Preparation of Sterically Demanding 2,2-Disubstituted-2-Hydroxy Acids by Enzymatic Hydrolysis

Andrea Pinto,Diego Romano,Laura Carzaniga,Immacolata Serra,Martina Contente,Francesco Molinari,Fabio Rancati,Roberta Mazzucato

doi:10.3390/catal9020113

Abstract

Preparation of optically-pure derivatives of 2-hydroxy-2-(3-hydroxyphenyl)-2-phenylacetic acid of general structure 2 was accomplished by enzymatic hydrolysis of the correspondent esters. A screening with commercial hydrolases using the methyl ester of 2-hydroxy-2-(3-hydroxyphenyl)-2-phenylacetic acid (1a) showed that crude pig liver esterase (PLE) was the only preparation with catalytic activity. Low enantioselectivity was observed with substrates 1a–d, whereas PLE-catalysed hydrolysis of 1e proceeded with good enantioselectivity (E = 28), after optimization. Enhancement of the enantioselectivity was obtained by chemical re-esterification of enantiomerically enriched 2e, followed by sequential enzymatic hydrolysis with PLE. The preparation of optically-pure (S)-2e was validated on multi-milligram scale.

Highlights

Enzymatic hydrolysis of chiral esters using carboxylesterases is an established method for obtaining kinetic and dynamic resolution [1,2,3,4,5]
In 2019, this 9,work, we have studied the enzymatic hydrolysis of esters 1, derivatives of sterically
Two major problems encountered the enzymatic for the synthesis of antimuscarinic agents

Summary

Introduction

Enzymatic hydrolysis of chiral esters using carboxylesterases is an established method for obtaining kinetic and dynamic resolution [1,2,3,4,5]. Esters of carboxylic acids with sterically-demanding α-substitutions are not hydrolysed by most of the lipases, and protein engineering for making natural enzymes able to accept these substrates is still limited to relatively bulky carboxylic acids [7]. Enzymatic hydrolysis of carboxylic acid esters having an α-quaternary or α-tertiary centre is still a difficult task [8]; in contrast to the broad spectrum of esters with bulky alcohol moieties accepted as substrates [9,10]. Hetero-atoms (e.g., O and N) or by EW-functional groups (e.g., -NO2 , -CN, -CF3 ) is often required to observe enzymatic hydrolytic activity [11,12,13]. α-,α-Disubstituted malonate diesters are among the few α-,α-,α-trisubstituted carboxylic esters accepted by carboxylesterases; in particular, pig liver esterase (PLE) is suited for catalyzing the enantioselective monohydrolysis of differently substituted malonate diesters [14], including ester derivatives, such as dimethyl

Methods

Results

Conclusion