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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.

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.

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.

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.

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 IC 50 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 R 2 = 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.

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.

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.