Biochemical routes

Biochemical Routes. Enzymatic oxidation of benzene or phenol leading to dilute solution of dihydroxybenzenes is known (62). Glucose can be converted into quinic acid [77-95-2] by fermentation. The quinic acid is subsequently oxidized to hydroquinone and -benzoquinone with manganese dioxide (63). 

The alternative pathway is the biochemical route. It processes starches/sugars into ethanol, a standard technology with installations world-wide, but in a biorefinery the start is the whole-plant material or biomass residues containing hemicel-lulose, which is broken into sugars that then can be fermented to ethanol and/or other alcohols such as butanol. As mentioned before, there is the need to develop novel and/or improved biocatalysts for alternative organic fuels, such as biobutanol, by fermentation processes. 

Therefore, in the absence of significant improvements also on the (bio)catalysis side, the competitiveness of an enzymatic biochemical route must is still uncertain. 

It can be concluded that the biochemical production of liquid fuels from biomass is technologically feasible, but much work is still needed to optimize the various aspects of the processes. The present day economic climate is not favourable for production of these fuels from biomass by biochemical routes. 

The disadvantages of all biochemical routes is the lack of variable tacticity in the polymer and, even more important, the need for time-consuming purification. PHB materials of feasible properties are only achieved with high production costs. In the 1990s, ICl sold a copolymer of 3-HB and 3-HV (BIOPOL) for about 10-20 /kg whereas the price of PP was less than 2 /kg. Therefore, a fermentative synthesis is feasible for smaller applications but not cannot compete with packaging materials such as poly(olefin)s [43 5] (Fig. 10). 

Metabolic processes utilize a variety of differing and contrasting biochemical routes to enable synthesis of degradation and activation or deactivation of substances in addition, they facilitate cellular uptake and excretory mechanisms. Moreover, there are various links between different metabolic pathways and functional processes. Intermediate chemical products generated in the course of metabolic reactions may be taken up by other pathways or cycles. Substrates are shifted between subcellular structures, and the metabolic end-products of one process are often used as the original substrate for new syntheses. 

Several fundamentally distinct approaches to the procurement and evalu-ation of biocatalysts useful in the detoxication of drugs or chemicals of abuse arc outlined below. The author has arbitrarily limited the presen-tation to a few select detoxication catalysts in the field of drug abuse. In some cases, other nondetoxicating biochemical routes of transformation are included as well. 

Thus, large-volume products such as monosodium L-glutamate, L-lysine, and l-menthol have traditionally been prepared through biochemical routes, even though efficient procedures are available to produce their racemic forms. 

Fig. 8 depicts mass indices S-1 and environmental factors E and gives an indication of the mass efficiency for the four routes A-D. The amounts of chemicals needed for the production of 1 kg HPB ester varied between approximately 40 kg and 105 kg. In all cases, the major components were water and the solvents needed for the reactions and/or extractions, a picture that is typical for fine chemical synthesis. Route D clearly had the lowest consumption of materials. The main drawback for the two biochemical routes A and B were the need for rather large amounts of water and solvents (for extraction), even though it has to be pointed out that these processes were not optimized. Comparable variations were observed for the substrate consumption, i.e., how much starting material was needed to produce 1 kg of HPB ester (see Fig. 8b). In this case, however, both the highest (C) and the lowest (D) consumptions were observed for the chemical routes. The...

The same trends can be seen in Fig. 9 a and 9 b, which show the mass indices S-1 for the different reaction steps with and without taking water into account. In most cases, one step clearly dominated the mass consumption. For the biochemical routes, this was the reduction (step 3), and for the chemical routes, it was one step of the intermediate synthesis. 

The variation in mass consumption for the four routes was significant and generally due to the reduction steps. However, these differences might be smaller when taking into account that most of the solvents can be recycled and that the biochemical routes would profit most in this respect. 

Among all EHS aspects, the safety concerns were the most significant. The use of flammable substances, especially hydrogen in combination with noble metal catalysts in C and D and possible peroxide formations in D, has to be addressed. Toxicity was a minor issue in all routes, except perhaps for sulfuric and hydrochloric acid, which have a very low workplace threshold value. In contrast, the eutrophication potential could be a major issue for the biochemical routes A and B. 

Both biochemical routes (A and B) are attractive alternatives to the chemical routes, provided that space-time yields and the solvent/water/buffer consumption can be improved. 

In order to maximize ethanol production in relation to glycerol and pyravate, the metabolic pathways need to be manipulated. Figure 7.1 shows the biochemical routes to glycerol, pyravate, and ethanol, illustrating targets for reduecting carbon flux to ethanol. 

Saxena, R.C., D.K. Adhikari and H.B. Goyal (2009) Biomass-based energy fuel through biochemical routes a review , Renewable and Sustainable Energy Reviews, Vol. 13, No. 1, pp. 167-78. 

It should be realized at the outset that all organisms have to possess the capacity to make deoxyribonucleotides firom ribonucleotides. This is the only process which permits the cell to utilize one fraction of the total nucleotides formed de novo in pyrimidine and purine biosynthesis for DNA replication there is no alternative biochemical route producing 2-deoxyribose, its phosphates, or N-glycosides from other molecules (Scheme II). 

Figure 7.1. Overview of the biochemical routes leading to glycerol, pyruvate, and ethanol. Furthermore, valine biosynthesis and diacetyl formation are shown, which may be bypassed by introduction of a heterologous a-acetolactate decarboxylase that directly converts a-acetolactate to acetoin. GPDl and GPD2, glycerol dehydrogenases 1 and 2 ADHl, alcohol dehydrogenase 1 ILV2, acetolactate synthetase ID/5, acetolactate reductoisomerase [Refs in 502].

Detailed work on optimization followed the first results, with the aim of proposing gold as an alternative process to the biochemical route. This led to a highly efficient catalytic system. The work also took advantage of the mechanistic studies discussed in Section 13.4. Starting from TOP of a few hundred h units, we reached the impressive value close to 60000h", which is similar to the behavior of enzymatic catalysis [16]. 

This method, based on the use of microbial cells or enzymes, exploits three important features of biocatalysts (1) directing a reaction exclusively toward one enantiomer, (2) transforming a prochiral center to a chiral product, and (3) carrying out transformations on nonfunctionalized centers. The traditional problem associated with the enzymatic method is the presumption that these reactions should, of necessity, be carried out in dilute aqueous solutions to mimic biological systems. This leads to problems such as expensive separations and sensitivity of fermentations to deactivating influences. Despite these limitations, the biochemical route offers an attractive alternative for synthesizing an enantiomer directly (Knowles, 1986 Sheldon, 1996). 

Biochemical routes for the formation of nitroxyl ions are shown in Fig. 5.25 but without considering inorganic or non-enzymatic solution chemistry. In cells, reac-... 

Isoprene units all originate by the same biochemical route through isopentenyl pyrophosphate. This latter compound is formed from mevalonic acid in a series of enzyme-assisted steps using energy transfer from ATP ADP hydrolysis. Mevalonic acid (mevalonate) is obtained by condensation of acetyl-CoA with acetoacetyl-CoA. 

In a related fashion, asymmetric amination of ( )-cinnamic acid yields L-phenylalanine using L-phenylalanine ammonia lyase [EC 4,3,1,5] at a capacity of 10,000 t/year [1274, 1601], A fascinating variant of this biotransformation consists in the use of phenylalanine aminomutase from Taxus chinensis (yew tree), which interconverts ot- to p-phenylalanine in the biochemical route leading to the side chain of taxol [1602], In contrast to the majority of the cofactor-independent C-0 and C-N lyases discussed above, its activity depends on the protein-derived internal cofactor 5-methylene-3,5-dihydroimidazol-4-one (MIO) [1603], Since the reversible a,p-isomerization proceeds via ( )-cinnamic acid as achiral intermediate, the latter can be used as substrate for the amination reaction. Most remarkably, the ratio of a- vs, 3-amino acid produced (which is 1 1 for the natural substrate, R = H) strongly depends on the type and the position of substituents on the aryl moiety While o-substituents favor the formation of a-phenylalanine derivatives, / -substituted substrates predominantly lead to p-amino analogs, A gradual switch between both pathways occurred with m-substituted compounds. With few exceptions, the stereoselectivity remained exceUent (Scheme 2,215) [1604, 1605],... 

Starting from renewable raw materials the C3-Platform can be accessed both by chemical as well as biochemical routes (Figure 1.6). With biodiesel setup on a firm and... 

Sequestration of CO2 should not be an issue of gasification of biomass to syngas. Biomass covers a wide field of materials ranging from vegetable biomass such as wood, straw, grain, black liquor from the paper industry, animal biomass and various waste. Gasification of biomass may be an alternative to biochemical routes [419]. However, there are still problems to be solved. 

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