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NMR-based investigations of acyl-functionalized piperazines concerning their conformational behavior in solution

机译：基于NMR的酰基官能化哌嗪在溶液中的构象行为的研究

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Selected N -benzoylated piperazine compounds were synthesized to study their conformational behavior using temperature-dependent ~(1) H NMR spectroscopy. All investigated piperazines occur as conformers at room temperature resulting from the restricted rotation of the partial amide double bond. In the case of selected mono- N -benzoylated and unsymmetrically N , N ′-substituted derivatives, the appearance of the ~(1) H NMR spectrum was further shaped by the limited interconversion of the piperazine chair conformations. Therefore, two different coalescence points T _(C) were determined and their resulting activation energy barriers Δ G ~(?) were calculated to be between 56 and 80 kJ mol ~(?1) . In most of the cases, T _(C) and Δ G ~(?) for the amide site appeared to be higher than the corresponding values for the ring inversion. The influences of substituents on rotational and inversion barriers were analyzed by correlation to Hammett constants. The obtained results are discussed and interpreted in the context of literature data. An additional aryl substituent connected at the amine site led to reduced rotational and inversion barriers compared to the free secondary amine. To support and evidence the findings from the NMR analyses, single crystals of selected piperazines were obtained and XRD analyses were performed. To underline the results, two potential TGase 2 inhibitors were investigated showing energy barriers with similar values.
机译：合成了所选的N-苯甲酰化哌嗪化合物，以使用温度依赖性〜（1）H NMR光谱研究其构象行为。由于部分酰胺双键的受限旋转，所有研究的哌嗪在室温下均以构象形式存在。在选择的单-N-苯甲酰化和不对称的N，N'-取代的衍生物的情况下，〜（1）H NMR谱的出现通过哌嗪椅构象的有限互变而进一步成形。因此，确定了两个不同的聚结点T_（C），并且计算出它们产生的活化能垒ΔG〜（η）在56和80kJ mol〜（？1）之间。在大多数情况下，酰胺位点的T _（C）和ΔG〜（η）似乎高于环反转的相应值。通过与Hammett常数的相关性分析了取代基对旋转和反转壁垒的影响。在文献数据的上下文中讨论和解释了获得的结果。与游离仲胺相比，在胺位点连接的另一个芳基取代基导致旋转和转化障碍的减少。为了支持和证明NMR分析的结果，获得了所选哌嗪的单晶，并进行了XRD分析。为了强调结果，研究了两种潜在的TGase 2抑制剂，它们显示出具有相似值的能垒。

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