Nature-inspired development of unnatural meroterpenoids as the non-toxic anti-colon cancer agents

Natural sesquiterpene quinone/quinols: chemistry, biological activity, and synthesis

Covering: 2010 to 2021Sesquiterpene quinone/quinols (SQs) are characterized by a C15-sesquiterpenoid unit incorporating a C6-benzoquinone/quinol moiety. Numerous unprecedented carbon skeletons have been constructed with various connection patterns between the two parts. The potent anti-cancer, anti-inflammatory, anti-microbial, anti-viral, and fibrinolytic activities of SQs are associated with their diverse structures. The representative avarol has even entered the stage of clinical phase II research as an anti-HIV agent, and was developed as paramedic medicine against psoriasis. This review provides an overall summary of 558 new natural SQs discovered between 2010 and 2021, including seven groups and sixteen structure-type subgroups, which comprehensively recapitulates their chemical structures, spectral characteristics, source organisms, biological activities, synthesis, and biosynthesis, aiming to expand the application scope of this unique natural product resource.

Biological activities of meroterpenoids isolated from different sources

Meroterpenoids are natural products synthesized by unicellular organisms such as bacteria and multicellular organisms such as fungi, plants, and animals, including those of marine origin. Structurally, these compounds exhibit a wide diversity depending upon the origin and the biosynthetic pathway they emerge from. This diversity in structural features imparts a wide spectrum of biological activity to meroterpenoids. Based on the biosynthetic pathway of origin, these compounds are either polyketide-terpenoids or non-polyketide terpenoids. The recent surge of interest in meroterpenoids has led to a systematic screening of these compounds for many biological actions. Different meroterpenoids have been recorded for a broad range of operations, such as anti-cholinesterase, COX-2 inhibitory, anti-leishmanial, anti-diabetic, anti-oxidative, anti-inflammatory, anti-neoplastic, anti-bacterial, antimalarial, anti-viral, anti-obesity, and insecticidal activity. Meroterpenoids also possess inhibitory activity against the expression of nitric oxide, TNF- α, and other inflammatory mediators. These compounds also show renal protective, cardioprotective, and neuroprotective activities. The present review includes literature from 1999 to date and discusses 590 biologically active meroterpenoids, of which 231 are from fungal sources, 212 are from various species of plants, and 147 are from marine sources such as algae and sponges.

Bio-inspired construction of a tetracyclic ring system with an avarane skeleton: total synthesis of dactyloquinone A

We report the asymmetric construction of an avarane skeleton. The strategy involves a Lewis acid-catalyzed cyclization reaction, which drives the methyl groups of two different configurations at the C-4 site to migrate by 1, 2-rearrangement.

Effect of acidic culture conditions on the proliferation, apoptosis, and migration ability of human tongue squamous cell carcinoma cells and its related mechanism

OBJECTIVES

This study aims to explore the effect of acidic culture conditions on the proliferation, apoptosis, and migration ability of human tongue squamous cell carcinoma SCC15 and CAL27 cells and its potential molecular mechanism.

METHODS

After acidic culture for different periods, methyl thiazolyl tetrazolium (MTT) method was adop-ted to detect the cell proliferation of SCC15 and CAL27. Flow cytometry was employed to detect the apoptosis level of SCC15 and CAL27 cells. The migration ability of SCC15 and CAL27 after acidic culture was detected by scratch hea-ling test. Real-time fluorescence quantitative polymerase chain reaction (FQ-PCR) was used to detect the mRNA expression of cyclooxygenase 2 (COX-2) and survivin in SCC15 and CAL27 cells after acidic culture.

RESULTS

After culture for 24 h under acidic microenvironment, SCC15 and CAL27 cells grew rapidly and reached the stationary phase after adjustment for 3 days. The apoptosis levels of SCC15 and CAL27 cells decreased after acidic culture, but the most significant reduction occurred after 6 h of acidic culture. The scratch healing rates of SCC15 and CAL27 cells increased after acidic culture. The results of FQ-PCR showed that the mRNA expression levels of COX-2 and survivin in SCC15 and CAL27 cells increased after acidic culture.

CONCLUSIONS

Extracellular acidic microenvironment can inhibit the apoptosis of tongue squamous carcinoma cells, promote their migration, and induce more adaptable and malignant tongue squamous carcinoma cells. The mechanism may be related to COX-2 and survivin and their signal pathways.

Total Synthesis of Anti-Cancer Meroterpenoids Dysideanone B and Dysiherbol A and Structural Reassignment of Dysiherbol A

The first total synthesis of marine anti-cancer meroterpenoids dysideanone B and dysiherbol A have been accomplished in a divergent way. The synthetic route features: 1) a site and stereoselective α-position alkylation of a Wieland-Miescher ketone derivative with a bulky benzyl bromide to join the terpene and aromatic moieties together and set the stage for subsequent cyclization reactions; 2) an intramolecular radical cyclization to construct the 6/6/6/6-tetracycle of dysideanone B and an intramolecular Heck reaction to forge the 6/6/5/6-fused core structure of dysiherbol A. A late-stage introduction of the ethoxy group in dysideanone B reveals that this group might come from the solvent ethanol. The structure of dysiherbol A has been revised based on our chemical total synthesis.

Computational Investigation of Multifaceted Cationic Rearrangement and Stereo- and Regioselectivity in the Formation of Dysideanone's Analogues

Mechanistic studies of regiodivergent arylations of cycloalkanols to furnish enantioenriched dysideanone's analogues are performed by employing density functional theory (DFT) calculations (B3LYP-D3(SMD)/6-311++G**//B3LYP-D3/6-31+G** level of theory). On the basis of our calculations, remote γ'-C-H arylation is preferred for unsubstituted carbinol 1, an outcome from combined factors like carbocationic stability, less steric hindrance during C-C coupling, and facile dearomatization. Meanwhile, in the presence of dimethyl substituent 1^Me, regioselective γ-arylation is favored by 3.4 kcal/mol, and both findings are in agreement with the reported experimental observations. Most importantly, we concur that the barrier associated with the formation of carbocation 6 and its substituted analogues correlates with the C-H arylation outcomes. Furthermore, the β-arylation route remains unlikely for all the reaction pathways explored in this study.

Aspects in the Total Syntheses of Higher Terpenoids Starting From Wieland–Miescher Ketone and Its Derivative: A Review

Synthetic studies of higher terpenoids starting from Wieland–Miescher ketone since 2012 have been compiled.

Meroterpenoids from the Fungus Ganoderma sinensis and First Absolute Configuration Clarification of Zizhine H

Five new meroterpenoids, zizhines P-S and U (1−4,7), together with two known meroterpenoids (5 and 6) were isolated from Ganoderma sinensis. Their structures including absolute configurations were assigned by using spectroscopic, computational, and chemical methods. Racemics zizhines P and Q were purified by HPLC on chiral phase. Biological evaluation found that 4, 5 and 6 are cytotoxic toward human cancer cells (A549, BGC-823, Kyse30) with IC₅₀ values in the range of 63.43–80.83 μM towards A549, 59.2 ± 2.73 μM and 64.25 ± 0.37 μM towards BGC-823, 76.28 ± 1.93 μM and 85.42 ± 2.82 μM towards Kyse30.

Unexpected Racemization in the Course of the Acetalization of (+)-(S)-5-Methyl-Wieland–Miescher Ketone with 1,2-Ethanediol and TsOH under Classical Experimental Conditions

(+)-(S) and (−)-(R)-5-methyl-Wieland-Miescher ketone (+)-1 and (−)-1, are important synthons in the diastereo and enantioselective syntheses of biological and/or pharmacological interesting compounds. A key step in these syntheses is the chemoselective C(1)O acetalization to (+)-5 and (−)-5, respectively. Various procedures for this transformation have been described in the literature. Among them, the classical procedure based on the use of 1,2-ethanediol and TsOH in refluxing benzene in the presence of a Dean-Stark apparatus. Within our work on bioactive natural products, it occurred to us to observe the partial racemization of (+)-5 in the course of the acetalization of (+)-1 by means of the latter methodology. Aiming to investigate this drawback, which, to our best knowledge, has no precedents in the literature, we acetalized with 1,2-ethanediol and TsOH in refluxing benzene and in the presence of a Dean–Stark apparatus under various experimental conditions, enantiomerically pure (+)-1. It was found that the extent of racemization depends on the TsOH/(+)-1 and 1,2-ethanediol/(+)-1 ratios. Mechanism hypotheses for this partial and unexpected racemization are provided.

In Vitro Antiproliferative Evaluation of Synthetic Meroterpenes Inspired by Marine Natural Products

Several marine natural linear prenylquinones/hydroquinones have been identified as anticancer and antimutagenic agents. Structure-activity relationship studies on natural compounds and their synthetic analogs demonstrated that these effects depend on the length of the prenyl side chain and on the type and position of the substituent groups in the quinone moiety. Aiming to broaden the knowledge of the underlying mechanism of the antiproliferative effect of these prenylated compounds, herein we report the synthesis of two quinones 4 and 5 and of their corresponding dioxothiazine fused quinones 6 and 7 inspired to the marine natural product aplidinone A (1), a geranylquinone featuring the 1,1-dioxo-1,4-thiazine ring isolated from the ascidian Aplidium conicum. The potential effects on viability and proliferation in three different human cancer cell lines, breast adenocarcinoma (MCF-7), pancreas adenocarcinoma (Bx-PC3) and bone osteosarcoma (MG-63), were investigated. The methoxylated geranylquinone 5 exerted the highest antiproliferative effect exhibiting a comparable toxicity in all three cell lines analyzed. Interestingly, a deeper investigation has highlighted a cytostatic effect of quinone 5 referable to a G0/G1 cell-cycle arrest in BxPC-3 cells after 24 h treatment.

Lycorine inhibited the cell growth of non-small cell lung cancer by modulating the miR-186/CDK1 axis

AIMS

Lycorine is a kind of natural alkaloid with anti-cancer potential. It has been demonstrated that lycorine processes high activity and specificity against the progression of cancers. However, the underlying molecular mechanisms by which lycorine regulates the formation and development of non-small cell lung cancer (NSCLC) remain largely unknown.

MAIN METHODS

The effects of lycorine on the growth of NSCLC cells were determined by the cell counting kit-8 (CCK-8) assay, colony formation and flow cytometry analysis. RT-qPCR was performed to detect the expression of microRNA with lycorine treatment. The binding of miRNA and target genes was confirmed by luciferase reporter assay.

KEY FINDINGS

Lycorine significantly inhibited the proliferation and induced apoptosis of NSCLC cells. Mechanistically, lycorine up-regulated the expression of microRNA-186 in NSCLC cells. Depletion of miR-186 significantly reversed the suppressive effect of lycorine on the proliferation of NSCLC cells. Furthermore, the cyclin dependent kinase 1 (CDK1) was identified as one of the binding candidates of miR-186. Experimental analysis showed that miR-186 bound the 3'-untranslated region (3'-UTR) of CDK1 and suppressed the level of CDK1 in NSCLC cells. Consistently, exposure of lycorine significantly decreased the expression of CDK1. Restoration of CDK1 remarkably attenuated the inhibition of lycorine on the proliferation of NSCLC cells.

SIGNIFICANCE

Our results uncovered the novel molecular mechanism of lycorine in suppressing the progression of NSCLC partially via regulating the miR-186/CDK1 axis.