Browsing by Author "Canete, Alvaro"

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    An unusual mulinane diterpenoid from the Chilean plant Azorella trifurcata (Gaertn) Pers
    (2014) Areche, Carlos; Sepulveda, Beatriz; San Martin, Aurelio; Garcia-Beltran, Olimpo; Simirgiotis, Mario; Canete, Alvaro
    Four new mulinane-type diterpenoids besides the known compounds mulin-11,13-dien-20-oic acid, 13 alpha-hydroxyazorellane, 13 beta-hydroxyazorellane, mulinolic acid, azorellanol, and mulin-11,13-dien-18-acetoxy-16,20-dioic acid were isolated from the Chilean plant Azorella trifurcata. One of the new metabolites isolated, 7 alpha-acetoxy-9-epi-13 beta-hydroxymulinane, possesses a new trans-syn-trans arrangement in a tricyclic ring system not previously encountered in nature. Among the mulinane diterpenoids isolated, mulin-11,13-dien-20-oic acid showed the gastroprotective effect on HCl-EtOH-induced gastric lesions in mice (ED50 = 55mg kg(-1)). Regarding the mode of gastroprotective action for this active compound, its effect was reduced by pre-treatment of the mice with indomethacin and N-ethylmaleimide, suggesting that prostaglandins and sulfhydryl compounds are positively involved in the gastroprotective activity using this model.
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    Spectral and Kinetic Study of 3-Styrylquinoxalin-2(1H)-ones Photoreduced by N-Phenylglycine and Amines
    (2019) Diaz-Hernandez, Dafne; Canete, Alvaro; Pavez, Lynda; Perez-Sanhueza, Alberto; Gunther, German; Szreder, Tomasz; De la Fuente, Julio R.
    The photoreduction by amines and N-phenyl-glycine, NPG, of six styrylquinoxalin-2(1H)-ones derivatives substituted in the styryl moiety, R-SQ was studied by using flash photolysis. The photoreaction is initiated via a single electron transfer from the electron donor (amines or NPG) to R-SQ excited triplet state, R-3-SQ*, with the formation of a triplet state radical ion pair or a charge transfer exciplex, (3)[CRIP/CTE]. These species live longer than the respective R-3-SQ* and have very similar transient spectra. In the presence of NPG, these (3)[CRIP/CTE] evolve on mu s time scale to the respective hydrogenated radicals, R-SQH(center dot), whose transient spectra and reaction rate constants with NPG are reported. The identity of these hydrogenated radicals was supported by the spectra obtained with the alpha-H donor triethylamine and previous pulse radiolysis studies in 2-propanol. Our findings allow proposing a radical chain reaction mechanism that explains the observed spectral behavior and rationalizes formation of the main product formed by binding of four PhNHCH2 center dot derived from NPG decarboxylation.
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    Supramolecular Control of Reactivity toward Hydrolysis of 7-Diethylaminocoumarin Schiff Bases by Cucurbit[7]uril Encapsulation
    (2021) Alcazar, Jackson J.; Geue, Niklas; Valladares, Veronica; Canete, Alvaro; Perez, Edwin G.; Garcia-Rio, Luis; Santos, Jose G.; Aliaga, Margarita E.
    A series of aromatic Schiff bases, featuring 7-diethylamino-coumarin and with five different substituents at an adjacent phenyl ring, were synthesized and characterized. With the aim of assessing the stability of these dyes in acidic medium, their hydrolysis reactions were kinetically studied in the absence and presence of the macrocycle cucurbit[7]uril (CB[7]). Our results are consistent with a model containing three different forms of substrates (un-, mono-, and diprotonated) and three parallel reaction pathways. The pK(a) values and the rate constants were estimated and discussed in terms of the presence of a hydroxyl group at the ortho position and electron-releasing groups on the phenyl ring of the dyes. The kinetic study in the presence of CB[7] led to two different behaviors. Promotion of the reaction by CB[7] was observed for the hydrolysis of the Schiff bases containing only one coordination site toward the macrocycle. Conversely, an inhibitor effect was observed for the hydrolysis of a Schiff base with two coordination sites toward CB[7]. The latter effect could be explained with a model as a function of a prototropic tautomeric equilibrium and the formation of a 2:1 host/guest complex, which prevents the attack of water. Therefore, the kinetic results demonstrated a supramolecular control of the macrocycle toward the reactivity and stability of 7-diethylaminocoumarin Schiff bases in acidic medium.