Reinaldo R. Vargas

Asymmetric sulfoxidation of a β-carbonyl sulfide series by chloroperoxidase

Abstract The chloroperoxidase (CPO)-catalyzed oxidation of a series of β-carbonyl sulfides to sulfoxides has been studied at room temperature in aqueous citrate buffer. For dialkyl β-carbonyl sulfides, the products with methyl and ethyl substituents are obtained in ca. 100% yield. However when the alkyl group is n- propyl or i -propyl the yield drops dramatically (25%). An aryl sulfide derivative afforded product in very low yield (4%), but when the phenyl group bears a carbonyl, and the sulfur substituents are methyl or ethyl, the oxidation occurs with high yields (91–95%). Steric control of the sulfoxidation reaction is also confirmed with cyclohexanone derivatives, where a low product yield is observed even at high enzyme concentrations. Noteworthy are the yields obtained with cyclopentanone sulfide (65%) and an unexpected quantitative yield obtained with the γ-butyrolactone sulfide.

Anodic cleavage of lignin model dimers in methanol

Abstract The anodic oxidation in methanol of some lignin model compounds, the C17 – C18 compounds ((1) – (5), has been studied to ascertain factors influencing cleavage of Cα  Cβ bonds cf. substitution. Cyclic voltammetric oxidation peak potentials were influenced by structure but not by pH. Preparative-scale electrolyses gave 3,4-dimethoxybenzaldehyde as the major product from compounds (1) – (3), corresponding to cleavage of th Cα  Cβ bonds. In contrast compounds (4) and (5) were not cleaved with significant efficiency. The results are convincingly rationalised in terms of rapid cleavage of the Cα  Cβ bonds in the first-formed radical cations.

Sulfenylation of β-keto sulfoxides. III. Diastereoselectivity induced by a chiral phase transfer catalyst

Abstract The asymmetric induction in the sulfenylation of several β-keto sulfoxides under phase transfer catalytic conditions in the presence of the chiral catalyst N-benzylquininium chloride was investigated. It is concluded that the diastereoselectivity is not accompanied by enantiomeric resolution.

Graft copolymers with immobilized peroxidase for organic synthesis

The graft copolymer poly(propylene)-graft-poly(acrylic acid) (PP-G-AA) was prepared by radiation-induced graft copolymerization of acrylic acid onto polypropylene spheres and characterized by thermal analysis and scanning electron microscopy (SEM). Maximum percentage of grafting (70%) was obtained at a total dose of 12 kGy using 30% (w/w) of acrylic acid. The Michaelis constant, KM, and the maximum reaction velocity, VMax, were determined for the free horseradish peroxidase and for the immobilized horseradish peroxidase. The enzyme affinity for the substrate (KM/Vmax) remains quite good after immobilization. The sulfoxidation reaction of a ketosulfide was investigated with the immobilized peroxidase.

Anodic methoxylation of cinnamate esters

Este trabalho descreve a oxidacao eletroquimica do 4-metoxi-cinamato de metila e de outros esteres metilicos do acido cinâmico di- e tri- metoxilado, em solucao metanolica neutra ou alcalina. Nos estudos eletroquimicos foram empregadas voltametria ciclica, bem como eletrolises preparativas a potencial ou corrente controlados, em celas de um ou dois compartimentos. A influencia de parâmetros tais como densidade de corrente, tipo de cela, material do eletrodo, solvente, concentracao do substrato e base foi investigada para o 4-metoxi-cinamato de metila. Os produtos observados foram resultantes de metoxilacoes nucleares e/ou na cadeia lateral, entretanto com o aumento do numero de metoxilas no anel aromatico foram observados principalmente produtos referentes a metoxilacao no anel aromatico. As estruturas dos produtos tambem dependem do tipo de procedimento empregado no seu isolamento.

Horseradish Peroxidase-Catalyzed Conjugation of Eugenol with Basic Amino Acids

L-Lysine is shown to yield an adduct with the quinone methide intermediate formed during the horseradish peroxidase (HRP)-catalyzed aerobic oxidation of eugenol (4-allyl-2-methoxyphenol). Adduct formation is evidenced by (i) lysine quenching of the characteristic quinone methide absorption band measured at 350 nm; arginine and gamma-aminobutyric acid, but not alanine or propionic acid showed similar behaviour (ii) lysine-promoted a 400 mV decrease of the eugenol oxidation voltammetric wave (1.00 V), concomitantly with an increase in current intensity and (iii) reverse phase HPLC isolation of the lysine eugenol adduct, followed by GC-MS analysis. The MS spectrum is consistent with a 2:1 lysine:eugenol adduct (MW = 455). If operative in vivo, binding of lysine to eugenol might lead to protein inactivation and possibly be involved in eugenol toxicity.

Electrosynthesis of γ-asarone

Abstract γ-Asarone is synthesised in high yield, and conveniently, by anodic methoxylation of methyl eugenol, at constant current. The method is extremely simple and inexpensive.