical origin of certain noncanonical bases, which suggests that they are fossils of an early Earth. 相似文献
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Synthesis of Bridged Diketopiperazines by Using the Persistent Radical Effect and a Formal Synthesis of Bicyclomycin
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Tynchtyk Amatov Dr. Radek Pohl Dr. Ivana Císařová Dr. Ullrich Jahn 《Angewandte Chemie (International ed. in English)》2015,54(41):12153-12157
A conceptually new and unified approach to diverse bridged diketopiperazines (DKPs) with widely variable ring sizes was developed by taking advantage of the persistent radical effect. This method enables synthesis of the core structures of bridged DKP alkaloids and was applied to a formal synthesis of the antibiotic bicyclomycin. 相似文献
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Dr. Sebastian Armin Schwengers Dr. Gabriela Guillermina Gerosa Dr. Tynchtyk Amatov Dr. Naoki Yasukawa Sebastian Brunen Dr. Markus Leutzsch Benjamin Mitschke Dr. Grigory André Shevchenko Prof. Dr. Dr. h.c. Benjamin List 《Angewandte Chemie (International ed. in English)》2023,62(35):e202307081
We disclose a highly regioselective, catalytic one-step dehydrogenation of α-substituted cyclic ketones in the presence of 2,3-dichlorobenzo-5,6-dicyano-1,4-benzoquinone (DDQ). The high regioselectivity originates from a phosphoric acid-catalyzed enolization, selectively affording the thermodynamically preferred enol, followed by the subsequent oxidation event. Our method provides reliable access to several α-aryl and α-alkyl substituted α,β-unsaturated ketones. 相似文献
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