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A new application of solid-supported reagents was developed to separate the alkylated N7/N9 regioisomers derived from commercially available 2-amino-6-chloropurine. Simple filtration through an alumina/H+ pad or scavenging by AG/Dowex-50W-X8 resin provides diverse N9 regioisomers selectively in moderate yields with high purities (>90%). This purification method can be conveniently used in a high-throughput format and facilitates the synthesis of a purine library without laborious regioisomer separation and aqueous work-up. The first library synthesis of 6,9-disubstituted purines is reported using the combination of this novel separation method in conjunction with polymer-supported reagents. 相似文献
2.
在前文工作的基础上,结合MNDO/EHMO分子轨道方法和自然杂化轨道方法,具体计算了CC键和CP键的核自旋偶合常数.计算结果表明,1JCC和1JCP主要由成键原子的轨道杂化作用和键极性这两种结构因素所决定.为从简单价键理论角度解释和计算1JCC和1JCP值提供了简便直观的方法. 相似文献
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Crowley BM Mori Y McComas CC Tang D Boger DL 《Journal of the American Chemical Society》2004,126(13):4310-4317
The first total synthesis of the ristocetin aglycon is described employing a modular and highly convergent strategy. An effective 12-step (12% overall) synthesis of the ABCD ring system 3 from its amino acid subunits sequentially features an intramolecular aromatic nucleophilic substitution reaction for formation of the diaryl ether and closure of the 16-membered CD ring system (65%), a respectively diastereoselective (3:1, 86%) Suzuki coupling for installation of the AB biaryl linkage on which the atropisomer stereochemistry can be further thermally adjusted, and an effective macrolactamization (51%) for closure of the 12-membered AB ring system. A similarly effective 13-step (14% overall) synthesis of the 14-membered EFG ring system 4 was implemented employing a room-temperature intermolecular S(N)Ar reaction of an o-fluoronitroaromatic for formation of the FG diaryl ether (69%) and a key macrolactamization (92%) with formation of the amide linking residues 1 and 2. The two key fragments 3 and 4 were coupled, and the remaining 16-membered DE ring system was closed via diaryl ether formation to provide the ristocetin tetracyclic ring system (15 steps, 8% overall) enlisting an unusually facile (25 degrees C, 8 h, DMF, >/=95%) and diastereoselective (>/=15:1) aromatic nucleophilic substitution reaction that benefits from substrate preorganization. 相似文献
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Kathleen E. Duncan Ravindra Kolhatkar Ganesh Subramaniam Ramesh Narasimhan Eleanor Jennings Susan Hettenbach Amanda Brown Charles McComas William Potter Kerry Sublette 《Applied biochemistry and biotechnology》1999,78(1-3):421-434
A remote site in the Tallgrass Prairie Preserve (Osage County, OK) was contaminated with crude oil by a pipeline break in
1992. In 1996, the contaminated soil was bioremediated by blending with uncontaminated soil, prairie hay, buffalo manure,
and commercial fertilizers, and spreading in a shallow layer over uncontaminated soil to create a landfarm. The landfarm was
monitored for two years for aerobic and anaerobic bacteria, soil gases indicative of microbial activity, and for changes in
the concentration of total petroleum hydrocarbons (TPH). Levels of hydrocarbon degraders and soil gas indicators of aerobic
degradation were stimulated in the landfarm during the first warm season relative to uncontaminated prairie soil. However,
these same indicators were less conclusive during the second warm season, indicating depletion of the more easily degradable
hydrocarbons, although the landfarm still contained 6,800 mg/kg TPH on the average at the beginning of the second warm season.
Methane formation and methanogen counts were clearly stimulated in the first warm season relative to uncontaminated prairie
soil, in dicating that methanogenesis plays an important role in the mineralization of hydrocarbons even in these shallow
soils. 相似文献
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[reaction: see text] The madindolines are believed to inhibit cytokine signaling through the gp130 receptor. Model compounds of madindolines were synthesized and tested for thiol reactivity. The heterocyclic moiety of madindoline was shown to form thiol adducts via the Savige-Fontana reaction. The enedione moiety was found to be unreactive toward simple thiols unless the quaternary center was removed. Using the powerful Moore reaction, we have synthesized (+/-)-madindoline A and B in 11 steps. 相似文献
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Shuwen He Peng Li Xing Dai Hong Liu Zhong Lai Dong Xiao Casey C. McComas Chunyan Du Yuehui Liu Jingjun Yin Qun Dang Nicolas Zorn Xuanjia Peng Ravi P. Nargund Anandan Palani 《Tetrahedron letters》2017,58(14):1373-1375
We report a general approach for the synthesis of 5,6-dihydroindolo-naphthyridine ring system via an intramolecular cyclization of the indole NH to an alkene moiety as the key step. 相似文献
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This paper provides an overview of blended science instruction, a term used to represent instructional plans by which the science disciplines are connected to each other and occasionally to other school subjects. The central rationales for such instruction, the historical development of blended instructional plans, and a review of the current proponents and forms of such instruction are provided. The primary varieties of blended instruction, including integrated, unified, and coordinated science, are compared and contrasted. Special attention is given to the major recommendations in support of blended science coming from philosophical, psychological, pedagogical, and pragmatic domains. The conclusions section includes some of the challenges facing those who plan an integrated teaching focus. 相似文献
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赵乃良 《高校应用数学学报(A辑)》1996,(1):91-96
Nira Dyn等提出的四点插值法是一种典型的自由曲线离散造型方法,但该方法不能控制插值点的切向。本文利用薄板样很可能 量的极小化原理给出了具有切向控制的四点分插值条件。用户可以方便地交互控制任一插值点的切向,使得四点插值法更为有效和实用。 相似文献
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E and Z 2-phenylcyclopropyl bromides react with the title reagents to yield E and Z cinnamyl acetates respectively. No reaction is observed when halide nucleophiles or other aprotic solvents are used suggesting a novel mechanistic role for the acetate ion. 相似文献