Enantiopure 2,2′-dihydroxy-3,3′-dimethoxy-5,5′-diallyl-6,6′-dibromo-1,1′-biphenyl: a conformationally stable C2-dimer of a eugenol derivative

Waste residues from Opuntia ficus indica for peroxidase-mediated preparation of phenolic dimeric compounds

A methodology to detect peroxidase activity in Opuntia ficus indica cladodes waste extracts was performed and then used towards phenolic compounds. The extracts were able to dimerize three different molecules. Dimeric compounds were produced with yields ranging from 11% to 55%. The influence of H2O2 concentration was also tested, finding better yields when the peroxide-to-substrate ratio was 1:1. Some water-miscible solvents were used trying to increase overall yields, but no-significant positive results were found. In fact, one of them, THF, seemed to inhibit dimerization reaction. Hence, we have tested an alternative natural peroxidase source obtained from the wastes of a local highly-consumed vegetable and studied their enzymatic activity towards the preparation of biologically active, valuable compounds.

Synthesis and Antileishmanial Activity of Natural Dehydrodieugenol and Its Mono- and Dimethyl Ethers

The study of chemistry of naturally occurring compounds and the synthesis of their derivatives is fundamentally important for the development of new drugs. In this work, dehydrodieugenol (DHDE) was obtained through oxidative coupling of eugenol, promoted by an aqueous mixture of potassium ferricyanide (K3 [Fe(CN)6 ]) and NH3  · H2 O. The partial methoxylation of DHDE with MeI and K2 CO3 mainly resulted in the molecular-shaped monomethyl ether (DHDE-1MeO) and its dimethyl ether derivative (DHDE-2MeO). The products from the reactions were characterized by (1) H- and (13) C-NMR spectroscopy. Additionally, these studies have reported the antileishmanial activity of DHDE against Leishmania amazonensis (IC50 value of 42.20 μg ml(-1) ) and shown that partial methoxylation of DHDE results in a significant increase in its antiparasitic activity (IC50 value of 13.68 μg ml(-1) ). Based on in vitro bioassays, DHDE-1MeO has shown the highest leishmanicidal activity in promastigota form. Production by direct one-step synthesis of this monomethoxylated compound can be considered to be a cost-effective and environmentally friendly method with a short reaction time.

Hydroxylated biphenyl derivatives are positive modulators of human GABA(A) receptors

A series of 7 hydroxylated biphenyl derivatives (1-7) were prepared to evaluate their ability to modulate the function of several ligand gated ion channel (LGIC) recombinant receptors expressed in Xenopus laevis oocytes. Compounds 1, 3, 4, 6 and 7 are natural occurring compounds whereas the synthesis of compounds 2 and 5 was previously reported (Delogu et al., 2004; Fabbri et al., 2007). None of the compounds tested were able to modify, the activity of the strychnine-sensitive glycine receptor, or the activity of nicotinic receptor. The function of the 5HT(3A) receptor was partially inhibited by all compounds tested, however this inhibition occurred at relatively high concentrations (100 μM). All compounds, with the exception of compound 6, potentiate the action of gamma-aminobutyric acid (GABA)-evoked Cl(-) currents in Xenopus laevis oocytes expressing recombinant human α(1)β(2)γ(2L) GABA(A) receptors. Compounds 1, 2, 5 and 7 enhance the function of the GABA(A) receptor at concentrations higher than 3-10 μM. Compound 4 was the most efficacious. However, compound 3 was the most potent (EC(50) 0.8 μM). The potency of compound 3 in modulating the function of the GABA(A) receptor was comparable to that of diazepam, propofol or allopregnanolone. The enhancement of the GABA evoked Cl(-) currents by compound 3 was not affected by flumazenil. Compound 3 did not induce loss of the righting reflex in rats suggesting that it is not an anesthetic agent, however, its ability in protecting the animals from seizures induced by picrotoxin confirm that its action occurs through the GABA(A) receptor.

Antiproliferative and pro-apoptotic activity of eugenol-related biphenyls on malignant melanoma cells

Background

Malignant melanoma is one of the most aggressive skin cancer and chemotherapeutic agents currently in use are still unsatisfactory. Prevention and early diagnosis are the only effective tools against this tumour whose incidence and mortality rates are highly increased during the last decades in fair skin populations. Therefore the search for novel therapeutic approaches is warranted. Aim of this work was to identify and test new compounds with antiproliferative and cytotoxic activity on melanoma cells. We tested eugenol together with six natural and synthetic eugenol-related compounds for their capability to inhibit cell growth on primary melanoma cell lines established from patients' tissue samples.

Results

Eugenol and isoeugenol monomers and their respective O-methylated forms did not show to inhibit melanoma cells proliferation. Conversely, the dimeric forms (biphenyls) showed some antiproliferative activity which was mild for dehydrodieugenol, higher for its O,O'-methylated form (O,O'-dimethyl-dehydrodieugenol), and markedly pronounced for the racemic mixture of the brominated biphenyl (6,6'-dibromo-dehydrodieugenol) (S7), being its enantiomeric form (S) the most effective compared to the other compounds. Such activity resulted to be selective against tumour cells, without affecting cultured normal human skin fibroblasts. Dose and time dependence curves have been obtained for the enantiomeric form S7-(S). Then IC₅₀ and minimal effective doses and times have been established for the melanoma cell lines tested. TUNEL and phosphatidylserine exposure assays demonstrated the occurrence of apoptotic events associated with the antiproliferative activity of S7-(S). Cytotoxic activity and apoptosis induced by treating melanoma cells with eugenol-related biphenyls was partially dependent by caspase activation.

Conclusion

Our findings demonstrate that the eugenol related biphenyl (S)-6,6'-dibromo-dehydrodieugenol elicits specific antiproliferative activity on neuroectodermal tumour cells partially triggering apoptosis and its activity should be further investigated on in vivo melanoma models in order to evaluate the real anticancer effectiveness on such tumour.