Photoisomerizable peptides are promising drug candidates in photopharmacology. While azobenzene‐ and diarylethene‐containing photoisomerizable peptides have already demonstrated their potential in this regard, reports on the use of spiropyrans to photoregulate bioactive peptides are still scarce. This work focuses on the design and synthesis of a spiropyran‐derived amino acid, (S)‐2‐amino‐3‐(6'‐methoxy‐1',3',3'‐trimethylspiro‐[2H‐1‐benzopyran‐2,2'‐indolin‐6‐yl])propanoic acid, which is suitable for the preparation of photoisomerizable peptides. The utility of this amino acid is demonstrated by incorporating it into the backbone of BP100, a known membrane‐active peptide, and by examining the photoregulation of the membrane perturbation by the spiropyran‐containing peptides. The toxicity of the peptides (against the plant cell line BY‐2), their bacteriotoxicity (E. coli), and actin–auxin oscillator modulation ability were shown to be significantly dependent on the photoisomeric state of the spiropyran unit.

Coumarin and its derivatives have emerged as promising candidates in drug discovery. While the activity of coumarins as anticancer agents with different biological targets has been thoroughly investigated, reports on the potential of coumarins in the inhibition of thioredoxin reductase (TrxR) are still scarce. We focus on the design and synthesis of 3,4-unsubstituted coumarin analogues with systematic incorporation of substituents at the fifth to eighth positions of coumarin, which allowed definitive structure–activity relationship analysis to be conducted. In the obtained library, the substitution at the sixth position of the coumarin core with an aromatic or a cyclopropyl group turned out to be more activity enhancing. A bulky aromatic substituent with a large CF₃ group encourages ligand alignment in a manner that enables covalent bond formation with the catalytic TrxR1 residue, according to the docking results. Our observations indicate that the activity of a series of coumarin analogues towards thioredoxin reductase 1 (TrxR1) is dependent on the nature (size and electronic effect) and the position of the substituent and more importantly – the accessibility of the Michael acceptor functionality. Several compounds (with at least 90% inhibition of the rat TrxR1 enzyme at 200 μM concentration) were further examined in in vitro cell-based assays to assess the cytotoxic effects on various cancer cell lines. The analogue 6-(4-(trifluoromethyl)phenyl)-2H-chromen-2-one was selected as the lead compound for further optimization. The results presented herein pave the way for the development of the next generation of coumarin-based TrxR1 inhibitors, where modification of the Michael acceptor moiety and incorporation of different aryl substituents at the sixth position of the coumarin core are planned.

Thioredoxin reductase is an essential enzyme that plays a crucial role in maintaining cellular redox homeostasis by catalyzing the reduction of thioredoxin, which is involved in several vital cellular processes. The overexpression of TrxR is often associated with cancer development. A series of 1,2-dithiolane-4-carboxylic acid analogs were obtained to verify the selectivity of 1,2-dithiolane moiety toward TrxR. Asparagusic acid analogs and their bioisoters remain inactive toward TrxR, which proves the inability of the 1,2-dithiolane moiety to serve as a pharmacophore during the interaction with TrxR. It was found that the Michael acceptor functionality-containing analogs exhibit higher inhibitory effects against TrxR compared to other compounds of the series. The most potent representatives exhibited micromolar TrxR1 inhibition activity (IC₅₀ varied from 5.3 to 186.0 μM) and were further examined with in vitro cell-based assays to assess the cytotoxic effects on various cancer cell lines and cell death mechanisms.