Acid diethyl ester enzymatic hydrolysis

Biocatalysis plays a central role in the manufacturing of statin side chains (Figure 6.2). A first set of approaches exploits enzymatic desymmetrization reactions, for example, of the methoxyacetyl ester of glutaric acid diethyl ester with commercially available a-chymotrypsin as explored by Ciba SC with a yield of 94% and enantiomeric excess of up to 98% [1]. In the optimized procedure, the substrate was available in a concentration of 1 M at an enzyme/substrate ratio of 7% (wt/wt), and the reaction took approximately a day. The subsequent steps to the final acetonide also involved a pig-liver esterase (PLE) catalyzed selective hydrolysis of the methoxyacetyl group (Figure 6.2a). 

A)-alcohol (7) by Sphingomonas paucimobilis SC 16113 (Fig. 6) (2) the enzymatic resolution of racemic (a-methyl)phenylalanine amide (8) and a-(4-methoxyphenyl)alanine amide (10) by amidase from Mycobacterium neoaurum ATCC 25795 to prepare the corresponding (S)-amino acids (9) and (11), and (3) the asymmetric hydrolysis of methyl-(4-methoxyphenyl)-propanedioic acid, diethyl ester (12), to the corresponding (X)-monoester (13) by pig liver esterase (Fig. 7). 

Enantioselective Hydrolysis of Diethyl Methyl-(4-Methoxy-phenyO-Propanedioate. The (5 )-monoester (26) (Fig. 6B) is a key intermediate for the syntheses of 33-receptor agonists. The enantioselective enzymatic hydrolysis of diester (27) to the desired acid ester (26) by pig liver esterase (32) has been demonstrated. In various organic solvents, the reaction yields and e.e. of the monoester (25) were dependent upon the solvent used. High e.e. (>91%) were obtained with methanol, ethanol, and toluene as a cosolvent. Ethanol gave the highest reaction yield (96.7%) and e.e. (96%). 

With the procedure of Okishio et al. (24,124) freeze-dried rat liver homogenates are exhaustively extracted with 95% ethanol containing 0.1% ammonium hydroxide, and the extract is taken to dryness. The residue is dissolved in aqueous NaOH, pH 11, and applied to an Amberlyst A-26 anion exchanger. After alkaline or enzymatic hydrolysis the free bile acids are extracted with diethyl ether after acidification. The bile acids are methylated and then purified on aluminum oxide. The bile acid methyl ester fraction eluted from this column is taken to dryness and the residue is trifluoroacet-ylated and analyzed on a triple-component column (QF-1-SE-30-NGS) for quantitative determination. 

Oligomeric PET model compounds have been widely used to study enzymatic hydrolysis of PET, since their degradation is faster and easier to analyze compared to a polymeric substrate. Diethyl terephthalate (DET), diethyl p-phthalate (DP), h/i(benzoyloxyethyl) terephthalate (PET trimer), ethylene glycol dibenzyl ester (BEB), and hA-(p-methylbenzoic acid)-ethylene glycol ester (PET dimer) have been employed (Eig. 2). Their degradation by PET hydrolases from Fusarium solani [27, 38], T. insolens [1, 5, 48, 101], P. mendocina [25, 49], T. fusca [26, 27, 38], Burkholderia cepacia [26, 27, 38], Aspergillus oryzae [103], Bacillus spp. [87], and porcine liver esterase [109, 110] has been reported, and the corresponding hydrolysis products have been partially characterized (Table 1). 

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