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Yun Zhu Michael Stollenz Samuel R. Zarcone Sugam Kharel Hemant Joshi Nattamai Bhuvanesh Joseph H. Reibenspies John A. Gladysz 《Chemical science》2022,13(45):13368
The diphosphine complexes cis- or trans- PtCl2(P((CH2)n)3P ) (n = b/12, c/14, d/16, e/18) are demetalated by MC X nucleophiles to give the title compounds (P((CH2)n)3)P (3b–e, 91–71%). These “empty cages” react with PdCl2 or PtCl2 sources to afford trans- MCl2(P((CH2)n)3P ). Low temperature 31P NMR spectra of 3b and c show two rapidly equilibrating species (3b, 86 : 14; 3c, 97 : 3), assigned based upon computational data to in,in (major) and out,out isomers. These interconvert by homeomorphic isomerizations, akin to turning articles of clothing inside out (3b/c: ΔH‡ 7.3/8.2 kcal mol−1, ΔS‡ −19.4/−11.8 eu, minor to major). At 150 °C, 3b, c, e epimerize to (60–51) : (40–49) mixtures of (in,in/out,out) : in,out isomers, which are separated via the bis(borane) adducts 3b, c, e·2BH3. The configurational stabilities of in,out-3b, c, e preclude phosphorus inversion in the interconversion of in,in and out,out isomers. Low temperature 31P NMR spectra of in,out-3b, c reveal degenerate in,out/out,in homeomorphic isomerizations (ΔG‡Tc 12.1, 8.5 kcal mol−1). When (in,in/out,out)-3b, c, e are crystallized, out,out isomers are obtained, despite the preference for in,in isomers in solution. The lattice structures are analyzed, and the D3 symmetry of out,out-3c enables a particularly favorable packing motif. Similarly, (in,in/out,out)-3c, e·2BH3 crystallize in out,out conformations, the former with a cycloalkane solvent guest inside.It’s not a magic trick. Molecules can turn themselves inside out, just like articles of clothing or other familiar household objects. This behavior is demonstrated for the title compounds through a combination of synthesis, rate, and NMR studies. 相似文献
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Das Pritam Kumar Mallik Arnab Kumar Molla Altaf Hossain Santra Apurba Kumar Ganguly Ranjan Saha Abhijit Kumar Sugam Aswal V. K. 《Journal of Thermal Analysis and Calorimetry》2022,147(10):5617-5635
Journal of Thermal Analysis and Calorimetry - Nanofluids have gained recent attention because of their potential applications in diverse engineering fields like enhancing thermal transport,... 相似文献
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JETP Letters - The magnetic properties of Co-doped CdS has been investigated by ab initio calculations using the GGA + U approximation. The study reveals the ferromagnetic ordering of Co-doped CdS... 相似文献
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Kharel MK Pahari P Shepherd MD Tibrewal N Nybo SE Shaaban KA Rohr J 《Natural product reports》2012,29(2):264-325
Covering: 1997 to 2010. The angucycline group is the largest group of type II PKS-engineered natural products, rich in biological activities and chemical scaffolds. This stimulated synthetic creativity and biosynthetic inquisitiveness. The synthetic studies used five different strategies, involving Diels-Alder reactions, nucleophilic additions, electrophilic additions, transition-metal mediated cross-couplings and intramolecular cyclizations to generate the angucycline frames. Biosynthetic studies were particularly intriguing when unusual framework rearrangements by post-PKS tailoring oxidoreductases occurred, or when unusual glycosylation reactions were involved in decorating the benz[a]anthracene-derived cores. This review follows our previous reviews, which were published in 1992 and 1997, and covers new angucycline group antibiotics published between 1997 and 2010. However, in contrast to the previous reviews, the main focus of this article is on new synthetic approaches and biosynthetic investigations, most of which were published between 1997 and 2010, but go beyond, e.g. for some biosyntheses all the way back to the 1980s, to provide the necessary context of information. 相似文献
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Sugam Kharel Kyle J. Cluff Nattamai Bhuvanesh John A. Gladysz Janet Blümel 《化学:亚洲杂志》2019,14(15):2704-2711
The three secondary phosphine oxides [CH2=CH(CH2)4]2HPO ( 1 ), [CH2=CH(CH2)5]2HPO ( 2 ), and [CH2=CH(CH2)6]2HPO ( 3 ), and two diphosphine dioxides, {[CH2=CH(CH2)6]2PO(CH2)7}2 ( 4 ) and {[CH2=CH(CH2)6]2PO(CH2)4}2 ( 5 ), incorporating long methylene chains, are described. The single crystal X‐ray structures of 1 , 2 , and 5 have been determined. The phosphine oxides 3 , 4 , and 5 have been adsorbed on silica in submonolayer quantities to give 3 a – 5 a . The 1H, 13C, and 31P solid‐state NMR spectra of polycrystalline 3 – 5 have been analyzed and compared with those of 3 a – 5 a . The changes of the solid‐state NMR characteristics upon adsorption and the surface mobilities of the phosphine oxides are discussed. 相似文献
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Fang Cui Gujarati Himali Osinaga Faith Hsia Victor Cheney Marcos A. Kharel Madan K. 《Research on Chemical Intermediates》2021,47(9):3673-3690
Research on Chemical Intermediates - A routine release of slow-degrading agrochemicals in the environment has resulted in their gradual accumulation posing a major threat both to the terrestrial... 相似文献
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Kharel MK Pahari P Shaaban KA Wang G Morris C Rohr J 《Organic & biomolecular chemistry》2012,10(21):4256-4265
The functional roles of all proposed enzymes involved in the post-PKS redox reactions of the biosynthesis of various landomycin aglycones were thoroughly studied, both in vivo and in vitro. The results revealed that LanM2 acts as a dehydratase and is responsible for concomitant release of the last PKS-tethered intermediate to yield prejadomycin (10). Prejadomycin (10) was confirmed to be a general pathway intermediate of the biosynthesis. Oxygenase LanE and the reductase LanV are sufficient to convert 10 into 11-deoxylandomycinone (5) in the presence of NADH. LanZ4 is a reductase providing reduced flavin (FMNH) co-factor to the partner enzyme LanZ5, which controls all remaining steps. LanZ5, a bifunctional oxygenase-dehydratase, is a key enzyme directing landomycin biosynthesis. It catalyzes hydroxylation at the 11-position preferentially only after the first glycosylation step, and requires the presence of LanZ4. In the absence of such a glycosylation, LanZ5 catalyzes C5,6-dehydration, leading to the production of anhydrolandomycinone (8) or tetrangulol (9). The overall results provided a revised pathway for the biosynthesis of the four aglycones that are found in various congeners of the landomycin group. 相似文献