The conversion of the lactone functionality of porpholactones, porphyrin analogs in which a porphyrin β,β'-double bond was replaced by a lactone moiety, to a thionolactone functionality using Lawesson's reagent is described. The resulting novel thionolactones were spectroscopically characterized and their electronic structure defined using experimental (UV-vis, fluorescence, cyclic voltammetry) and theoretical methods (molecular modelling at the B3LYP/6-31G(d) level). The structures of two benchmark thionolactones were determined by single crystal X-ray diffractometry. The idealized planarity of the chromophores rationalize the bathochromically shifted optical spectra of the thionolactones when compared to the lactones on electronic grounds. The thionolactone moiety can be used as a synthetic handle in the preparation of oxazolochlorins using RANEY® nickel-induced hydrodesulfurization reactions. Importantly, the meso-pentafluorophenyl-based porphothionolactone fluoresces by at least a factor of 60 less compared to the corresponding lactone. The hypochlorite-selective conversion of the thionolactone to the lactone is the basis for the use of this thionolactone as a switch-on chemodosimeter for hypochlorite, a widely used disinfectant and molecule of biological significance in some inflammatory processes.

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Various natural polysulfanes (RS x R', x ≥ 3, R ≠ H), such as diallyltrisulfide and diallyltetrasulfide from garlic, are mostly harmless to humans, higher animals and plants, yet highly active against diverse microbes, including several fungi. Such natural organic sulfur compounds (OSCs) possess considerable practical potential against a wide range of agricultural pests. Unfortunately, their use is often hampered due to the inherently offensive smell, chemical instability and low water solubility. However, since the biological activity of polysulfanes is primarily based on their unique sulfur-sulfur motif, it is possible to preserve this motif and to modify the side-chain(s). Ultimately, such changes result in synthetic polysulfanes which retain or even exceed the activity of their natural analogues, and also show improved physico-chemical properties. The resulting acid-, ether-and ester-based tetrasulfanes synthesized as part of this study are odorless and highly active against the grey mold fungus Botrytis cinerea. Some, but not all, of the synthetic polysulfanes are recognized by an active fungal efflux mechanism mediated by the ABC transporter AtrB. Remarkably, some of them even induce transcription of the AtrB-encoding gene, mediated by transcription factor Mrr1. Taken together, the activity of synthetic polysulfanes against B. cinerea, combined with a likely low ecotoxicity of such sulfur compounds, bodes well for possible future applications against this and eventually other agronomically important plant pathogens.

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