A new series (6) of C₅-curcuminoid derivatives (2E,6E-2,6-dibenzylidene-4-hydroxycyclohexanones) is described here with their evaluation for in vitro antiproliferative activities. Evaluation of 31 compounds against human A2780 (ovarian), C33A (cervix) and MDA-MB-231 (breast) cancer cell lines was performed to obtain structure activity relation data. The best performer was (2E,6E)-2,6-bis(3′-nitrobenzylidene)-4-hydroxycyclohexanone (6h) with IC₅₀ values of 0.68 μM (A2780), 0.69 μM (C33A) and 0.92 μM (MDA-MB-231) compared to cisplatin with 1.30 μM, 3.69 μM and 19.13 μM, respectively. According to calculated physicochemical properties some members in series 6, namely (2E,6E)-2,6-bis[(4′-pyridinyl)methylene]-4-hydroxycyclohexanone (6p) [IC₅₀ = 0.76 μM (A2780), 2.69 μM (C33A), 1.28 μM (MDA-MB-231)] seem to have improved bioavailability compared to curcumin. Selected members of series 6 were involved in circular dichroism spectroscopic measurements in order to determine their interaction with natural DNA. Based on these data, we conclude that these derivatives do not bind to DNA in vitro. A proposal is summarized based on mass spectrometric assessment for fingerprint analysis in biological research of such C₅-curcuminoids.

Parkinson’s disease (PD) is recognized as one of the most common neurodegenerative disorders globally. The primary factor contributing to this condition is the loss of dopaminergic neurons, which results in both motor and nonmotor symptoms. The etiology of neurodegeneration remains unclear. However, it is characterized by the elevated production of reactive oxygen species, which subsequently leads to oxidative stress, lipid peroxidation, mitochondrial dysfunction, and inflammation. The investigation of the applicability of natural compounds and their derivatives to various diseases is becoming increasingly important. The possible role of curcumin from Curcuma longa L. and its derivatives in the treatment of PD has been partially investigated, but there are no data on the action of synthetic cyclic C₅-curcuminoids and chalcones tested in a Parkinson’s model. Two chalcones and five synthetic cyclic C₅-curcuminoids with potential antioxidant properties were investigated in an in vitro model of 6-hydroxydopamine (6-OHDA)-induced neurodegeneration in differentiated SH-SY5Y cells. Reactive oxygen species (ROS) production, total antioxidant capacity, antioxidant enzyme activity, thiol and ATP levels, caspase-3 activity, and cytokine release were examined after treatment with the test compounds. Based on these results, one cyclic chalcone (compound 5) and three synthetic cyclic C₅-curcuminoids (compounds 9, 12, and 13) decreased oxidative stress and apoptosis in our in vitro model of neurodegeneration. Compounds 5 and 9 were also successful in decreasing the production of pro-inflammatory cytokines (IL-6, IL-8, and TNF-α), while promoting the release of anti-inflammatory cytokines (IL-4 and IL-10). These findings indicate that these two compounds exhibit potential antioxidant, anti-apoptotic, and anti-inflammatory properties, rendering them promising candidates for drug development.

Curcumin and natural curcuminoids possess numerous beneficial properties, including antioxidant, antitumor, and anti-inflammatory effects. However, their application is challenging because of instability and rapid metabolism. Cyclic C₅-curcuminoids, a subgroup of curcuminoids, are chemically more stable and less susceptible to hydrolysis or metabolism. In our study, seven synthetic compounds—five cyclic C₅-curcuminoids (compounds 8, 9, 11, 12, and 13) and two cyclic chalcones (compounds 4 and 5)—were examined using an in vitro 6-hydroxydopamine-induced neuronal damage model established with all-trans retinoic acid-differentiated SH-SY5Y and BV-2 microglial cells. The antioxidant, anti-apoptotic (including ferroptosis markers (iron, GSH/GSSG, and malondialdehyde)), apoptotic (PARP, cytochrome c, caspase 9, active caspase-3, and oligonucleosome release), and anti-inflammatory effects of these compounds were also investigated. Compounds 5, 9, 12, and 13 significantly decreased reactive oxygen species production (percentage changes: 5: 28.9%; 9: 32%; 12: 29.8%; 13: 49.2%) and increased antioxidant capacity (percentage changes: 5: 63.4%; 9: 85.8%; 12: 31.2%; 13: 85.9%) and antioxidant enzyme activity (catalase, superoxide dismutase, and glutathione peroxidase) in SH-SY5Y cells. Compounds 5, 9, and 12 decreased microglial activation by downregulating Iba1 expression (fold changes: 5: 0.73; 9: 0.39; 12: 0.33) and decreasing glutamate concentration (percentage changes: 5: 26.5%; 9: 41.2%; 12: 27.3%). Together with compound 13, they reduced pro-inflammatory cytokine (IL-6, TNFα) secretion and induced anti-inflammatory cytokine (IL-10) release in SH-SY5Y and BV-2 cells. Based on these results, the blood–brain barrier penetrations of compounds 5, 9, 12, and 13 were also investigated. The highest blood–brain barrier penetration was observed for compound 12 (P_app value 13.6 × 10⁻⁶ cm/s). Synthetic cyclic C₅-curcuminoids derived from curcumin overcome the limitations of stability and bioavailability and exhibit strong antioxidant, anti-inflammatory, and anti-apoptotic effects, making them promising candidates for treating neurodegenerative diseases.