Semi Synthetic

Many semi-synthetic penicillins are made from 6-aminopenicillanic acid (6-APA, R = NH2>. 

The formation of nitrosamines, e.g. n-nitrosodiedianolamine, which are possible human carcinogens, can occur in synthetic or semi-synthetic fluids which contain a nitrite salt and diethanolamine or triethanolamine. 

Figure 6.14 Enzymatic side chain cleavage of penicillins. 6-Aminopenicillanic acid, a valuable intermediate for the production of various semi-synthetic penicillins, can be obtained through enzyme-mediated hydrolysis of the phenylacety group of penicillin G or the phenoxyacetyl group of penicillin V. The active site of the enzyme recognises the aromatic side chain and the amide linkage, rather than the penidllin nucleus. Chemical entitles other than penicillins are therefore often good substrates, as long as they contain the aromatic acetamide moiety.

Before we leave our discussion of preparing 6-aminopenicillanic acid for use as a starting material in the manufacture of semi-synthetic penicillins, we should point out that similar processes are used in the manufacture of semi-synthetic cephalosporins. Here tire key intermediate is 7-aminodeacetoxycephalosporanic add (7-ADCA). We have drawn outline schemes comparing the production of semi-synthetic penicillins and cephalosporins in Figure 6.15. You will see that the two schemes are very similar. 

Figure 6.15 Production of semi-synthetic penicillins (left) and cephalosporins (right), from enzymatically obtained intermediates 6-APA and 7-ADCA respectively.

Another important enzymatic process in the production of 7-ADCA, for use in the production of semi-synthetic cephalosporins, is the hydrolysis of 7-aminocephalosporanic add (7-ACA) by the enzyme acetyl esterase. This process, again using immobilisation techniques, is illustrated in Figure 6.16. Hie deacylated product can be used, for example, as an intermediate in the production of the important oral cephalosporin cefuroxime. We will return to cephalosporin antibiotics later in this chapter. 

In section 6.6.1, we described how enzymatic methods have come to dominate the production of the important intermediates used in the manufacture of semi-synthetic -lactams. In principle, the hydrolytic penicillin acylases may be used in the reverse direction to add acyl groups to 6-APA. For example, a two-step enzymatic process has been described for the preparation of ampiciilin (D-(-)-a-aminobenzylpenidllin structure shown in Figure 6.17). 

Also illustrated in Figure 6.17 there is another important antibiotic, amoxicillin. Both amoxicillin and ampiciilin can be made enzymatically or chemically. Although enzymes are available that can be applied very well for the conversion of 6-APA into a variety of semi-synthetic penicillins, economic reasons are still impeding large scale applications. 

In our discussion of the diversification of the fMactams, we explained how acylases and acylating enzymes may be used in the production of modified (semi-synthetic) P-lactams. However, the potential of using enzymes to modify oiganic molecules is much wider than this. 

Table 4.1.5 Relative Rates of the Regeneration of Semi-synthetic Aequorins in the absence and presence of Ca2+ at 24°C (Shimomura, 1995d)...

Knight, M. R., Read, N. D., Campbell, A. K., and Trewavas, A. J. (1993). Imaging calcium dynamics in living plants using semi-synthetic recombinant aequorins. J. Cell Biol. 121 83-90. 

Shimomura, O., Musicki, B., and Kishi, Y. (1988). Semi-synthetic aequorin an improved tool for the measurement of calcium ion concentration. Biochem. J. 251 405 410. 

Toma, S., et al. (2004). The crystal structure of semi-synthetic aequorins. Protein Science 14 409-416. 

In the strict sense, opiates are drugs which are derived from opium and include the natural products morphine, codeine, thebaine and many semi-synthetic congeners derived from them. In the wider sense, opiates are morphine-like drugs with non-peptidic structures. The old term opiates is now more and more replaced by the term opioids which applies to any substance, whether endogenous or synthetic, pqrtidic or non-peptidic, that produces morphine-like effects through an action on opioid receptors. 

The presence of impurities like free fatty acids in egg or soybean phosphatidylcholine, or in the (semi)synthetic phosphatidylcholines (e.g., DMPC, DPPC, DSPC) can be detected by monitoring the electrophoretic behavior of liposome dispersions of these phospholipids in aqueous media with low ionic strength a negative charge will be found on these liposomes when free fatty acids are present in the bilayers. 

Trezzini, G. E. and Zryd, J.P., Characterization of some natural and semi-synthetic betaxanthins, Phytochemistry, 30, 1901, 1991. 

Detailed information about carotenoids found in food or extracted from food and evaluated for their potential as food colorants appeared in Sections 4.2 and 6.2. We would like to mention some new data about the utilization of pure carotenoid molecules or extracts as allowed food additives. Looking to the list of E-coded natural colorants (Table 7.2.1), we can identify standardized colorants E160a through f, E 161a, and E161b as natural or semi-synthetic derivatives of carotenoids provided from carrots, annatto, tomatoes, paprika, and marigold. In addition, the extracts (powders or oleoresins) of saffron, - paprika, and marigold are considered more economical variants in the United States and European Union. 

Safer compared to single phase semi-synthetics. 

Rasor and Tischer (1998) have brought out the advantages of enzyme immobilization. Examples of penicillin-G to 6-APA, hydrolysis of cephalospwrin C into 7-ACA, hydrolysis of isosorbide diacetate and hydrolysis of 5-(4-hydroxy phenyl) hydantom are cited. De Vroom (1998) has reported covalent attachment of penicillin acylase (EC 3.51.11) from E.Coli in a gelatine-based carrier to give a water insoluble catalyst assemblase which can be recycled many times, and is suitable for the production of semi-synthetic antibiotics in an aqueous environment. The enzyme can be applied both in a hydrolytic fashion and a synthetic fashion. 6-APA was produced from penicillin-G similarly, 7-ADCA was produced from desa acetoxycephalosporin G, a ring expansion product of penicillin G. 

The three most important types of synthetic fibres used commonly as textiles are polyester, polyamides (nylon) and acrylic fibres. Polyester and the semi-synthetic fibre cellulose acetate are dyed almost exclusively with the use of disperse dyes. Polyamide fibres may be coloured using either acid dyes, the principles of which have been discussed in the section on protein fibres, or with disperse dyes. Acrylic fibres are dyed mainly using basic (cationic) dyes. 

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