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991.
Ascorbic acid (AA) is one of the essential nutrients in bee pollen, however, it is unstable and likely to be oxidized. Generally, the oxidation form (dehydroascorbic acid (DHA)) is considered to have equivalent biological activity as the reduction form. Thus, determination of the total content of AA and DHA would be more accurate for the nutritional analysis of bee pollen. Here we present a simple, sensitive, and reliable method for the determination of AA, total ascorbic acids (TAA), and DHA in rape (Brassica campestris), lotus (Nelumbo nucifera), and camellia (Camellia japonica) bee pollen, which is based on ultrasonic extraction in metaphosphoric acid solution, and analysis using hydrophilic interaction liquid chromatography (HILIC)-ultraviolet detection. Analytical performance of the method was evaluated and validated, then the proposed method was successfully applied in twenty-one bee pollen samples. Results indicated that contents of AA were in the range of 17.54 to 94.01 µg/g, 66.01 to 111.66 µg/g, and 90.04 to 313.02 µg/g for rape, lotus, and camellia bee pollen, respectively. In addition, percentages of DHA in TAA showed good intra-species consistency, with values of 13.7%, 16.5%, and 7.6% in rape, lotus, and camellia bee pollen, respectively. This is the first report on the discriminative determination between AA and DHA in bee pollen matrices. The proposed method would be valuable for the nutritional analysis of bee pollen. 相似文献
992.
993.
Juyeol Lee Jihun Kang Sukhyun Lee Young Ho Rhee 《Angewandte Chemie (International ed. in English)》2020,59(6):2349-2353
A de novo first collective total synthesis of 11‐deoxylandomycins is reported. A signature step is featured by the Pd‐catalyzed asymmetric addition of alcohol to ene‐alkoxyallenes that assembles oligomeric 2,3,6‐trideoxyoligosaccharides. The unique feature of the protocol is illustrated by a flexible access to various natural 11‐deoxylandomycins as well as non‐natural analogues. 相似文献
994.
Mumdooh Ahmed Alexander Marchanka Teresa Carlomagno 《Angewandte Chemie (International ed. in English)》2020,59(17):6866-6873
Solid‐state NMR (ssNMR) is applicable to high molecular‐weight (MW) protein assemblies in a non‐amorphous precipitate. The technique yields atomic resolution structural information on both soluble and insoluble particles without limitations of MW or requirement of crystals. Herein, we propose and demonstrate an approach that yields the structure of protein–RNA complexes (RNP) solely from ssNMR data. Instead of using low‐sensitivity magnetization transfer steps between heteronuclei of the protein and the RNA, we measure paramagnetic relaxation enhancement effects elicited on the RNA by a paramagnetic tag coupled to the protein. We demonstrate that this data, together with chemical‐shift‐perturbation data, yields an accurate structure of an RNP complex, starting from the bound structures of its components. The possibility of characterizing protein–RNA interactions by ssNMR may enable applications to large RNP complexes, whose structures are not accessible by other methods. 相似文献
995.
Mary‐Ann J. Siegert Caroline H. Knittel Roderich D. Süssmuth 《Angewandte Chemie (International ed. in English)》2020,59(14):5500-5504
The toxic bicyclic octapeptide α‐amanitin is mostly found in different species of the mushroom genus Amanita, with the death cap (Amanita phalloides) as one of the most prominent members. Due to its high selective inhibition of RNA polymerase II, which is directly linked to its high toxicity, particularly to hepatocytes, α‐amanitin received an increased attention as a toxin‐component of antibody‐drug conjugates (ADC) in cancer research. Furthermore, the isolation of α‐amanitin from mushrooms as the sole source severely restricts compound supply as well as further investigations, as structure–activity relationship (SAR) studies. Based on a straightforward access to the non‐proteinogenic amino acid dihydroxyisoleucine, we herein present a robust total synthesis of α‐amanitin providing options for production at larger scale as well as future structural diversifications. 相似文献
996.
Xing Li Hyaeyeong Kim Jacob L. Litke Jiahui Wu Samie R. Jaffrey 《Angewandte Chemie (International ed. in English)》2020,59(11):4511-4518
Spinach and Broccoli are fluorogenic RNA aptamers that bind DFHBI, a mimic of the chromophore in green fluorescent protein, and activate its fluorescence. Spinach/Broccoli‐DFHBI complexes exhibit high fluorescence in vitro, but they exhibit lower fluorescence in mammalian cells. Here, computational screening was used to identify BI, a DFHBI derivative that binds Broccoli with higher affinity and leads to markedly higher fluorescence in cells compared to previous ligands. BI prevents thermal unfolding of Broccoli at 37 °C, leading to more folded Broccoli and thus more fluorescent Broccoli‐BI complexes in cells. Broccoli‐BI complexes are more photostable owing to impaired photoisomerization and rapid unbinding of photoisomerized cis‐BI. These properties enable single mRNA containing 24 Broccoli aptamers to be imaged in live mammalian cells treated with BI. Small molecule ligands can thus promote RNA folding in cells, and thus allow single mRNA imaging with fluorogenic aptamers. 相似文献
997.
998.
999.
Si‐Hua Hou Adriana Y. Prichina Mengxi Zhang Guangbin Dong 《Angewandte Chemie (International ed. in English)》2020,59(20):7848-7856
To show the synthetic utility of the catalytic C?C activation of less strained substrates, described here are the collective and concise syntheses of the natural products (?)‐microthecaline A, (?)‐leubehanol, (+)‐pseudopteroxazole, (+)‐seco‐pseudopteroxazole, pseudopterosin A–F and G—J aglycones, and (+)‐heritonin. The key step in these syntheses involve a Rh‐catalyzed C?C/C?H activation cascade of 3‐arylcyclopentanones, which provides a rapid and enantioselective route to access the polysubstituted tetrahydronaphthalene cores presented in these natural products. Other important features include 1) the direct C?H amination of the tetralone substrate in the synthesis of (?)‐microthecaline A, 2) the use of phosphoric acid to enhance efficiency and regioselectivity for problematic cyclopentanone substrates in the C?C activation reactions, and 3) the direct conversion of serrulatane into amphilectane diterpenes by an allylic cyclodehydrogenation coupling. 相似文献
1000.
Jing Zhang Meng Liu Chuanhua Wu Gaoyuan Zhao Peiqi Chen Lin Zhou Xingang Xie Ran Fang Huilin Li Xuegong She 《Angewandte Chemie (International ed. in English)》2020,59(10):3966-3970
The first total synthesis of the Euphorbia diterpenoid pepluanol B in both racemic and enantioenriched form involves 20 steps from a known bicyclic diol. This synthesis features an unprecedented bromo‐epoxidation to control the eight‐membered‐ring conformation. In addition, salient reactions for the construction of the tetracyclic backbone include a sterically challenging aldol reaction to establish the quaternary center, a ring closing metathesis (RCM) to forge the eight‐membered ring, and a diastereoselective cyclopropanation to assemble the embedded cyclopropane motif. 相似文献