Labeling radioactive isotopes

Classical feeding experiments with both stable and radioactive isotopic labels (7) enabled the biosynthetic origin of the polyethers to be elucidated and for a general stereochemical model to be proposed (1). More recent work on this class of compounds has focused on a genetic approach, and unusual and interesting genes specific to polyether biosynthesis have been isolated from these clusters. 

In the case of single dose administration of a radioactive isotope-labeled drug, measurements should be made edter at least recovery of 95% of the drug radioactivity or after 7 days elapsed, whichever period is shorter. 

Considerable work has been published concerning the incorporation of radioactive-isotope-labeled olefins in hydrocarbons during Fischer-Tropsch reactions. The pioneering work of Kummer and Emmett [89] and of Hall et al. [88] suggested that ethylene acted as a chain initiator over iron catalysts. The same results were obtained over cobalt catalyst by Eidus et al. [131]. 

The synthesis of the radioactive labelled eompounds needed for these studies is a very specialized discipline and it is necessary to observe a number of mles in order to obtain compounds with the desired specifications. The main points to be considered are choice of radioactive isotope, labelling position, specifie activity, radiochemical parity, number of steps used, radiochemical yield and, finally, the cost of the procednre. This latter point must be considered because the eost of obtaining radioactive labelled eompounds is high, mainly because of the great amount of time required rather than because of the cost of the labelled starting materials. Nevertheless, this eost is justified by the quality of the results obtained. 

As with DOI, the presence of a heavy atom, the bromine atom, in DOB makes the radioactive isotope labelled material a powerful research tool. Studies with DOB labelled with either 82Br or 77Br have been used in human subjects to follow the distribution of the drug. The use of a whole body scanner permits the imaging of the intact body, with the travelings of the radioactivity easily followed from outside. 

Reactions in plants are of course catalyzed by enzymes, but the reactions are simply those allowed by organic chemical principles. Familiar processes such as methylation, oxidation, reduction, decarboxylation, aldol condensations, and so on, are frequently involved. In many cases it is difficult to determine the exact sequence of events, but the broad outlines of the biosynthesis of many alkaloids have been elucidated. To take a simple case for illustration of a biosynthetic pathway, the synthesis of coniine in the hemlock tree will be presented. Coniine (3.6) is the poison in hemlock that was used to kill Socrates. As found in Scheme 3.5, the amino acid lysine is the precursor of coniine. The use of radioactive isotopic labels is invaluable in proving such pathways. 

Detection can be carried out either with an online detector coupled to the eluent flow, or by collection and subsequent analysis of discrete fractions. For collected fractions, a range of analytical methods can be used, both quantitative (e.g., radioactive isotope labeling and metal analysis) and more qualitative (e.g., microscopic techniques). Online detectors suitable for coupling to the FFF channels include both non-destructive flow through cell systems and destructive analysis systems. It is often desirable to use online detection if possible since the total analysis time is much less than for discrete fraction analysis. Regardless of detector type, the dead volumes and flows in the system between the FFF channel and detector or fraction collector must be accurately determined and corrected for. 

Isotope labeling— Although radioactive isotope labeling has been used for 2D-electrophoresis, it is not a popular method because of the exceptional safety requirements. There is a need for a separate laboratory room, advanced equipment (radioactivity counters), and conditions designed for... 

The recent advent of various analytical techniques has made it possible to carry out the practical studies of the end groups of polymers. The radioactive isotope labelling method has been used over a long period to determine the initiator fragment incorporated at chain ends by measuring the specific activities of radioactive samples prepared with C-labelled initiator [4-8]. In recent years, high-field nuclear magnetic resonance (NMR) techniques have been successfully applied to study polymer chain ends [1-7,9,10]. A number of reports have been published on the NMR studies of the... 

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