Andrés García-Granados

Solution- and solid-phase synthesis and anti-HIV activity of maslinic acid derivatives containing amino acids and peptides

Maslinic acid (1) has been coupled at C-28 with several alpha- and omega-amino acids by using solution- and solid-phase synthetic procedures. Twelve derivatives (2-13) with a single amino acid residue were prepared in solution phase, whereas a dipeptide (14), a tripeptide (15), and a series of conjugate dipeptides (16-24) were synthesized in solid phase. The anti-HIV activity of these compounds was assessed on MT-2 cells infected with viral clones carrying the luciferase gene as a reporter. While in maslinic acid (1) were present both cytotoxic and antiviral activities, only the derivatives 13 and 24 showed anti-HIV-1 activity and therefore represent a novel class of anti-HIV-1 compounds.

Biotransformation of oleanolic and maslinic acids by Rhizomucor miehei.

Microbial transformation of oleanolic acid by Rhizomucor miehei produced three metabolites. A known compound, a 30-hydroxyl derivative (queretaroic acid), and two 7β,30- and 1β,30-dihydroxylated metabolites, respectively. The action of the same fungus (R. miehei) on maslinic acid produced an olean-11-en-28,13β-olide derivative, a metabolite hydroxylated at C-30, an 11-oxo derivative, and two metabolites with an 11α,12α-epoxy group, hydroxylated or not at C-30. Their structures were elucidated by extensive analyses of their spectroscopic data, and also by chemical correlations.

Maslinic acid derivatives induce significant apoptosis in b16f10 murine melanoma cells

Maslinic acid (2α,3β-dihydroxyolean-12-en-28-oic acid), a natural dihydroxylated pentacyclic triterpene acid isolated from olive-pressing residues, has been investigated together with some of its derivatives regarding the induction of apoptosis in B16F10 melanoma cells. Some of the compounds tested are described in this work, but others come from previous studies. Ten of these derivatives induce over 80% of apoptosis, clearly promoting cell death in B16F10 melanoma. By contrast, the induction cell death through necrosis was very slightly significant with these compounds. These results indicate that maslinic acid derivatives are promising chemopreventive and chemotherapeutic agents.

Semi-synthesis of acylated triterpenes from olive-oil industry wastes for the development of anticancer and anti-HIV agents

A broad set of potential bioactive conjugate compounds has been semi-synthesized through solution- and solid-phase organic procedures, coupling two natural pentacyclic triterpene acids, oleanolic (OA) and maslinic acids (MA), at the hydroxyl groups of the A-ring of the triterpene skeleton, with 10 different acyl groups. These acyl OA and MA derivatives have been tested for their anti-proliferative (against the b16f10 murine melanoma cancer cells) and antiviral (as inhibitors of the HIV-1-protease) effects. Several derivatives have shown high levels of early and total apoptosis (up to 90%). Most of the compounds that exhibited anti-proliferative effects also generated ROS, probably involving the activation of an intrinsic apoptotic route. The only four compounds that did not cause the release of ROS could be related to the participation of a probable extrinsic activation of the apoptosis mechanism. A great number of these acyl OA and MA derivatives have proved to be potent inhibitors of the HIV-1-protease, the most active inhibitors having IC50 values between 0.31 and 15.6 μM, these values being between 4 and 186 times lower than their non-acylated precursors. The potent activities exhibited in the apoptosis-activation processes and in the inhibition of the HIV-1-protease by some OA and MA acylated derivatives imply that these compounds could be used as new, safe, and effective anticancer and/or antiviral drugs.

Assessment of the safety of maslinic acid, a bioactive compound from Olea europaea L.

SCOPE Maslinic acid, the main pentacyclic triterpene of the cuticle of Olea europaea L. fruit, has multiple beneficial effects on health, most notably antitumor and hypoglycemic properties. Notwithstanding the biological activities, there is a lack of knowledge about its safety. Therefore, the purpose of this study was to evaluate whether high doses of maslinic acid have harmful effects on Swiss CD-1 male mice. METHODS AND RESULTS The single oral administration of the pentacyclic triterpene at 1000 mg/kg to mice did not produce any signs of morbidity or mortality. The repeated daily oral administration of 50 mg/kg of maslinic acid for 28 days did not induce any sign of toxicity during the experimental period. Body weight did not differ between mice that received the triterpene and the control group. Similarly, hematological and biochemical variables were not affected by the treatment. Histopathologic examination of the organs revealed that there were no differences between the control and the treated mice. CONCLUSION Taken together the results obtained from the acute and the repeated intake of maslinic acid indicate that the compound does not exert any adverse effects on the variables tested in mice, thus suggesting a sufficient margin of safety for its putative use as a nutraceutical.

Biotransformation of 6β-Eudesmanolides Functionalized at C-3 with Curvularia lunata and Rhizopus nigricans Cultures

Abstract A series of biotransformations of 6β-santonin and its derivatives with functions at C-3, were carried out with Curvularia lunata and Rhizopus nigricans cultures. Rhizepus nigricans was more active in the biotransformation process against these substrates. The biotransformation of 6β-santonin yielded its 2α-hydroxy-1,2-dihydro derivative. The biotransformation of ketones at C-3 obtained by partial or total hydrogenation of double bonds in ring A led to 3S alcohols. Incubation of the 3S-hydroxyl-4S-13S- 6α-eudesmanolide with Rhizopus nigricans produced epimerization at C-4 and hydroxylation at C-8, C-1 or C-4, in decreasing order. This epimerization is probably produced with the participation of the hydraxyl goup at C-3. Microbial functionalization at C-8 can provide access to the synthesis of 8,12-eudesmanolides.

Products with biological activity obtained from in vitro micropropagated Sideritis foetens

Abstract A method for the in vitro micropropagation of Sideritis foetens species is described. About one million plants were produced from a single nodal segment in one year. Phytochemical studies of plants indicated that this method increases their diterpene content, although the same type of products as in natural plants are obtained. ent-6α- Acetoxy-3β,8α-dihydroxylabda-13(16),14-diene, ent-6α,8α,18-trihydroxylabda-13(16),14-diene, ent-6α-acetoxy-8α-18- dihydroxy-labda-13(16),14-diene and ent -18-acetoxy-6α,8α-dihydroxylabda-13(16),14-diene were isolated from micropropagated plants. ent -3β,6β-Dihydroxy-13- epi -manoyl oxide and ent -16,18-dihydroxy-6-oxomanoyl oxide (ketomanoyl) were obtained by chemical methods from these natural products. Both products inhibit basal adenylatecyclase activity and activity previously stimulated by forskolin or fluoride, but were without effect on glucagon-enhanced activity.

Chemical-microbiological synthesis of 6β-eudesmanolides by Curvularia lunata cultures from eudesmanes with functions at C-1 and C-6

The biotransformation of several 1,6-difunctionalized eudesmanes was carried out with Curvularia lunata cultures in order to obtain 11-R and 11-S 12-hydroxy derivatives, which were oxidized with RuH2(Ph3P)4 to give 11-R and 11-S-6seudesmanolides. The best results were achieved by biotransformatlon of the 1,6-diketo compound, which allowed us to obtain a considerable yield of 11-R-eudesmanolides.

Solid-Phase Library Synthesis of Bi-Functional Derivatives of Oleanolic and Maslinic Acids and Their Cytotoxicity on Three Cancer Cell Lines

A wide set of 264 compounds has been semisynthesized with high yields and purities. These compounds have been obtained through easy synthetic processes based on a solid-phase combinatorial methodology. All the members of this library have one central core of a natural pentacyclic triterpene (oleanolic or maslinic acid) and differ by 6 amino acids, coupled with the carboxyl group at C-28 of the triterpenoid skeleton, and by 10 different acyl groups attached to the hydroxyl groups of the A-ring of these molecules. According to the literature on the outstanding and promising pharmacological activities of other similar terpene derivatives, some of these compounds have been tested for their cytotoxic effects on the proliferation of three cancer cell lines: B16-F10, HT29, and Hep G2. In general, we have found that around 70% of the compounds tested show cytotoxicity in all three of the cell lines selected; around 60% of the cytotoxic compounds are more effective than their corresponding precursors, that is, oleanolic (OA) or maslinic (MA) acids; and nearly 50% of the cytotoxic derivatives have IC50 values between 2- to 320-fold lower than their corresponding precursor (OA or MA).

Parasitostatic effect of maslinic acid. I. Growth arrest of Plasmodium falciparum intraerythrocytic stages.

BackgroundNatural products have played an important role as leads for the development of new drugs against malaria. Recent studies have shown that maslinic acid (MA), a natural triterpene obtained from olive pomace, which displays multiple biological and antimicrobial activities, also exerts inhibitory effects on the development of some Apicomplexan, including Eimeria, Toxoplasma and Neospora. To ascertain if MA displays anti-malarial activity, the main objective of this study was to asses the effect of MA on Plasmodium falciparum-infected erythrocytes in vitro.MethodsSynchronized P. falciparum-infected erythrocyte cultures were incubated under different conditions with MA, and compared to chloroquine and atovaquone treated cultures. The effects on parasite growth were determined by monitoring the parasitaemia and the accumulation of the different infective stages visualized in thin blood smears.ResultsMA inhibits the growth of P. falciparum Dd2 and 3D7 strains in infected erythrocytes in, dose-dependent manner, leading to the accumulation of immature forms at IC50 concentrations, while higher doses produced non-viable parasite cells. MA-treated infected-erythrocyte cultures were compared to those treated with chloroquine or atovaquone, showing significant differences in the pattern of accumulation of parasitic stages. Transient MA treatment at different parasite stages showed that the compound targeted intra-erythrocytic processes from early-ring to schizont stage. These results indicate that MA has a parasitostatic effect, which does not inactivate permanently P. falciparum, as the removal of the compound allowed the infection to continueConclusionsMA displays anti-malarial activity at multiple intraerythrocytic stages of the parasite and, depending on the dose and incubation time, behaves as a plasmodial parasitostatic compound. This novel parasitostatic effect appears to be unrelated to previous mechanisms proposed for current anti-malarial drugs, and may be relevant to uncover new prospective plasmodial targets and opens novel possibilities of therapies associated to host immune response.