For the fluorescence imaging of biologically active small compounds, the development of compact fluorophores that do not perturb bioactivity is required. Here we report a compact derivative of fluorescent 1,3a,6a-triazapentalenes, 2-isobutenylcarbonyl-1,3a,6a-triazapentalene (TAP-VK1), as a fluorescent labeling reagent. The reaction of TAP-VK1 with various aliphatic thiols proceeds smoothly to afford the corresponding 1,4-adducts in high yields, and nucleophiles other than thiols do not react. After the addition of thiol groups in dichloromethane, the emission maximum of TAP-VK1 shifts to a shorter wavelength and the fluorescence intensity is substantially increased. The utility of TAP-VK1 as a compact fluorescent labeling reagent is clearly demonstrated by the labeling of Captopril, which is a small molecular drug for hypertension. The successful imaging of Captopril, one of the most compact drugs, in this study demonstrates the usefulness of compact fluorophores for mechanistic studies.

对于具有生物活性的小分子化合物的荧光成像，需要开发不会干扰生物活性的紧凑型荧光团。在这里，我们报告了荧光 1,3a,6a-triazapentalene、2-isobutenylcarbonyl-1,3a,6a-triazapentalene (TAP-VK1) 的紧凑型衍生物作为荧光标记试剂。TAP-VK1 与各种脂肪族硫醇的反应顺利进行，以高产率提供相应的 1,4-加合物，硫醇以外的亲核试剂不反应。在二氯甲烷中加入硫醇基后，TAP-VK1 的发射最大值移动到更短的波长并且荧光强度显着增加。TAP-VK1 作为紧凑型荧光标记试剂的效用通过标记卡托普利（一种治疗高血压的小分子药物）得到了清楚的证明。