Alternative syntheses

Succinyl-CoA derived from propionyl-CoA can enter the TCA cycle. Oxidation of succinate to oxaloacetate provides a substrate for glucose synthesis. Thus, although the acetate units produced in /3-oxidation cannot be utilized in glu-coneogenesis by animals, the occasional propionate produced from oxidation of odd-carbon fatty acids can be used for sugar synthesis. Alternatively, succinate introduced to the TCA cycle from odd-carbon fatty acid oxidation may be oxidized to COg. However, all of the 4-carbon intermediates in the TCA cycle are regenerated in the cycle and thus should be viewed as catalytic species. Net consumption of succinyl-CoA thus does not occur directly in the TCA cycle. Rather, the succinyl-CoA generated from /3-oxidation of odd-carbon fatty acids must be converted to pyruvate and then to acetyl-CoA (which is completely oxidized in the TCA cycle). To follow this latter route, succinyl-CoA entering the TCA cycle must be first converted to malate in the usual way, and then transported from the mitochondrial matrix to the cytosol, where it is oxida-... 

Accordingly, for decades scientific investigations have been carried out to achieve the direct fluorination which would be attractive as a one-step synthesis alternative. Although the early reports concerned gas-phase direct fluorinations, the most relevant work in the last three decades was based on contacting fluorine gas with the aromatic compound dissolved in a liquid phase. These attempts at gas/liquid... 

Although most applications were of the cherry-picking type design, the combinatorial design of new chemical libraries should also be feasible. In this case, the scores obtained with the various models can be used to sort the virtual library, followed by building block frequency analysis cf. Focus2D) to determine which reagents should be used in chemical synthesis. Alternatively, combinatorial optimization approaches, such as those in described in ref. 4, can be applied where the model-predicted scores are used as the objective function for optimization. 

The proteasome and other proteases generate free amino acids. Ubiquitinated proteins are processed to peptide fragments from which the ubiquitin is subsequently removed and recycled. The peptide fragments are further digested to yield free amino acids, which can be used for biosynthetic reactions, most notably protein synthesis. Alternatively, the aminO group can be removed and processed to urea (p. 661) and the carbon skeleton can be used to synthesize carbohydrate or fats or used directly as a fuel for cellular respiration. 

Chain branches in stepwise polymerization may occur due to side reactions such as the addition of an -OH to a double bond in unsaturated polyester synthesis. Alternatively, chain branches can be a delibemte addition such as in polyurethane synthesis where a functionality greater than 2 is brought to bear (e.g. by using a triol chain extender) so that chain branching can occur. In systems of stepwise polymerization in which the reagents are polyftinctional these branches will lead to the occurrence of crosslinks and gelation. This is... 

Quinazolines can be prepared by several methods. AT-Acylanthranilic acids undergo cyclization with ammonia or primary amines via amides 14 forming quinazolin-4(3ii0-ones 15 (Niementowski synthesis). Alternatively o-(acylamino)benzaldehydes or -acetophenones react with ammonia producing quinazolines 16 (Bischler synthesis) ... 

Synthesis, alternate silica and surfactant 08-P-09 Synthesis, mesoporous silica, pH effect 06-P-20 ... 

The use of HMPA was mandatory for the success of the synthesis. Alternatively. (3-phosphanylpropyl)-cyclopentadlenyl anions 12 and 13 were prepared In 51% and 65% yield In a sequence of nucleophilic substitution reactions starting from l-bromo-3-chloropropane (11) by treatment with lithium phos-phides ° and then with NaCp in THF. followed by hydrolysis and deprotonation with butyllithium."... 

Ethylene from cracking of the alkane gas mixtures or the naphtha fraction can be directly polymerized or converted into useful monomers. (Alternatively, the ethane fraction in natural gas can also be converted to ethylene for that purpose). These include ethylene oxide (which in turn can be used to make ethylene glycol), vinyl acetate, and vinyl chloride. The same is true of the propylene fi action, which can be converted into vinyl chloride and to ethyl benzene (used to make styrene). The catalytic reformate has a high aromatic fi action, usually referred to as BTX because it is rich in benzene, toluene, and xylene, that provides key raw materials for the synthesis of aromatic polymers. These include p-xylene for polyesters, o-xylene for phthalic anhydride, and benzene for the manufacture of styrene and polystyrene. When coal is used as the feedstock, it can be converted into water gas (carbon monoxide and hydrogen), which can in turn be used as a raw material in monomer synthesis. Alternatively, acetylene derived from the coal via the carbide route can also be used to synthesize the monomers. Commonly used feedstock and a simplified diagram of the possible conversion routes to the common plastics are shown in Figure 2.1. 

This enzyme catalyses an intermediate step in cholesterol synthesis. Alternate donors are GTP, CTP, or UTP. It may be assayed radiochemically using C labelled mevalonate [502]. 

Study of the repression control of the histidine operon has suggested that it may be more complicated than the model proposed by Jacob and Monod. This possibility is predicated on failure to find a pure repressor gene. This failure has left open the possibility that control may be exerted by aminoacylated tRNA alone, possibly at the level of protein synthesis rather than mRNA synthesis. Alternatively, the repressor could be encoded by one of the regulatory genes discussed, but could also serve an additional function vital to the cell. The necessity of maintaining this second function would prevent the isolation of mutants which had totally lost repressor activity. In line with this latter possibility, the complex of histidyl-tRNA synthetase with aminoacylated tRNA may serve as the repressor. The mutual affinity of these two macromolecules and their concentrations within the cell are such that a large portion of the aminoacylated tRNA may be complexed to the synthetase [20,118a]. 

Changes in dietary carbohydrate that reduce milk fat content tend to increase protein content if dietary protein supply is adequate. The effect may require 2 3 weeks to manifest itself and be of the order of 8 g protein/kg nulk. It is probable that the increased propionic acid production on such diets has a sparing effect on certain glucogenic amino acids such as glutamate, and more of these are then available to the mammary gland for protein synthesis. Alternatively, such diets are often associated with an increase in microbial protein synthesis in the rumen, which will increase amino acid supply to the mammary gland. The increased intake of energy per se, which usually occurs on such diets, would have the same effect. 

A major advance in polypeptide synthesis came in 1962 when R. Bruce Merrifield of the Rockefeller University described a solid-phase synthesis (alternatively called polymer-supported synthesis) of the tetrapeptide, Leu-Ala-Gly-Ala, by a technique that now bears his name. Merrifield was awarded the 1984 Nobel Prize in Chemistry for his work in developing the solid-phase method for peptide synthesis. 

This case study is a reactor-separator-recycle system to produce monochlorobenzene. The operating parameters and sizes for one of the synthesis alternatives are optimised using the detailed models and the costing information provided. Each unit has a capital cost, Cc, and an operating cost, Q, which is incorporated into the objective function through a pay out time of 2.5 years. The principal units are a CSTR and two separation columns. The models have been reformulated in terms of component flowrates, Fsj. The reactor is a continuous stirred tank reactor (CSTR) which models the reaction between chlorine and benzene (A) to produce monochlorobenzene ( B) and dichlorobenzene (C) at a constant temperature. The maximum (global) profit is 2081/day. 

A large step towards bio-functional nanotubes was taken by the same research group. An alumina membrane was first coated with two alternating layers of poly(ethylene imine) and poly(styrenesulfonic acid). Cytochrome c, with a positively charged surface at pH 7, was then alternated five times with poly(styrenesulfonic acid) in a LbL nanotube synthesis. Alternatively, cytochrome e and glutaraldehyde were employed to build up five covalent bilayers. Dissolution of the alumina template with 5% phosphoric acid yielded the protein-containing nanotubes. ... 

This section describes two possible synthesis alternatives for the synchronization of SENDs and RECVs in the Workbench since the Workbench does not yet fully support the synthesis of processes, either could be adopted by the system as a valid implementation. Other synthesis alternatives may also be possible, and equally valid. 

---