Milagros Rico

Synthesis and biological studies of flexible brevetoxin/ciguatoxin models with marked conformational preference

Abstract A comparison of the more active polyether toxins which are selective activators of voltage-sensitive sodium channels (VSSC), indicate that these molecules are mostly flat, with a hinge part around the middle of the molecules and a large curvature at one of the ends. Assuming that the receptor is topographically complementary to the active molecules, from the result reported here we could conclude, that the specific requirements of the receptor region can be achieved by synthetic polyether models based on exclusive participation of oxane/oxepane moieties. A new convergent approach to give oxepene rings via double reduction of methyl diacetals is explored. In searching for biological models to further characterize Na+ channels, our studies show that different voltage-dependent Na+ channels are expressed in the rat uterus and activated by brevetoxin-B. However, selected compound models synthesized in this work, failed to inhibit or activate Na+ channel function.

Model studies directed towards microalgal polyether toxins. Use of 2-phenyl-sulphonyl cyclic ethers in the preparation of trans, syn, trans α-alkyl, β-hydroxy-substituted tetrahydropyran subunits

A synthesis of optically active C7- and C8 -tetrahydropyranyl subunits with suitable functionalities for futher elaboration of transfused polyether toxins was achieved from glucal acetate via the use of 2-phynylsulphonyl intermediates. The bicyclic trans,syn,trans oxane-oxepanyl substructure 26 was prepared through the application of this methodology.

Phenolic Constituents, Antioxidant and Preliminary Antimycoplasmic Activities of Leaf Skin and Flowers of Aloe vera (L.) Burm. f. (syn. A. barbadensis Mill.) from the Canary Islands (Spain)

The methanol extracts of leaf skins and flowers of Aloe vera from the Canary Islands were analyzed for their phenolic profiles and screened for their antioxidant and antimycoplasmic activities. The use of reversed phase high performance liquid chromatography (RP-HPLC) allowed the identification of 18 phenolic constituents. Leaf skin extracts were characterized by the abundance of catechin, sinapic acid and quercitrin. Gentisic acid, epicatechin and quercitrin were the most prominent phenolic compounds of the flowers. The in vitro antioxidant activities determined by using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) and ferric antioxidant reducing power (FRAP) assays revealed that both extracts exhibited antioxidant activity, being the leaf skin extract the most active fraction. The leaf skin extract was also found to be active against the microbial strains tested. Therefore, A. vera extracts from leaf skin and flowers can be considered as good natural antioxidant sources.

Phenolic Profile and Antioxidant Activity of Crude Extracts from Microalgae and Cyanobacteria Strains

Aqueous and methanolic extracts of several microalgae (Ankistrodesmus sp., Spirogyra sp., Euglena cantabrica, and Caespitella pascheri) and cyanobacteria (Nostoc sp., Nostoc commune, Nodularia spumigena, Leptolyngbya protospira, Phormidiochaete sp., and Arthrospira platensis) were screened for their radical scavenging activity against the stable radical 1,1-diphenyl-2-picrylhydrazyl. Despite the fact that water was a more efficient solvent to extract greater amount of extractable substances, it seems that methanol was more efficient to extract a selected group of compounds with a higher antioxidant activity. In addition, the identification of 4 simple phenolics (gallic, syringic, protocatechuic, and chlorogenic acids) and the flavonoids (+) catechin and ( ) epicatechin was carried out by using reverse phase high performance liquid chromatography. The strain Euglena cantabrica showed the highest concentration of phenolic compounds, particularly gallic and protocatechuic acids (5.87 and 2.97 mg per gram of dried biomass, resp.). Aqueous and methanolic extracts of microalgae Euglena cantabrica also exhibited the highest antioxidant activity, probably due to the presence of the high contents of phenolics.

Screening of the antioxidant properties of crude extracts of six selected plant species from the Canary Islands (Spain)

The extracts of six common plants from the Canary Islands were screened for their antioxidant activities and compared with several phenolic compounds of natural origin (quercetin, catechin, rutin and gentisic acid) and synthetic (butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT)). The in vitro antioxidant activity determined by using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) method revealed that Plantago major L., Artemisia canariensis (Bess.) Lessing and Bidens aurea (Dryand.) Sherff exerted greater activity than the other plants (90.9%, 89.0% and 88.2% inhibition rate, respectively). The most active plants were Bidens aurea (Dryand.) Sherff and Plantago major L. (9.5 and 7.2 trolox μmol equivalents), when the cupric ion reducing antioxidant capacity assay (CUPRAC) was used. All the plants species exhibited higher antioxidant capacities than the synthetic antioxidants BHA and BHT. Among the natural phenolic compounds, gentisic acid was the most active. However, two of the plant extracts showed higher antioxidant activity than any other of the pure compounds studied, even than that of gentisic acid. The use of reversed phase high performance liquid chromatography (RP-HPLC) allowed the identification of the natural phenolic constituents listed above in Bidens aurea (Dryand.) Sherff and Plantago major L. extracts. Catechin and quercetin were the most prominent phenolic compounds. The presence of phenolic compounds in the plant extracts and their high antioxidant activities underline their phytomedicinal potentials. These plants may be exploited in the production of health foods and as an antioxidant carrier in the food and pharmaceutical industries.

Secondary Metabolites from Two Species of Tolpis and Their Biological Activities

Phytochemical research of two Tolpis species, T. proustii and T. lagopoda, led to the isolation of three new compounds: 30-chloro-3β-acetoxy-22α-hydroxyl-20(21)-taraxastene (1), 3β,22α-diacetoxy-30-ethoxy-20(21)-taraxastene (2) and 3β,28-dihydroxy-11α-hydroperoxy-12-ursene (3). The structures of the new compounds were elucidated by means of extensive IR, NMR, and MS data and by comparison of data reported in the literature. The in vitro antioxidant activities of the extracts were assessed by the DPPH and ABTS scavenging methods. The cytotoxicity of several known compounds and its derivatives was also assessed against human myeloid leukemia K-562 and K-562/ADR cell lines.

Production of Primary and Secondary Metabolites Using Algae

Over the past few decades, there has been an increase in the number of research studies focused on all aspects of the ecology, physiology, biochemistry, cell biology, molecular biology, systematics and uses of algae. This chapter will provide an overview of the potential human health advantages associated with the use of algae as a source of high-value products, especially focused on those metabolites with biological activities and potential therapeutic applications in the pharmaceutical and food industries. Moreover, the production of polyphenols by marine microalgae will be also considered, as well their impact on the biogeochemical cycles of trace metals and the phytoplankton implications. These data will support as a baseline for future research in wastewater and marine environments.