Epoxide-opening cascades triggered by a Nicholas reaction: Total synthesis of teurilene

Natural inspiration: Based on the biosynthesis of squalene‐derived polyethers, a total synthesis of teurilene is described. The carbocation formation in the Nicholas reaction serves to control the initiation of a polyepoxide ring‐opening cascade. The three furan rings present in teurilene were obtained in excellent yield in one step. Boc=tert‐butoxycarbonyl, TMS=trimethylsilyl.

Rodríguez-López, Julio; Pinacho Crisóstomo, Fernando R.; Ortega, Nuria; López Rodríguez, Matías; Martín, Víctor S.; Martín, Tomás

Angewandte Chemie - International Edition 52(13): 3659-3662 (2013)
DOIDigital.CSIC

Synthesis of Chiral β-Iodo- and Vinylorganophosphorus(V) Compounds by Fragmentation of Carbohydrate Anomeric Alkoxyl Radicals

A new general methodology for the synthesis of chiral vinylphosphonate and vinylphosphine oxide carbohydrate derivatives has been developed using the anomeric alkoxyl radical fragmentation reaction as the key step. The synthetic sequence proceeded via β-iodophosphonate and β-iodophosphine oxide intermediates, which may be interesting synthons for the introduction of phosphorus into organic molecules. These vinylphosphonates could be easily transformed into 2-methylene-1-phosphapentofuranoses (3-methylene-1,2-oxaphospholanes) and β-aminophosphonates, isosteres of biologically active α-methylene-γ-lactones and β-amino acids, respectively.

Hernández-Guerra, Daniel; Rodríguez Morales, María S.; Suárez, Ernesto

Organic Letters 15(2): 250-253 (2013)
DOIDigital.CSIC

Iron(III) Catalyzed Direct Synthesis of cis-2,7-Disubstituted Oxepanes. The Shortest Total Synthesis of (+)-Isolaurepan

Prins cyclization of bis-homoallylic alcohols with aldehydes catalyzed by iron(III) salts shows excellent cis selectivity and yields to form 2,7-disubstituted oxepanes. The iron(III) is able to catalyze this process with unactivated olefins. This cyclization was used as the key step in the shortest total synthesis of (+)-isolaurepan.

Purino, Martín A.; Ramírez, Miguel A.; Daranas, Antonio: Martín, Víctor; Padrón, Juan I.

Organic Letteer 14(23): 5904-5907 (2012)
DOI

Conformation and Chiral Effects in α,β,α-Tripeptides

Short α,β,α-tripeptides comprising a central chiral trisubstituted β2,2,3*-amino acid residue form unusual γ-turns and δ-turns in CDCl3 and DMSO-d6 solutions but do not form β-turns. Thermal coefficients of backbone amide protons, 2D-NMR spectra, and molecular modeling revealed that these motifs were strongly dependent on the configuration (chiral effect) of the central β-amino acid residue within the triad. Accordingly, SSS tripeptides adopted an intraresidual γ-turn like (C6) arrangement in the central β-amino acid, whereas SRS diastereomers preferred an extended δ-turn (C9) conformation. A different SRS-stabilizing bias was observed in the crystal structures of the same compounds, which shared the extended δ-turn (C9) found in solution, but incorporated an additional extended β-turn (C11) to form an overlapped double turn motif.

Saavedra, Carlos J.; Boto, Alicia; Hernández, Rosendo; Miranda, José Ignacio; Aizpurua, Jesus M.

J. Org. Chem. 77(14): 5907-5913 ( 2012)
DOI

Synthesis of α,γ-peptide hybrids by selective conversion of glutamic acid units

The site-selective modification of small peptides at a glutamate residue allows the ready preparation of α,γ-hybrids. In this way, a single peptide can be transformed into a variety of hybrid derivatives. The process takes place under very mild conditions, and good global yields are obtained.

Saavedra, Carlos J.; Boto, Alicia; Hernández, Rosendo

Organic Letters 14(13): 3542-3545 (2012)
DOIDigital.CSIC

Synthesis of α,γ-peptide hybrids by selective conversion of glutamic acid units

The site-selective modification of small peptides at a glutamate residue allows the ready preparation of α,γ-hybrids. In this way, a single peptide can be transformed into a variety of hybrid derivatives. The process takes place under very mild conditions, and good global yields are obtained.

Saavedra, Carlos J.; Boto, Alicia; Hernández, Rosendo

Organic Letters 14(13): 3542-3545 (2012)
DOIDigital.CSIC

Towards a Structural Basis for the Relationship Between Blood Group and the Severity of El Tor Cholera

It has long been known that people with blood group O are more severely affected by El Tor cholera than those with blood groups A or B. Microcalorimetry and NMR spectroscopy are used to evaluate the ability of the B‐subunits of cholera toxin and E. coli heat‐labile toxin to bind to selected blood group oligosaccharides.

Mandal, Pintu K.; Branson, Thomas R.; Hayes, Edward D.; Ross, James F.; Gavín, José A.; Hernández Daranas, Antonio; Turnbull, W. Bruce

Angewandte Chemie - International Edition 51(21): 5143-5146 (2012)
DOIDigital.CSIC

Major components of Spanish cultivated Artemisia absinthium populations: Antifeedant, antiparasitic, and antioxidant effects

The objective of this study was the valorization of Spanish Artemisia absinthium populations from Teruel (Aragón) and Sierra Nevada (Granada). These populations were experimentally cultivated in the field and under controlled conditions. Three major components were isolated from a two year-old population obtained from the Teruel population cultivated in Ejea-Zaragoza in 2003, and identified by NMR experiments as the sequiterpene lactone hydroxypelenolide (I) and the flavones artemetin (II) and casticin (III). The I–III content of the plant extracts was analyzed by HPLC-DAD. The insect antifeedant properties of plant extracts from different years and crops were tested against Spodoptera littoralis, Myzus persicae and Rhopalosiphum padi. Additionally we studied their antioxidant, phytotoxic and antiparasitic effects.

Gonzalez-Coloma, Azucena; Bailen, Maria; Diaz, Carmen E.; Fraga, Braulio M.; Martínez-Díaz, Rafael; Zuñiga, Gustavo E.; Contreras, Rodrigo A.; Cabrera, Raimundo; Burillo, Jesus

Industrial Crops and Products 37(1): 401-407 (2012)
DOI

Supercritical CO2 extraction of Persea indica: Effect of extraction parameters, modelling and bioactivity of its extracts

The objective of the work was to optimize the extraction of Persea indica L. bioactive compounds by means of supercritical fluid extraction (SFE) and analyze their insecticidal effects. P. indica L. is one of the dominant species of the Canarian laurel forest, a relict of the Tertiary flora. Different extraction conditions (pressure, plant material particle size, temperature, CO2 flow) and the influence of entrainer were tested and the evolution of the extracted compounds was screened by HPLC–MS. A comparison with conventional techniques such as hydrodistillation (HD) or organic solvent extraction (OSE) was also presented. Particularly, four CO2 densities ranging from 628.61 kg/m3 to 839.81 kg/m3 were studied in the range of 10.0–20.0 MPa and 40–50 °C. The extracts contained insecticidal ryanodanes of great interest, previously described as insecticidal components of P. indica. The insecticidal antifeedant activity of selected extracts was inspected. A model based on mass transfer equations, the Sovová model, was successfully applied to correlate the experimental data.

Martín, L; González-Coloma, A.; Díaz, C. E.; Mainara, A. M.; Urieta, J. S.

The Journal of Supercritical Fluids 57(2): 120-128 (2011)
DOI

A New Catalytic Prins Cyclization Leading to Oxa- and Azacycles

A new Prins cyclization process that builds up one carbon−carbon bond, one heteroatom-carbon bond, and one halogen-carbon bond, (in an oxa- and azacycle) relies on an iron catalyst system formed from Fe(acac)3 and trimethylsilyl halide. The method displays a broad substrate scope and is economical, environmentally friendly, and experimentally simple. This catalytic method permits the construction of chloro, bromo and iodo heterocycles, by the suitable combination of iron(III) source, the corresponding trimethylsilyl halide and the solvent, in high yields.

Miranda, Pedro O.; Carballo, Ruben M.; Martín, Víctor S.; Padrón, Juan I.

Organic Letters 11(2): 357-360 (2009)
DOIDigital.CSIC