Neurodegenerative diseases, including Alzheimer's disease, are marked by cholinergic dysfunction, oxidative stress, and reduced neurotrophic support, which drives the quest for multifunctional therapeutic agents. This pilot study presents four novel monoterpene-aminoadamantane conjugates (MACs 1-4) designed to combine the antioxidant and neuromodulatory characteristics of monoterpenes with the neuroprotective properties of aminoadamantane derivatives. Their physicochemical characteristics, blood-brain barrier permeability, and binding affinity to human acetylcholinesterase (AChE) were evaluated using molecular docking and in silico descriptor analysis. In vivo, the neuroprotective efficacy of the MACs was investigated in a scopolamine-induced dementia model in rats, employing behavioral tests. Biochemical assays conducted in the hippocampus and prefrontal cortex assessed AChE activity, antioxidant enzyme performance, lipid peroxidation levels, total glutathione content, and BDNF concentrations. The findings indicate that MAC1, MAC3, and MAC4 demonstrate favorable calculated blood-brain barrier permeability, strong predicted affinity for AChE, and significant in vivo alleviation of scopolamine-induced memory deficits, in conjunction with improvement of key markers of oxidative stress and cholinergic function. These results show that the structural hybridization of myrtenal with aminoadamantane frameworks produces promising multifunctional ligands that are relevant for Alzheimer's-type neurodegeneration.

Tyrosyl-DNA phosphodiesterase 1 (TDP1) is a DNA repair enzyme that can reduce the efficacy of some anticancer drugs targeting topoisomerase 1 (TOP1) making it a promising target for antitumor therapy when combined with TOP1 poisons. Here we describe the synthesis of a number of adamantane-monoterpene conjugates 20a–g and 21a–g connected through a 1,3,4-thiadiazol-2(3 H )-imine linker, where acyclic, monocyclic, and bicyclic structural types of monoterpenes were used. All the synthesized compounds demonstrated activity against TDP1 in micromolar range, with the most potent inhibitor being compound 21a (IC 50 1.2 μM). The cytotoxic effects of these compounds determined in the HEK293A and HeLa cell lines were low to moderate. These findings imply that such compounds are promising for further development of new TDP1 inhibitors with favorable physicochemical properties.

Multidrug resistance is the dominant obstacle to effective chemotherapy for malignant neoplasms. It is well known that neoplastic cells use a wide range of adaptive mechanisms to form and maintain resistance against antitumor agents, which makes it urgent to identify promising therapies to solve this problem. Hydroxamic acids are biologically active compounds and in recent years have been actively considered to be potentially promising drugs of various pharmacological applications. In this paper, we synthesized a number of hydroxamic acids containing a p-substituted cinnamic acid core and bearing bicyclic pinane fragments, including derivatives of (−)-myrtenol, (+)-myrtenol and (−)-nopol, as a Cap-group. Among the synthesized compounds, the most promising hydroxamic acid was identified, containing a fragment of (−)-nopol in the Cap group 18c. This compound synergizes with cisplatin to increase its anticancer effect and overcomes cisplatin resistance, which may be associated with the inhibition of histone deacetylase 1 and glycolytic function. Taken together, our results demonstrate that the use of hydroxamic acids with a bicyclic pinane backbone can be considered to be an effective approach to the eradication of tumor cells and overcoming drug resistance in the treatment of malignant neoplasms.

Novel monoterpene-based hydroxamic acids of two structural types were synthesized for the first time. The first type consisted of compounds with a hydroxamate group directly bound to acyclic, monocyclic and bicyclic monoterpene scaffolds. The second type included hydroxamic acids connected with the monoterpene moiety through aliphatic (hexa/heptamethylene) or aromatic linkers. An in vitro analysis of biological activity demonstrated that some of these molecules had powerful HDAC6 inhibitory activity, with the presence of a linker area in the structure of compounds playing a key role. In particular, it was found that hydroxamic acids containing a hexa- and heptamethylene linker and (-)-perill fragment in the Cap group exhibit excellent inhibitory activity against HDAC6 with IC50 in the submicromolar range from 0.56 ± 0.01 µM to 0.74 ± 0.02 µM. The results of the study of antiradical activity demonstrated the presence of moderate ability for some hydroxamic acids to scavenge 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2ROO• radicals. The correlation coefficient between the DPPH radical scavenging activity and oxygen radical absorbance capacity (ORAC) value was R2 = 0.8400. In addition, compounds with an aromatic linker based on para-substituted cinnamic acids, having a monocyclic para-menthene skeleton as a Cap group, 35a, 38a, 35b and 38b, demonstrated a significant ability to suppress the aggregation of the pathological β-amyloid peptide 1-42. The 35a lead compound with a promising profile of biological activity, discovered in the in vitro experiments, demonstrated neuroprotective effects on in vivo models of Alzheimer’s disease using 5xFAD transgenic mice. Together, the results obtained demonstrate a potential strategy for the use of monoterpene-derived hydroxamic acids for treatment of various aspects of Alzheimer’s disease.

To date, compounds having an adamantane moiety have found wide application in the pharmaceutical indus-try. Despite the fact that most biologically active adamantyl-bearing derivatives contain substituents in the first position of the adamantane molecule, some derivatives with substituents in the second position have also shown valuable pharmacological properties. While 1-adamantanecarboxylic acid is an inexpensive and commercially available reagent, its 2-substituted analogue is substantially less available, and therefore, the development and optimization of approaches to the synthesis of 2-adamantanecarboxylic acid are of great importance. In this work, a three-stage method for the synthesis of 2-adamantanecarboxylic acid has been optimized, based on the Corey- Chaykovsky reaction of 2-adamantanone with trimethylsulphoxonium iodide in the presence of potassium hy-droxide, followed by acid-catalyzed opening of the oxirane ring and oxidation of aldehyde 9 to the target carbox-ylic acid. The total yield of the target product is 70 %.

Inhibiting tyrosyl-DNA phosphodiesterase 1 (TDP1) is a promising strategy for increasing the effectiveness of existing antitumor therapy since it can remove the DNA lesions caused by anticancer drugs, which form covalent complexes with topoisomerase 1 (TOP1). Here, new adamantane–monoterpene conjugates with a 1,2,4-triazole or 1,3,4-thiadiazole linker core were synthesized, where (+)-and (−)-campholenic and (+)-camphor derivatives were used as monoterpene fragments. The campholenic derivatives 14a–14b and 15a–b showed activity against TDP1 at a low micromolar range with IC50 ~5–6 μM, whereas camphor-containing compounds 16 and 17 were ineffective. Surprisingly, all the compounds synthesized demonstrated a clear synergy with topotecan, a TOP1 poison, regardless of their ability to inhibit TDP1. These findings imply that different pathways of enhancing topotecan toxicity other than the inhibition of TDP1 can be realized.

Alzheimer’s disease (AD) is a neurodegenerative disease associated with memory impairment and other central nervous system (CNS) symptoms. Two myrtenal–adamantane conjugates (MACs) showed excellent CNS potential against Alzheimer’s models. Adamantane is a common pharmacophore for drug design, and myrtenal (M) demonstrated neuroprotective effects in our previous studies. The aim of this study is to evaluate the MACs’ neuroprotective properties in dementia. Methods: Scopolamine (Scop) was applied intraperitoneally in Wistar rats for 11 days, simultaneously with MACs or M as a referent, respectively. Brain acetylcholine esterase (AChE) activity, noradrenaline and serotonin levels, and oxidative brain status determination followed behavioral tests on memory abilities. Molecular descriptors and docking analyses for AChE activity center affinity were performed. Results: M derivatives have favorable physicochemical parameters to enter the CNS. Both MACs restored memory damaged by Scop, showing significant AChE-inhibitory activity in the cortex, in contrast to M, supported by the modeling analysis. Moderate antioxidant properties were manifested by glutathione elevation and catalase activity modulation. MACs also altered noradrenaline and serotonin content in the hippocampus. Conclusion: For the first time, neuroprotective properties of two MACs in a rat dementia model were observed. They were stronger than the natural M effects, which makes the substances promising candidates for AD treatment.

Tyrosyl-DNA phosphodiesterase 1 (Tdp1) is a promising target for anticancer therapy due to its ability to counter the effects topoisomerase 1 (Top1) poison, such as topotecan, thus, decreasing their efficacy. Compounds containing adamantane and monoterpenoid residues connected via 1,2,4-triazole or 1,3,4-thiadiazole linkers were synthesized and tested against Tdp1. All the derivatives exhibited inhibition at low micromolar or nanomolar concentrations with the most potent inhibitors having IC50 values in the 0.35–0.57 µM range. The cytotoxicity was determined in the HeLa, HCT-116 and SW837 cancer cell lines; moderate CC50 (µM) values were seen from the mid-teens to no effect at 100 µM. Furthermore, citral derivative 20c, α-pinene-derived compounds 20f, 20g and 25c, and the citronellic acid derivative 25b were found to have a sensitizing effect in conjunction with topotecan in the HeLa cervical cancer and colon adenocarcinoma HCT-116 cell lines. The ligands are predicted to bind in the catalytic pocket of Tdp1 and have favorable physicochemical properties for further development as a potential adjunct therapy with Top1 poisons.

A number of new chiral bispidines containing monoterpenoid fragments have been obtained. The bispidines were studied as ligands for Ni-catalyzed addition of diethylzinc to chalcones. The conditions for chromatographic analysis by HPLC-UV were developed, in which the peaks of the enantiomers of all synthesized chiral products were separated, which made it possible to determine the enantiomeric excess of the resulting mixture. It was demonstrated that bispidine-monoterpenoid conjugates can be used as the ligands for diethylzinc addition to chalcone C=C double bond but not as inducers of chirality. Besides products of ethylation, formation of products of formal hydrogenation of the chalcone C=C double bond was observed in all cases. Note, that this formation of hydrogenation products in significant amounts in the presence of such catalytic systems was found for the first time. A tentative scheme explaining the formation of all products was proposed.

Hydroxamic acids are one of the most promising and actively studied classes of chemical compounds in medicinal chemistry. In this study, we describe the directed synthesis and effects of HDAC6 inhibitors. Fragments of adamantane and natural terpenes camphane and fenchane, combined with linkers of various nature with an amide group, were used as the CAP groups. Accordingly, 11 original target compounds were developed, synthesized, and exposed to in vitro and in vivo biological evaluations, including in silico methods. In silico studies showed that all synthesized compounds were drug-like and could penetrate through the blood–brain barrier. According to the in vitro testing, hydroxamic acids 15 and 25, which effectively inhibited HDAC6 and exhibited anti-aggregation properties against β-amyloid peptides, were chosen as the most promising substances to study their neuroprotective activities in vivo. All in vivo studies were performed using 5xFAD transgenic mice simulating Alzheimer’s disease. In these animals, the Novel Object Recognition and Morris Water Maze Test showed that the formation of hippocampus-dependent long-term episodic and spatial memory was deteriorated. Hydroxamic acid 15 restored normal memory functions to the level observed in control wild-type animals. Notably, this effect was precisely associated with the ability to restore lost cognitive functions, but not with the effect on motor and exploratory activities or on the level of anxiety in animals. Conclusively, hydroxamic acid 15 containing an adamantane fragment linked by an amide bond to a hydrocarbon linker is a possible potential multitarget agent against Alzheimer’s disease.

Camptothecin derivatives are among the most common drugs used in the treatment of cancer. The mechanism of action of these drugs is associated with inhibiting topoisomerase 1 (Top1), an enzyme that plays an important role in cell division processes. However, there is a number of problems related to this type of therapy, particularly an ability of DNA repair system to remove damage caused by antitumor drugs. Tyrosyl-DNA phosphodiesterase 1 (Tdp1) is considered to play a key role in the repair of DNA lesions, thus preventing cancer cell death. Therefore, developing Tdp1 inhibitors is of great interest in modern medicinal chemistry. Pharmacophore groups have found wide application in medicinal chemistry. On the other hand, modification of natural metabolites is one of the most fruitful methods for the development of potential drugs. In an attempt to combine these approaches, we have synthesized adamantanecarbonylthiosemicarbazide that has been transformed into the corresponding 1,3,4-thiadiazole and 1,2,4-triazole derivatives under alkaline and acidic conditions respectively, followed by the modification of heterocyclic compounds with monoterpenoid residues. All the compounds were found to exhibit inhibitory activity against Tdp1 at micromolar concentrations. Among thiadiazoles, the amides of 3,7-dimethyloctanoic or (-)-myrtenic acids demonstrated the most pronounced activity, IC50 being 0.35±0.05 and 0.45±0.09 μM, respectively. As for triazoles, the best IC50 values were found for compounds containing (-)-nopol (0.57±0.14 μM) and 3,7-dimethyloctanol (0.54±0.09 μM) moieties. It is worth noting that 1,3,4-thiadiazoles tended to demonstrate higher activity compared to 1,2,4-triazoles. This work is supported by the Russian Science Foundation under grant 19-13-00040.

Platinum nanoparticles supported on MgO, Al2O3, ZrO2, TiO2 were utilized for monoterpenoid oximes hydrogenation. Monocyclic menthone and carvone oximes synthesized from bio-derived monoterpenoids with a different structure were used to explore the effect of substrate structure on the reaction regularities. The oximes hydrogenation was carried out under hydrogen atmosphere at 100 °C using methanol as a solvent. Platinum catalysts were prepared by the impregnation methods. The catalysts were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray fluorescence spectroscopy, nitrogen physisorption. Hydrogenation of carvone oxime containing a conjugated oxime group and several reducible functional groups resulted in both hydrogenation and deoximation giving 5-isopropyl-2-methylcyclohexanamine and carvomenthone over Pt/Al2O3 and Pt/ZrO2 catalysts. Menthone oxime hydrogenation over Pt/Al2O3 catalysts with an average particle size of 0.8 nm provided the desired menthylamine formation with the selectivity of 90% at complete oxime conversion. Platinum catalysts based on MgO, ZrO2 and TiO2 enhanced menthone oxime deoximation to menthone.

Eleven amide and thioamide derivatives with monoterpene and adamantine substituents were synthesised. They were tested for their activity against the tyrosyl-DNA phosphodiesterase 1 DNA (Tdp1) repair enzyme with the most potent compound 47a, having an IC50 value of 0.64 µM. When tested in the A-549 lung adenocarcinoma cell line, no or very limited cytotoxic effect was observed for the ligands. However, in conjunction with topotecan, a well-established Topoisomerase 1 (Top1) poison in clinical use against cancer, derivative 46a was very cytotoxic at 5 µM concentration, displaying strong synergism. This effect was only seen for 46a (IC50—3.3 µM) albeit some other ligands had better IC50 values. Molecular modelling into the catalytic site of Tdp1 predicted plausible binding mode of 46a, effectively blocking access to the catalytic site.