Synthesis and antimycobacterial activity of triterpeni≿ A-ring azepanes

Recent advances in the chemistry and biology of oleanolic acid and its derivatives

The pentacyclic triterpenes represent a significant class of plant bioactives with a variety of structures and a wide array of biological activities. These are biosynthetically produced via the mevalonate pathway although occasionally mixed pathways may also occur to introduce structural divergence. Oleanolic acid is one of the most explored bioactive from this class of compounds and possesses a broad spectrum of pharmacological and biological activities including liver protection, anti-cancer, atherosclerosis, anti-inflammation, antibacterial, anti-HIV, anti-oxidative, anti-diabetic etc. This review provides an overview of the latest research findings, highlighting the versatile medicinal and biological potential of oleanolic and its future prospects.

Synthesis of methotrexate-betulonic acid hybrids and evaluation of their effect on artificial and Caco-2 cell membranes

An efficient protocol for the synthesis of novel methotrexate-betulonic acid hybrids with a (tert-butoxycarbonylamino)-3,6-dioxa-8-octanamine (Boc-DOOA) linkage has been developed. Reaction of N-(2-(2-(2-aminoethoxy)ethoxy)ethyl)-betulonamide with methotrexate resulted in a mixture of isomeric conjugates which were separated by column chromatography. Their structures and composition have been fully established by 1H NMR, 13C spectra, FAB mass spectrometry and elemental analysis. The identity of conjugates was confirmed by LC-MS data. Membranotropic properties of the new hybrids were assessed on the basis of their interactions with artificial lipid membranes by differential scanning calorimetry (DSC) method. The ability of the conjugates to penetrate Caco-2 cells is inferior to methotrexate. Probably, this is due to the increasing lipophilicity, the affinity of these hybrid molecules for the lipid bilayer increases, which is confirmed by experiments with artificial membranes.

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.

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 3β-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 3β-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.

Synthesis of imidazo[1,2-a]benzoazepines by alkyne-carbonyl-metathesis

Imidazo[1,2-a]benzoazepines were prepared in good yields by combination of Pd catalyzed cross coupling reactions with alkyne-carbonyl metathesis (ACM).

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.

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.

The Introduction of Hydrazone, Hydrazide, or Azepane Moieties to the Triterpenoid Core Enhances an Activity Against M. tuberculosis

BACKGROUND

Triterpenoids exhibit a wide spectrum of antimicrobial activity.

OBJECTIVE

The objective of this study was to synthesize a series of nitrogen derivatives based on lupane, oleanane, and ursane triterpenoids with high antitubercular activity.

METHODS

Isonicotinoylhydrazones were prepared via the reaction of 3-oxotriterpenic acids or betulonic aldehyde with isoniazid (INH) in yields of 54-72%. N-Acylation of betulonic or azepanobetulinic acids led to lupane C28 hydrazides and dihydrazides. The derivatives were evaluated for their in vitro antimycobacterial activities against Mycobacterium tuberculosis (MTB) H37RV and single-drug resistance (SDR)-TB in the National Institute of Allergy and Infectious Diseases, USA. Molecular docking was performed to evaluate the possible binding modes of investigated compounds in the active site of Diterpene synthase (Rv3378c).

RESULTS

The obtained compounds are represented by C3 or C28 conjugates with hydrazine hydrate or INH. Some compounds demonstrated from high minimum inhibitory concentration (MIC ≤ 10 μg/mL) to excellent (MICs from 0.19 to 1.25 μg/mL) activity against MTB H37RV. Two lupane conjugates with INH were the leading compounds against MTB H37RV and some SDR-strains with MICs ranged from 0.19 to 1.70 μg/mL. Molecular docking of active compounds to diterpene synthase showed that these moieties accommodate the active site of the enzyme.

CONCLUSION

It was revealed that the conjugation of lupanes with INH at C3 is more effective than at C28 and the lupane skeleton is preferable among oleanane and ursane types. The replacement of native hexacarbocyclic A ring to seven-member azepane ring is favorably for inhibition of both MTB H37RV and SDR-strains. These data could possibly mean that the antitubercular activity against INH-resistant strains (INH-R) came from both triterpenoid and isoniazid parts of the hybrid molecules. Azepanobetulin showed the highest activity against both INH-R strains in comparison with other triterpenoids and INH. Thus, the introduction of hydrazone, hydrazide (dihydrazide), or azepane moieties into the triterpenoid core is a promising way for the development of new anti-tubercular agents.

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.

Evaluation of Cytotoxicity and α-Glucosidase Inhibitory Activity of Amide and Polyamino-Derivatives of Lupane Triterpenoids

A series of two new and twenty earlier synthesized branched extra-amino-triterpenoids obtained by the direct coupling of betulinic/betulonic acids with polymethylenpolyamines, or by the cyanoethylation of lupane type alcohols, oximes, amines, and amides with the following reduction were evaluated for cytotoxicity toward the NCI-60 cancer cell line panel, α-glucosidase inhibitory, and antimicrobial activities. Lupane carboxamides, conjugates with diaminopropane, triethylenetetramine, and branched C3-cyanoethylated polyamine methyl betulonate showed high cytotoxic activity against most of the tested cancer cell lines with GI50 that ranged from 1.09 to 54.40 µM. Betulonic acid C28-conjugate with triethylenetetramine and C3,C28-bis-aminopropoxy-betulin were found to be potent micromolar inhibitors of yeast α-glucosidase and to simultaneously inhibit the endosomal reticulum α-glucosidase, rendering them as potentially capable to suppress tumor invasiveness and neovascularization, in addition to the direct cytotoxicity. Plausible mechanisms of cytotoxic action and underlying disrupted molecular pathways were elucidated with CellMinner pattern analysis and Gene Ontology enrichment analysis, according to which the lead compounds exert multi-target antiproliferative activity associated with oxidative stress induction and chromatin structure alteration. The betulonic acid diethylentriamine conjugate showed partial activity against methicillin-resistant S. aureus and the fungi C. neoformans. These results show that triterpenic polyamines, being analogs of steroidal squalamine and trodusquemine, are important substances for the search of new drugs with anticancer, antidiabetic, and antimicrobial activities.

Antimycobacterial activity of azepanobetulin and its derivative: In vitro, in vivo, ADMET and docking studies

The antimycobacterial investigation of azepanobetulin and its amide derivative was performed. Both compounds showed increased in vitro antibacterial activity on the H37Rv MTB strain in aerobic and anaerobic conditions. Basing on differences between MIC and IC₅₀ values a predominant bactericidal effect for amide in contrast to azepanobetulin with a bacteriostatic antibacterial mechanism is defined. Both compounds showed a strong antibacterial effect against resistant MTB strains with amide derivative being slightly more active. Amide derivative also showed a higher antibacterial potency against non-tuberculous mycobacterial strains (M. avium, M. abscessus). Molecular docking studies showed that the inhibition of tuberculosinyl adenosine transferase (Rv3378c) could constitute an antimycobacterial mechanism of action for these triterpenic azepane derivatives. The pharmacokinetic profile was evaluated by ADMET studies and azepanobetulin showing the better results was evaluated by in vivo experiments. This compound has demonstrated a statistically significant antimycobacterial activity compared to control, but inferior to isoniazid. Our findings show that pentacyclic triterpene derivatives holding a seven-membered azepane A-ring are the promising template for the development of new agents with high antibacterial potential against M. tuberculosis H37Rv, non-tuberculous mycobacterial and drug- resistant strains.

Synthesis and cholinesterase inhibiting potential of A-ring azepano- and 3-amino-3,4-seco-triterpenoids

In this study, a series of A-ring azepano- and 3-amino-3,4-seco-derivatives were synthesized from betulin, oleanolic, ursolic and glycyrrhetinic acids aiming to develop new cholinesterase inhibitors. Azepanobetulin, azepanoerythrodiol and azepanouvaol were modified to give amide and tosyl derivatives, while azepano-anhydrobetulines and azepano-glycyrrhetols were obtained for the first time. Oleanane and ursane type 3-amino-3,4-seco-4(23)-en triterpenic alcohols were synthesized by reducing the corresponding 2-cyano-derivatives accessible from Beckmann type 2 rearrangements. The compounds were screened in colorimetric Ellman's assays to determine their ability to act as inhibitors for the enzymes acetylcholinesterase (AChE, from electric eel) and butyrylcholinesterase (BChE, from equine serum). While most of these compounds were only moderate inhibitors for AChE, several of them were shown to be inhibitors for BChE acting as mixed-type inhibitors. Azepanobetulin 1, its C28-amide derivatives 7 and 8, azepano-11-deoxo-glycyrrhetol 12 and azepanouvaol 18 held inhibition constants K_i ranging between 0.21 ± 0.06 to 0.68 ± 0.19 μM. Thus, they were approximately 4 to 10 times more active than standard galantamine hydrobromide. For all of the compounds reasonably high docking scores for BChE were obtained being in good agreement with the experimental results from the enzymatic studies. As a result, A-ring azepano-triterpenoids were found to be new scaffolds for the development of BChE inhibitors.

A-Ring-Modified Triterpenoids and Their Spermidine–Aldimines with Strong Antibacterial Activity

Synthesis of A-ring-modified lupane, oleanane and ursane type triterpenoid conjugates with spermidine through an aldimine linkage or diethylentriamine via an amide bond is described. These derivatives were evaluated for their in vitro antimicrobial properties against human pathogens. Except for derivatives 1 and 7, all compounds have moderate to weak minimum inhibitory concentrations (MICs) against Gram-positive Staphylococcus aureus bacteria, with MICs varying from 3.125 to 200 µM. Compound 11 is efficient against Escherichia coli and Pseudomonas aeruginosa, with MICs of 25 and 50 µM, respectively, while all other derivatives do not possess important antimicrobial activities against these Gram-negative bacteria.

Synthesis and Сytotoxicity of A-Azepanobetulinic Acid N-Methyl-Piperazinylamide

The synthesis of A-azepanobetulinic acid N-methylpiperazinylamide was performed through a series of transformations (oximation, Beckmann rearrangement, reduction) of previously synthesized betulonic acid N-methylpiperazinylamide. In vitro cytotoxic activity was detected for the obtained compound against a number of cancer cell lines, and its potential was revealed as an antibacterial agent.

Betulin and its derivatives as novel compounds with different pharmacological effects

Betulin (B) and Betulinic acid (BA) are natural pentacyclic lupane-structure triterpenoids which possess a wide range of pharmacological activities. Recent evidence indicates that B and BA have several properties useful for the treatment of metabolic disorders, infectious diseases, cardiovascular disorders, and neurological disorders. In the current review, we discuss B and BA structures and derivatives and then comprehensively explain their pharmacological effects in relation to various diseases. We also explain antiviral, antibacterial and anti-cancer effects of B and BA. Finally, we discuss the delivery methods, in which these compounds most effectively target different systems.

Biological Activity and In Silico Study of 3-Modified Derivatives of Betulin and Betulinic Aldehyde

A series of 3-substituted derivatives of betulin and betulinic aldehyde were synthesized as promising anticancer agents. The newly triterpenes were tested against five human cancer cell lines like biphenotypic B myelomonocytic leukaemia (MV-4-11), adenocarcinoma (A549), prostate (Du-145), melanoma (Hs294T), breast adenocarcinoma (MCF-7) and normal human mammary gland (MCF-10A). The compound 9 showed towards Du-145, MCF-7 and Hs294T cells significant antiproliferative activity with IC₅₀ ranging from 7.3 to 10.6 μM. The evaluation of ADME properties of all compounds also includes their pharmacokinetic profile. The calculated TPSA values for synthetized derivatives are in the range between 43.38 Ų and 55.77 Ų suggesting high oral bioavailability. The molecular docking calculations showed that triterpene 9 fits the active site of the serine/threonine protein kinase Akt.

Design and synthesis of novel oleanolic acid based chromenes as anti-proliferative and anti-inflammatory agents

A novel approach has been developed for the synthesis of oleanolic acid based anti-proliferative and anti-inflammatory chromenes.