Synthetic modifications of abietane diterpene acids to potent antimicrobial agents.

Among abietane type semisynthetic diterpenoids, a series of quinopimaric and maleopimaric acid derivatives modified at the carboxyl and carbonyl groups, and in ring E were synthesised to obtain new compounds with antimicrobial potency against Mycobacterium tuberculosis H37Rv and key ESKAPE pathogens. It was found that compound 8 exhibited low toxicity to human embryonic kidney cell line HEK-293 (> 32 µg/mL) and showed significant bacteriostatic activity against methicillin-resistant Staphylococcus aureus (MRSA) (MIC ≤ 0.25 µg/mL) and excellent antifungal activity against Cryptococcus neoformans var. grubii (MICs ≤0.25 µg/mL) being ≈4 and ≈30 fold more active than vancomycin and fluconazole. It also showed moderate activity against fungus Candida albicans (MIC ≤ 0.25 µg/mL). Compound 9 inhibited M. tuberculosis H37Rv with MIC of 1.25 µg/mL. The docking studies suggest possible interactions of the leading compounds with the molecular targets.

Synthesis and evaluation of diterpenic Mannich bases as antiviral agents against influenza A and SARS-CoV-2.

A chemical library was constructed based on the resin acids (abietic, dehydroabietic, and 12-formylabietic) and its diene adducts (maleopimaric and quinopimaric acid derivatives). The one-pot three-component CuCl-catalyzed aminomethylation of the abietane diterpenoid propargyl derivatives was carried out by formaldehyde and secondary amines (diethylamine, pyrrolidine, morpholine, and homopiperazine). All compounds were tested for cytotoxicity and antiviral activity against influenza virus A/Puerto Rico/8/34 (H1N1) in MDCK cells and SARS-CoV-2 pseudovirus in BHK-21-hACE2 cells. Among 21 tested compounds, six derivatives demonstrated a selectivity index (SI) higher than 10, and their IC50 values ranged from 0.19 to 5.0 µM. Moreover, two derivatives exhibited potent anti-SARS-CoV-2 infection activity. The antiviral activity and toxicity strongly depended on the nature of the diterpene core and heterocyclic substituent. Compounds 12 and 21 bearing pyrrolidine moieties demonstrated the highest virus-inhibiting activity with SIs of 128.6 and 146.8, respectively, and appeared to be most effective when added at the time points 0-10 and 1-10 h of the viral life cycle. Molecular docking and dynamics modeling were adopted to investigate the binding mode of compound 12 into the binding pocket of influenza A virus M2 protein. Compound 9 with a pyrrolidine group at C20 of 17-formylabietic acid was a promising anti-SARS-CoV-2 agent with an EC50 of 10.97 µM and a good SI value > 18.2. Collectively, our data suggested the potency of diterpenic Mannich bases as effective anti-influenza and anti-COVID-19 compounds.

Synthesis, modification, and biological activity of propargylated methyl dihydroquinopimarates.

The introduction of the alkynyl moiety to the abietane diterpenic core by modification of the cycle E of methyl dihydroquinopimarate is described. The arylpropargyl, aminopropargyl, and 1,2,3-triazole derivatives are synthesized via Sonogashira reaction, Mannich reaction and click-chemistry, correspondingly. The antitumor effect towards the NCI-60 cancer cell line panel and antimicrobial activity against key ESKAPE pathogens of the synthesized compounds were studied in vitro. The cytotoxicity and hemolytic activity of the abietane derivatives was tested using HEK293 human embryonic kidney cell line and the human red blood cells, correspondingly. The methyl dihydroquinopimarate propargyl analogs showed high antitumor activity against leukemia (CCRF-CEM; SR), non-small cell lung cancer (NCI-H522), melanoma (LOX IMVI; MALME-3M), ovarian cancer (IGROV1), and renal cancer (786-0; UO-31) cell lines. The Mannich's diterpene bases with pyrrolidine and diethylamine fragments exhibited fungicidal activity towards Cr. neoformans (MIC= 16 µg/ml), while possessing low toxicity. The described modifications of the abietane diterpenoids have great potential for further development of new cytotoxic and fungicidal compounds.

Evaluation of A-azepano-triterpenoids and related derivatives as antimicrobial and antiviral agents.

A series of semisynthetic triterpenoids with A-ring azepano- and A-seco-fragments as well as hydrazido/hydrazono-substituents at C3 and C28 has been synthesized and evaluated for antimicrobial activity against key ESKAPE pathogens and DNA viruses (HSV-1, HCMV, HPV-11). It was found that azepanouvaol 8, 3-amino-3,4-seco-4(23)-en derivatives of uvaol 21 and glycyrrhetol-dien 22 as well as azepano-glycyrrhetol-tosylate 32 showed strong antimicrobial activities against MRSA with MIC ≤ 0.15 µM that exceeds the effect of antibiotic vancomycin. Azepanobetulinic acid cyclohexyl amide 4 exhibited significant bacteriostatic effect against MRSA (MIC ≤ 0.15 µM) with low cytotoxicity to HEK-293 even at a maximum tested concentration of >20 µM (selectivity index SI 133) and may be considered a noncytotoxic anti-MRSA agent. Azepanobetulin 1, azepanouvaol 8, and azepano-glycyrrhetol 15 showed high potency towards HCMV (EC50 0.15; 0.11; 0.11 µM) with selectivity indexes SI50 115; 136; 172, respectively. The docking studies suggest the possible interactions of the leading compounds with the molecular targets.

Cytotoxic Potential of a-Azepano- and 3-Amino-3,4-SeCo-Triterpenoids.

Semi-synthetic triterpenoids, holding an amino substituted seven-membered A-ring (azepano-ring), which could be synthesized from triterpenic oximes through a Beckmann type rearrangement followed by a reduction of lactame fragment, are considered to be novel promising agents exhibiting anti-microbial, alpha-glucosidase, and butyrylcholinesterase inhibitory activities. In this study, in an attempt to develop new antitumor candidates, a series of A-ring azepano- and 3-amino-3,4-seco-derivatives of betulin, oleanolic, ursolic, and glycyrrhetinic acids were evaluated for their cytotoxic activity against five human cancer cell lines and non-malignant mouse fibroblasts by means of a colorimetric sulforhodamine assay. Azepanoallobetulinic acid amide derivative 11 was the most cytotoxic compound of this series but showed little selectivity between the different human tumor cell lines. Flow cytometry experiments showed compound 11 to act mainly by apoptosis (44.3%) and late apoptosis (21.4%). The compounds were further screened at the National Cancer Institute towards a panel of 60 cancer cell lines. It was found that compounds 3, 4, 7, 8, 9, 11, 15, 16, 19, and 20 showed growth inhibitory (GI50) against the most sensitive cell lines at submicromolar concentrations (0.20-0.94 µM), and their cytotoxic activity (LC50) was also high (1-6 µM). Derivatives 3, 8, 11, 15, and 16 demonstrated a certain selectivity profile at GI50 level from 5.16 to 9.56 towards K-562, CCRF-CEM, HL-60(TB), and RPMI-8226 (Leukemia), HT29 (Colon cancer), and OVCAR-4 (Ovarian cancer) cell lines. Selectivity indexes of azepanoerythrodiol 3 at TGI level ranged from 5.93 (CNS cancer cell lines SF-539, SNB-19 and SNB-75) to 14.89 for HCT-116 (colon cancer) with SI 9.56 at GI50 level for the leukemia cell line K-562. The present study highlighted the importance of A-azepano-ring in the triterpenic core for the development of novel antitumor agents, and a future aim to increase the selectivity profile will thus lie in the area of modifications of azepano-triterpenic acids at their carboxyl group.

Synthesis, structure, and antitumor activity of 2,9-disubstituted perhydro 2,3a,7b,9,10a,14b-hexaazadibenzotetracenes.

Catalytic methods for the synthesis of previously unknown 2,9-disubstituted 3bR*,7aR*,10bR*,14aR*-cis-14c,14d-perhydro-2,3a,7b,9,10a,14b-hexaazadibenzotetracenes have been developed. The structures were established by 1D (1H, 13C) and 2D (COSY, HSQC, HMBC) NMR spectroscopy, MALDI TOF/TOF mass spectrometry, and X-ray diffraction analysis. Primary screening of the synthesized perhydro hexaazadibenzotetracenes for antitumor activity was carried out.