Derivatives of DANPY (Dialkylaminonaphthylpyridinium), a DNA-Binding Fluorophore: Practical Synthesis of Tricyclic 2-Amino-6-bromonaphthalenes by Bucherer Reaction.

A simple and convergent way to synthesize 2-amino-6-bromonaphthalenes involves condensation of free secondary amines with the corresponding 2-naphthol under Bucherer conditions. The amination protocol relies on common Teflon-capped pressure flasks and has been used to modify the tertiary aminonaphthalene core of DANPY, a biocompatible chromophore shown to be safe and effective for staining a variety of cellular targets. Following a Suzuki reaction with pyridine 4-boronic acid, additional diversity is introduced upon N-alkylation to install the pyridinium cation. New DANPY derivatives and intermediates reported herein reflect the modularity of the dye nucleus, including the addition of groups useful for applications in membrane staining and DNA-based biophotonics.

DANPY (dimethylaminonaphthylpyridinium): an economical and biocompatible fluorophore.

Dyes with nonlinear optical (NLO) properties enable new imaging techniques and photonic systems. We have developed a dye (DANPY-1) for photonics applications in biological substrates such as nucleic acids; however, the design specification also enables it to be used for visualizing biomolecules. It is a prototype dye demonstrating a water-soluble, NLO-active fluorophore with high photostability, a large Stokes shift, and a favorable toxicity profile. A practical and scalable synthetic route to DANPY salts has been optimized featuring: (1) convergent Pd-catalyzed Suzuki coupling with pyridine 4-boronic acid, (2) site-selective pyridyl N-methylation, and (3) direct recovery of crystalline intermediates without chromatography. We characterize the optical properties, biocompatibility, and biological staining behavior of DANPY-1. In addition to stability and solubility across a range of polar media, the DANPY-1 chromophore shows a first hyperpolarizability similar to common NLO dyes such as Disperse Red 1 and DAST, a large two-photon absorption cross section for its size, substantial affinity to nucleic acids in vitro, an ability to stain a variety of cellular components, and strong sensitivity of its fluorescence properties to its dielectric environment.