Figure 1 CV of 0.1mol/L of LiClO4 in 4 mL of
MeCN and 2 mL of H2O solution containing different
compounds: (a) blank experiment; (b) Sodium p -tolylsulfinate2a (0.8 mmol); (c) Se (0.6 mmol); (d) Indole 1a (0.5
mmol); (e) TBAI (0.5 mmol); (f) Sodium p -tolylsulfinate2a (0.8 mmol), Se (0.6 mmol), Indole 1a (0.5 mmol),
TBAI (0.5 mmol); with a GC disk working electrode, Pt counter electrode,
and Ag/AgCl reference electrode at 0.01 V/s scan rate.
Based on these findings and those of previous
studies,[13] we propose the reaction mechanism
depicted in Scheme 8. Initially, single-electron-transfer (SET)
oxidation of 2a at the anode generates a sulfonyl radicalA that reacts with elemental selenium to generate the free
radical intermediate TsSe• (B ). Subsequently, the radical
addition of 1a with intermediate B gives the radical
species C . Then 3-iodoindoline E is obtained through
radical cross-coupling of C and the iodine radical from the
anodic oxidation of iodine ions. Alternatively, SET oxidation ofC at the anode produces the cation intermediate D that
is quickly attacked by I– to give intermediateE . Subsequent elimination of HI could afford the desired
product 3aa .
Scheme 8 Plausible reaction mechanism
Owing to the unique scaffolding of chalcogenosulfonates, we envision
that the obtained compounds will serve as a promising platform for the
design and discovery of fungicides. A total of 28 chalcogenosulfonates
were tested for in vitro antifungal activity against two
phytopathogenic fungi at 100 μ g/L, using commercialized fungicide
azoxystrobin as positive control agent. As shown in the Supplementary
Information (Table S5), compounds 3ag (79.5% inhibition),3ai (81.2% inhibition), 3al (82.2% inhibition),3bf (83.4% inhibition), 4ae (79.1% inhibition), and5ag (79.7% inhibition) showed better antifungal activities
than azoxystrobin (78.5% inhibition) against Botrytis. cinerea .
Notably, compounds 3ag (86.4% inhibition), 3ai(89.4% inhibition), 3al (92.6% inhibition), 3bf(90.2% inhibition), 4ae (87.9% inhibition), and 5ag(85.5% inhibition) showed potent antifungal activities that were higher
than the activities of azoxystrobin (85.3% inhibition) againstRhizoctonia. solani .
To better understand the antifungal activities of these compounds, the
half maximal effective concentration (EC50) values of
compounds with more than 75% inhibition rate at 100 μg/L were
considered (Figure 2). Compounds 3ai and 4ae showed
the best antifungal activities among 28 chalcogenosulfonates, and their
EC50 values were much lower than those of commercial
azoxystrobin pesticides. These findings enable the adoption of a new
course in studying the biological activity of chalcogen-containing
organic compounds.