2-硝基咪唑是一种重要的医药中间体,可用于合成多种抗癌药物,通过对其结构进行修饰,有望开发新型活性药物分子。以2-氨基嘧啶和3-溴丙酮酸乙酯为起始原料,经过缩合环化、肼解、氧化和取代合成了一系列1-烷基-2-硝基-1 H-咪唑-5-甲酸乙酯...2-硝基咪唑是一种重要的医药中间体,可用于合成多种抗癌药物,通过对其结构进行修饰,有望开发新型活性药物分子。以2-氨基嘧啶和3-溴丙酮酸乙酯为起始原料,经过缩合环化、肼解、氧化和取代合成了一系列1-烷基-2-硝基-1 H-咪唑-5-甲酸乙酯(7a~7d)及其同分异构体1-烷基-2-硝基-1 H-咪唑-4-甲酸乙酯(8a~8d),该方法克服了传统合成路线中氮原子上取代基仅为甲基的局限性。研究不同取代基对2种异构体比例的影响,结果表明:随着取代基团的给电子能力增强,更加有利于化合物7的生成。所有合成化合物的结构都经过1 H NMR,13 C NMR和MS(ESI)确证或表征。展开更多
The integration of rivers and basins highly implies the possible existence of certain relationships between hierarchical characteristics of river networks and primary basin factors.Here we investigated river networks ...The integration of rivers and basins highly implies the possible existence of certain relationships between hierarchical characteristics of river networks and primary basin factors.Here we investigated river networks in two large basins,the Yangtze River and the Yellow River,characterized with basic factors such as annual precipitation,slope,soil erodibility and vegetation.Hierarchical analysis demonstrated a fair self-similarity of river networks at the stream-order 1-5 in both rivers,described by the structural parameters including bifurcation ratio,side-branching ratio,drainage density,and length of headwater-river.Besides precipitation,basin slope was essential in shaping river networks in both basins,showing a significant positive correlation(R^2=0.39-0.85)to bifurcation ratio,side-branching ratio,and drainage density.Given the same basin slope(5°-15°),the higher soil erodibility and sparse vegetation would promote greater side-branching ratio and drainage density in the Yellow River,which were estimated 11.97%and 63.70%larger,respectively than those in the Yangtze River.This study highlights the importance to formulate basin-specific strategies for water and soil conservation in terms of different structures of river networks.展开更多
文摘2-硝基咪唑是一种重要的医药中间体,可用于合成多种抗癌药物,通过对其结构进行修饰,有望开发新型活性药物分子。以2-氨基嘧啶和3-溴丙酮酸乙酯为起始原料,经过缩合环化、肼解、氧化和取代合成了一系列1-烷基-2-硝基-1 H-咪唑-5-甲酸乙酯(7a~7d)及其同分异构体1-烷基-2-硝基-1 H-咪唑-4-甲酸乙酯(8a~8d),该方法克服了传统合成路线中氮原子上取代基仅为甲基的局限性。研究不同取代基对2种异构体比例的影响,结果表明:随着取代基团的给电子能力增强,更加有利于化合物7的生成。所有合成化合物的结构都经过1 H NMR,13 C NMR和MS(ESI)确证或表征。
基金supported by the National Natural Science Foundation of China(Grant No.51721006)
文摘The integration of rivers and basins highly implies the possible existence of certain relationships between hierarchical characteristics of river networks and primary basin factors.Here we investigated river networks in two large basins,the Yangtze River and the Yellow River,characterized with basic factors such as annual precipitation,slope,soil erodibility and vegetation.Hierarchical analysis demonstrated a fair self-similarity of river networks at the stream-order 1-5 in both rivers,described by the structural parameters including bifurcation ratio,side-branching ratio,drainage density,and length of headwater-river.Besides precipitation,basin slope was essential in shaping river networks in both basins,showing a significant positive correlation(R^2=0.39-0.85)to bifurcation ratio,side-branching ratio,and drainage density.Given the same basin slope(5°-15°),the higher soil erodibility and sparse vegetation would promote greater side-branching ratio and drainage density in the Yellow River,which were estimated 11.97%and 63.70%larger,respectively than those in the Yangtze River.This study highlights the importance to formulate basin-specific strategies for water and soil conservation in terms of different structures of river networks.
