Two-step desymmetrization of dipyrazolidyl 3-phenylglutarate via lipase-catalyzed hydrolysis in organic solvents

Synthesis of substituted 2H-chromenes catalyzed by lipase immobilized on magnetic multiwalled carbon nanotubes

Porcine pancreas lipase (PPL) was immobilized on magnetic multiwalled carbon nanotubes successfully for the synthesis of substituted 2H-chromenes. The catalytic activity of immobilized PPL was much higher than that of free PPL. Effects of reaction medium, temperature, and enzyme dosage were also investigated. Under optimum reaction conditions (acetylacetone (1 mmol), salicylaldehyde (1 equivalent), methanol (10 equivalent), and immobilized PPL (protein content: 30 mg; 65 °C; DMF 5 mL; 5 H), the immobilized PPL showed an excellent catalytic performance on the synthesis of substituted 2H-chromenes. Moreover, the immobilized PPL exhibited satisfactory thermostability, operational simplicity, and reusability in this reaction.

CALB-Catalyzed Two-Step Alcoholytic Desymmetrization of 3-Methylglutaric Diazolides in MTBE

Optically pure 3-substituted glutarates can be prepared from the alcoholic ring-opening of cyclic anhydride derivatives, esterification of 3-substituted glutaric acid, and hydrolysis, alcoholysis, aminolysis, and ammonolysis of the diester derivatives via hydrolases or organocatalysts. Unfortunately, most of them mainly focus on the first-step desymmetrization, leading to the difficulty on producing optically pure enantiomers. As a general trend in lipase-catalyzed desymmetrization of 3-methylglutarates, poorer enantiomeric excesses with lower chemical yields were found, as the methyl substituent is relatively small to induce a high enzyme stereodiscrimination. The two-step desymmetrization for CALB-catalyzed alcoholysis of 3-methylglutaric di-1,2,4-triazolide 1a in anhydrous MTBE is first developed to increase the enzyme activity in each reaction step. The enantioselectivity for the second-step kinetic resolution is furthermore improved by using 3-methylglutaric dipyrazolide 1b as the substrate. The kinetic and thermodynamic analysis is, moreover, addressed for shedding insights into the desymmetrization process.