Ignacio Rodríguez-García

Silver-mediated synthesis of heterocycles.

2.1. Oxygen Nucleophiles 3174 2.2. Nitrogen Nucleophiles 3177 3. Ag(I)-Mediated Addition of Nucleophiles to Allenes 3178 3.1. Oxygen Nucleophiles 3178 3.1.1. Allenic Alcohols 3178 3.1.2. Allenic Aldehydes and Ketones 3179 3.1.3. Allenic Acids 3180 3.2. Nitrogen Nucleophiles 3180 3.2.1. Allenic Amines 3180 3.2.2. Allenic Sulfonamides 3182 3.2.3. Allenic Carbamates 3182 3.2.4. Allenic Amides 3182 3.2.5. Allenic Oximes 3183 4. Ag(I)-Mediated Additions to Alkenes 3183 5. Ag(I)-Mediated Cycloaddition Reactions 3185 5.1. 1,3-Dipolar Cycloaddition Reactions of Azomethine Ylides 3185

Evaluation of the antioxidant activity of three microalgal species for use as dietary supplements and in the preservation of foods

The antioxidant activity of the microalgal ethanolic extracts of Porphyridium cruentum, Phaeodactylum tricornutum and Chlorella vulgaris was determined by means of the β-carotene-linoleate model system. The results show that the activity of C. vulgaris extract was higher than those obtained for the other microalgal extracts tested and for the synthetics BHA (butylated hydroxyanisole), and BHT (butylated hydroxytoluene). In addition, the major constituents present in the ethanolic extracts of the three microalgae species were analyzed by means of GC and GC-mass spectrometry. The results showed that the tested microalgae may be an important source of natural antioxidants, as an alternative to higher plants or the production by chemical synthesis.

Occurrence and characterization of oils rich in γ-linolenic acid (III) : the taxonomical value of the fatty acids in Echium (Boraginaceae)

Fourteen species of the genus Echium (Fam. Boraginaceae) collected in the Macaronesia were surveyed in a search for high levels of gamma-linolenic acid (GLA, 18:3omega6) in the seed oil. High amounts of this fatty acid were found in all of them, ranging from 18.85% (E. pitardii var. pitardii) to 27.42% (E. gentianoides) on total seed fatty acids. The GLA content related to total seed weight was also significant, ranging from 1.26% (E. handiense) to 8.22% (E. gentianoides). In addition, considerable amounts of stearidonic acid (SA, 18:4omega3) were detected, ranging from 3.78% (E. bonnetii var. bonnetii) to 8.81% (E. pininana) on total fatty acids. Besides all the perennial species, the four herbaceous Echium taxa endemic to the Macaronesia also showed high GLA percentages. This is in contrast to the low GLA level found in continental Echium species, all of them bearing an herbaceous habit. These results are in good agreement with the available genetic data and show the ability of GLA to discriminate between Macaronesian and continental Echium species. The analysis of five other Macaronesian species belonging to plant families rich in GLA are also reported.

Pterocarpans: interesting natural products with antifungal activity and other biological properties

Among the phytoalexins with the highest antifungal activity is the isoflavonoid based group of pterocarpans. Here, we present a comprehensive inventory of the structures and sources of pterocarpans, and summarize some of their most interesting biological activities.

Ti-Catalyzed Straightforward Synthesis of Exocyclic Allenes

Exocyclic allenes constitute useful building blocks in organic synthesis and have recently been identified as key intermediates in the synthesis of natural products. Here the first general method for the most straightforward synthesis of exocyclic allenes reported to date is presented. This method is based on the Barbier-type cyclization of propargyl halides catalyzed by titanium; a safe, abundant, and ecofriendly metal. The reaction proceeds under mild conditions compatible with different functional groups and provides good yields of five-, six-, and seven-membered carbocycles and nitrogen-containing heterocycles bearing an exocyclic allene group. Experimental evidence supporting the proposed reaction mechanism is also provided. Moreover, this procedure can be carried out in an enantioselective manner by using chiral titanocene(III) catalysts. The utility of this method has been proved in the synthesis of the natural alkaloid stemoamide.

Ti-Catalyzed Homolytic Opening of Ozonides: A Sustainable C–C Bond-Forming Reaction

The unprecedented homolytic opening of ozonides promoted and catalyzed by titanocene(III) is reported. This novel reaction proceeds at room temperature under neutral, mild conditions compatible with many functional groups and provides carbon radicals suitable to form C-C bonds via both homocoupling and cross-coupling processes. The procedure has been advantageously exploited for the straightforward synthesis of the natural product brittonin A.

Synthesis of (±)-aureol by bioinspired rearrangements.

A bioinspired and sustainable procedure for the straightforward synthesis of (±)-aureol has been achieved in eight steps (14% overall yield) from epoxyfarnesol. The key steps are the titanocene(III)-catalyzed radical cascade cyclization of an epoxyfarnesol derivative and a biosynthetically inspired sequence of 1,2-hydride and methyl shifts.

Saikosaponins from roots of Bupleurum gibraltaricum and Bupleurum spinosum.

Two new saikosaponins have been identified in the butanolic fraction of the ethanol extract of the roots of Bupleurum spinosum: 3beta,16alpha,23,28-tetrahydroxyoleana-11,13(18)-dien- 30-oic acid 3-O-beta-D-glucopyranosyl-(1 --> 2)-beta-D-glucopyranosyl-(1 --> 3)-beta-D-fucopyranoside, and 3beta,16alpha,23,28,30-pentahydroxyoleana-11,13(18)-diene 3-O-beta-D-glucopyranosyl-(1 --> 2)-beta-D-glucopyranosyl-(1 --> 3)-beta-D-fucopyranoside. 3Beta,16beta,23-trihydroxy-13,28-epoxyolean-11-ene 3-O-beta-D-glucopyranosyl-(1 --> 2)-beta-D-glucopyranosyl-(1 --> 3)-beta-D-fucopyranoside was also isolated, and this structure agreed with the one proposed for bupleuroside I, but their spectroscopic data have not been described until now. From the same fraction of the roots of Bupleurum gibraltaricum, the known compound buddlejasaponin IV has been isolated as the predominant component (90%). Structures were elucidated using spectroscopic analysis, specially 2D-NMR experiments.

The fat from frozen mammals reveals sources of essential fatty acids suitable for Palaeolithic and Neolithic humans.

The elucidation of the sources of n-3 fatty acids available for the humans in the Upper Palaeolithic and Neolithic is highly relevant in order to ascertain the availability of such nutrients in that time frame as well as to draw useful conclusions about healthy dietary habits for present-day humans. To this end, we have analysed fat from several frozen mammals found in the permafrost of Siberia (Russia). A total of 6 specimens were included in this study: 2 mammoths, i.e. baby female calf called “Lyuba” and a juvenile female called “Yuka”, both specimens approximately from the same time, i.e. Karginian Interstadial (41,000 and 34,000 years BP); two adult horses from the middle Holocene (4,600 and 4,400 years BP); and two bison very close to the Early Holocene (8,200 and 9,300 years BP). All samples were analysed by gas-liquid chromatography-mass spectrometry (GLC-MS) and GLC-flame ionization detector (GLC-FID). As demonstrated in this work, the fat of single-stomached mammals often consumed by Palaeolithic/Neolithic hunters contained suitable amounts of n-3 and n-6 fatty acids, possibly in quantities sufficient to meet the todays recommended daily intake for good health. Moreover, the results also suggest that mammoths and horses at that time were hibernators.

Selective reduction of aromatic ketones in aqueous medium mediated by Ti(III)/Mn: a revised mechanism.

An experimental study on the role played by each of the reagents involved in the selective reduction of aromatic ketones in aqueous medium is reported. In this reaction, the reduction of aromatic ketones is mediated by Cp2TiCl. Moreover, the presence of Mn in the reaction medium is mandatory. To account for these findings, a substantially revised mechanism is proposed.