Discovery of a synthetic taiwaniaquinoid with potent in vitro and in vivo antitumor activity against breast cancer cells.

Taiwaniaquinoids are a unique family of diterpenoids predominantly isolated from Taiwania cryptomerioides Hayata. Previously, we evaluated the antiproliferative effect of several synthetic taiwaniaquinoids against human lung (A-549), colon (T-84), and breast (MCF-7) tumor cell lines. Herein, we report the in vitro and in vivo antitumor activity of the most potent compounds. Their cytotoxic activity against healthy peripheral blood mononuclear cells (PBMCs) has also been examined. We underscore the limited toxicity of compound C36 in PBMCs and demonstrate that it exerts its antitumor effect in MCF-7 cells (IC50 = 1.8 µM) by triggering an increase in reactive oxygen species, increasing the cell population in the sub-G1 phase of the cell cycle (90 %), and ultimately activating apoptotic (49.6 %) rather than autophagic processes. Western blot results suggested that the underlying mechanism of the C36 apoptotic effects was linked to caspase 9 activation and a rise in the Bax/Bcl-2 ratio. In vivo analyses showed normal behavior and hematological parameters in C57BL/6 mice post C36 treatment. Moreover, no significant impact was observed on the biochemical parameters of these animals, indicating that C36 did not induce liver toxicity. Furthermore, C36 demonstrated a significant reduction in tumor growth in immune-competent C57BL/6 mice implanted with E0771 mouse mammary tumor cells, effectively improving survival rates. These findings position taiwaniaquinoids, particularly compound C36, as promising therapeutic candidates for human breast cancer.

Evaluation of Anticancer and Anti-Inflammatory Activities of Some Synthetic Rearranged Abietanes.

Synthesis of the rearranged abietane diterpenes pygmaeocins C and D, viridoquinone, saprorthoquinone, and 1-deoxyviroxocine has been successfully achieved. The anticancer and anti-inflammatory activities of selected orthoquinonic compounds 5, 7, 13, and 19, as well as pygmaeocin C (17), were evaluated for the first time. The antitumor properties were assessed using three cancer cell lines: HT29 colon cancer cells, Hep G2 hepatocellular carcinoma cells, and B16-F10 murine melanoma cells. Compounds 5 and 13 showed the highest cytotoxicity in HT29 cells (IC50 = 6.69 ± 1.2 µg/mL and IC50 = 2.7 ± 0.8 µg/mL, respectively). Cytometric studies showed that this growth inhibition involved phase S cell cycle arrest and apoptosis induction, possibly through the activation of the intrinsic apoptotic pathway. Morphological apoptotic changes, including nuclear fragmentation and chromatin condensation, were also observed. Furthermore, the anti-inflammatory activity of these compounds was evaluated on the basis of their ability to inhibit nitric oxide production on the lipopolysaccharide activated RAW 264.7 macrophage cell line. Although all compounds showed high anti-inflammatory activity, with percentages between 40 and 100%, the highest anti-inflammatory potential was obtained by pygmaeocin B (5) (IC50NO = 33.0 ± 0.8 ng/mL). Our results suggest that due to their dual roles, this type of compound could represent a new strategy, contributing to the development of novel anticancer agents.

Synthesis of Tricyclic Pterolobirin H Analogue: Evaluation of Anticancer and Anti-Inflammatory Activities and Molecular Docking Investigations.

Pterolobirin H (3), a cassane diterpene isolated from the roots of Pterolobium macropterum, exhibits important anti-inflammatory and anticancer properties. However, its relatively complex tetracyclic structure makes it difficult to obtain by chemical synthesis, thus limiting the studies of its biological activities. Therefore, we present here a short route to obtain a rational simplification of pterolobirin H (3) and some intermediates. The anti-inflammatory activity of these compounds was assayed in LPS-stimulated RAW 264.7 macrophages. All compounds showed potent inhibition of NO production, with percentages between 54 to 100% at sub-cytotoxic concentrations. The highest anti-inflammatory effect was shown for compounds 15 and 16. The simplified analog 16 revealed potential NO inhibition properties, being 2.34 higher than that of natural cassane pterolobirin H (3). On the other hand, hydroxyphenol 15 was also demonstrated to be the strongest NO inhibitor in RAW 264.7 macrophages (IC50 NO = 0.62 ± 0.21 µg/mL), with an IC50NO value 28.3 times lower than that of pterolobirin H (3). Moreover, the anticancer potential of these compounds was evaluated in three cancer cell lines: HT29 colon cancer cells, Hep-G2 hepatoma cells, and B16-F10 murine melanoma cells. Intermediate 15 was the most active against all the selected tumor cell lines. Compound 15 revealed the highest cytotoxic effect with the lowest IC50 value (IC50 = 2.45 ± 0.29 µg/mL in HT29 cells) and displayed an important apoptotic effect through an extrinsic pathway, as evidenced in the flow cytometry analysis. Furthermore, the Hoechst staining assay showed that analog 15 triggered morphological changes, including nuclear fragmentation and chromatin condensation, in treated HT29 cells. Finally, the in silico studies demonstrated that cassane analogs exhibit promising binding affinities and docking performance with iNOS and caspase 8, which confirms the obtained experimental results.

Unprecedented Elimination Reactions of Cyclic Aldols: A New Biosynthetic Pathway toward the Taiwaniaquinoid Skeleton.

The acid treatment of 6,7-seco-abietane dialdehydes gives, in high yield, the corresponding derivatives with the 4a-methyltetrahydrofluorene skeleton of taiwaniaquinoids. A mechanism involving the elimination of formic acid from the cyclic aldol intermediate is proposed here. This process can be postulated as a new biogenetic pathway from abietane diterpenes to taiwaniaquinoids. Using this novel reaction, the first enantiospecific synthesis of bioactive natural cupresol and taxodal has been obtained.

Semisynthesis and Evaluation of Anti-Inflammatory Activity of the Cassane-Type Diterpenoid Taepeenin F and of Some Synthetic Intermediates.

A new strategy for the semisynthesis of the aromatic cassane-type diterpene taepeenin F (6) is reported. The introduction of the methyl group at C-14, characteristic of the target compound, was achieved via dienone 13, easily prepared from abietic acid (10), the major compound in renewable rosin. Biological assays of selected compounds are reported. The antiproliferative activity against HT29, B16-F10, and HepG2 tumor cell lines has been investigated. Salicylaldehyde 21 was the most active compound (IC50 = 7.72 µM). Products 16 and 21 displayed apoptotic effects in B16-F10 cells, with total apoptosis rates of 46 and 38.4%, respectively. This apoptotic process involves a significant arrest of the B16-F10 cell cycle, blocking the G0/G1 phase. Dienone 16 did not cause any loss of the mitochondrial membrane potential (MMP), while salicylaldehyde 21 caused a partial loss of the MMP. The anti-inflammatory activity of the selected compounds was investigated with the LPS-stimulated RAW 264.7 macrophages. All compounds showed potent NO inhibition, with percentages between 80 and 99% at subcytotoxic concentrations. Dienone 16 inhibited LPS-induced differentiation of RAW 264.7 cells, by increasing the proportion of cells in the S phase. In addition, salicylaldehyde 21 had effects on the cell cycle, recovering the cells from the G0/G1 full arrest produced in response to LPS action.

Synthesis and Biological Evaluation of Cassane Diterpene (5α)-Vuacapane-8(14), 9(11)-Diene and of Some Related Compounds.

A set of thirteen cassane-type diterpenes was synthesized and an expedient synthetic route was used to evaluate 14-desmethyl analogs of the most active tested cassane. The anti-inflammatory activities of these 13 compounds were evaluated on a lipopolysaccharide (LPS)-activated RAW 264.7 cell line by inhibition of nitric oxide (NO) production, some of them reaching 100% NO inhibition after 72 h of treatment. The greatest anti-inflammatory effect was observed for compounds 16 and 20 with an IC50 NO of 2.98 ± 0.04 µg/mL and 5.71 ± 0.14 µg/mL, respectively. Flow-cytometry analysis was used to determine the cell cycle distribution and showed that the inhibition in NO release was accompanied by a reversion of the differentiation processes. Moreover, the anti-cancer potential of these 13 compounds were evaluated in three tumor cell lines (B16-F10, HT29, and Hep G2). The strongest cytotoxic effect was achieved by salicylaldehyde 20, and pterolobirin G (6), with IC50 values around 3 µg/mL in HT29 cells, with total apoptosis rates 80% at IC80 concentrations, producing a significant cell-cycle arrest in the G0/G1 phase, and a possible activation of the extrinsic apoptotic pathway. Additionally, initial SAR data analysis showed that the methyl group at the C-14 positions of cassane diterpenoids is not always important for their cytotoxic and anti-inflammatory activities.

Deconjugative α-Alkylation of Cyclohexenecarboxaldehydes: An Access to Diverse Terpenoids.

A general and efficient method for the deconjugative α-alkylation of α,ß-unsaturated aldehydes promoted by a synergistic effect between tBuOK and NaH, which considerably increases the reaction rate under mild conditions, is reported. The ß,γ-unsaturated aldehyde, resulting from the α-alkylation, is transformed in high yield into the corresponding allyl acetate via a lead(IV) acetate-mediated oxidative fragmentation. This strategy could be used for the construction of the carbon skeleton of a wide variety of alkyl or arylterpenoids.

In Vivo Biological Evaluation of a Synthetic Royleanone Derivative as a Promising Fast-Acting Trypanocidal Agent by Inducing Mitochondrial-Dependent Necrosis.

The life-long and life-threatening Chagas disease is one of the most neglected tropical diseases caused by the protozoan parasite Trypanosoma cruzi. It is a major public health problem in Latin America, as six to seven million people are infected, being the principal cause of mortality in many endemic regions. Moreover, Chagas disease has become widespread due to migrant populations. Additionally, there are no vaccines nor effective treatments to fight the disease because of its long-term nature and complex pathology. Therefore, these facts emphasize how crucial the international effort for the development of new treatments against Chagas disease is. Here, we present the in vitro and in vivo trypanocidal activity of some oxygenated abietane diterpenoids and related compounds. The 1,4-benzoquinone 15, not yet reported, was identified as a fast-acting trypanocidal drug with efficacy against different strains in vitro and higher activity and lower toxicity than benznidazole in both phases of murine Chagas disease. The mode of action was also evaluated, suggesting that quinone 15 kills T. cruzi by inducing mitochondrion-dependent necrosis through a bioenergetics collapse caused by a mitochondrial membrane depolarization and iron-containing superoxide dismutase inhibition. Therefore, the abietane 1,4-benzoquinone 15 can be considered as a new candidate molecule for the development of an appropriate and commercially accessible anti-Chagas drug.

Synthesis of Cyclosiphonodictyol A and Its Bis(sulfato).

The first synthesis of the marine benzoxepane hydroquinone cyclosiphonodictyol A and its bis(sulfato) from commercial (+)-sclareolide is reported. The key steps of the synthetic sequence (11 steps, 46% global) are the nucleophilic attack of a hindered tertiary alkoxide, a ring-closing metathesis reaction, and the Diels-Alder cycloaddition of a dienol acetate.

Protecting-Group-Free Synthesis of Cassane-Type Furan Diterpenes via a Decarboxylative Dienone-Phenol Rearrangement.

An expeditious route to obtaining cassane-type furan diterpenes starting from (+)-sclareolide, an inexpensive commercially available natural lactone, has been achieved by using a solvent-free Diels-Alder cycloaddition and an unprecedented decarboxylative dienone-phenol rearrangement as key steps. Its applicability is showcased by the first synthesis of (5α)-vouacapane-8(14),9(11)-diene. The synthesis, which requires no protecting group, is efficient and atom- and step-economical (10 steps, 20% global).

Synthesis and antiproliferative activity of podocarpane and totarane derivatives.

The synthesis of podocarpanes, including 12,19-dihydroxy-13-acetyl-8,11,13-podocarpatriene (23), isolated from Gaultheria yunnanensis and not previously synthesized, and totarane-type terpenoids, starting from the natural labdane trans-communic acid (15), is described. Their antiproliferative activities against MCF-7, T-84 and A-549 human tumoural cell lines are studied. An antiproliferative effect was induced by compounds 23, 27 and 28, with IC50 < 10 µM in two (27) or three cell lines (23 and 28). No correlation with log P values was observed. The totarane o-quinone 27, and especially the catechol 28, which is readily oxidisable to compound 27, were the most active compounds, highlighting the functional groups present in C11 and C12. Compound 28 showed limited toxicity in normal peripheral blood mononuclear cells (78.5% cell viability versus non-treated control cultures at 10 µM), and appeared to exert an antiproliferative effect in A-549 cells (IC50 0.6 µM) through a mechanism that involves the induction of apoptosis mediated by an increased Bax/Bcl-2 ratio. The results of the present study indicate that compound 28, at least, might be useful as an antitumoral agent. Further studies are required to elucidate the cellular and molecular elements involved in its effect, and the activity/toxicity in preclinical models.

Bioinspired Synthesis of Pygmaeocins and Related Rearranged Abietane Diterpenes: Synthesis of Viridoquinone.

A bioinspired synthesis of rearranged abietane diterpenes, related to pygmaeocins, is described. In this process, the key step is the 1,2-migration of the C-20 angular methyl to the C-5 position of the abietane skeleton, which occurs when a C6-C7 unsaturated dehydroabietane derivative is treated with SeO2 in dioxane under reflux (19 examples for this rearrangement are described). Utilizing this reaction, an enantiospecific synthesis of pygmaeocin C and the first synthesis of viridoquinone, starting from the abietane phenol ferruginol, are reported. A tentative mechanism for this reaction and a possible biosynthetic pathway for this family of metabolites are postulated.

Diastereoselective Intramolecular Heck Reaction Assisted by an Acetate Group: Synthesis of the Decahydrobenzofluorene Derivative Dasyscyphin E.

The first synthesis of antifungal sesquiterpene quinol dasyscyphin E was achieved starting from trans-communic acid. The process described involves the first diastereoselective synthesis of this type of compound by cyclization of an aryl bicyclosesquiterpene. The acid was efficiently transformed into a sesquiterpene synthon, which was converted into the corresponding bromoaryl sesquiterpene. The key step of synthetic sequence was the cyclization of the latter under Heck reaction conditions, which yielded the tetracyclic skeleton of the target compound with complete diastereoselectivity. The participation of an acetate group is decisive, both for the course of the Heck reaction and for the stereoselectivity of the process.

Antiproliferative Activity of Natural Taiwaniaquinoids and Related Compounds.

The in vitro antiproliferative activities of some taiwaniaquinoids and related compounds with functionalized A, B, or C rings against human breast (MCF-7), colon (T-84), and lung (A-549) tumor cell lines were assayed. The most potent compounds, 16, 27, and 36, were more effective than the naturally occurring taiwaniaquinones A (4) and F (5) in all three cell lines. The structure-activity relationship study of these new taiwaniaquinoids highlighted the correlation between the bromo substituent and the antiproliferative activity, especially in MCF-7 cells. These findings indicate that some of the taiwaniaquinoids might be useful as cytostatic agents against breast, colon, and lung cancer cell lines.

Short Route to Cassane-Type Diterpenoids: Synthesis of the Supposed Structure of Benthaminin 1.

A short route toward aromatic cassane diterpenes from labdane terpenoids has been developed. In the key step, the aromatic ring with the oxygenated function at C-12 and the characteristic carbon group at C-14 of the target compounds is elaborated via a Diels-Alder/aromatization sequence of a furanosesquiterpene and methyl propiolate. On this basis, the synthesis of the proposed structure of benthaminin 1 from trans-communic acid has been achieved. The physical properties of the synthetic compound are somewhat different from those reported for the natural product.

Oxidative Coupling of (-)-Sclareol and Related Diols Leading to Oxepane Terpenoids.

Treatment of (-)-sclareol and related compounds with lead tetraacetate affords tetracyclic compounds bearing a 2,8-dioxabicyclo[5.2.0]nonane moiety with complete regio- and stereoselectivity. This process, which is also applicable to 1,5-diols with a similar substitution pattern, facilitates the development of efficient syntheses toward oxepane terpenoids, such as aplysistatin derivatives.

Meroxest improves the prognosis of immunocompetent C57BL/6 mice with allografts of E0771 mouse breast tumor cells.

INTRODUCTION: Recently, we have reported the antitumor properties of a new family of synthetic merosesquiterpenes, among which meroxest is highlighted, since it has high activity and specificity for ER+ breast cancer cells. In this paper, we characterize allografts of ER+ E0771 mouse breast tumor cells in immunocompetent C57BL/6 mice, and also analyze the effect of meroxest on the prognosis of the disease. MATERIAL AND METHODS: Twenty female C57BL/6 mice were injected with 106 E0771 cells. Once the tumors reached the appropriate size, the mice were divided into two groups, one control and another treated orally with 15 mg/kg of meroxest. After 20 days, tumor samples were taken for histopathological study and for determination of the expression of the prognostic markers Ki67 and vascular endothelial growth factor (VEGF) by immunofluorescence. RESULTS: In sections stained with hematoxylin-eosin, we observed that tumors have a well-defined capsule enclosing E0771 tumor cells. The central area of tumors contains necrotic regions with leukocyte infiltration. Meroxest treatment significantly reduces tumor size (68%, p < 0.05), induces changes in its structure, decreases the degree of leukocyte infiltration, and significantly reduces the expression of Ki67 (33%, p < 0.05) and VEGF (82%, p < 0.05). CONCLUSIONS: Meroxest improves the prognosis of mice since it reduces leukocyte infiltration, and decreases the expression of Ki67 and VEGF markers. Consequently, the merosesquiterpene could become a useful antiangiogenic drug in the treatment of breast cancer. These results encourage us to deepen the study of meroxest, in order to find more evidence that supports the convenience of its evaluation in a clinical study or trial.

Preparation of oxocene terpenes. The first enantiospecific synthesis of cytotoxic arenaran A.

The first syntheses of cytotoxic marine arenarans A and B starting from commercial (-)-sclareol are reported. The oxocene ring of the target compound is formed via ring-closing metathesis, a process that depends on certain structural requirements. The trans-fused structure of the natural product is confirmed by comparison with the cis-fused isomer, which was synthesized. This synthetic strategy is also applicable to the synthesis of other oxocene terpenes.

First enantiospecific syntheses of marine merosesquiterpenes neopetrosiquinones a and B: evaluation of biological activity.

The first enantiospecific syntheses of neopetrosiquinones A (6) and B (7), two merosesquiterpenes isolated from the deep-water sponge Neopetrosia cf. proxima, from the labdane diterpene trans-communic acid (10) have been achieved. A key step of the synthetic sequence is the simultaneous aromatization of the C ring and the benzylic oxidation on C-7 of an advanced intermediate, mediated by the oxygen-DDQ system. The in vitro antiproliferative activities of neopetrosiquinone B (7) and of the synthetic intermediates 8 and 9 against human breast (MCF-7), lung (A-549), and colon (T-84) tumor cell lines have been assayed. The most potent was compound 9 (IC50 = 4.1 µM), which was twice as active as natural compound 7 (IC50 = 8.3 µM) against A-549 cells. In addition, the treatment with these compounds resulted in an induction of apoptosis. These findings indicate that the terpene benzoquinones reported here might be potentially useful as anticancer agents.

Synthesis of the putative structure of 15-oxopuupehenoic acid.

Synthesis of the putative structure of the marine natural 15-oxopuupehenoic acid has been achieved starting from commercial (-)-sclareol. Key steps of the synthetic sequence are the Robinson annulation of a ß-ketoester and methyl vinyl ketone and an unprecedented cyclization of the resulting α,ß-enone, which is mediated by tin(IV) chloride in the presence of N-phenylselenophthalimide. The physical properties of the synthetic compound are somewhat different from those reported for the natural product.