Two novel structural types of tyrosyl-DNA phosphodiesterase 1 (TDP1) inhibitors with hexahydroisobenzofuran 11 and 3-oxabicyclo [3.3.1]nonane 12 scaffolds were discovered. These monoterpene-derived compounds were synthesized through preliminary isomerization of (+)-3-carene to (+)-2-carene followed by reaction with heteroaromatic aldehydes. All the compounds inhibit the TDP1 enzyme at micro- and submicromolar levels, with the most potent compound having an IC₅₀ value of 0.65 μM. TDP1 is an important DNA repair enzyme and a promising target for the development of new chemosensitizing agents. A panel of isogenic clones of the HEK293FT cell line knockout for the TDP1 gene was created using the CRISPR-Cas9 system. Cytotoxic effects of topotecan (Tpc) and non-cytotoxic compounds of the new structures were investigated separately and jointly in the TDP1 gene knockout cells. For two TDP1 inhibitors, 11h and 12k, a synergistic effect was observed with Tpc in the HEK293FT cells but was not found in TDP1 −/− cells. Thus, it is likely that the synergistic effect is caused by inhibition of TDP1. Synergy was also found for 11h in other cancer cell lines. Thus, sensitizing cancer cells using a non-cytotoxic drug can enhance the efficacy of currently used pharmaceuticals and, concomitantly, reduce toxic side effects.

The ability of actinobacteria of the genus Rhodococcus to biotransform the monoterpenoid (–)-isopulegol has been established for the first time. R. rhodochrous strain IEGM 1362 was selected as a bacterium capable of metabolizing (–)-isopulegol to form new, previously unknown, 10-hydroxy (2) and 10-carboxy (3) derivatives, which may presumably have antitumor activity and act as respiratory stimulants and cancer prevention agents. In the experiments, optimal conditions were selected to provide the maximum target catalytic activity of rhodococci. Using up-to-date (TEM, AFM-CLSM, and EDX) and traditional (cell size, roughness, and zeta potential measurements) biophysical and microbiological methods, it was shown that (–)-isopulegol and halloysite nanotubes did not negatively affect the bacterial cells. The data obtained expand our knowledge of the biocatalytic potential of rhodococci and their possible involvement in the synthesis of pharmacologically active compounds from plant derivatives.

Background: This study explored the biotransformation of (–)-isopulegol using immobilized cells of Rhodococcus rhodochrous IEGM 1362 to optimize the production of new bioactive compounds. Methods: An efficient biocatalyst based on R. rhodochrous IEGM 1362 cells immobilized in a macroporous polyvinyl alcohol (PVA) cryogel matrix was developed for the production of bioactive derivatives of (–)-isopulegol. The biological characteristics of the immobilized cells were investigated using scanning and transmission electron microscopy and energy-dispersive X-ray spectroscopy methods. Results: The use of the biocatalyst increased the overall yield of target products from 54% with free cells to 87% with immobilized cells in a single cycle. Major derivatives identified included (1R,2S,5R)-5-(hydroxymethyl)-2-(prop-1-en-2-yl)cyclohexanol and (1R,3R,4S)-3-hydroxy-4-(prop-1-en-2-yl)cyclohexanecarboxylic acid, both exhibiting potential pharmacological activity. The biocatalyst retained functional activity toward monoterpenoid over 13 exploitation cycles, meeting industrial biotechnology requirements. Immobilized cells were characterized by the absence of endogenous reserve inclusions (in particular lipids) and a high intracellular iron content. Conclusions: The developed immobilized biocatalyst is promising for scaling up the production of biologically active compounds.

The development of highly efficient methods for the synthesis of chemical products by using renewable raw materials is one of the topical areas of medicinal chemistry. The paper presents the synthesis of (2aR,2a¹S,5aR,9bR)-4-isopropyl-7,8-dimethoxy-2a¹-methyl-2,2a,2a¹,3,5a,9b-hexahydrofluoreno[9,1-bc]furan. The title compound was obtained through Prins–Friedel–Crafts cascade reactions of trans-4-hydroxymethyl-2-carene, which was synthesized from 3-carene, one of the main components of gum turpentine. The product yield after purification was 48%. The compound’s structure was confirmed by X-ray diffraction analysis.