Enzymatic regioselective synthesis of bile acids derivatives

ALICIA BALDESSARI, CONSTANZA PÍA MANGONE; MARÍA ANTONELA ZÍGOLO; GUADALUPE E. GARCÍA LIÑARES

Lille

Simposio; 10th European Symposium on Biochemical Engineering Sciences and 6th International Forumon Industrial Bioprocesses; 2014

European Society of Biochemical Engineering Sciences

Bile acids (BAs) are hydroxyl derivatives of 5β-cholanic acid (Figure 1, R1, R2, R3: H or OH and R4: H). They are amphiphilic compounds showing two different faces: a hydrophobic face (β) containing angular methyl groups and a hydrophilic face (α) with hydroxyl groups. The ratio of the hydrophobic to the hydrophilic surface area of BAs determines their broad biological activity: dietary lipid adsorption, cholesterol homeostasis, skin penetration enhancers, etc. With the aim of getting a variation in the above mentioned ratio, in this work we are reporting the enzymatic synthesis of a series of derivatives involving the modification of the hydroxyl (R1, R2, R3: OAc) and the carboxyl (R4: alkyl) groups. In steroid chemistry, it is difficult to achieve reactions in a regioselective way and protection and deprotection steps are required in order to obtain only the desired product. To avoid this problem we have used lipases and fungi as reaction catalysts, due to their good performance in steroid transformations [1,2]. In this work we have studied the influence of various reaction parameters in the enzymatic reactions, such as lipase source, acylating agent/ or alcohol /substrate ratio, enzyme/substrate ratio, solvent and temperature. Through the enzymatic approach it was possible to obtain twelve mono-, diacetyl and ester derivatives of deoxycholic, chenodeoxycholic and lithocholic acid. We have also obtained acetylated ester products, in which the lipase catalyzed both reactions simultaneously, with the acylating agent and the alcohol. The lipase showed to be very efficient affording most of products in high yield (77-98%) and regioselectivity. Every product was completely identified by spectroscopic methods (FTIR, 1H and 13C NMR and HRMS). Some of the derivatives showed activity as Leishmania mexicana growth inhibitors. The advantages showed by the enzymatic methodology, such as mild reaction conditions and low environmental impact, make the biocatalysis a convenient way to prepare these derivatives of bile acids with application as potential antiparasitic agents. [1] Paula G. Quintana et al., Eur. J. Org. Chem, 4306-12, 2012. [2] Paula G. Quintana et al., J. Mol. Cat. B : Enzymatic, 97, 110-17, 2013. Key-words: Bile acids, Lipase, Acetylation, Esterification.