Precursor addition

Table 8.7 The most important process conditions for the production of L-phenylalanine by direct fermentation precursor addition, phenylpyruvic add (PPA) bloconversion, acetamidocinnamic add (ACA).

Extra cost compared to direct fermentation are mainly concerned with addition of PPA (precursor addition) or ACA (bioconversion). Table 8.9 compares estimated costs for foe PPA and ACA process based on foe data considered previously (section 8.6.1 and 8.6.2). Costs are estimated for production of 100 tonnes per year. 

Bardaji, M., Lagrma, A. and Jones, P.G. (2001) Reactivity of anAcetylenephosphine Gold(III) Precursor Addition to the Triple Bond or Formation of Alkynyl Derivatives. Organometallics, 20(18), 3906-3912. 

The reaction of 49 with alkylamines has been examined in the context of Cp2Mg-MR3-NH3 (M = group 13 metal) mixtures as CVD precursors. Addition of primary and secondary amines to 49 at ambient temperature in toluene affords stable amine adducts in good yield (Table 3). Most adducts can be sublimed at under 100 °C/0.05 torr in... 

Friedrichsen and co-workers (133) approached substituted benzotropolones from an aromatic substituted carbonyl ylide with a tethered alkyne as the intramolecular dipolarophUe (Scheme 4.67). Starting from an aromatic anhydride, Friedrichsen was able to make the tethered alkyne via addition of either pentyn-ol or hexyn-ol, then transform the recovered benzoic acid to the a-diazocarbonyl cycloaddition precursor. Addition of rhodium acetate resulted in the tandem formation of cyclic carbonyl ylide followed by cycloaddition of the tethered alkyne producing the tricyclic constrained ether 252. Addition of BF3 OEt2 opened the ether bridge, forming the benzotropylium ion, which subsequently rearranged to form the tricyclic benzotropolone (253). 

According to the opinion of the authors of Ref. 32, the negative results of the experiments above do not mean that metal-free Pc could not be theoretically obtained from these precursors additional detailed studies (combination of different techniques, such as UV irradiation, microwave treatment, use of other inert solvents, electrolysis in the systems producing free radicals, etc.) are required for successful resolution of this problem. However, under the same conditions it is possible to obtain some transition metal complexes of the Pc due to the template effects (see below). 

This evidence that benzyne is at least one of the intermediates in acetylene pyrolysis has many implications. However, as the ratios of products from acetylene and hexafluorobenzene differ appreciably from those obtained from phthalic anhydride, it might be best at this point to call acetylene a benzynoid precursor. Additional data will be needed and are being accumulated to determine to what extent acetylene reactions proceed at high temperatures through a benzyne intermediate (Fields and Meyerson, 1967a). 

Sequestering ligands Required educt/ organic precursor Additional reactants for synthesis of hgand Minimum value Log C/N < C/N< Real values of C/N... 

Cyciopropaniminium salts 376, 379 and 396 are intermediates in the nucleophilic substitution of aminocyclopropane derivatives. Salts 379 or 396 were prepared in solution from suitable precursors Addition of nucleophiles such as MeO... 

The most successful way to achieve overproduction is to make use of mutants. Another way to overcome feedback regulation is to naake use of a kind of semi-fermentaticHi process called precursor addition fermentation this will be considered later in this chapter. 

The production of L-phenylalanine by precursor addition is given in reaction 3 (Hgure... 

As can be seen from Table 8.7 productivity (expressed in g h b is highest for precursor addition. The production of L-phenylalanine from phenylpyruvic add also has the shortest reaction time to obtain hi conversions. The pH commonly used is around 75, quite normal for biological processes. Only the enzyme phenylalanine ammonia lyase shows an optimiim pH of lO.The process temperature varies between 30 and 40°C with an average of 35°C. No extreme temperatures have been reported due to the fact that denaturation occurs at hi temperatures. The optimal concentration for cells frequently used is 10-20 g 1". However, conversion of ACA is done with hi cell mass concentrations in recent studies possibly to compensate for substrate inhibition and thus to maintain hi product concentration. The processes using PPA and ACA need an amino add as amino donor, usually L-aspartic add is used. 

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