Stimuli-Responsive Lactonization-Based Persulfide Generators

Abstract

Reactive sulfur species (RSS), including thiols, hydrogen sulfide (H2S), persulfides, and polysulfides, play crucial roles in physiological and pathological processes. These species contribute to redox signaling, cellular defence, and metabolic regulation. The generation of RSS within cells occurs through various enzymatic pathways, and enhancement of such species has beneficial effects. Hence, reliable generation of these species upon activation by particular stimuli is necessary. Although several methodologies are known, several generate electrophilic by-products, which are cytotoxic in nature. Hence, to overcome these limitations, we considered the formation of a lactone as a key step in the generation of persulfide, and this strategy is expected to generate persulfide along with a non-electrophilic by-product. Firstly, using a biphenyl-based scaffold, an esterase-sensitive persulfide donor was developed. Upon activation by esterase, this compound produces a persulfide and non-electrophilic lactone as a by-product. Along with the generation, the analytical detection of these species remains challenging due to their reactive and transient nature. Secondary assays are needed to detect persulfide generated by these chemical tools. Since the lactone is fluorescent, this strategy produced a reporter for persulfide as well, eliminating the need for secondary assays for persulfide detection. Symptomatic with persulfide generation, the donor was able to protect cells from oxidative stress. Using a similar biphenyl scaffold, we next prepared a compound that generates persulfide upon entry into cells through 3-mercaptopyruvate sulfurtransferase (3-MST), an enzyme involved in the biosynthesis of persulfide. The compound was found to efficiently generate H2S/persulfide in biochemical assays and permeated cells to enhance persulfides, and the compound was found to promote antioxidant response. Next, to enhance the selectivity from a therapeutic benefit standpoint, the reactive oxygen species (ROS)-activated persulfide generators were synthesized and validated as persulfide generators through 3-MST pathway. We found a good anti-inflammatory response in an animal model for oxidative stress. This strategy was next extended to a known thiol-based radioprotectant WR-1065. This new prodrug undergoes activation by H2O2 and generates WR-1065 and a benign lactone. Together, we have developed distinct approaches for the generation of persulfide, along with non-electrophilic lactone byproducts, and some have an in-built fluorescence reporter. The approaches developed herein will help address important questions regarding the generation and detection of persulfides and understand their therapeutic utility.