Biotransformation of Aromatic Ketones by Linum usitatissimum

Abstract

Acetophenone is a component of castoreum, the exudate from the castor sacs of the mature beaver [1]. Linum usitatissimum L. (Linaceae), known as flax or linseed, is a good source of oil and meal, which is rich in fiber, protein, and fat. Its oil is arguably one of the richest source of polyunsaturated fatty acids, used in food and in the prevention of cardiovascular diseases [2,3].The use of natural catalysts offers a clean way to perform chemical process under mild reaction conditions with less or no usage of organic solvents, a high degree of selectivity due to the high chemo-, regio-and enantioselectivity of enzymes, while working under mild and environmental friendly conditions linked to the principles of green chemistry [4][5][6][7][8]. Thus, the biocatalysts can be an interesting alternative to prepare chiral alcohols and can also act as chiral auxiliaries in asymmetric synthesis of chiral molecules, and as a result the production of single enantiomers of molecules has become increasingly important in the food, cosmetic, and pharmaceutical industries, from the corresponding prochiral ketones [6,[9][10][11][12][13]. Therefore, researchers have strived to find solutions for the replacement of conventional chemical routes by application of enzymes.Reports in the literature describe the use of different plant species for biotransformation, with several advantages such as their disposal after use, their biodegrability, as well as their wide availability at low cost [6,[8][9][10][11][14][15][16][17].In particular, the potential source of enzymes from Brazilian northwestern plants and their use as biocatalysts in bioreduction reactions have been related [10,11,14,17,18]. In order to contribute to the study of vegetables as natural catalyst, this paper reports the use of whole plant cell of seeds of L. usitatissimum as a biocatalyst for the reduction reactions of aromatic ketones.The enzymatic reduction of acetophenone (1) as standard substrate prochiral ketone and derivatives 2-14 using L. usitatissimum as biocatalyst is reported. All reactions were carried out using 50 mg of substrate and 20 g of biocatalyst in a buffer solution (Na 2 HPO 4 -KH 2 PO 4 ), pH 6.0, over a period of 72 h at 25qC without a co-solvent which are the optimal reaction conditions among the tested parameters.The bioreduction pattern of acetophenone (1) by L. usitatissimum occurred with a bioconversion value of 70.4%, a very good enantioselectivity (93.7% ee), and a satisfactory yield of (S)-alcohol. The study of reduction enzymatic reaction of acetophenone 1 and other prochiral ketones derived from acetophenones 2 to 12, including D-tetralone 13 and 1-acetonaphthone 14, was performed (Scheme 1).The results showed that L. usitatissimum exhibited a broad spectrum of enantionselectivity among the acetophenones and their derivatives, with a very good enantioselectivity (>75% ee) for acetophenone (1) and its derivatives 2, 6, 8, 9, and 10 (Table 1). It was observed that the best enantiomeric excess (ee) compared with acetophenone (1) was obtaine...