| Summary: | 碩士 === 國立成功大學 === 化學系 === 88 === Abstract
Penicillin G acylase has been widely used to produce 6-aminopenicilanic acid by hydrolysing penicillin G. In the suitable environment, however, penicillin G acylase has also been used to synthesize β-lactam antibiotics.
In this thesis, two topics were examined. First, enzymatic synthesis of cephalothin from 7-aminocephalosporanic acid (7-ACA) and derivatives of 2-thienylacetic acid (2-TA derivations) using penicillin G acylase was studied. The effects of pH, temperature, initial substrate concentrations and reaction time on the conversion of 2-thienylacetamide (2-TAA) and 7-ACA to cephalothin were examined.
To improve the solubility of 2-TA derivatives, we synthesize two amide derivatives of 2-TA; 2-TAA and 2-thienylacetohydroxamic acid (2-TAH). The solubility of 2-TAA and 2-TAH in aqueous solution is 87 mM and 120 mM, respectively. Enzymatic conversion of 2-TAH to cephalothin yielded side products which were derived from reactions between hydroxyamine and 7-ACA. But they were not found in the conversion of 2-TAA to cephalothin. So we choose 2-TAA and 7-ACA as the reactants. The optimum reaction condition was determined at pH 6.5 and 15℃. The best conversion yield of 72 % was obtained when the initial concentration of 2-TAA and 7-ACA was at 400 mM and 100 mM, respectively. Besides, we developed a simple method to purify cephalothin with final purity of 91 % and the recovery yield 96 %.
The second topic was to study the stability of β-lactam antibiotics synthesized by penicillin G acylase. We used four acyl donors and four acyl acceptors for this study. When the acyl donors contained an α-amino group, the products of β-lactam antibiotic were degraded. When the α-amino group of acyl donors were acylated, they were not hydrolyzed by penicillin G acylase and could even inhibit penicillin G acylase. Because the acylated acyl donor inhibits penicillin G acylase , we hypothesize that the acylated α-amino group of ampicillin and cephalexin may inhibit penicillin G acylase and β-lactamase. The inhibitory effect of acylated ampicillin and cephalexin to penicillin G acylase and β-lactamase were examined and the data showed that they could inhibit penicillin G acylase but not β-lactamase.
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