Vitamin C, from glucose

E. herbicola. The resultant organism can carry out both steps a and b of Eq. 20-3 leaving only step c, a nonenzymatic acid-catalyzed reaction, to complete an efficient synthesis of vitamin C from glucose. Higher plants make large amounts of L-ascorbate, which in leaves may account for 10% of the soluble carbohydrate content. However, the pathway of synthesis differs from that in Fig. 20-2. Both D-mannose and L-galactose are efficient precursors. The pathway in Eq. 20-4, which starts with GDP-d-mannose and utilizes known enzymatic processes, has been suggested. The GDP-D-mannose-3,... 

Therefore, if the vitamin C or its direct precursor, 2-KLG, could be produced by one single step fermentation process, the final cost of the vitamin C will be significantly decreased. Current research on the one-step fermentation process is focnsed mainly on the following three aspects (1) Classical two-step based one-step fermentation process for 2-KLG production (2) Innovative two-step based one-step fermentation process 2-KLG (3) Direct production of vitamin C from glucose. 

An obvious way to target chiral compounds is to start with a compound in which the chiral center is already present. Here natural products and derivatives offer a rich pool of generally inexpensive starting materials. Examples include L-hydroxy and amino adds. Sometimes, just one out of many chiral centers is predestined to remain, as in the synthesis of vitamin C from D-glucose, or in the preparation of (S)-3-hydroxy-y-butyrolactone from ladose. 

Brewers and bakers dried yeasts are used as dietary supplements. They contribute some protein and trace minerals, and some B vitamins, but no vitamin C, vitamin B 2 or fat-soluble vitamins. The glucose tolerance factor (GTE) of yeast, chromium nicotinate, mediates the effect of insulin. It seems to be important for older persons who caimot synthesize GTE from inorganic dietary chromium. The ceU wall fraction of bakers yeast reduces cholesterol levels in rats fed a hypercholesteremic diet. 

How analytical methods deal with interferences is one of the more ad hoc aspects of method validation. There is a variety of approaches to studying interference, from adding arbitrary amounts of a single interferent in the absence of the analyte to establish the response of the instrument to that species, to multivariate methods in which several interferents are added in a statistical protocol to reveal both main and interaction effects. The first question that needs to be answered is to what extent interferences are expected and how likely they are to affect the measurement. In testing blood for glucose by an enzyme electrode, other electroactive species that may be present are ascorbic acid (vitamin C), uric acid, and paracetamol (if this drug has been taken). However, electroactive metals (e.g., copper and silver) are unlikely to be present in blood in great quantities. Potentiometric membrane electrode sensors (ion selective electrodes), of which the pH electrode is the... 

As with all methods, this approach has some limitations it uses acetonitrile, which is toxic, and the separation of glucose from fructose can sometimes be problematic after extended use of the column. However, sample preparation is easy since it requires only dilution to the required level (often 1 10) and filtration prior to analysis to remove particulate materials, which protects and extends the useful life of the column. The degradation of the resolution between glucose and fructose is caused by the partial inactivation of the column by materials in the matrix, but this resolution can be recovered by reducing the acetonitrile concentration in the solvent. The same column can also be used to assay the level of ascorbic acid (vitamin C) in a soft drink or fruit juice, although different detection and solvent systems are used. 

Once a structure is known, organic chemists try to synthesize the compound in the laboratory. If the starting materials are inexpensive and the synthesis process is simple enough, it may become more economical to manufacture a compound than to isolate it from a plant or bacterium. In the case of vitamin C, a complete synthesis was achieved in 1933, and it is now much cheaper to synthesize it from glucose than to extract it from citrus or other natural sources. Worldwide, more than 80 million pounds are synthesized each year. 

Vitamin C, classified as either a pharmaceutical [5] or a food additive [6], has annual sales of 325 million dollars, the largest of all pharmaceuticals produced [7]. Pharmaceuticals, in general, lead in profitability for all industries [6]. Although vitamin C can be extracted from natural sources, it is primarily synthesized. In fact, it was the first vitamin to be produced in commercial quantities [6]. Jaffe [8] outlines the synthesis. Starting with D-glucose, vitamin C is produced in five chemical steps, one of which is a biochemical oxidation using the bacterium Acetobacter suboxydans. D-glucose is obtained from cornstarch in a process, which will be described later. 

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