Response surface methodology was successfully applied to optimize lipase-catalyzed regioselective esterification of pyridoxine (PN). Effects of various reaction conditions, including reaction temperature, time, enzyme loading, substrate molar ratio, and water activity, were investigated. A central composite design was employed to search for the optimal conversion of PN. A quadratic polynomial regression model was used for analysis of the experimental data at a 95% level (p < 0.05). The analysis confirmed that the water activity was the most significant factor affecting the conversion of PN. It was also suggested that the conversion was strongly affected by independent variables of temperature, time, substrate molar ratio, and water activity as well as interaction terms of temperature and enzyme loading/substrate molar ratio/water activity, time and enzyme loading/substrate molar ratio, substrate molar ratio, and water activity. The coefficient of determination of the model was found to be 0.963. Three sets of optimum reaction conditions were established, and the verified experimental trials were performed for validating the optimum points. A scale-up experiment was also done under the first set of optimal conditions.

Optimization of lipase-catalyzed regioselective acylation of pyridoxine (vitamin B6).

Photoaddition of 2,3-dimethylmaleic anhydride to selenophthene†

The 13C NMR spectra of a representative series of photoadducts derived from methylmaleic anhydrides and thiophene, containing the same basic carbon skeleton, were studied in order to establish a model for future structure elucidation of similar compounds. Selective heteronuclear 13C{1H} NOE was applied to stereochemical studies on the same compounds with the dual purpose of confirming previous assignments and to gain experience in the use of this technique, rarely applied in organic chemistry. The technique was employed in two different ways, by irradiating the selected proton resonance with and without modulation [νm=½J(CH)].

Application of the selective 13C{1H} nuclear Overhauser effect to structure elucidation of photoadducts derived from maleic anhydrides and thiophene

It has been possible for the first time to prepare an oxetane by photoaddition of benzophenone to thiophene in presence of BF 3 . A photocycloaddition promoted by an electron transfer mechanism is proposed for this reaction.

Synthesis of an elusive oxetane by photoaddition of benzophenone to thiophene in the presence of a Lewis acid

Decomposition studies of photoaddition products derived from five-membered heterocyclics and maleic anhydride and maleimide derivatives by DSC, TG and MS

— Oxetanes were synthesized by 1,2-photoaddition of benzophenone to several methyl-substituted furans. The photochemical conversion of oxobicyclic analogues of norbornadiene to the corresponding oxoquadricyclenes was studied, and finally the sensitized 1,2-photoaddition of citraconic anhydride to furan was accomplished.



RESUMEN

Se han sintetizado oxetanos por fotoadicion 1,2 de benzofenona a distintos metil furanos. Se ha estudiado la conversion fotoquimica de analogos oxobiciclicos del norbonadieno, y finalmente se ha logrado la fotoadicion 1,2 sensitivizada de anhidrido citraconico a furano.

Luis Cortes

Papers

Photochemical cycloadditions of organic compounds

Bromination of the 1,2,3,6-tetrahydro-3,6-endo-oxyphthalic anhydride system. Stereochemistry and mechanism of the reaction

Derivatives of 3,6-Endoxo-5-methyl-Δ4-tetrahydrophthalic Acid. Structural Assignments by Nuclear Magnetic Resonance Spectroscopy