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21.
A new cyclic depsipeptide stereocalpin A (1) has been isolated from the MeOH extract of the Antarctic lichen Stereocaulon alpinum by various chromatographic methods. The structure of stereocalpin A (1) was mainly determined by analysis of the NMR spectroscopic data and by chemical methods. Stereocalpin A (1) is a unique cyclic peptide incorporating an unprecedented 5-hydroxy-2,4-dimethyl-3-oxo-octanoic acid in the structure. Stereocalpin A (1) shows moderate cytotoxicity against three human solid tumor cell lines. 相似文献
22.
Let , 1?μ?n, be a polynomial of degree n such that p(z)≠0 in |z|<k, k>0, then for 0<r?R?k, Dewan, Yadav and Pukhta [K.K. Dewan, R.S. Yadav, M.S. Pukhta, Inequalities for a polynomial and its derivative, Math. Inequal. Appl. 2 (2) (1999) 203-205] proved
23.
Alison Domzalski Liliana Margent Valeria Vigo Faizunnahar Dewan Naga Vara Kishore Pilarsetty Yujia Xu Akira Kawamura 《Molecules (Basel, Switzerland)》2021,26(19)
2,5-diketopiperazines (DKPs) are cyclic dipeptides ubiquitously found in nature. In particular, cyclo(Phe-Pro), cyclo(Leu-Pro), and cyclo(Val-Pro) are frequently detected in many microbial cultures. Each of these DKPs has four possible stereoisomers due to the presence of two chirality centers. However, absolute configurations of natural DKPs are often ambiguous due to the lack of a simple, sensitive, and reproducible method for stereochemical assignment. This is an important problem because stereochemistry is a key determinant of biological activity. Here, we report a synthetic DKP library containing all stereoisomers of cyclo(Phe-Pro), cyclo(Leu-Pro), and cyclo(Val-Pro). The library was subjected to spectroscopic characterization using mass spectrometry, NMR, and electronic circular dichroism (ECD). It turned out that ECD can clearly differentiate DKP stereoisomers. Thus, our ECD dataset can serve as a reference for unambiguous stereochemical assignment of cyclo(Phe-Pro), cyclo(Leu-Pro), and cyclo(Val-Pro) samples from natural sources. The DKP library was also subjected to a biological screening using assays for E. coli growth and biofilm formation, which revealed distinct biological effects of cyclo(D-Phe-L-Pro). 相似文献
24.
Photochemical cyclization of 3 afforded 5, 4 and 8.5 on LAH reduction furnished (±)-glaucine (6) and on treatment with ethanolic HCl afforded (±)-norglaucine (7). 10 obtained by the photocyclization of 9 was converted into 7 and 11 via 12. 相似文献
25.
S. I. Yun Ki-Dong Oh Kwon-Sang Ryu Chang-Geon Kim H. L. Park H. J. Seo Chae Kum 《Applied physics. B, Lasers and optics》1986,40(2):95-98
We have used a modified photothermal probe beam deflection system with a back pumping configuration for the measurements of the temperature-dependent thermal diffusivity of atmospheric air. The results are consistent and reasonably well agree with the literature values. The measured thermal diffusivity values are the same for the same measuring temperature regardless of the beam offsets and the deflecting surface temperatures. For the gas with known temperature-dependent thermal diffusivity, this method can be used to deduce the temperature of a gas from the measured thermal diffusivity value. 相似文献
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Roy Debasish Siraz M. M. Mahfuz Dewan Md. Jafor Pervin S. Rahman A. F. M. Mizanur Khandaker Mayeen Uddin Yeasmin S. 《Journal of Radioanalytical and Nuclear Chemistry》2022,331(3):1299-1307
Journal of Radioanalytical and Nuclear Chemistry - A study was conducted to assess the concentrations of primordial radionuclides in fifteen sandy soil samples collected from a newly discovered... 相似文献
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29.
Dawson F.P. Dewan S.B. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1990,18(1):119-126
A discussion is presented of the protection of the tokamak fusion reactor neutral-beam ion source, located at the Princeton Plasma Physics Laboratory. The system design is based on three operational protection requirements that include provisions for ion-source current pulse matching, ion-source fault current extinction, and metallic fault current extinction. A power circuit configuration satisfying these requirements is illustrated and briefly described. Simplified analytical expressions relating the protection requirements to the circuit parameters are developed. Experimental findings are in good agreement with a computer simulation of the circuit model, although several side effects introduced by the circuit configuration have been observed. The side effects observed include ion-source current overshoot and the existence of a negative ion source current. Modifications to counteract these side effects are briefly described 相似文献
30.
The resonant cross sections for weak production of nucleon resonances is extracted from experimental data on high energy \(\bar v\) -collisions and compared with predictions of theoretical models. 相似文献