1.Penicillin acylase-catalyzed ampicillin synthesis using a pH gradient: a new approach to optimization.
Youshko MI1, van Langen LM, de Vroom E, van Rantwijk F, Sheldon RA, Svedas VK. Biotechnol Bioeng. 2002 Jun 5;78(5):589-93.
The penicillin acylase-catalyzed synthesis of ampicillin by acyl transfer from D-(-)-phenylglycine amide (D-PGA) to 6-aminopenicillanic acid (6-APA) becomes more effective when a judiciously chosen pH gradient is applied in the course of the process. This reaction concept is based on two experimental observations: 1) The ratio of the initial synthesis and hydrolysis rates (V(S)/V(H)) is pH-dependent and exhibits a maximum at pH 6.5-7.0 for a saturated solution of 6-APA; 2) at a fixed 6-APA concentration below saturation, V(S)/V(H) increases with decreasing pH. Optimum synthetic efficiency could, therefore, be achieved by starting with a concentrated 6-APA solution at pH 7 and gradually decreasing the pH to 6.3 in the course of 6-APA consumption. A conversion of 96% of 6-APA and 71% of D-PGA into ampicillin was accomplished in an optimized procedure, which significantly exceeds the efficiency of enzymatic synthesis performed at a constant pH of either 7.
2.Enzyme distribution derived from macroscopic particle behavior of an industrial immobilized penicillin-G acylase.
van Roon JL1, Joerink M, Rijkers MP, Tramper J, Schroën CG, Beeftink HH. Biotechnol Prog. 2003 Sep-Oct;19(5):1510-8.
The macroscopic kinetic behavior of an industrially employed immobilized penicillin-G acylase, called Assemblase, formed the basis for a discussion on some simple intraparticle biocatalytic model distributions. Assemblase catalyzes the synthesis of the widely used semisynthetic antibiotic cephalexin. Despite the obvious advantages of immobilization, less cephalexin and more of the unwanted byproduct d-(-)-phenylglycine are obtained due to diffusional limitations when the immobilized enzyme is employed. To rationally optimize Assemblase, the parameters particle size, enzyme loading, and enzyme distribution, which severely determine the macroscopic particle performance, were studied on the basis of macroscopic observations. Laser diffraction measurements showed that the particle sizes in Assemblase vary as much as 100-fold. The relative and total enzyme loadings in Assemblase and fractions thereof of different sizes were determined by initial-rate d-(-)-phenylglycine amide hydrolysis, cephalexin synthesis experiments, and active-site titration.
3.A two-step, one-pot enzymatic synthesis of cephalexin from D-phenylglycine nitrile.
Wegman MA1, van Langen LM, van Rantwijk F, Sheldon RA. Biotechnol Bioeng. 2002 Aug 5;79(3):356-61.
A cascade of two enzymatic transformations is employed in a one-pot synthesis of cephalexin. The nitrile hydratase (from R. rhodochrous MAWE)-catalyzed hydration of D-phenylglycine nitrile to the corresponding amide was combined with the penicillin G acylase (penicillin amidohydrolase, E.C. 3.5.1.11)-catalyzed acylation of 7-ADCA with the in situ-formed amide to afford a two-step, one-pot synthesis of cephalexin. D-Phenylglycine nitrile appeared to have a remarkable selective inhibitory effect on the penicillin G acylase, resulting in a threefold increase in the synthesis/hydrolysis (S/H) ratio. 1,5-Dihydroxynaphthalene, when added to the reaction mixture, cocrystallized with cephalexin. The resulting low cephalexin concentration prevented its chemical as well as enzymatic degradation; cephalexin was obtained at 79% yield with an S/H ratio of 7.7.
4.Synthesis of optically active amino acid derivatives via dynamic kinetic resolution.
Choi YK1, Kim Y, Han K, Park J, Kim MJ. J Org Chem. 2009 Dec 18;74(24):9543-5. doi: 10.1021/jo902034x.
The complete conversion of racemic amino acid amides to optically active amino acid derivatives was accomplished via lipase/palladium-catalyzed dynamic kinetic resolution (DKR). In the DKR, a lipase catalyzes the selective acylation of L-substrate in the presence of acyl donor while unreacted D-substrate is isomerized by a Pd nanocatalyst to L-substrate. The DKR reactions provided good yields (80-98%) and high enantiomeric excess (95-98% ee). Interestingly, the DKR reactions of phenylglycine amide in the presence of Z-Gly-OMe or Z-Gly-Gly-OMe yielded optically active di- and tripeptide .
