Synthesis of spin labels for ESR imaging of living rat head

Spin labels (7, 10, 13, 16, 22, 27) were synthesized from piperidinyloxyl (1), pyrrolidinyloxyl (2), and oxazolidinyloxyl (3). These compounds were injected into the carotid artery of anesthetized rats, and the ESR spectra of the rat brain were immediately recorded by the use of an L-band ESR spectrometer. Based on the spectra obtained, we considered whether or not these spin labels can pass the blood brain barrier and bind to brain tissue components.