Novel, functionalized piperazine derivatives were successfully synthesized and fully characterized by 1H/13C/19F NMR, MS, elemental analysis and lipophilicity. All piperazine compounds occur as conformers resulting from the partial amide double bond. Furthermore, a second conformational shape was observed for all nitro derivatives due to the limited change of the piperazine chair conformation. Therefore, two coalescence points were determined and their resulting activation energy barriers were calculated using 1H NMR. To support this result, single crystals of 1-(4-nitrobenzoyl)piperazine (3a, monoclinic, space group C2/c, a = 24.587(2), b = 7.0726(6), c = 14.171(1) Å, β = 119.257(8)°, V = 2149.9(4) Å3, Z = 4, Dobs = 1.454 g/cm3) and the alkyne derivative 4-(but-3-yn-1-yl)-1-(4-fluorobenzoyl)piperazine (4b, monoclinic, space group P21/n, a = 10.5982(2), b = 8.4705(1), c = 14.8929(3) Å, β = 97.430(1)°, V = 1325.74(4) Å3, Z = 4, Dobs = 1.304 g/cm3) were obtained from a saturated ethyl acetate solution. The rotational conformation of these compounds was also verified by XRD. As proof of concept for future labeling purposes, both nitropiperazines were reacted with [18F]F–. To test the applicability of these compounds as possible 18F-building blocks, two biomolecules were modified and chosen for conjugation either using the Huisgen-click reaction or the traceless Staudinger ligation.
新型功能化哌嗪衍生物成功合成并通过1H/13C/19F NMR、MS、元素分析和亲脂性进行了全面表征。所有哌嗪化合物均以部分酰胺双键引起的构象体形式存在。此外,由于哌嗪椅式构象的变化有限,所有硝基衍生物都观察到了第二种构象形状。因此,确定了两个合并点,并使用1H NMR计算了它们产生的活化能垒。为了支持这一结果,从饱和的乙酸乙酯溶液中获得了1-(4-硝基苯甲酰基)哌嗪(3a,单斜晶系,空间群C2/c,a = 24.587(2),b = 7.0726(6),c = 14.171(1) Å,β = 119.257(8)°,V = 2149.9(4) ų,Z = 4,Dobs = 1.454 g/cm³)和炔烃衍生物4-(丁-3-炔-1-基)-1-(4-氟苯甲酰基)哌嗪(4b,单斜晶系,空间群P21/n,a = 10.5982(2),b = 8.4705(1),c = 14.8929(3) Å,β = 97.430(1)°,V = 1325.74(4) ų,Z = 4,Dobs = 1.304 g/cm³)的单晶。这些化合物的旋转构象也通过XRD得到了验证。为了证明未来标记目的的概念,两种硝基哌嗪与[18F]F–反应。为了测试这些化合物作为可能的18F构建块的适用性,两种生物分子被修饰并选择用于通过Huisgen-点击反应或无痕Staudinger连接进行偶联。