Phenylacetylcarbinol

Enzymatic Processes for Fine Chemicals and Pharmaceuticals Kinetic Simulation for Optimal /2-Phenylacetylcarbinol Production... 

Ephedrine and pseudoephediine are a vasodilator and decongestant respectively used widely in the treatment of asthma and the symptoms of colds and influenza. These pharmaceuticals were derived originally fi om the plant Ephedra sinica and used in traditional Chinese medicinal preparations. Although some are still produced fi om such sources, the major production is via a fermentation process followed by a chemical catalytic reaction. As shown in Figure 1, the intermediate / -phenylacetylcarbinol (PAC) is produced by decarboxylation of pyruvate followed by ligation to benzaldehyde. 

Phenylacetylcarbinol 15 Ephedrine Treatment for asthma Lyase Saccharomyces cerevisiae Single-stage fermentation [9]... 

L-phenylacetylcarbinol benz aldehy det-pyruvate pyruvate decarboxy... 

Another example is the commercialized formation of R-phenylacetylcarbinol (R-PAC) from benzaldehyde and pyravate by fermenting brewer s yeast (see chapter 4.16 Neuberg Hirsch, 1921). Pymvate decarboxylase is responsible for the formation of an activated acetaldehyde from the decarboxylation of pyravate and the condensation of this activated acetaldehyde with benzaldehyde. Nowadays, about 1000 tons per aimum (tpa) R-PAC is produced this way. 

Hauer, M. Breuer, M. Pohl, Studies on the continuous production of (R)-(-)-phenylacetylcarbinol in an enzyme-membrane reactor. J. Mol. 

M. Breuer, M. Pohl, B. Hauer, B. Lingen, High-throughput assay of R) -phenylacetylcarbinol synthesized by pyruvate decarboxylase. Anal. Bioanal. Chem. 2002, 374, 1069-1073. 

Pyruvate decarboxylase Production of (R)-phenylacetylcarbinol, a precursor of ephedrine in MES-KOH buffer /1 -pentanol [28]... 

Microwave-assisted stepwise imine formation and subsequent reduction with NaBH4 were also used as the key steps in the synthesis of ephedrine from L-phenylacetylcarbinol. The reactions were performed on a multigram scale in a domestic microwave oven to provide the product in satisfactory yield within a total reaction time of 19 min (Scheme 4.27)49. 

Shukla, V.B., Madyar, V.R., Khadilkar, B.M. and Kulkarni, P.R., Biotransformation of benzaldehyde to l-phenylacetylcarbinol (l-PAC) by Torulaspora delbrueckii and conversion to ephedrine by microwave radiation, /. Chem. Technol. BiotechnoL, 2002, 77, 137-140. 

Pyruvate decarboxylase (PDC, E.C. 4.1.1.1) accepts other substrates besides pyruvate, its natural reactant As early as 1921, Neubergand Hirsch described the reaction of yeast with benzaldehyde and pyruvate to phenylacetylcarbinol (2-keto-3-hydroxy-propylbenzene) (Neuberg, 1921) in a carboligase side reaction which yields ephedrine after reaction with methylamine and catalytic hydrogenation (Figure 7.37). 

The reaction was already being used in the 1930s by Knoll (Ludwigshafen, Germany) (later BASF, since 2001 Abbott) (German Patent DE 546459, 1932) to produce ephedrine via (R)-phenylacetylcarbinol, (R)-PAC. Recently, efforts have been renewed to obtain an isolated enzyme process or a whole-cell process based on recombinant DNA technology. It was found that pyruvate could be substituted by the less expensive acetaldehyde, which did not produce C02 as a side product. 

Optimization of a continuous enzymic reaction yielding (R)-phenylacetylcarbinol (PAC), an L-ephedrine intermediate (Chapter 7, Section 7.5.2), from acetaldehyde and benzaldehyde with PDC from Zymomonas mobilis demonstrated that... 

PDC pyruvate decarboxylase (R)-PAC (R)-phenylacetylcarbinol KDN 2-keto-3-deoxy-D-glycero-D-galacto-nonopyranulosonic add UDPGA /J-D-uridine diphosphoglucuronic add dTDP deoxythymine diphosphate ... 

The a-keto acid decarboxylases such as pyruvate (E.C. 4.1.1.1) and benzoyl formate (E.C. 4.1.1.7) decarboxylases are a thiamine pyrophosphate (TPP)-dependent group of enzymes, which in addition to nonoxidatively decarboxylating their substrates, catalyze a carboligation reaction forming a C-C bond leading to the formation of a-hydroxy ketones.269-270 The hydroxy ketone (R)-phenylacetylcarbinol (55), a precursor to L-ephedrine (56), has been synthesized with pyruvate decarboxylase (Scheme 19.35). BASF scientists have made mutations in the pyruvate decarboxylase from Zymomonas mobilis to make the enzyme more resistant than the wild-type enzyme to inactivation by acetaldehyde for the preparation of chiral phenylacetylcarbinols.271... 

Fermentation of the inexpensive industrial chemicals benzaldehyde and acetaldehyde with Sacchromyces cervisiae microorganisms leads to (R)-phenylacetylcarbinol, which is converted to the important drug substance (IR, 2S)-ephedrine. 

Pyruvate decarboxylase catalyzes the nonoxidative decarboxylation of pyruvate to acetaldehyde and carbon dioxide. When an aldehyde is present with pyruvate, the enzyme promotes an acyloin condensation reaction. The mechanistic reason for this fortuitous reaction is well understood and involves the aldehyde outcompeting a proton for bond formation with a reactive thiamine pyrophosphate-bound intermediate (90,91). When acetaldehyde is present, the product formed is acetoin. Benzalde-hyde results in the production of phenylacetylcarbinol (Fig. 26). Both of these condensations are enantioselective, forming the R enantiomer preferentially in both cases. 

The ability of pyruvate decarboxylase from many microbial sources to produce phenylacetylcarbinol has been exploited for many years in the synthesis of ephedrine, a natural adrenergic compound (92). The acyloin is reductively aminated to produce the ethanolamine product, (1R,2S)-ephediine, with two chiral centers. 

S. Bringer-Meyer and H. Sahm, Acetoin and Phenylacetylcarbinol formation by the pyruvate decarboxylases of Zymomanas mobilis and Sacdiaromyces calbergensis, Bi ocof., 1 321 (1988). 

V B Shukala, P R Kulkami, L-Phenylacetylcarbinol (I PAC) Biosynthesis and Industrial Applications. World Journal of Microbiology and Biotechnology 16 499 -506,2000. 

In 1921, Neuberg and Hirsch discovered that yeasts could condense added ben-zaldehyde with pyruvate-derived acetaldehyde to form the chiral product, l-(-f) phenylacetylcarbinol (also named Neuberg s ketone). This alpha-hydroxyketone (acyloin) can easily be chemically converted into L-(-)-ephedrine, an important broncho dilator still made by a bioprocess. 

The sympathomimetic ephedrine is produced using benzaldehyde as the starting material. Benzaldehyde is converted biotechnically using Carl Neuberg s synthesis (1921) with acetaldehyde which arises from fermentation of molasses to produce optically active phenylacetylcarbinol ((-)- -hydroxy-1-phenylacetone), which is transformed into L-(—)-ephedrine by catalytic hydrogenation in the presence of methylamine. 

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