Design, synthesis, and evaluation of nile red analogs for myelin imaging as near-infrared fluorescence probe

Myelination is a fundamental biological process in the vertebrate nervous system. Direct detection and quantification of myelin content in vivo can facilitate diagnosis and therapeutic treatment of myelin-related diseases such as multiple sclerosis. Over the past decade, a series of myelin-specific molecule probes with stilbene structural frame have been developed. Herein, a class of novel Nile Red analogs containing the structure feature similar to stilbene have been designed and synthesized. Their structures were confirmed by 1 H NMR, 13 C NMR, and HRMS analyses. All of them fluoresce in the near-infrared range with emission wavelengths ranging from 651 nm to 691 nm. In vitro assays revealed that these compounds can specifically bind to myelinated fibers and 9-diethylamino-1-methylamino-5H-benzo[a]phenoxazin-5-one ( 20 , 1-MeNHNR ) was screened as lead compound. Ex vivo imaging and in vivo near-infrared fluorescence (NIRF) imaging demonstrated that 1-MeNHNR is a promising NIRF probe for myelin imaging. Seven novel nile red derivatives with similar stilbene structure and two amino groups have been synthesized. Lead compound 1-MeNHNR was screened and proven to be a potential near-infrared fluorescence probe for myelin imaging. • New nile red derivatives with similar stilbene structural frame and two amino groups were synthesized. • All of them fluoresces in the near-infrared range and can specifically bind to myelinated fibers. • 1-MeNHNR was screened as lead compound and proven to be a promising near-infrared fluorescence probe for myelin imaging.