Synthesis and bioevaluation of water-soluble ß-cyclodextrin-diterpene acid conjugates.

A series of ß-cyclodextrin (ß-CD)-conjugates were prepared by combining three abietane-type diterpene acids with two azide-functionalized ß-CDs via click chemistry, and the antiviral activity against wild-type and omicron SARS-CoV-2 spike pseudovirus as well as the antibacterial activity against Escherichia coli were investigated. All the synthesised conjugates exhibited no significant cytotoxicity to BHK-21-hACE2 cells with cell viability over 80% at concentration of 15 µM. Among the conjugates, the heptavalent ß-CD-dehydroabietic acid conjugate 6b exhibited higher anti-SARS-CoV-2 activity against the omicron variant compared to the other conjugates. This study suggested that the multivalent diterpene acid derivatives may have potential application against coronaviruses as entry inhibitors.

Diethoxyphosphoryloxy-oleanolic acid is a nanomolar-inhibitor of butyrylcholinesterase.

A series of new betulin, lupeol, erythrodiol, and oleanolic acid phosphoryloxy- and furoyloxy-derivatives has been synthesized and their structure was confirmed by NMR spectroscopy. Synthesized compounds were subjected to Ellman's assays to determine their ability to inhibit the enzymes AChE and BChE. Among them, diethoxyphosphoryloxy-oleanolic acid inhibited BChE with a value of 99%, thereby acting as a mixed-type inhibitor holding very low Ki values of Ki = 6.59 nM and Ki ' = 1.97 nM, respectively.

New Dipterocarpol-Based Molecules with α-Glucosidase Inhibitory and Hypoglycemic Activity.

Dammarane triterpenoids are affordable and bioactive natural metabolites with great structural potential, which makes them attractive sources for drug development. The aim of the study was to investigate the potency of new dipterocarpol derivatives for the treatment of diabetes. Two dammaranes (dipterocarpol and its 20(24)-diene derivative) were modified by a Claisen-Schmidt aldol condensation to afford C2(E)-arylidenes in good yields. The majority of the synthesized compounds exhibited an excellent-to-moderate inhibitory effect toward α-glucosidase (from S. saccharomyces), among them eight compounds showed IC50 values less than 10 µM. 3-Oxo-dammarane-2(E)-benzylidenes (holding p-hydroxy- 3 l and p-carbonyl- 3 m substituents) demonstrated the most potent α-glucosidase inhibition with IC50 0.753 and 0.204 µM, being 232- and 857-times more active than acarbose (IC50 174.90 µM), and a high level of NO inhibition in Raw 264.7 cells with IC50 of 1.75 and 4.57 µM, respectively. An in vivo testing of compound 3 m (in a dose of 20 mg/kg) on a model of streptozotocin-induced T1DM in rats showed a pronounced hypoglycemic activity, the ability to reduce effectively the processes of lipid peroxidation in liver tissue and decrease the excretion of glucose and pyruvic acid in the urine. Compound 3 m reduced the death of diabetic rats and preserved their motor activity.

Evaluation of A-ring hydroxymethylene-amino- triterpenoids as inhibitors of SARS-CoV-2 spike pseudovirus and influenza H1N1.

A set of triterpene A-ring hydroxymethylene-amino-derivatives was synthesized and their antiviral activity was studied. The synthesized compounds were tested for their potential inhibition of SARS-CoV-2 pseudovirus in BHK-21-hACE2 cells and influenza A/PuertoRico/8/34 (H1N1) virus in MDCK cell culture. Compounds 6, 8 and 19 showed significant anti-SARS-CoV-2 pseudovirus activity with EC50 value of 3.20-11.13 µM, which is comparable to the positive control amodiaquine (EC50 3.17 µM). Among them, 28-O-imidazolyl-azepano-betulin 6 and C3-hydroxymethylene-amino-glycyrrhetol-11,13-diene 19 were identified as the lead compounds with SI values of 7 and 10. The binding mode of compound 6 into the RBD domain of SARS-CoV-2 spike glycoprotein (PDB code: 7DK3) by docking and molecular dynamics simulation was investigated.

Antiviral opportunities of Mannich bases derived from triterpenic N-propargylated indoles.

Oleanolic and glycyrrhetic acids alkyne derivatives were synthesized as a result of propargylation of the indole NH-group condensed with the triterpene A-ring, the following aminomethylation led to a series of Mannich bases. The synthesized compounds were tested for their potential inhibition of influenza A/PuertoRico/8/34 (H1N1) virus in Madin-Darby canine kidney (MDCK) cell culture and SARS-CoV-2 pseudovirus in baby hamster kidney-21-human angiotensin-converting enzyme 2 (BHK-21-hACE2) cells. Mannich bases of oleanolic and glycyrrhetic acids N-propargylated indoles 7, 8, and 12 were the most efficacious against influenza virus A with IC50 7-10 µM together with a low toxicity (CC50 > 145 µM) and high selectivity index SI value 20. Indolo-oleanolic acid morpholine amide Mannich base holding N-methylpiperazine moiety 9 showed anti-SARS-CoV-2 pseudovirus activity with EC50 value of 14.8 µM. Molecular docking and dynamics modeling investigated the binding mode of the compounds 7 and 12 into the binding pocket of influenza A virus M2 protein and compound 9 into the RBD domain of SARS-CoV-2 spike glycoprotein.

Antiviral potency of lupane and oleanane alkynyl-derivatives against human cytomegalovirus and papillomavirus.

A library of 18 structurally diverse semisynthetic lupane, oleanane, and ursane types triterpenoids, including C19- or C28-(1,2,3-triazolyl)- and aminomethylated derivatives obtained by the «click¼ reaction with various aromatic and sugar azides or by Mannich reaction with secondary amines, were tested for antiviral activity against HCMV, HSV-1, and HPV-11 types. C28-Triazolyl-derivative with a benzyl substituent of 2,3-indolo-oleanolic acid was the most active against the HCMV virus with EC50 < 0.05 (SI > 81). Lupane 3,28-diacetoxy-triazolyl derivatives with phenyl- and fluorophenyl-fragments possess the highest activity among all screened compounds toward HPV-11 type virus with EC50 values of 2.97 µM and 1.20 µM, SI90 values of 28 and >125, respectively. One can see that modification of triterpenic alkynes to Mannich bases was more efficient in increasing an activity against HSV-1 than their conversion to triazoles.

Inhibitory properties of quinopimaric acid derivatives towards cholinesterases.

A series of new diterpene quinopimaric acid derivatives modified at the hydroxyl group with different pharmacophore fragments has been synthesised and their (along with previously obtained compounds) inhibitory properties towards cholinesterases were studied. Thereby an indole-3-acetyl derivative 7 and a propargyl substituted compound 28 were shown to be excellent and acetylcholinesterase-selective inhibitors. Both compounds inhibited the enzyme as a mixed type inhibitor, and Ki values of 0.41 and 0.44 µM and Ki' values of 0.98 and 2.26 µM were determined. The binding interactions between all active compounds and ligands protein were confirmed through molecular docking study.

Acetylcholinesterase Inhibitory Activity of Modified Lupane, Oleanane, and Ursane A-seco-Triterpenoids.

A series of new lupane, ursane, and oleanane type triterpenic A-seco-derivatives containing bromo-, azido-, alkyne-, 1H-tetrazol-5-yl-, 5-methyloxazol-2-yl-, N-(4-(4-methylpiperazin-1-yl)but-2-yn-1-yl), and a carbonyl group at C2, C24, C28, C30 positions has been synthesized. The bioactivity was evaluated by Ellman's method, and the results showed that most of the compounds displayed moderate acetylcholinesterase inhibitory activities in vitro. Among them, A-seco-derivatives of 28-oxo-allobetuline and betulinic acid with bromo- and azido-groups exhibited the most potent inhibitory activity against AChE. Extra experiments showed methyl 2-cyano-3,4-seco-dibromo- and 2-cyano-3,4-seco-diazido-derivatives of betulinic acid as mixed-type inhibitors, with Ki values as low as Ki =0.18 µM and Ki =0.21 µM, respectively.

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.

Abietic, maleopimaric and quinopimaric dipeptide Ugi-4CR derivatives and their potency against influenza A and SARS-CoV-2.

A set of 12 abietane diterpene derivatives have been synthesised by the Ugi-four component reaction (Ugi-4CR) and tested for cytotoxicity and activity against influenza virus A/Puerto Rico/8/34 (H1N1) and SARS-CoV-2 pseudovirus. Five dipeptide derivatives demonstrated a selectivity index (SI) higher than 10 and IC50 values from 2 to 32 µM against influenza virus. Compound 11 was found to be a lead with SI of 200, and time-of-addition experiments showed the viral entry into the cell and the binding of the virus to the receptor as a possible target. Compound 7 was the only one showed weak anti-SARS-CoV-2 activity with EC50 value of 80.96 µM. Taken together, our data suggest the potency of diterpene acids-Ugi products as new effective anti-influenza compounds.

Synthesis, Anti-Influenza H1N1 and Anti-Dengue Activity of A-Ring Modified Oleanonic Acid Polyamine Derivatives.

A series of sixteen A-ring modified (2,3-indolo-, 2-benzylidene) oleanonic acid derivatives, holding some cyclic amines, linear polyamines and benzylaminocarboxamides at C28, has been synthesized and screened for antiviral activity against influenza A/PuertoRico/8/34 (H1N1) and Dengue virus serotypes of DENV-1, -2, -3, -4. It was found that 28-homopiperazine 2 and 3-N-phthalyl 22 amides of oleanonic acid demonstrated high potency with selectivity index SI 27 (IC50 21 µM) and 42 (IC50 12 µM). Oleanonic acid aminoethylpiperazine amide 6 and C-azepano-erythrodiol 23 appeared to be the most effective compounds against DENV-1 (IC50's 67 and 107 µM) and -2 (IC50's 86 and 68 µM correspondingly) serotypes.

New Molecules of Diterpene Origin with Inhibitory Properties toward α-Glucosidase.

The incidence of diabetes mellitus (DM), one of the most common chronic metabolic disorders, has increased dramatically over the past decade and has resulted in higher rates of morbidity and mortality worldwide. The enzyme, α-Glucosidase (α-GLy), is considered a therapeutic target for the treatment of type 2 DM. Herein, we synthesized arylidene, heterocyclic, cyanoetoxy- and propargylated derivatives of quinopimaric acid (levopimaric acid diene adduct with p-benzoquinone) 1-50 and, first, evaluated their ability to inhibit α-GLy. Among the tested compounds, quinopimaric acid 1, 2,3-dihydroquinopimaric acid 8 and its amide and heterocyclic derivatives 9, 30, 33, 39, 44, with IC50 values of 35.57-65.98 µM, emerged as being good inhibitors of α-GLy. Arylidene 1ß-hydroxy and 1ß,13α-epoxy methyl dihydroquinopimarate derivatives 6, 7, 26-29, thiadiazole 32, 1a,4a-dehydroquinopimaric acid 40 and its indole, nitrile and propargyl hybrids 35-38, 42, 45, 48, and 50 showed excellent inhibitory activities. The most active compounds 38, 45, 48, and 50 displayed IC50 values of 0.15 to 0.68 µM, being 1206 to 266 more active than acarbose (IC50 of 181.02 µM). Kinetic analysis revealed the most active diterpene indole with an alkyne substituent 45 as a competitive inhibitor with Ki of 50.45 µM. Molecular modeling supported this finding and suggested that the indole core plays a key role in the binding. Compound 45 also has favorable pharmacokinetic and safety properties, according to the computational ADMET profiling. The results suggested that quinopimaric acid derivatives should be considered as potential candidates for novel alternative therapies in the treatment of type 2 diabetes.

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.

Azepanodipterocarpol is potential candidate for inhibits influenza H1N1 type among other lupane, oleanane, and dammarane A-ring amino-triterpenoids.

A series of lupane-, oleanane- and dammarane-based triterpenoids with 3ß-amino, A-ring azepano- and 3,4-seco-fragments has been synthesized and evaluated for antiviral activity against influenza A(H1N1) virus. It was found that azepanodipterocarpol 8 and 3ß-amino-28-oxoallobetulin 11 showed antiviral activity with IC50 1.1 and 2.6 µg ml-1, and selectivity index of 19 and 10, respectively.

From Marine Metabolites to the Drugs of the Future: Squalamine, Trodusquemine, Their Steroid and Triterpene Analogues.

This review comprehensively describes the recent advances in the synthesis and pharmacological evaluation of steroid polyamines squalamine, trodusquemine, ceragenins, claramine, and their diverse analogs and derivatives, with a special focus on their complete synthesis from cholic acids, as well as an antibacterial and antiviral, neuroprotective, antiangiogenic, antitumor, antiobesity and weight-loss activity, antiatherogenic, regenerative, and anxiolytic properties. Trodusquemine is the most-studied small-molecule allosteric PTP1B inhibitor. The discovery of squalamine as the first representative of a previously unknown class of natural antibiotics of animal origin stimulated extensive research of terpenoids (especially triterpenoids) comprising polyamine fragments. During the last decade, this new class of biologically active semisynthetic natural product derivatives demonstrated the possibility to form supramolecular networks, which opens up many possibilities for the use of such structures for drug delivery systems in serum or other body fluids.

Development of New Antimicrobial Oleanonic Acid Polyamine Conjugates.

A series of oleanolic acid derivatives holding oxo- or 3-N-polyamino-3-deoxy-substituents at C3 as well as carboxamide function at C17 with different long chain polyamines have been synthesized and evaluated for antimicrobial activities. Almost all series presented good to moderate activity against Gram-positive S. aureus, S. faecalis and B. cereus bacteria with minimum inhibitory concentration (MIC) values from 3.125 to 200 µg/mL. Moreover, compounds possess important antimicrobial activities against Gram-negative E. coli, P. aeruginosa, S. enterica, and EA289 bacteria with MICs ranging from 6.25 to 200 µg/mL. The testing of ability to restore antibiotic activity of doxycycline and erythromycin at a 2 µg/mL concentration in a synergistic assay showed that oleanonic acid conjugate with spermine spacered through propargylamide led to a moderate improvement in terms of antimicrobial activities of the different selected combinations against both P. aeruginosa and E. coli. The study of mechanism of action of the lead conjugate 2i presenting a N-methyl norspermidine moiety showed the effect of disruption of the outer bacterial membrane of P. aeruginosa PA01 cells. Computational ADMET profiling renders this compound as a suitable starting point for pharmacokinetic optimization. These results give confidence to the successful outcome of bioconjugation of polyamines and oleanane-type triterpenoids in the development of antimicrobial agents.

Synthesis of messagenin and platanic acid chalcone derivatives and their biological potential.

The chalcone derivatives of 20-oxo-lupanes have been synthesised and screened for some types of biological activity. Ozonolysis of lupanes afforded 20-oxo-derivatives with the following condensation using different aromatic aldehydes by Claisen‒Schmidt reaction to the target compounds. The E configuration of 19-[3-(pyridin-3-yl)-prop-2-en-1-one]-fragment was established by X-ray analysis. Screening of cytotoxic activity against NCI-60 cancer cell line panel revealed, that messagenin derivative 9 has the highest activity with GI50 value ranged from 0.304 to 0.804 µM. A colorimetric SRB assay revealed for the 2,30-bis-furfurylidene derivative 11 and 30-bromo-20-oxo-29-nor-3,28-diacetoxy-betulin 16 cytotoxic activity against breast carcinoma MCF-7 and ovarian carcinoma A2780 cell lines. Compounds 11 and 13 acted also as inhibitors of the enzyme α-glucosidase (from S. saccharomyces) with IC50 values of 1.76 µM and 3.3 µM thus being 97- and 52-fold more active than standard acarbose. Antiviral potency of compounds 12 and 14 against HCMV, HSV-1 and HPV is also discussed.[Formula: see text].

Allobetulone rearrangement to l8αH,19ßH-ursane triterpenoids with antiviral activity.

Allobetulone E-ring rearrangement under treating with HClO4 in Ac2O under reflux afforded new triterpenoids: 3,28-diacetoxy-21-acetyl-2(3),20(21)-18α,19ßH-ursandiene 3 and 3,28-diacetoxy-2(3),18(19)-oleandiene 4. 18α,19ßH-Ursanes were transformed at A- and E-rings into indolo- and bis-furfurylidene 7 derivatives. Structure elucidation was performed using COSY, NOESY, HSQC and HMBC experiments, and X-Ray analysis for 3. The potential of newly obtained 18α,19ßH-ursanes was evaluated against HCMV and HPV-11, the NCI-60 cancer cell panel and inhibition of α-glucosidase. All of the compounds have shown viral inhibition towards HCMV compared to standard drug Acyclovir. 3ß-Acetoxy-21ß-acetyl-20ß,28-epoxy-18α,19ßН-ursane 1 showed moderate activity (EC50 4.87 µM) towards the HCMV-resistant isolate (GDGr K17) compared to standard drug Cidofovir and was four times more potent than Ganciclovir. Compound 7 inhibited the cell growth of the three melanoma and one colon cancer cell. 3-Oxo-21ß-acetyl-20ß,28-epoxy-18α,19ßН-ursane 5 and compound 7 inhibited α-glucosidase with IC50 28.0 µM and 4.0 µM being from 6 to 44 times more active than acarbose.

Hollongdione arylidene derivatives induce antiproliferative activity against melanoma and breast cancer through pro-apoptotic and antiangiogenic mechanisms.

The use of natural compounds as starting point for semisynthetic derivatives has already been proven as a valuable source of active anticancer agents. Hollongdione (4,4,8,14-tetramethyl-18-norpregnan-3,20-dion), obtained by few steps from dammarane type triterpenoid dipterocarpol, was chemically modified at C2 and C21 carbon atoms by the Claisen-Schmidt aldol condensation to give a series of arylidene derivatives. The anticancer activity of the obtained compounds was assessed on NCI-60 cancer cell panel, revealing strong antiproliferative effects against a large variety of cancer cells. 2,21-Bis-[3-pyridinyl]-methylidenohollongdione 9 emerged as the most active derivative as indicated by its GI50 values in the micromolar range which, combined with its high selectivity index values, indicated its suitability for deeper biological investigation. The mechanisms involved in compound 9 antiproliferative activity, were investigated through in vitro (DAPI staining) and ex vivo (CAM assay) tests, which exhibited its apoptotic and antiangiogenic activities. In addition, compound 9 showed an overall inhibition of mitochondrial respiration. rtPCR analysis identified the more intimate activity at pro-survival/pro-apoptotic gene level. Collectively, the hollongdione derivative stand as a promising therapeutic option against melanoma and breast cancer provided that future in vivo analysis will certify its clinical efficacy.

New Investigations with Lupane Type A-Ring Azepane Triterpenoids for Antimycobacterial Drug Candidate Design.

Twenty lupane type A-ring azepano-triterpenoids were synthesized from betulin and its related derivatives and their antitubercular activity against Mycobacterium tuberculosis, mono-resistant MTB strains, and nontuberculous strains Mycobacterium abscessus and Mycobacterium avium were investigated in the framework of AToMIc (Anti-mycobacterial Target or Mechanism Identification Contract) realized by the Division of Microbiology and Infectious Diseases, NIAID, National Institute of Health. Of all the tested triterpenoids, 17 compounds showed antitubercular activity and 6 compounds were highly active on the H37Rv wild strain (with MIC 0.5 µM for compound 7), out of which 4 derivatives also emerged as highly active compounds on the three mono-resistant MTB strains. Molecular docking corroborated with a machine learning drug-drug similarity algorithm revealed that azepano-triterpenoids have a rifampicin-like antitubercular activity, with compound 7 scoring the highest as a potential M. tuberculosis RNAP potential inhibitor. FIC testing demonstrated an additive effect of compound 7 when combined with rifampin, isoniazid and ethambutol. Most compounds were highly active against M. avium with compound 14 recording the same MIC value as the control rifampicin (0.0625 µM). The antitubercular ex vivo effectiveness of the tested compounds on THP-1 infected macrophages is correlated with their increased cell permeability. The tested triterpenoids also exhibit low cytotoxicity and do not induce antibacterial resistance in MTB strains.