In this task, you are given a sentence. You are expected to recognize the name of any form of chemical substances. Although there might be several correct answers, you need to write one of them.

[EX Q]: Synthesis of quinoline derivatives: discovery of a potent and selective phosphodiesterase 5 inhibitor for the treatment of Alzheimer's disease.
[EX A]: quinoline

[EX Q]: Use of the norepinephrine transporter as a reporter gene for non-invasive imaging of genetically modified cells.
[EX A]: norepinephrine

[EX Q]: Liver X Receptors and female reproduction: when cholesterol meets fertility!
[EX A]:
cholesterol