Design, Synthesis and Evaluation of Nitroreductase Activated Hydrogen sulfide Donors

Abstract

Hydrogen sulfide was long considered as a toxic gas, but recently found to play key roles in the physiological processes. Hydrogen sulfide is now recognized as a “gasotransmitter” along with carbon monoxide and nitric oxide. Endogenous production of Hydrogen sulfide in mammals and most bacteria is mainly attributed to Cystathionine-β-synthase (CBS), Cystathionine-γ-lyase (CSE) 3-Mercaptopyruvate sulfurtransferase (3MST) and their bacterial orthologs. Hydrogen sulfide was recently found to play protective role in bacteria against stress induced by antibiotics. The precise mechanism by which this occurs is yet to be understood. Methodologies to relatively enhance Hydrogen sulfide within cells are required. Commercial sources of Hydrogen sulfide mainly include various inorganic sulfide salts like Sodium sulfide and NaHS, which have poor bio-availability and lack of selectivity. A variety of organic Hydrogen sulfide donor molecules have been reported as well but have drawbacks such as: Thiol activated Hydrogen sulfide donors may not be a suitable strategy as thiols are targets of Hydrogen sulfide; Light activated Hydrogen sulfide donors require the use of high intensity light which may not be compatible with certain cellular studies. Our laboratory has developed a series of nitroreductase (NTR) activated Hydrogen sulfide donors that may be suited for reliably enhancing Hydrogen sulfide levels within bacterial cells. However, these donors were found to have low water solubility. In this work, using levulinic acid as the starting material, we developed a general strategy to functionalize these Hydrogen sulfide donors with: (a) a 2-(2-ethoxyethoxy)ethyl group that increased aqueous solubility; (b) a fluorophore that facilitates tracking of this compound within cells; and (c) a sugar which might improve site-directed delivery of Hydrogen sulfide.