Recent advances of honokiol：pharmacological activities, manmade derivatives and structure-activity relationship.

Honokiol (HNK) is a typical natural biphenyl polyphenol compound. It has been proven to have a wide range of biological activities, including pharmacological effects such as anti-cancer, anti-inflammatory, neuroprotective, and antimicrobial. However, due to the poor stability, water solubility, and bioavailability of HNK, HNK has not been used in clinical treatment. This article reviews the latest research on the pharmacological activity of HNK and summarizes the HNK derivatives designed and improved by several researchers. Reviewing these contents could promote the research process of HNK and guide the design of better HNK derivatives for clinical application in the future.

Semisynthesis and biological evaluation of novel honokiol thioethers against colon cancer cells HCT116 via inhibiting the transcription and expression of YAP protein.

Honokiol, derived from Magnolia officinalis (a traditional Chinese medicine), has been reported to have anticancer activity. Here, a series of novel honokiol thioethers bearing a 1,3,4-oxadiazole moiety were prepared and evaluated for their anticancer activities against three types of digestive system tumor cells. Biological evaluation showed that honokiol derivative 3k exhibited the best antiproliferative activity against HCT116 cells with an IC50 value of 6.1 µmol/L, superior to the reference drug 5-fluorouracil (IC50: 9.63 ± 0.27 µmol/L). The structure-activity relationships (SARs) indicated that the introduction of -(4-NO2)Ph, 3-pyridyl, -(2-F)Ph, -(4-F)Ph, -(3-F)Ph, -(4-Cl)Ph, and -(3-Cl)Ph groups was favorable for enhancing the anticancer activity of the title honokiol thioethers. Further study revealed that honokiol thioether 3k can well inhibit the proliferation of colon cancer cells HCT116, arresting the cells in G1 phase and inducing cell death. Moreover, a preliminary mechanism study indicated that 3k directly inhibits the transcription and expression of YAP protein without activating the Hippo signaling pathway. Thus, honokiol thioether 3k could be deeply developed for the development of honokiol-based anticancer candidates.

Synthesis of obovatol and related neolignan analogues as α-glucosidase and α-amylase inhibitors.

Diabetes mellitus is a metabolic disease characterized by hyperglycemia, which can be counteracted by the inhibition of α-glucosidase (α-Glu) and α-amylase (α-Amy), enzymes responsible for the hydrolysis of carbohydrates. In recent decades, many natural compounds and their bioinspired analogues have been studied as α-Glu and α-Amy inhibitors. However, no studies have been devoted to the evaluation of α-Glu and α-Amy inhibition by the neolignan obovatol (1). In this work, we report the synthesis of 1 and a library of new analogues. The synthesis of these compounds was achieved by implementing methodologies based on: phenol allylation, Claisen/Cope rearrangements, methylation, Ullmann coupling, demethylation, phenol oxidation and Michael-type addition. Obovatol (1) and ten analogues were evaluated for their in vitro inhibitory activity towards α-Glu and α-Amy. Our investigation highlighted that the naturally occurring 1 and four neolignan analogues (11, 22, 26 and 27) were more effective inhibitors than the hypoglycemic drug acarbose (α-Amy: 34.6 µM; α-Glu: 248.3 µM) with IC5O value of 6.2-23.6 µM toward α-Amy and 39.8-124.6 µM toward α-Glu. Docking investigations validated the inhibition outcomes, highlighting optimal compatibility between synthesized neolignans and both the enzymes. Concurrently circular dichroism spectroscopy detected the conformational changes in α-Glu induced by its interaction with the studied neolignans. Detailed studies through fluorescence measurements and kinetics of α-Glu and α-Amy inhibition also indicated that 1, 11, 22, 26 and 27 have the greatest affinity for α-Glu and 1, 11 and 27 for α-Amy. Surface plasmon resonance imaging (SPRI) measurements confirmed that among the compounds studied, the neolignan 27 has the greater affinity for both enzymes, thus corroborating the results obtained by kinetics and fluorescence quenching. Finally, in vitro cytotoxicity of the investigated compounds was tested on human colon cancer cell line (HCT-116). All these results demonstrate that these obovatol-based neolignan analogues constitute promising candidates in the pursuit of developing novel hypoglycemic drugs.

Natural Small Molecules Enabled Efficient Immunotherapy through Supramolecular Self-Assembly in P53-Mutated Colorectal Cancer.

Nanomedicine, constructed from therapeutics, presents an advantage in drug delivery for cancer therapies. However, nanocarrier-based treatment systems have problems such as interbatch variability, multicomponent complexity, poor drug delivery, and carrier-related toxicity. To solve these issues, the natural molecule honokiol (HK), an anticancer agent in a phase I clinical trial (CTR20170822), was used to form a self-assembly nanoparticle (SA) through hydrogen bonding and hydrophobicity. The preparation of SA needs no molecular precursors or excipients in aqueous solution, and 100% drug-loaded SA exhibited superior tumor-targeting ability due to the enhanced permeability and retention (EPR) effect. Moreover, SA significantly enhanced the antitumor immunity relative to free HK, and the mechanism has notable selectivity to the p53 pathway. Furthermore, SA exhibited excellent physiological stability and inappreciable toxicity. Taken together, this supramolecular self-assembly strategy provides a safe and "molecular economy" model for rational design of clinical therapies and is expected to promote targeted therapy of HK, especially in colorectal cancer patients with obvious p53 status.

Total Synthesis and Anti-Tobacco Mosaic Virus Activity of the Furofuran Lignan (±)-Phrymarolin II and Its Analogues.

Phrymarolin II, a furofuran lignan isolated from Phryma leptostachya L., features a 3,7-dioxabicyclo[3.3.0]octane skeleton. Herein, we report an alternative total synthesis of (±)-phrymarolin II (2), which was performed in 9 steps from commercially available sesamol. The key steps of the synthesis included a zinc-mediated Barbier-type allylation and a copper-catalyzed anomeric O-arylation. Our total synthesis allowed the synthesis of analogues of (±)-phrymarolin II. Most derivatives displayed good to excellent in vivo activity against tobacco mosaic virus (TMV). (±)-Phrymarolin II (2) and compounds (±)-31d and (±)-31g exhibited similar or higher activity than commercial ningnanmycin, which indicated that phrymarolin lignans are a promising new class of plant virus inhibitors.

Dibenzocyclooctadiene lignans from Kadsura coccinea alleviate APAP-induced hepatotoxicity via oxidative stress inhibition and activating the Nrf2 pathway in vitro.

Phytochemical investigation on the roots of Kadsura coccinea led to the isolation five previously unknown dibenzocyclooctadiene lignans, named heilaohusuins A-E (1-5). Their structures determined by NMR spectroscopy, HR-ESI-MS, and ECD spectra. Hepatoprotection effects of a series of dibenzocyclooctadiene derivatives (1-68) were investigated against acetaminophen (APAP) induced HepG2 cells. Compounds 2, 10, 13, 21, 32, 41, 46, and 49 showed remarkable protective effects, increasing the viabilities to > 52.2% (bicyclol, 52.1 ± 1.3%) at 10 µM. The structure-activity relationships (SAR) for hepatoprotective activity were summarized, according to the activity results of dibenzocyclooctadiene derivatives. Furthermore, we found that one new dibenzocyclooctadiene lignan heilaohusuin B attenuates hepatotoxicity, the mechanism might be closely correlated with oxidative stress inhibition via activating the Nrf2 pathway.

Novel 1,3,4-thiadiazole/oxadiazole-linked honokiol derivatives suppress cancer via inducing PI3K/Akt/mTOR-dependent autophagy.

Honokiol is a bioactive biphenolic component derived from Magnoliae officinalis Cortex (known as "Hou Po" in Chinese), a traditional Chinese herbal medicine. A series of novel 1,3,4-thiadiazole/oxadiazole-linked honokiol derivatives were synthesized and tested for anticancer activity against seven human cancer cell lines in this study. Among all derivatives, 8a had the most potent cytotoxic effect on all tested cancer cells, with IC50 values ranging from 1.62 ± 0.19 to 4.61 ± 0.51 µM, which were 10.38-34.36 folds more potent than the parental honokiol (IC50 values of 30.96 ± 1.81-55.67 ± 0.31 µM). On A549, HCT116, and MDA-MB-231 cell lines, 8a demonstrated 5.69-fold, 5.65-fold, and 4.83-fold greater cytotoxicity than cisplatin, respectively. Compound 8a also had higher selectivity (SI values of 8.41-49.38) towards seven cancer cell lines over the normal cell lines than cisplatin (SI values of 1.24-2.52). The analysis of structure-activity relationships (SARs) revealed that honokiol derivatives bearing 1,3,4-thiadiazoles (8a-j) possessed stronger anticancer activity than those containing 1,3,4-oxadiazoles. Further mechanistic investigation indicated that 8a induced cytotoxic autophagy in cancer cells in a time- and dose-independent manner via suppressing the PI3K/Akt/mTOR pathway. Molecular docking suggested that 8a could bind to the PI3Kα active sites. Additionally, 8a inhibited the migration and invasion of A549 and MDA-MB-231 cancer cells.

Semi-Synthesis and In Vitro Anti-Cancer Evaluation of Magnolol Derivatives.

Magnolol (MAG), a biphenolic neolignan, has various biological activities including antitumor effects. In this study, 15 MAG derivatives were semi-synthesized and evaluated for their in vitro anticancer activities. From these derivatives, compound 6a exhibited the best cytotoxic activity against four human cancer cell lines, with IC50 values ranging from 20.43 to 28.27 µM. Wound-healing and transwell assays showed that compound 6a significantly inhibited the migration and invasion of MDA-MB-231 cells. In addition, Western blotting experiments, performed using various concentrations of 6a, demonstrated that it downregulates the expression of HIF-1α, MMP-2, and MMP-9 in a concentration-dependent manner. Overall, these results suggest that substituting a benzyl group having F atoms substituted at the C2 position on MAG is a viable strategy for the structural optimization of MAG derivatives as anticancer agents.

Design, synthesis, and evaluation of cytotoxic activities of arylnaphthalene lignans and aza-analogs.

A concise and versatile synthetic strategy for the total synthesis of arylnaphthalene lignans and aza-analogs was developed. The main objective was to develop synthetic tactics for the creation of the lactone and lactam unit that would give access to an array of synthetic, natural, and/or bioactive compounds through rather simple chemical manipulation. The flexibility and potentiality of these new processes were further illustrated by the total synthesis of retrojusticidin B (13b), justicidin C (14b), and methoxy-vitedoamine A (22a). In this study, a series of novel aryl-naphthalene lignans and aza-analogs were synthesized, and the cytotoxic activities of all compounds on cancer cell growth were evaluated. The target compounds were structurally characterized by 1 H NMR (nuclear magnetic resonance), 13 C NMR, infrared, high-resolution mass spectrometry, and X-ray crystallography. The IC50 values of these compounds on five tumor cell lines (A549, HS683, MCF-7, SK-MEL-28, and B16-F1) were obtained by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) colorimetric assay. Five of the compounds exhibited excellent activity compared to 5-fluorouracil and etoposide against the five cell lines tested, with IC50 values ranging from 1 to 10 µM.

Synthesis, Characterization and Biological Evaluation of Magnolol and Honokiol Derivatives with 1,3,5-Triazine of Metformin Cyclization.

Herein, we sought to evaluate the contribution of the 1,3,5-triazine ring through the metformin cyclization unit to the biological activity of magnolol and honokiol-conjugates. One of the phenolic OH groups of magnolol or honokiol was replaced by a 1,3,5-triazine ring to further explore their synthesis and medicinal versatility. In this study, a robust procedure of three steps was adopted for the synthesis of magnolol and honokiol derivatives by alkylation of potassium carbonate with a 1,3,5-triazine ring. To our knowledge, this is the first report to connect one of the phenolic OH positions of magnolol or honokiol to a 1,3,5-triazine ring cyclized by metformin. The structural characterization of three new compounds was carried out via spectroscopic techniques, i.e., 13C NMR, 1H NMR, and HRMS. Surprisingly, these compounds showed no cytotoxicity against RAW 264.7 macrophages but significantly inhibited the proliferation of MCF-7 (human breast cancer cells), HepG2 (human hepatoma cells), A549 (human lung carcinoma cells), and BxPC-3 (human pancreatic carcinoma cells) tumor cell lines. Furthermore, the compounds also significantly inhibited the release of inflammatory cytokines, including nitric oxide (NO), tumor necrosis factor-α (TNF-α), and interleukin-1ß (IL-1ß) in the lipopolysaccharide (LPS)-activated mouse cells (RAW 264.7). Among them, compound 2 demonstrated promising broad-spectrum antiproliferative potential with half inhibitory concentration (IC50) values ranging from 5.57 to 8.74 µM and it significantly decreased caspase-3 and Bcl-2 expression in HepG2 cells. These interesting findings show that derivatization of magnolol and honokiol with 1,3,5-triazine affects and modulates their biological properties.

Synthesis, DNA/RNA-interaction and biological activity of benzo[k,l]xanthene lignans.

Interactions of two newly synthesized and six previously reported benzoxanthene lignans (BXLs), analogues of rare natural products, with DNA/RNA, G-quadruplex and HSA were evaluated by a set of spectrophotometric methods. Presence/absence of methoxy and hydroxy groups on the benzoxanthene core and minor modifications at C-1/C-2 side pendants - presence/absence of phenyl ring and presence/absence of methoxy and hydroxy groups on phenyl ring - influenced the fluorescence changes and the binding strength to double-stranded (ds-) and G-quadruplex structures. In general, compounds without phenyl ring showed stronger fluorescence changes upon binding than phenyl-substituted BXLs. On the other hand, BXLs with an unsubstituted phenyl ring showed the best stabilization effects of G-quadruplex. Circular dichroism spectroscopy results suggest mixed binding mode, groove binding and partial intercalation, to ds-DNA/RNA and end-stacking to top or bottom G-tetrads as the main binding modes of BXLs to those targets. All compounds exhibited micromolar binding affinities toward HSA and an increased protein thermal stability. Moderate to strong antiradical scavenging activity was observed for all BXLs with hydroxy groups at C-6, C-9 and C-10 positions of the benzoxanthene core, except for derivative bearing methoxy groups at these positions. BXLs with unsubstituted or low-substituted phenyl ring and one derivative without phenyl ring showed strong growth inhibition of Gram-positive Staphylococcus aureus. All compounds showed moderate to strong tumor cell growth-inhibitory activity and cytotoxicity.

Anticancer Effects of Honokiol via Mitochondrial Dysfunction Are Strongly Enhanced by the Mitochondria-Targeting Carrier Berberine.

Mitochondrion is a favorable therapeutic target in cancer, given its regulation of bioenergetics and cell death. Honokiol exhibits antiproliferative effects through mitochondria-mediated death signaling. To enhance its anticancer potential and selectivity, we conjugated honokiol to berberine, a mitochondria-targeting carrier. All designed derivatives displayed 1 order of magnitude increased cytotoxicity compared with the parent compounds, especially with massive cytoplasmic vacuoles. Biological evaluation demonstrated the representative compound 6b localized within the mitochondria, and mitochondrial dilation resulted in vacuolization. 6b induced vacuolation-associated cell death and apoptosis with obvious mitochondrial dysfunction, as demonstrated by booming reactive oxygen species generation, opening mitochondrial permeability transition pore, and reducing mitochondrial membrane potential. The targeting property also conferred 6b with selectivity for tumor cells compared to normal cells. 6b inhibited cancer cell proliferation in the zebrafish xenograft model. These results demonstrate that berberine-linked honokiol derivatives open up a direction for novel mitochondrial-targeting antitumor agents.

Semisynthesis of novel magnolol-based Mannich base derivatives that suppress cancer cells via inducing autophagy.

Magnolol, a natural bioactive neolignan, was found in the bark of a traditional Chinese medicine Magnoliae officinalis ("Hou Po" in Chinese). In this study, thrity-two magnolol-based Mannich base derivatives 3a-p and 4a-p were synthesized, and evaluated for their anti-proliferative activities against a panel of human tumor cell lines (T47D, MCF-7, Hela and A549). Among all derivatives, compound 3p displayed the most potent antiproliferative activity against T47D, MCF-7 and Hela cell lines with IC50 values of 0.91, 3.32 and 1.71 µM, respectively. Compared with the parental magnolol and the positive drug cisplatin, 3p exhibited up to 76.1-fold and 10.3-fold enhancement of cytotoxic effect on T47D cancer cells, respectively. Mechanism study revealed that the most potent derivative 3p suppressed cancer cells via inducing autophagy. Moreover, 3p also possessed suppressive effects on migration of T47D and Hela cancer cells. In addition, some interesting structure-activity relationships (SARs) were also summarized.

Structure-activity relationship study of cytotoxic neolignan derivatives using multivariate analysis and computation-aided drug design.

Dehydrodieugenol B and five related natural neolignans were isolated from the Brazilian plant species Nectandra leucantha. Three of these compounds were shown to be active against murine (B16F10) and human (A2058) melanoma cells but non-toxic to human fibroblasts (T75). These results stimulated the preparation of a series of 23 semi-synthetic derivatives in order to explore structure-activity relationships and study the biological potential of these derivatives against B16F10 and A2058 cell lines. These structurally-related neolignan derivatives were analyzed by multivariate statistics and machine learning, which indicated that the most important characteristics were related to their three-dimensional structure and, mainly, to the substituents on the neolignan skeleton. The results suggested that the presence of hydroxyl or alkoxyl groups at positions 3, 4 and 5 (with appropriate sidechains) promoted an increase in electropological and charge density, which seem to be important for biological activity against murine (B16F10) and human (A2058) melanoma cells.

Synthesis and biological evaluation of Schizandrin derivatives as tubulin polymerization inhibitors.

A series of oxime ester-derivatives were prepared by utilizing the schizandrin (1), a major compound isolated from Schisandra grandiflora, which is deployed in different traditional system of medicine. The in vitro antiproliferative activities of the synthesized compounds were assessed against a selected panel of human cancer cell lines (A549, RKO P3, DU145 and Hela) and normal cell (HEK293). Several of these derivatives were found more potent in comparison to parent compound, schizandrin (1). Particularly, 4a and 4b demonstrated potent activity against DU-145 and RKOP3 cell lines with IC50 values of 3.42 µM and 3.35 µM respectively. To characterize the molecular mechanisms involved in antitumoral activity, these two compounds, 4a and 4b were selected for further studies. Cell cycle analysis revealed that both the compounds were able to induce apoptosis and cell cycle arrest at G0/G1 phase. To know the extent of apoptosis in DU145 and RKOP3 cell lines, Annexin V-FITC were performed. Moreover, the tubulin polymerization assay indicated that 4a and 4b exhibits potent inhibitory effect on the tubulin assembly. Molecular docking studies and competitive binding assay also indicated that 4a and 4b effectively bind at the colchicine binding site of the tubulin.

Synthesis of Bisphenol Neolignans Inspired by Honokiol as Antiproliferative Agents.

Honokiol (2) is a natural bisphenol neolignan showing a variety of biological properties, including antitumor activity. Some studies pointed out 2 as a potential anticancer agent in view of its antiproliferative and pro-apoptotic activity towards tumor cells. As a further contribution to these studies, we report here the synthesis of a small library of bisphenol neolignans inspired by honokiol and the evaluation of their antiproliferative activity. The natural lead was hence subjected to simple chemical modifications to obtain the derivatives 3-9; further neolignans (12a-c, 13a-c, 14a-c, and 15a) were synthesized employing the Suzuki-Miyaura reaction, thus obtaining bisphenols with a substitution pattern different from honokiol. These compounds and the natural lead were subjected to antiproliferative assay towards HCT-116, HT-29, and PC3 tumor cell lines. Six of the neolignans show GI50 values lower than those of 2 towards all cell lines. Compounds 14a, 14c, and 15a are the most effective antiproliferative agents, with GI50 in the range of 3.6-19.1 µM, in some cases it is lower than those of the anticancer drug 5-fluorouracil. Flow cytometry experiments performed on these neolignans showed that the inhibition of proliferation is mainly due to an apoptotic process. These results indicate that the structural modification of honokiol may open the way to obtaining antitumor neolignans more potent than the natural lead.

Synthesis and in vitro antitumor evaluation of honokiol derivatives.

Honokiol is a natural bioactive neolignan and has been widely researched and structural modified as an anticancer agent. In this paper, 18 honokiol derivatives were synthesized and investigated for their antitumor activity. Among these, the promising compound 5a exhibited much higher anti-proliferative activity with IC50 value of 10.41 µM. Transwell assays showed that 5a could significantly inhibit the invasion and migration of I-10 cells at 2.5 µM, which was further confirmed by the western blotting experiments with down-regulation of the HIF-1α and its associated downstream proteins MMP-2 and MMP-9. Overall, these results provided useful suggestion for further structural optimization of honokiol derivatives.

Comparative analysis of stilbene and benzofuran neolignan derivatives as acetylcholinesterase inhibitors with neuroprotective and anti-inflammatory activities.

Stilbenes and benzofuran neolignans are important groups of plant phenolics therefore they play a significant role in plants and human health. The objective of this study was to investigate the structure-activity relationships of naturally occurring stilbene and benzofuran neolignan derivatives as acetylcholinesterase inhibitors. A series of these compounds were prepared and assessed for their inhibition on acetylcholinesterase activity. δ-Viniferin, pterostilbene trans-dehydrodimer, pallidol, grossamide, and boehmenan exerted acetylcholinesterase inhibitory potential. The several oligomeric compounds protected against cell damage resulting from t-BHP exposure and inhibited lipopolysaccharide/interferon-gamma (LPS/IFNγ)-induced NO production in vitro. Our findings highlight the great potential of pterostilbene trans-dehydrodimer, pallidol, and boehmenan as multifunctional nutraceuticals for management of neurodegenerative diseases.

Synthesis, cytotoxicity and anti-invasion activity of three natural diphyllin L-arabinopyranosides.

The concise syntheses of three new natural diphyllin L-arabinopyranosides, Phyllanthusmin D (1), Phyllanthusmin B (4), Phyllanthusmin C (6) and a known analogue 7-O-[(2,3,4-tri-O-acetyl)-α-Larabinopyranosyl)] diphyllin (7) have been achieved employing phase transfer catalysis glycosylation and orthoester rearrangement. In biological assays, 4 showed the best cytotoxicity against human gastric carcinoma MGC803 Cells with the IC50 value 39 µg/mL. Transwell invasion assay showed that glycosides 1, 4, and 7 significantly suppressed MGC-803 cell invasion compared with control.

Design of 92 New 9-Norlignan Derivatives and Their Effect on Cell Viabilities of Cancer and Insect Cells.

Ninety-two new 9-norlignan derivatives containing more effective compounds against both cancer and insect cells than lead compounds were synthesized. Against HeLa cells, 7-(3,4-dimethoxyphenyl)-7'-(3'-hydroxy-4'-methoxyphenyl) derivative 63 (IC50 = 0.9 ± 0.2 µM) was to be around 6-fold more potent than lead compound 5. Moreover, against HL-60 cells, 7-(4-trifluoromethylphenyl)-7'-(3'/4'-hydroxyphenyl) derivatives 78 and 79 (IC50 = 2.2 ± 0.4 µM and 2.4 ± 0.6 µM) were 3-fold more potent than lead compound 5. Furthermore, against Sf9 cells from the common cutworm, the 7-(4-trifluoromethylphenyl) derivatives bearing electron-withdrawing groups 76-96 showed a wider range of activity (around 20-fold difference), giving valuable information on the structure-activity relationship. The 7-(4-trifluoromethylphenyl)-7'-(2'/3'-hydroxyphenyl) derivatives 77 and 78 (IC50 = 4.7 ± 0.6 µM and 4.9 ± 0.9 µM) had around 2-fold higher activity against Sf9 cells than lead compound 5. The 7-(4-trifluoromethylphenyl)-7'-(3'-hydroxyphenyl) derivative 78 was also effective against mosquito NIAS-AcAl-2 cells with an IC50 value of 5.4 ± 0.3.