Marine Sesquiterpene Research Articles

Divergent total synthesis of sesquiterpene (hydro)quinone meroterpenoids dysideanones A and E–G

The first total synthesis of marine sesquiterpene (hydro)quinone meroterpenoids dysideanones A and E–G (1 and 4–6) has been accomplished in an enantioselective and divergent way. The sesquiterpene fragment and the aromatic moiety were efficiently connected via a site-selective and diastereoselective intermolecular alkylation of Wieland–Miescher ketone derivative 9 and benzyl bromide 10. The core 6/6/6/6-fused backbone of dysideanones was efficiently constructed through an intramolecular radical cyclization reaction. Dysideanone G (6) was easily prepared on a gram-scale and dysideanones A, E, and F (1, 4, and 5) were divergently transformed from dysideanone G (6) in one or two steps

In Silico Drug Design of Anti-Breast Cancer Agents.

Cancer is a condition marked by abnormal cell proliferation that has the potential to invade or indicate other health issues. Human beings are affected by more than 100 different types of cancer. Some cancer promotes rapid cell proliferation, whereas others cause cells to divide and develop more slowly. Some cancers, such as leukemia, produce visible tumors, while others, such as breast cancer, do not. In this work, in silico investigations were carried out to investigate the binding mechanisms of four major analogs, which are marine sesquiterpene, sesquiterpene lactone, heteroaromatic chalcones, and benzothiophene against the target estrogen receptor-α for targeting breast cancer using Schrödinger suite 2021-4. The Glide module handled the molecular docking experiments, the QikProp module handled the ADMET screening, and the Prime MM-GB/SA module determined the binding energy of the ligands. The benzothiophene analog BT_ER_15f (G-score -15.922 Kcal/mol) showed the best binding activity against the target protein estrogen receptor-α when compared with the standard drug tamoxifen which has a docking score of -13.560 Kcal/mol. TRP383 (tryptophan) has the highest interaction time with the ligand, and hence it could act for a long time. Based on in silico investigations, the benzothiophene analog BT_ER_15f significantly binds with the active site of the target protein estrogen receptor-α. Similar to the outcomes of molecular docking, the target and ligand complex interaction motif established a high affinity of lead candidates in a dynamic system. This study shows that estrogen receptor-α targets inhibitors with better potential and low toxicity when compared to the existing market drugs, which can be made from a benzothiophene derivative. It may result in considerable activity and be applied to more research on breast cancer.

Divergent total synthesis of marine meroterpenoids (+)-dysidavarones A–C

Here, we report a concise and divergent enantioselective total synthesis of marine sesquiterpene quinone meroterpenoids (+)-dysidavarones A–C (1–3) using predysidavarone 6 as a key common intermediate. The highly strained and bridged eight-membered carbocycle of predysidavarone 6 was constructed by a one-pot intermolecular alkylation and intramolecular arylation of Wieland–Miescher ketone derivative 11 and benzyl bromide 12. The total synthesis of (+)-dysidavarones A–C (1–3) was achieved from predysidavarone 6 in a divergent manner by a late-stage introduction of the ethoxy group, which reveals the possible source of the ethoxy group within (+)-dysidavarones A–C (1–3) and provides a late-stage modifiable route for the synthesis of dysidavarone analogs for further anti-cancer activity evaluation.

Complexing the Marine Sesquiterpene Euplotin C by Means of Cyclodextrin-Based Nanosponges: A Preliminary Investigation.

Euplotin C is a sesquiterpene of marine origin endowed with significant anti-microbial and anti-tumor properties. Despite the promising functional profile, its progress as a novel drug candidate has failed so far, due to its scarce solubility and poor stability in aqueous media, such as biological fluids. Therefore, overcoming these limits is an intriguing challenge for the scientific community. In this work, we synthesized β-cyclodextrin-based nanosponges and investigated their use as colloidal carriers for stably complex euplotin C. Results obtained proved the ability of the carrier to include the natural compound, showing remarkable values of both loading efficiency and capacity. Moreover, it also allowed us to preserve the chemical structure of the loaded compound, which was recovered unaltered once extracted from the complex. Therefore, the use of β-cyclodextrin-based nanosponges represents a viable option to vehiculate euplotin C, thus opening up its possible use as pharmacologically active compound.

Marine Sesquiterpenes for Plant Protection: Discovery of Laurene Sesquiterpenes and Their Derivatives as Novel Antiviral and Antiphytopathogenic Fungal Agents.

The unreasonable use or long-term use of a single variety of pesticide has led to drug resistance and made the pesticides ineffective. Therefore, the creation of new, efficient, and low-risk pesticides is imminent. Marine natural products play a vital role in serving as new lead compounds. In this work, we realized the efficient preparation of nine marine sesquiterpenes with the Stork-Danheiser reaction as the key step and designed and synthesized a series of their derivatives. The antiviral activity and antifungal activity research showed that these compounds exhibited good to excellent biological activities. Compounds 7b and 8e displayed significantly higher antiviral activities against tobacco mosaic virus (TMV) than ribavirin and could be used as new antiviral candidates. The antiviral mode of action research indicated that compound 8e inhibited the formation of the 20S protein disk by acting on the TMV coat protein and therefore inhibited the assembly of TMV particles. This work provides a new idea for the development of new pesticides based on marine sesquiterpenes.

Investigating the Antiparasitic Potential of the Marine Sesquiterpene Avarone, Its Reduced form Avarol, and the Novel Semisynthetic Thiazinoquinone Analogue Thiazoavarone.

The chemical analysis of the sponge Dysidea avara afforded the known sesquiterpene quinone avarone, along with its reduced form avarol. To further explore the role of the thiazinoquinone scaffold as an antiplasmodial, antileishmanial and antischistosomal agent, we converted the quinone avarone into the thiazinoquinone derivative thiazoavarone. The semisynthetic compound, as well as the natural metabolites avarone and avarol, were pharmacologically investigated in order to assess their antiparasitic properties against sexual and asexual stages of Plasmodium falciparum, larval and adult developmental stages of Schistosoma mansoni (eggs included), and also against promastigotes and amastigotes of Leishmania infantum and Leishmania tropica. Furthermore, in depth computational studies including density functional theory (DFT) calculations were performed. A toxic semiquinone radical species which can be produced starting both from quinone- and hydroquinone-based compounds could mediate the anti-parasitic effects of the tested compounds.

Unified Synthesis of the Marine Sesquiterpene Quinones (+)‐Smenoqualone, (–)‐Ilimaquinone, (+)‐Smenospongine, and (+)‐Isospongiaquinone

The marine sesquiterpene quinones (+)‐smenoqualone, (–)‐ilimaquinone, (+)‐smenospongine, and (+)‐isospongiaquinone were efficiently synthesized in a unified manner starting from a known trans‐decalin derivative, which is accessible from (+)‐5‐methyl Wieland–Miescher ketone. The synthetic method involved the following key steps: (i) assembly of the whole carbon skeleton by coupling the decalin segment to an aromatic moiety; (ii) p‐quinone formation by strategic salcomine oxidation of phenolic intermediates; (iii) direct conversion of (–)‐ilimaquinone into (+)‐isospongiaquinone by pTsOH‐induced isomerization of the C‐4 olefinic double bond; (iv) site‐selective amination of a dimethoxy‐p‐quinone intermediate by substitution of the C‐18 methoxy group with an amino group; and (v) one‐step construction of the requisite tetracyclic core structure by sequential BF3·Et2O‐induced rearrangement/cyclization of an olefinic decalin intermediate having an aromatic moiety. The syntheses of (+)‐smenoqualone and (+)‐smenospongine are reported here for the first time.

Total Synthesis of Marine Sesquiterpene Quinones (+)‐Cyclospongiaquinone‐1 and (–)‐Dehydrocyclospongiaquinone‐1 with a Tetracyclic Benzo[a]xanthene Skeleton

Two marine sesquiterpene quinones, (+)‐cyclospongiaquinone‐1 and (–)‐dehydrocyclospongiaquinone‐1, were efficiently synthesized in 10 and 12 steps and overall yields of 33 and 24 %, respectively, from commercially available (+)‐sclareolide. The synthetic strategy involves the following crucial steps: (i) assembly of the carbon skeleton by coupling the decalin segment to the aromatic moiety; (ii) one‐step construction of the dihydropyran ring by acid‐induced acetonide deprotection/ether cyclization of an olefinic decalin intermediate that contains the aromatic moiety; (iii) formation of the p‐benzoquinone moiety by oxidation of a p‐methoxyphenolic derivative to produce (+)‐cyclospongiaquinone‐1; and (iv) oxidative dehydrogenation at the C‐12–C‐12a bond of a tetracyclic intermediate to obtain (–)‐dehydrocyclospongiaquinone‐1.

Biotransformations versus chemical modifications: new cytotoxic analogs of marine sesquiterpene ilimaquinone

Highly biologically active marine sesquiterpene ilimaquinone was selected for chemical modifications. Its biotransformation was investigated using a combinatorial approach as an original way to screen different strains of microorganisms. Mucor circinelloides ATCC 8541 was able to structurally modify ilimaquinone into three different compounds. A stereospecific epoxidation was observed and compared to chemical epoxidation. A hydroxylation of the decalin ring was also observed as well as an unexpected substitution on the quinone ring by ethanolamine. Compounds were evaluated against several cell lines.

Suberosanes as Potential Antitumor Agents: First Enantioselective Total Synthesis of (1S)-Suberosanone and Configurational Assignment of Suberosenol A

The first enantioselective total syntheses of two marine sesquiterpenes, natural (1<i>S</i>)-suberosanone and (1<i>S</i>)-suberosenol A, are achieved leading to the assignment of the absolute configuration of natural suberosenol A. A new access to (1<i>S</i>)-suberosenone from a key tricyclic enone was also developed leading to an overall improvement of the synthesis, allowing an efficient route to suberosenol A. Hyperbaric asymmetric Michael addition and a highly efficient silver trifluoroacetate mediated α-alkylation for the formation of ring A completed the key steps of the synthesis. Regrettably, synthetic (1<i>S</i>)-suberosanone did not retain the reported picomolar cytotoxic activity displayed by the natural product, the reason for which remains to be elucidated.

Approach to Merosesquiterpenes via Lewis Acid Catalyzed Nazarov-Type Cyclization: Total Synthesis of Akaol A.

A Lewis acid catalyzed Nazarov-type cyclization of arylvinylcarbinol has been developed for the asymmetric synthesis of carbotetracyclic core of merosesquiterpenes. The reaction works only in the presence of 2 mol % of Sn(OTf)2 and Bi(OTf)3 in dichloroethane under elevated temperature. The methodology offers the synthesis of a variety of enantioenriched arylvinylcarbinols from commercially available (3aR)-sclareolide 9 in six steps with an eventual concise total synthesis of marine sesquiterpene quinol, akaol A (1a).

Synthesis and biological activity of amino acid derivatives of avarone and its model compound

A series of eighteen derivatives of marine sesquiterpene quinone avarone and its model system tert-butylquinone with amino acids has been synthesized by nucleophilic addition of amino acids to the quinones. In vitro cytotoxic activity toward human cancer cell lines (HeLa, A549, Fem-X, K562, MDA-MB-453) and normal MRC-5 cell line was determined. Several compounds showed very strong inhibitory activity with IC50 values less than 10μM. Avarone derivatives were more active than the corresponding tert-butylquinone derivatives. The results of the cytofluorimetric analysis of cell cycle of HeLa cells showed that apoptosis might be one of possible mechanism of action of these compounds in cancer cells. In order to examine the influence of caspases on cell death, the apoptotic mechanisms induced by the tested compounds were determined using specific caspases 3, 8 and 9 inhibitors. For all compounds antibacterial activities against six strains of Gram-positive and four strains of Gram-negative bacteria were determined, as well as antifungal activity against three fungal species.

Synthesis of the Sesquiterpenes Albicanol, Drimanol, and Drimanic Acid, and the Marine Sesquiterpene Hydroquinone Deoxyspongiaquinol

AbstractA TiIII‐mediated radical cyclization cascade has been used for the synthesis of the sesquiterpenes (+)‐albicanol, (+)‐drimanol, and (+)‐drimanic acid. Starting from all‐trans‐farnesol, (+)‐albicanol could be prepared in seven steps in an overall yield of 14.9 %. Furthermore, a highly diastereoselective hydrogenation of (+)‐albicanol to give (+)‐drimanol has been developed. We used the synthesized (+)‐drimanic acid to achieve the first synthesis of the marine sesquiterpene hydroquinone deoxyspongiaquinol and the quinone deoxyspongiaquinone. Thus, this synthetic strategy gave access to five natural products.

Further in vitro Evaluation of Antimicrobial Activity of the Marine Sesquiterpene Hydroquinone Avarol

This work extends in vitro screening of antimicrobial activity of the sesquiterpene hydroquinone avarol, a main secondary metabolite of the Mediterranean sponge species Dysidea avara. The antimicrobial activity was in part evaluated by microdilution method against selected bacterial and fungal strains. Additionally, the screening included evaluation of anti-quorum sensing (anti-QS) effects. At a different extent avarol was proven to be active against all the microorganisms tested (MIC 0.002-0.008 mg/mL and MBC 0.004-0.016 mg/mL; MIC 0.004-0.015 mg/mL and MFC 0.008-0.030 mg/mL; respectively). This marine natural product also showed moderate anti-QS effects, reducing Pseudomonas aeruginosa PAO1 biofilm formation (75%), its twitching and protrusions motilities as well as pyocianin production (39%). According to the best of our knowledge, this is the first report both on avarol anti Gram-negative bacterial activity and anti-QS effects.

Inducers of Hypoxic Response: Marine Sesquiterpene Quinones Activate HIF-1

The hypoxia-inducible factor-1 (HIF-1) transcription factor regulates cellular oxygen homeostasis. Agents that activate HIF-1 and downstream HIF targets represent potential drug leads for the prevention and/or treatment of ischemic disorders. In a search for small-molecule HIF-1 activators, 1936 marine invertebrate and algal extract samples (U.S. National Cancer Institute's Open Repository) were evaluated for HIF-1 activation activity in a cell-based reporter assay. Bioassay-guided fractionation of two active extracts of the sponge Dactylospongia elegans afforded four new sesquiterpene quinones (2-5), one new sesquiterpene phenol (6), the known Golgi disruptor ilimaquinone (1), and three previously reported ilimaquinone analogues (7-9). While antiproliferative activity was observed at higher concentrations, the sesquiterpene quinones (1-3) possessing a 2-hydroxy-5-methoxy-1,4-benzoquinone moiety activated HIF-1 and increased the expression of HIF-1 target gene vascular endothelial growth factor (VEGF) in T47D cells.

Bioconjugate of Lysozyme and the Antibacterial Marine Sesquiterpene Quinone Avarone and Its Derivatives

A conjugate of lysozyme with avarone, a bioactive sesquiterpene quinone of marine origin, and its three derivatives were synthesized. MALDI TOF mass spectral analysis and tryptic digestion showed that the only residue in lysozyme that was modified by all derivatives was lysine 97. The identity of the residue was in full correlation with the prediction obtained by molecular modeling. All bioconjugates preserved most of the enzymatic activity of lysozyme. The melting point of the conjugates was slightly increased in comparison to lysozyme, indicating a slight stabilization of structure. The antibacterial activity of all the conjugates to both Gram positive and Gram negative bacteria was stronger than the activity of either lysozyme or the quinones, the MIC values being in low micromolar range for some conjugates.

First enantiospecific synthesis of marine sesquiterpene quinol akaol A

The first enantiospecific synthesis of akaol A, a marine sesquiterpene quinol, has been achieved. Key steps of the synthetic sequence are the oxidative degradation of (-)-sclareol to a dinorlabdane ketoester, mediated by the ozone-lead(IV) acetate system, the diastereoselective α-methylation of a ketoaldehyde, followed by an intramolecular aldol condensation and the further Diels-Alder cycloaddition of a dienol ether.

Total Synthesis of 10-Isocyano-4-cadinene and Its Stereoisomers and Evaluations of Antifouling Activities

The first enantioselective total synthesis of 10-isocyano-4-cadinene, a marine sesquiterpene isolated from nudibranchs of the family Phyllidiidae, and determination of its absolute stereochemistry were achieved. 10-Isocyano-4-cadinene is expected to be a novel nontoxic antifouling agent. In the synthesis, intermolecular Diels-Alder reaction and samarium diiodide induced Barbier-type cyclization were employed as key steps. The absolute configuration of 10-isocyano-4-cadinene was determined as (1S,6S,7R,10S) by comparison of the optical rotations between natural and synthetic samples. In addition, the authors successfully synthesized 10-epi- and di-1,6-epi-10-isocyano-4-cadinene through the same synthetic pathway. Antifouling activities against Balanus amphitrite with the cadinenes were also evaluated.

ChemInform Abstract: Total Synthesis of (.+-.)-Dactylol and Related Studies.

The marine sesquiterpene (±)-dactylol was prepared from 2,5-dimethyl-7-(3-methyl-4-pentenyl)tropone in six steps. Salient features of the synthesis include: (1) a stereo- and regioselective intramolecular tropone-alkene [6π+2π] photocyclization to furnish the dactylol carbocyclic skeleton, (2) a regioselective Baeyer-Villiger oxidation of a bisneopentyl ketone, and (3) a chemoselective 1,4-reduction of a cyclocta-1,3-diene moiety

ChemInform Abstract: Intramolecular Additions of Allylsilanes to Conjugated Dienones. Direct Stereoselective Syntheses of (.+-.)-Neolemnanyl Acetate and (.+- .)-Neolemnane.

The total synthesis of the marine sesquiterpenes neolemnanyl acetate (1) and neolemnane (2) is reported. An intramolecular allylsilane addition to a conjugated dienone is used to assemble the basic 6,8-fused skeleton. Functionalization of the cyclooctane ring was achieved by means of a regiospecific photooxygenation