Search

Regiodivergent photocyclization of dearomatized acylphloroglucinol substrates has been developed to produce type A polycyclic polyprenylated acylphloroglucinol (PPAP) derivatives using an excited-state intramolecular proton transfer (ESIPT) process. Using this strategy, we achieved the enantioselective total syntheses of the type A PPAPs (-)-nemorosone and (-)-6-epi-garcimultiflorone A. Diverse photocyclization substrates have been investigated leading to divergent photocyclization processes as a function of tether length. Photophysical studies were performed, and photocyclization mechanisms were proposed based on investigation of various substrates as well as deuterium-labeling experiments.

Propolis is a natural product obtained from bees, used since ancient times for its multiple pharmacological properties. Several evidences indicate that the antiproliferative effect of propolis against different cancer cell lines can be ascribed to its components. However, little is known about the possible use of this natural product in the treatment of chemo-resistant tumors. Combination experiments were carried out in order to study the ability of Cuban propolis extracts (CP) and its main component (nemorosone) to chemosensitize doxorubicin-resistant human colon carcinoma cells (LoVo Dox) compared to the sensitive cells (LoVo). Antiproliferative effect was determined by MTT assay after 24, 48 and 72 h exposure. Synergistic, additive or antagonistic effects of different combined treatments (CP-Dox and nemorosone-Dox), was evaluated by isobologram-combination index method. The interaction mechanisms between CP or nemorosone with doxorubicin were studied by flow cytometry to investigate cell death pathway and cell cycle arrest. Reactive oxygen species production (ROS) and mitochondrial membrane potential (ΔΨm) modification were also evaluated. Data showed that both CP and its main component nemorosone were able to reduce cell proliferation in a concentration- and time-dependent manner. Combined treatments induced a cell growth inhibition with a significantly synergistic antiproliferative and cytotoxic effect. Co-treatments induced also cell cycle arrest which results in apoptosis by a marked ROS production and drastic alteration of ΔΨm. In summary, our findings evidence the potential role of Cuban propolis extracts and their main component nemorosone as new chemosensitizing agents against drug-resistant human colon carcinoma cells.

A general strategy for the synthesis of polycyclic polyprenylated acylphloroglucinols is described in which a scalable, Lewis acid catalyzed epoxide-opening cascade cyclization is used to furnish common intermediate 4. The utility of this approach is exemplified by the total syntheses of both ent-nemorosone and (+)-secohyperforin, which were each accomplished in four steps from this intermediate.

Three main types of Cuban propolis directly related to their secondary metabolite composition have been identified: brown, red and yellow propolis; the former is majoritarian and is characterized by the presence of nemorosone. In this study, brown Cuban propolis extracts were found cytotoxic against HepG2 cells and primary rat hepatocytes, in close association with the nemorosone contents. In mitochondria isolated from rat liver the extracts displayed uncoupling activity, which was demonstrated by the increase in succinate-supported state 4 respiration rates, dissipation of mitochondrial membrane potential, Ca2+ release from Ca2+-loaded mitochondria, and a marked ATP depletion. As in cells, the degree of such mitotoxic events was closely correlated to the nemorosone content. The propolis extracts that do not contain nemorosone were neither cytotoxic nor mitotoxic, except R-29, whose detrimental effect upon cells and mitochondria could be mediated by its isoflavonoids and chalcones components, well known mitochondrial uncouplers. Our results at least partly unravel the cytotoxic mechanism of Cuban propolis, particularly regarding brown propolis, and raise concerns about the toxicological implication of Cuban propolis consumption.

An approach to a model compound for polycyclic polyprenylated acylphloroglucinols is developed using a ring-closing metathesis approach to give a substituted cyclooctene. This undergoes cyclization via an intramolecular acylation leading to a substituted bicyclo[3.3.1]nonan-9-one related to hyperforin, nemorosone, clusianone, garsubellin A and other members of the polyprenylated acylphloroglucinol.

The remarkable biological activities of polyprenylated polycyclic acylphloroglucinols (PPAPs) combined with their highly decorated bicyclo[3.3.1]nonane-2,4,9-trione frameworks have inspired synthetic organic chemists over the last decade. The concise total syntheses of four natural products PPAPs; hyperforin and papuaforins A-C, and the formal synthesis of nemorosone are reported. Key to the realization of this strategy is the short and scalable synthesis of densely substituted PPAP scaffolds through a gold(I)-catalyzed 6-endo-dig carbocyclization of cyclic enol ethers for late-stage functionalization.

Estrogen receptor (ER) antagonists have been widely used for breast cancer treatment; however, patients have increasingly shown resistance and sensitivity to the high toxicity of these drugs, and identification of novel targeted therapies is therefore required. To determine whether nemorosone, a polycyclic polyisoprenylated benzophenone isolated from floral resins of Clusia rosea Jacq. and Cuban propolis samples, exerts anticancer effects on human breast cancer cells, estrogen receptor positive (ERα+) MCF-7 and estrogen receptor negative (ERα–) MDA-MB-231 and LNCaP cells were used. Cells were treated with nemorosone alone or in association with 17β-estradiol (E2) or an ER antagonist, ICI 182,780, a selective ER downregulator that completely abrogates estrogen-sensitive gene transcription. Nemorosone inhibited the cell viability of ERα+ but not of ERα– cells. In MCF-7, nemorosone induced inhibition of cell growth by blocking the cell cycle in the G0/G1phase. Moreover, the expression of pERK1/2 and pAkt, considered to be hallmarks of the nongenomic estrogen signalling pathway, were reduced in MCF-7 cells treated with nemorosone. All these effects were enhanced by ICI 182,780. However, nemorosone was not able to interfere with E2-induced Ca2+release. These findings suggest that nemorosone may have therapeutic application in the treatment of breast cancer because of its activity on ERα.

A broadly applicable asymmetric synthetic strategy utilizing N-amino cyclic carbamate alkylation that provides access to the various stereochemical permutations of a common structural motif found in many polycyclic polyprenylated acylphloroglucinols is described. The utility of this methodology is demonstrated through the first asymmetric total synthesis of the antiviral agent (+)-clusianone.

Neuroblastoma is the second most common solid tumour during childhood, characterized by rapid disease progression. Most children with metastasized neuroblastoma die despite intensive chemotherapy due to an intrinsic or acquired chemotherapy resistance. Thus, new therapeutic strategies are urgently needed. Here, we demonstrate that the novel compound nemorosone isolated from alcoholic extracts of Clusia rosea resins by reverse phase high pressure liquid chromatography (RP-HPLC) exerts cytotoxic activity in neuroblas-toma cell lines both parental and their clones selected for resistance against adriamycin, cisplatin, etoposide or 5-fluorouracil. Cell cycle studies revealed that nemorosone induces an accumulation in G0/G1- with a reduction in S-phase population combined with a robust up-regulation of p21Cip1. Furthermore, a dose-dependent apoptotic DNA laddering accompanied by an activation of caspase-3 activity was detected. Nemorosone induced a significant dephosphorylation of ERK1/2 in LAN-1 parental cells probably by the inhibition of its upstream kinase MEK1/2. No significant modulation of signal transducers JNK, p38 MAPK and Akt/PKB was detected. The enzymatic activity of immunoprecipitated Akt/PKB was strongly inhibited in vitro, suggesting that nemorosone exerts its anti-proliferative activity at least in part by targeting Akt/PKB in the cell lines studied. In addition, a synergistic effect with Raf-1 inhibitor BAY 43-9006 was found. Finally, nemorosone induced a considerable down-regulation of N-myc protein levels in parental LAN-1 and an etoposide resistant sub-line at the same drug-concentrations.

The first enantiospecific approach to garsubellin A and related phloroglucin natural product nemorosone, of contemporary interest from (−)alpha -pinene, has been delineated. Through a series of stereospecific operations, the requisite stereochemistry of the prenyl groups has been secured. Kende cyclization has been employed as the key step to construct the functionalized bicyclo[3.3.1]nonane core.

The total syntheses of the polyprenylated polycyclic acylphloroglucinols hyperforin (VI) and papuaforins A—C (III)-(V), and the formal synthesis of nemorosone (VII) are reported.

Three polycyclic polyprenylated benzoylphloroglucinol natural products, plukenetiones B, D, and E, are shown to be diastereomeric to the related compounds, nemorosone II and sampsonione G.

From the floral resins of Clusia nemorosa male, C. nemorosa hermaphrodite, Clusia rosea female, Clusia grandiflora male, C. grandiflora female, Clusia insignis male (all section Chlamydoclusia ). C. renggerioides male (with pistillodium), C. renggerioides male (without pistillodium), C. renggerioides female (all section Cordylandra ) belonging to the family Clusiaceae, we have isolated two novel polyisoprenylated benzophenones, nemorosone II and 6- epi -nemorosone, and a xanthone. The latter is the first member of this class of compounds ever isolated from the genus Clusia . HPLC allowed the quantification of these and other methylated benzophenones in the methylated resins revealing that indeed these are the major constituents of Clusia floral resins. Oleic, stearic and some unusual long chain esters and acids are the main constituents of the stamen oils.

The floral resins of five species of Clusia belonging to two taxonomic sections of the genus were investigated. These resins are used by pollinating bees for nest construction. The major components of these reins are polyisoprenylated benzophenones, a class of biologically active compounds. We found clusianone and three hitherto unknown compounds, grandone, nemorosone and hydroxy-nemorosone.

A direct synthesis of analogs of hyperforin and nemorosone containing the key bicyclic unit was accomplished from 2-carboxyethylcyclohexanone and benzoylcyclohexanone. Key steps included a manganic acetate-mediated cyclization and the formation of the beta-bromo enone.

The synthesis of an unnatural polyprenylated acylphloroglucinol (PPAP), regioisomeric with nemorosone and clusianone, has been accomplished. The separated enantiomers of this new PPAP, along with those of nemorosone and clusianone, have been screened for activity against HeLa (cervix carcinoma), MIA-PaCa-2 (pancreatic carcinoma), and MCF7 (mamma carcinoma) cancer cell lines. All of the isomers examined gave surprisingly similar results in the screens.

Nemorosone, the major constituent of the floral resin of Clusia rosea was isolated after exhaustive chromatography. This compound was fully characterized as it is in the nature, without methylation as reported before. A keto–enol equilibrium was observed and both isomers were totally characterized by NMR spectroscopic techniques. The previously announced structure for methyl-nemorosone was corrected on the basis of application of chemical methylation, high field 2D NMR techniques and NOE difference spectroscopy experiments on the natural product. Our studies concluded that an interchange occurred in the assignment of the benzoyl moiety position with an isoprenyl group in that structure.

[reaction: see text] The three-carbon alpha,alpha'-annulation of a sterically hindered cyclic beta-keto ester can be achieved by alkynylation with 3,3-diethoxypropyne, syn reduction of the alkyne with Co(2)(CO)(8) and Et(3)SiH, and an intramolecular aldol reaction. The method is potentially useful for the synthesis of nemorosone, hyperforin, and other polycyclic polyprenylated acylphloroglucinols.

The Copey tree (Clusia rosea) has a large distribution in Cuba and its floral resin is a rich source of polyisoprenylated benzophenones. To determine the presence of these natural products, we carried out a study by HPLC of 21 propolis samples produced by honey bees (Apis mellifera) from different provinces of Cuba. Nemorosone resulted to be the most abundant polyisoprenylated benzophenone and the mixture of xanthochymol and guttiferone E was also observed, but in minor proportion. We studied the biological activity of the pure natural product nemorosone and its methyl derivatives. We found that nemorosone has cytotoxic activity against epitheloid carcinoma (HeLa), epidermoid carcinoma (Hep-2), prostate cancer (PC-3) and central nervous system cancer (U251). It also exhibited antioxidant capacity. Methylated nemorosone exhibited less biological activity than the natural product

Nemorosone, the major constituent of the floral resin of Clusia rosea was isolated after exhaustive chromatography. This compound was fully characterized as it is in the nature, without methylation as reported before. A keto–enol equilibrium was observed and both isomers were totally characterized by NMR spectroscopic techniques. The previously announced structure for methyl-nemorosone was corrected on the basis of application of chemical methylation, high field 2D NMR techniques and NOE difference spectroscopy experiments on the natural product. Our studies concluded that an interchange occurred in the assignment of the benzoyl moiety position with an isoprenyl group in that structure.

A computational study (B3LYP), of the metallation of a bridged ketone, an important step in the synthesis of a polycyclic polyprenylated acylphloroglucinol (PPAP), nemorosone, shows three energetically distinct structural possibilities for the lithiated intermediate. These findings, along with observations of the reactivity of the intermediates in bridgehead substitutions, suggest that different intermediates may be formed depending upon the type of process used for lithiation.