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排序方式: 共有583条查询结果,搜索用时 31 毫秒
31.
Takeshi Yamada Yuki MizutaniYoshihide Umebayashi Naoko InnoMaiko Kawashima Takashi KikuchiReiko Tanaka 《Tetrahedron letters》2014
Tandyukisin (1), a novel decalin derivative with an enolic β-ketoaldehyde, has been isolated from a strain of Trichoderma harzianum OUPS-111D-4 originally derived from the marine sponge Halichondria okadai, and its structure has been elucidated on the basis of spectroscopic analyses using 1D and 2D NMR techniques. In addition, the absolute configuration for 1 was established by the application of CD spectrum to the tribenzoate derivative. This compounds exhibited moderate cytotoxicity against human cancer cell lines. 相似文献
32.
Naonobu Tanaka Rei Momose Azusa Takahashi-Nakaguchi Tohru Gonoi Jane Fromont Jun'ichi Kobayashi 《Tetrahedron》2014
Six new indole alkaloids, hyrtimomines F–K (1–6), were isolated from Okinawan marine sponges Hyrtios spp. The structures of 1–6 were elucidated on the basis of spectroscopic analysis. Hyrtimomine F (1) is a structurally unique bisindole alkaloid possessing an α-keto-?-caprolactam ring, while hyrtimomine G (2) is a symmetrical bisindole alkaloid. Hyrtimomines H–K (3–6) are indole alkaloids possessing β-carboline skeleton with an imidazolium unit. Antimicrobial activities of hyrtimomines F–K (1–6) were evaluated. 相似文献
33.
For the long-range infrared imaging system, the marine atmospheric turbulence degrades seriously the probability of object recognition and tracking. In this study, the angle of arrival fluctuations of an optical wave, which describes the distortion effects of marine atmospheric turbulence on an infrared optical imaging system, is investigated in detail both analytically and numerically. Analytic expressions of the angle of arrival fluctuations are derived for optical plane and spherical waves propagating through weak marine atmospheric turbulence with horizontal path, and they consider simultaneously finite turbulence inner scale, turbulence outer scale, wavelength, and aperture diameters. Numerical calculations are conducted to analyze the influence of marine weak turbulence on the infrared imaging. The results are useful for understanding the potential impact of deviations from the terrestrial turbulence. 相似文献
34.
Dr. Reiko Ueoka Dr. Roy A. Meoded Alejandro Gran-Scheuch Dr. Agneya Bhushan Prof. Dr. Marco W. Fraaije Prof. Dr. Jörn Piel 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(20):7835-7839
Bacterial trans-acyltransferase polyketide synthases (trans-AT PKSs) are multimodular megaenzymes that biosynthesize many bioactive natural products. They contain a remarkable range of domains and module types that introduce different substituents into growing polyketide chains. As one such modification, we recently reported Baeyer–Villiger-type oxygen insertion into nascent polyketide backbones, thereby generating malonyl thioester intermediates. In this work, genome mining focusing on architecturally diverse oxidation modules in trans-AT PKSs led us to the culturable plant symbiont Gynuella sunshinyii, which harbors two distinct modules in one orphan PKS. The PKS product was revealed to be lobatamide A, a potent cytotoxin previously only known from a marine tunicate. Biochemical studies show that one module generates glycolyl thioester intermediates, while the other is proposed to be involved in oxime formation. The data suggest varied roles of oxygenation modules in the biosynthesis of polyketide scaffolds and support the importance of trans-AT PKSs in the specialized metabolism of symbiotic bacteria. 相似文献
35.
The pH is an important parameter that affects the growth and development of marine organisms, environmental changes, and industrial and agricultural production processes. Nowadays, important trends in pH detection and analysis are higher stability, adaptation to extreme environmental conditions, miniaturization, portability, and digital intelligence. Several studies have focused on the application of the iridium oxide film (IROF) pH electrodes in water quality monitoring and physiological analysis. The central aim of this work was to review the preparation techniques of the IROF pH electrodes and to expand their application in the field of marine monitoring. The studied methods include electrochemical deposition, electrochemical growth, sputtering deposition, heat treatment, and novel preparation methods. The IROF pH electrodes prepared via these methods are more sensitive, have a wider pH measurement ranges, and can be miniaturized further than traditional glass and pH photometer. Hence, in environmental analysis, combining IROF pH electrodes with wireless technology for the physiological and biochemical analysis of marine organisms, seawater, and sediment pore water is an important development tendency. 相似文献
36.
Carmen FestaSimona De Marino Valentina SepeMaria Valeria D’Auria Giuseppe BifulcoRosa Andrés Maria Carmen TerencioMiguel Payá Cécile DebitusAngela Zampella 《Tetrahedron》2011,67(40):7780-7786
Two new cyclopeptides, perthamides E and F were isolated from the polar extracts of the sponge Theonella swinhoei. The new structures, featuring an unprecedented β-amino acid unit (AHMOA), were determined by interpretation of NMR and MS data. The absolute configuration of the AHMOA residue was proposed on the basis of quantum chemical calculation of NMR chemical shifts. Perthamides were proved to inhibit TNF-α and IL-8 release in primary human keratinocytes cells and therefore could represent potentially leads for the treatment of psoriasis. 相似文献
37.
Chunguang HanYoshi Yamano Fumitoshi KakiuchiKazuhiko Nakamura Daisuke Uemura 《Tetrahedron》2011,67(49):9622-9626
An oxidative cleavage of allyl vic-diols to aldehydes catalyzed by a Grubbs carbene complex using a co-oxidant has been established for the first time, with good yields. The utility of this selective cleavage reaction was demonstrated through the use of two huge marine molecules, symbiodinolide and N-p-BrBz palytoxin. 相似文献
38.
Daniel Francisco Palacios Juan A. Alfonso Haydn Barros John J. LaBrecque Karla Prez Marian R. Lossada 《Radiation measurements》2008,43(1):77-84
A semi-empirical method to determine radionuclide concentrations in large environmental samples without the use of reference material and avoiding the typical complexity of Monte-Carlo codes is proposed. The calculation of full-energy peak efficiencies was carried out from a relative efficiency curve (obtained from the gamma spectra data), and the geometric (simulated by Monte-Carlo), absorption, sample and intrinsic efficiencies for energies between 130 and 3000 keV. The absorption and sample efficiencies were determined from the mass absorption coefficients, whereas the intrinsic efficiency was approximated by an empirical function. The deviations between calculated and experimental efficiencies for a reference material in most cases are less than 10%. Radionuclide activities in marine sediment samples calculated by the proposed method and by the experimental comparative method were not significantly different. This new method can be used for routine environmental monitoring when uncertainties up to 10% are acceptable. 相似文献
39.
论中国海洋砂矿床类型 总被引:1,自引:0,他引:1
阮汀 《宁波大学学报(理工版)》1988,(2)
本文总结了作者二十多年砂矿工作的经验,搜集了国内近三百处海洋砂矿床(点)五十余种矿床类型划分的资料,比照国外同类型矿床,结合我国矿床特征,提出了新的海洋砂矿分类原则,矿床工业类型、成因-形态类型、成矿时代类型和保存类型等的划分系统,以及今后的找矿方向。 相似文献
40.
A concise synthesis of the isolaurepinnacin skeleton 6 was achieved via the intermolecular allylation of the α-acetoxy ether 3 followed by ring-closing metathesis. This methodology was successfully applied to the convergent synthesis of the oxocene 15, an advanced synthetic intermediate for the total synthesis of laurencin. 相似文献