Curcumin (Cur) is one of the most studied natural polyphenolic compounds, with many pharmacological properties and a luminescent skeleton. Natural fluorescent molecules are peculiar tools in nanomedicine for bioimaging and sensing, and this review focuses on the photophysical properties and applications of Cur in these biomedical fields. The first part of the review opens with a description of the Cur chemical skeleton and its connection with the luminescent nature of this molecule. The 1,6-heptadiene-3,5-dionyl chain causes the involvement of Cur in a keto–enol tautomerism, which influences its solvatochromism. The polyphenolic nature of its skeleton justifies the Cur generation of singlet oxygen and ROS upon photoexcitation, and this is responsible for the photophysical processes that may be related to the photodynamic therapy (PDT) effects of Cur. In the second part of the review, bioimaging based on Cur derivatives is reviewed, with a deeper attention paid to the molecular diagnostic and nano-formulations in which Cur is involved, either as a drug or a source of fluorescence. Theragnostics is an innovative idea in medicine based on the integration of diagnosis and therapy with nanotechnology. The combination of diagnostics and therapy provides optimal and targeted treatment of the disease from its early stages. Curcumin has been involved in a series of nano-formulations exploiting its pharmacological and photophysical characteristics and overcoming its strong lipophilicity using biocompatible nanomaterials. In the third part of the review, modifications of the Cur skeleton were employed to synthesize probes that change their color in response to specific stimuli as a consequence of the trapping of specific molecules. Finally, the methodologies of sensing biothiols, anions, and cations by Cur are described, and the common features of such luminescent probes reveal how each modification of the skeleton can deeply influence its natural luminescence.

In the present study, we focused our attention on Crataegus laciniata Ucria (Rosaceae), which is wild growing in western Sicily (Italy). The chemical profile of the C. laciniata flower’s (CLF) ethanolic (70%) extract showed the presence of both C-flavonoid and O-flavonoid derivatives. Beyond the main metabolites, like hyperoside and vitexin, there are several luteolin derivates, in addition to catechin and epicatechin dimers or trimers. Regarding the antioxidant activities, CLF showed a strong ability to scavenge DPPH and ABTS radicals and a good Fe³⁺-reducing antioxidant power. The investigation into the key enzymes in diabetes showed strong inhibition on α-amylase and α-glucosidase, whereas the skin-whitening properties are linked to inhibitory effects on tyrosinase. Moreover, we employed Danio rerio (zebrafish) for toxicity assessment, as it represents an ideal in vivo model due to its high correlation with humans in response to pharmaceutical and cosmetic testing. Zebrafish embryos exposed to CLF (25–100 µg/mL) showed marked depigmentation compared to phenylthiourea (PTU), in addition to a high survival percentage and the absence of malformations. In conclusion, this experimental study outlines that C. laciniata flowers could be a potential source of bioactive compounds for application in the pharmaceutical and cosmeceutical industries.

Herein, we describe our efforts to identify sigma receptor 1 (S1R) ligands through a screening campaign on our in-house collection of piperidine/piperazine-based compounds. Our investigations led to the discovery of the potent compound 2-[4-(benzyl)-1-piperidin-1-yl]-1-4-(4-phenylpiperazin-1-yl)ethanone (1) with high affinity toward S1R (K_i value of 3.2 nM) that was comparable to reference compound haloperidol (K_i value of 2.5 nM). Functional assay revealed that compound 1 acted as S1R agonist. To decipher the binding mode of this promising S1R ligand as a starting point for further structure-based optimization, we analysed the docking pose by using a S1R-structure derived from cocrystal structures of potent ligands in complex with target protein. The computational study was enriched with molecular dynamic simulations that revealed the crucial amino acid residues that interacted with the most interesting compound 1.

Tyrosinase (EC 1.14.18.1) is implicated in melanin production in various organisms. There is a growing body of evidence suggesting that the overproduction of melanin might be related to several skin pigmentation disorders as well as neurodegenerative processes in Parkinson’s disease. Based on this consideration, the development of tyrosinase inhibitors represents a new challenge to identify new agents in pharmaceutical and cosmetic applications. With the goal of identifying tyrosinase inhibitors from a synthetic source, we employed a cheap and facile preliminary assay using tyrosinase from Agaricus bisporus (AbTYR). We have previously demonstrated that the 4-fluorobenzyl moiety might be effective in interactions with the catalytic site of AbTYR; moreover, the additional chlorine atom exerted beneficial effects in enhancing inhibitory activity. Therefore, we planned the synthesis of new small compounds in which we incorporated the 3-chloro-4-fluorophenyl fragment into distinct chemotypes that revealed the ability to establish profitable contact with the AbTYR catalytic site. Our results confirmed that the presence of this fragment is an important structural feature to improve the AbTYR inhibition in these new chemotypes as well. Furthermore, docking analysis supported the best activity of the selected studied compounds, possessing higher potency when compared with reference compounds.

Tyrosinase inhibition represents an attractive challenge to fight skin hyperpigmentation for medicinal and cosmeceutical application. We have previously provided insights for the development of novel compounds with a specific shape and functional groups interacting with tyrosinases from distinct sources. We chose to employ the Agaricus bisporus tyrosinase (AbTYR) isoform as a cost-effective and rapid screening method prior to carrying out the assay toward human tyrosinase (hTYR). Through this approach, the inhibitor [4-(4-hydroxyphenyl)piperazin-1-yl](2-methoxyphenyl)methanone (MehT-3) has been identified as an effective inhibitor against both TYRs with potency comparable to that of the marketed inhibitor Thiamidol. Continuing our efforts, in this work we designed a focused small series of MehT-3 derivatives that were in silico predicted for their ability to occupy the cavity of AbTYR and hTYR; subsequently, we proceeded with the execution of a very simple and efficient synthetic procedure to obtain the designed compounds. As a result, we obtained potent AbTYR and hTYR inhibitors with affinity values ranging from 5.3 to 40.7 μM. Notably, compounds 2 and 3 emerged as the most promising candidates; they exhibited superior activity against hTYR and demonstrated low toxicity as effective antioxidant agents and sunscreen products. Overall, these achievements further strengthened our computational protocol, which could be effectively applied to develop newer tyrosinase inhibitors.

Targeting melanogenesis through tyrosinase inhibition represents a key therapeutic strategy, highlighting the need for novel molecules capable of modulating melanin synthesis and/or serving as fluorescent probes for cellular and melanoma tracking. In this study, two curcumin (CUR) derivatives, CUR-C3-PP 1 and CUR-CO-PP 2, were designed and successfully synthesized by strategic integration of a 4-(piperazin-1-yl)phenol pharmacophore into CUR skeleton. In vitro enzymatic assays against Agaricus bisporus tyrosinase (AbTYR) revealed that derivatives CUR-C3-PP 1 and CUR-CO-PP 2 amplified the diphenolase inhibitory capacity (IC₅₀ values of 51.20 μM and 12.89 μM, respectively) when compared to parent curcumin (IC₅₀ = 168.57 μM). Notably, CUR-CO-PP 2 emerged as the most potent candidate, significantly eclipsing native CUR and outperforming the standard inhibitor kojic acid (KA). Enzyme kinetics and molecular docking simulations rationalized this enhanced profile, and the mechanism of inhibitory effects for compounds CUR-C3-PP 1 and CUR-CO-PP 2. Cellular assays highlighted that CUR-C3-PP 1 retained functional intrinsic luminescence, displaying selective accumulation and intense fluorescence within the cytoplasm of B16-F10 melanoma cells alongside preferential cytotoxicity. Screening in zebrafish (Danio rerio) embryos confirmed that both derivatives maintain an excellent biocompatibility profile up to 20 μM. In vivo, both compounds elicited robust, dose-dependent depigmentation, with CUR-CO-PP 2 closely approaching the efficacy of the control 1-phenyl-2-thiourea (PTU). Collectively, our findings demonstrate that the imaging and anti-melanogenic properties of curcuminoids can be independently optimized through rational linker modification, establishing CUR-C3-PP 1 as a promising fluorescent tracer for imaging and CUR-CO-PP 2 as a candidate for depigmenting therapies.