Synthesis of naringin 6"-ricinoleate using immobilized lipase

Abstract

Background: Naringin is an important flavanone with several biological activities, including antioxidant action. However, this compound shows low solubility in lipophilic preparations, such as is used in the cosmetic and food industries. One way to solve this problem is to add fatty acids to the flavonoid sugar unit using immobilized lipase. However, there is limited research regarding hydroxylation of unsaturated fatty acids as an answer to the low solubility challenge. In this work, we describe the reaction of naringin with castor oil containing ricinoleic acid, castor oil's major fatty acid component, using immobilized lipase from Candida antarctica. Analysis of the 1H and 13 C NMR (1D and 2D) spectra and literature comparison were used to characterise the obtained acyl derivative.

Results: After allowing the reaction to continue for 120 hours (in acetone media, 50°C), the major product obtained was naringin 6″-ricinoleate. In this reaction, either castor oil or pure ricinoleic acid was used as the acylating agent, providing a 33% or 24% yield, respectively. The chemical structure of naringin 6″-ricinoleate was determined using NMR analysis, including bidimensional (2D) experiments.

Conclusion: Using immobilized lipase from C. antarctica, the best conversion reaction was observed using castor oil containing ricinoleic acid as the acylating agent rather than an isolated fatty acid. GRAPHICAL

Figure 1

Lipase-catalyzed regioselective esterification of naringin (1) with ricinoleic acid (2).

Figure 2

(A) Chromatogram from HPLC analysis of acylation reaction medium, after 120 hours at 50°C. (B) UV spectrum of naringin. (C) UV spectrum of naringin 6"-ricinoleate.

Figure 3

Synthesis of naringin 6"-ricinoleate by lipase.