title: Ethyl esterification of docosahexaenoic acid in an organic solvent-free system with immobilized Candida antarctica lipase.
abstract: Ethyl docosahexaenoate (EtDHA) is regarded as a potentially useful pharmaceutical substance on account of its beneficial physiological activities. We attempted the ethyl esterification of docosahexaenoic acid (DHA) in an organic solvent-free system using Candida antarctica lipase, which acts strongly on DHA and ethanol. Esterification of 88% was attained by shaking a mixture of DHA/ethanol (1:1, mol/mol) and 2 wt% immobilized C. antarctica lipase at 30 degrees C for 24 h. However, even in the presence of an excess amount of ethanol, the extent of esterification could not be raised above 90%. To attain a higher level of esterification, a two-step reaction was found to be effective. The first step was performed in a mixture of DHA/ethanol (1:1, mol/mol), and the reaction mixture was then dehydrated. In the second step, the resulting mixture was shaken at 30 degrees C for 24 h with 5 molar equivalents of ethanol against the remaining DHA using 2 wt% immobilized lipase. By means of this two-step procedure, 96% esterification was attained. Repetition of the first and second reactions showed that the immobilized lipase was reusable for at least 50 cycles. In addition, DHA remaining in the second-step reaction mixture was removed by a conventional alkali refining process, giving purified EtDHA with a high yield.
authors.affiliation: Osaka Municipal Technical Research Institute, 1-6-50 Joto-ku, Morinomiya, Osaka 536-8553, Japan. shimaday@omtri.city.osaka.jp
authors.forename: Y
authors.initials: Y
authors.lastname: Shimada
authors.forename: Y
authors.initials: Y
authors.lastname: Watanabe
authors.forename: A
authors.initials: A
authors.lastname: Sugihara
authors.forename: T
authors.initials: T
authors.lastname: Baba
authors.forename: T
authors.initials: T
authors.lastname: Ooguri
authors.forename: S
authors.initials: S
authors.lastname: Moriyama
authors.forename: T
authors.initials: T
authors.lastname: Terai
authors.forename: Y
authors.initials: Y
authors.lastname: Tominaga