Development of new synthetic methodologies for enzymatic resolutions

Ângelo Miguel Rodrigues da Rocha

Key information

Authors:

Ângelo Miguel Rodrigues da Rocha (Ângelo Miguel Rodrigues da Rocha)

Supervisors:

Carlos Alberto Mateus Afonso (Carlos Alberto Mateus Afonso); Luís Joaquim Pina da Fonseca (Luís Joaquim Pina da Fonseca)

Published in

09/11/2018

Abstract

Two distinct subjects of interest were studied in the course of this thesis, both extremely significant for the pharmaceutical industry. The main topic of research, enzymatic kinetic resolution of secondary amines and alcohols, comes from the evergrowing demand for optically pure chiral compounds. Of the many methods available to Industry for preparation of pure enantiomers, enzymatic kinetic resolution is one of the more common ones. In order to solve some major drawbacks, its combination with ionic liquids is an important area of research. We developed a method for the resolution of secondary alcohols using an ionic anhydride acylating agent prepared directly in the reaction medium containing the biocatalyst. After optimization of the reaction conditions, the method allowed the resolution of a number of substrates in very high conversions (46–48%) and enantiomeric ratios (E>170) along with an easy recovery of both enantiomers without the need for preparative chromatographic separation. Additionally, both the starting ionic acid and the biocatalyst could be recovered and reused up to nine cycles without significant loss of enantioselectivity. Two continuous flow methods were also successfully developed using PEG600 derivatives. For amines, PEG600 diester revealed to be an excellent acylating agent. Very good ees (above 95%) and yields (above 35%) could be achieved for both enantiomers with a short residence time (30 minutes). For breakage of the amide groups from the product we had to resort to chemical hydrolysis with HCl in water/methanol. The biocatalyst could be used for 20 hours without any loss of enantioselectivity. A different strategy was developed for alcohols in which the alcohol was bonded to PEG600 diacid and then an enzymatic hydrolysis process under flow conditions was employed. After optimization, we demonstrated that with this method we could obtain productivities of 64 and 68 mg h-1 g enzyme-1 for the (R) and (S) enantiomer, respectively, during a 195 minutes trial (13 cycles) in acetone/water and with a residence time of only 15 minutes.