Carlos A. Escobar

Structural Antitumoral Activity Relationships of Synthetic Chalcones

Relationships between the structural characteristic of synthetic chalcones and their antitumoral activity were studied. Treatment of HepG2 cells for 24 h with synthetic 2’-hydroxychalcones resulted in apoptosis induction and dose-dependent inhibition of cell proliferation. The calculated reactivity indexes and the adiabatic electron affinities using the DFT method including solvent effects, suggest a structure-activity relationship between the Chalcones structure and the apoptosis in HepG2 cells. The absence of methoxy substituents in the B ring of synthetic 2’-hydroxychalcones, showed the mayor structure-activity pattern along the series.

Chemical composition of precloacal secretions of Liolaemus lizards.

Interspecific chemical variation of precloacal pore secretions of Liolaemus lizards was characterized in 20 species, and intraspecific chemical variation was characterized using nine individuals of L. bellii. The latitude (Chile, 18° to 33° South latitude) and altitude (100 to 4350 m.a.s.l.) of the capture sites were recorded, as well as the number of precloacal pores of each lizard. Secretions were analyzed by GC-MS. A total of 49 compounds were found distributed among the 20 species of Liolaemus. Different chemical patterns occurred at intra- and interspecific levels. Compounds belonged to three main families: n-alkanes, long chain carboxylic acids, and steroids. Cholesterol and five carboxylic acids (tetradecanoic, hexadecanoic, hexadecenoic, octadecanoic, and Z-9-octadecenoic) appeared in all species. The number of precloacal pores correlated positively with altitude and negatively with latitude, suggesting that lizards produce more secretions under harsh environments.

Sources of pheromones in the lizard Liolaemus tenuis

Se realizaron pruebas experimentales con la especie Liolaemus tenuis (Tropiduridae), para determinar las potenciales fuentes de feromonas usadas en su comunicacion quimica. El estudio se centro en el fenomeno de auto-reconocimiento. Durante la estacion post-reproductiva, las fecas de ambos sexos y las secreciones precloacales (presentes solo en machos) fueron probadas. Los estimulos fueron presentados a los lagartos esparcidos sobre rocas, y el numero de lamidos (TF) a la roca fue utilizado como un bioensayo para determinar reconocimiento de feromonas. Las fecas contienen feromonas involucradas en auto-reconocimiento, ya que los lagartos realizaron menos TF confrontados con rocas con suspensiones de fecas propias que de un conespecifico o con agua (control). Con el objeto de evaluar la naturaleza quimica de las feromonas de auto-reconocimiento, las fecas fueron sometidas a una extraccion secuencial con tres solventes de polaridad creciente, obteniendose asi tres fracciones de fecas. No existio diferencia en el numero de TF hacia las distintas fracciones de fecas. Mas aun, los lagartos no mostraron diferencias en TF cuando fueron expuestos a fracciones fecales propias y de conespecificos. Esto sugiere que el procedimiento de separacion disgrego un estimulo complejo en partes que no son activas individualmente. Finalmente, los machos no discriminaron entre secreciones precloacales de ellos mismos y de otros machos. Probablemente estas secreciones sean portadoras de informacion relevante o detectable solo por hembras

Evaluation of Dimboa Analogs as Antifeedants and Antibiotics Towards the Aphid Sitobion avenae in Artificial Diets

A total of 25 compounds including benzoxazinones, benzoxazolinones, and N-glyoxylamide derivatives were tested as antifeedants and antibiotics towards the aphid Sitobion avenae in diet bioassays. The antifeedant and mortality indexes increased with the presence of electron-donating groups in the 7 position of the benzoxazinone moiety, the replacement of the oxygen atom by sulfur in the heterocyclic ring, the presence of a hemiacetal instead of an acetal at C-2 of the benzoxazine moiety (and hence the possibility of ring opening), and the presence of a hydroxyl group at C-4 of the benzoxazine moiety (hydroxamic acid) instead of a hydrogen atom (lactam). The results support earlier hypotheses on the chemical bases for the mode of action of these compounds.

Potential of Hydroxamic Acids in Breeding for Aphid Resistance in Wheat

Abstract Swedish wheats were analysed at the seedling stage for hydroxamic acids (Hx), a family of natural aphid resistance factors. Analysis comprised the historical development from old landraces to modern cultivars, and included cultivars in the Swedish National List of Cultivars for 1992–93. Spring and winter wheats contained similar average Hx concentrations, 2.12 ± 0.801 (n = 26) and 2.37 ± 0.816 (n = 49) mmol/kg fr. wt, respectively. Cultivars recommended for 1992–93 showed lower levels of Hx, 1.14 ± 0.574 (n = 7) and 1.97 ± 0.751 (n = 8), respectively. Breeding wheat for higher Hx levels as a means of obtaining increased aphid resistance is discussed.

Gold nanoparticles for photothermally controlled drug release

In this article, we describe how nanoparticles work in photothermally triggered drug delivery, starting with a description of the plasmon resonance and the photothermal effect, and how this is used to release a drug. Then, we describe the four major functionalization strategies and each of their different applications. Finally, we discuss the biodistribution and toxicity of these systems and the necessary requirements for the use of gold nanoparticles for spatially and temporally controlling drug release through the photothermal effect.

Syntheses of 2-Hydroxy-4,7-dimethoxy-2H-1,4-benzoxazin-3(4H)-one: A precursor of a bioactive electrophile from Gramineae

Abstract 2-Hydroxy-4,7-dimethoxy-2 H -1,4-benzoxazin-3(4 H )-one ( 8 ), the hitherto undescribed free hemiacetalic aglycone of a benzoxazinoid acetal glucoside naturally occurring in wheat, has been synthesized following two pathways, independently. This cyclic hydroxamic acid methyl ester proved to be very unstable when in solution. This gives rise to the assumption that HDIBOA naturally released from its acetal glucoside is by methoxide elimination a precursor to form a multi-centered electrophile that was recently reported to be the bioactive principle of the benzoxazinoid lead.

Aspergillus niger catalyzes the synthesis of flavonoids from chalcones

Abstract Flavonoids, which have many biological activities and have been widely used in nature, can be artificially synthesized. However, regioselective cyclization of chalcones is difficult by chemical methods. In this study, we demonstrated that Aspergillus niger is capable of cyclizing chalcones to flavanones, affording a mimic of plant biosynthetic processes. Chalcones 1–6 were biotransformated to the modified chalcones 8–14 and to the flavanones 15–27. The biotransformation showed that enzymatic cyclization and demethylation occurred during the first days of biotransformation; in contrast, hydroxylation is a later process. With a longer culturing time, it is possible to obtain more hydroxylated flavanones with excellent yields.

Five bicyclo[3.3.0]octa-2,6-dienes

A series of five compounds containing the bicyclo[3.3.0]octa-2,6-diene skeleton are described, namely tetramethyl cis,cis-3,7-dihydroxybicyclo[3.3.0]octa-2,6-diene-2,4-exo,6,8-exo-tetracarboxylate, C(16)H(18)O(10), (I), tetramethyl cis,cis-3,7-dihydroxy-1,5-dimethylbicyclo[3.3.0]octa-2,6-diene-2,4-exo,6,8-exo-tetracarboxylate, C(18)H(22)O(10), (II), tetramethyl cis,cis-3,7-dimethoxybicyclo[3.3.0]octa-2,6-diene-2,4-exo,6,8-exo-tetracarboxylate, C(18)H(22)O(10), (III), tetramethyl cis,cis-3,7-dimethoxy-1,5-dimethylbicyclo[3.3.0]octa-2,6-diene-2,4-exo,6,8-exo-tetracarboxylate, C(20)H(26)O(10), (IV), and tetramethyl cis,cis-3,7-diacetoxybicyclo[3.3.0]octa-2,6-diene-2,4-exo,6,8-exo-tetracarboxylate, C(20)H(22)O(12), (V). The bicyclic core is substituted in all cases at positions 2, 4, 6 and 8 with methoxycarbonyl groups and additionally at positions 3 and 7 with hydroxy [in (I) and (II)], methoxy [in (III) and (IV)] or acetoxy [in (V)] groups. The conformations of the methoxycarbonyl groups at positions 2 and 4 are exo for all five compounds. Each C(5) ring of the bicyclic skeleton is almost planar, but the rings are not coplanar, with dihedral angles of 54.93 (7), 69.85 (5), 64.07 (4), 80.74 (5) and 66.91 (7) degrees for (I)-(V), respectively, and the bicyclooctadiene system adopts a butterfly-like conformation. Strong intramolecular hydrogen bonds exist between the -OH and C=O groups in (I) and (II), with O...O distances of 2.660 (2) and 2.672 (2) A in (I), and 2.653 (2) and 2.635 (2) A in (II). The molecular packing is stabilized by weaker C-H...O(=C) interactions, leading to dimers in (I)-(III) and to a chain structure in (V). The structure series presented in this article shows how the geometry of the cycloocta-2,6-diene skeleton changes upon substitution in different positions and, consequently, how the packing is modified, although the intermolecular interactions are basically the same across the series.

Synthesis of 1,5-Benzodiazepines with Unusual Substitution Pattern from Chalcones Under Solvent-Free Microwave Irradiation Conditions

Abstract 1,5-Benzodiazepines have been synthesized from the corresponding 2′-hydroxychalcones [1-(2-hydroxyphenyl)-3-aryl-2-propen-1-ones] and o-phenylenediamine, both in methanol, under reflux and under solvent-free microwave irradiation conditions on alumina. The latter method proved to be advantageous.