Preparation of labeled compound

This procedure illustrates a general method for the reduction of aldehyde and ketone functions to methylene groups under very mild conditions. Since strong acids and bases are not employed, this procedure is of particular importance for the reduction of ketones possessing an adjacent chiral center. Moreover, the use of deuterated metal hydrides permits the preparation of labelled compounds. ... 

Since the greatest number of labeled compounds are 14C labeled, our discussion on the preparation of labeled compounds deals mainly with them. However, many of the general principles can be applied to other nuclides and molecules as well. 

Astatination by means of nucleophilic halogen exchange, occasionally with the help of catalysts, and electrophilic replacement via demetalation seem to have become the preferred techniques. Short synthesis and separation time together with the possibility of carrier-free preparation of labelled compounds are especially important factors, bearing in mind the short half-life of astatine isotopes and the requirement of high specific activity for chemical and biomedical investigations. 

Chemical effects of nuclear reactions do not only cause rupture of chemical bonds, they also lead to formation of new chemical bonds, a result that may be used for preparation of labelled compounds. Recoil labelling and self-labelling both involve radiation-induced reactions and also belong to the field of radiation chemistry. 

For preparation of labelled compounds the following parameters have to be considered ... 

Synthesis of labelled compounds requires reliable procedures and experience in radiochemistry. However, special kits are available for preparation of labelled compounds without experience in radiochemistry, and automated procedures have been developed for fast syntheses. 

Bu"3SnT) is prepared by the reaction of Bu"3SnLi with tritiated water or by the reaction of Bu"3SnCI with tritiated sodium borohydride. Representative preparations of labeled compounds with a high degree of stereoselectivity are shown in Schemes 16 and 17. ... 

The replacement of a carboxylic acid group by nitrile functionality can also be used for the preparation of labeled compounds, and conditions for alkaline hydrolysis which did not lead to conjugation in skipped dienes like linoleic acid were developed by the Barton group. In this case, the free-radical chain sequence is straightforward, with the methanesulfonyl (or p-toluenesulfonyl) radical acting as the chain carrier [26], This methodology also represents an interesting way for the preparation of nitriles without the necessity for amide formation followed by dehydration. 

Catalytic hydrogenolysis of C—O bonds of benzyl esters and similar compounds by deuterium has rarely been used for preparation of labeled compounds, whereas predeuterated Pd in D20 is recommended for formation of deuterated alcohols from epoxides.63... 

D30+ ions are, however, normally insufficiently powerful deuteron-donors for labeling aromatic hydrocarbons but as early as 1936 Ingold and his colleagues94 found that deuterium sulfate constituted a suitable reagent for preparation of labeled compounds. A concentration of 65 mole-% of acid caused side reactions as well as exchange, and at a concentration of 40 mole-% exchange is very slow, so experiments are carried out at add concentrations of 51-52 mole-% in D20. 

Furoquinoline alkaloids specifically labeled with 14C in the furan ring were required for biosynthetic studies (see Section VII of this chapter), and since existing routes produced low yields, Grundon and co-workers (195, 196) developed a more efficient synthesis from 4-methoxy-3-prenyl-2-quinolones 244-246. These compounds had previously been prepared from aromatic amines and substituted malonates, but direct allylation is more suitable for the preparation of labeled compounds, employing, for example, [14C]-3,3-dimethylallyl bromide. It was found that reaction of... 

A radioactively labeled (or "tagged") compound is one in which one of the atoms is radioactive. Preparation of labeled compounds may involve lengthy chemical synthesis starting with the radioactive nuclides in elementary form or in a simple compound. 

Isotopic reaction is a powerful tool in the studies of chemical reaction mechanisms and kinetics, as well as analytical chemistry. It is also frequently used in the preparation of labeled compounds. The exchange reaction can be represented by a simple reaction ... 

Catch (1964) has dealt with the procedures and problems encountered in the biological preparation of labeled compounds. He also includes a bibliography of work in this field and, although there are no references to syntheses of lipids, there is much useful general information. For convenience, we shall use ihe categories of processed enzymes, plants, and mammalian cells to discuss examples of published techniques that have been used in the biosynthetic preparation of labeled lipids. 

The combination of microbial excision of a structural fragment and subsequent re-incorporation of its labeled analog by chemical synthesis is an elegant and straightforward approach to the preparation of labeled compounds. As recently communicated, SSR126768 (S was demethylated by incubation with Mortierella isabellina MMP108 to obtain the required SSRl 136660 1571. Remethylation under standard conditions demonstrated that 5Z was a precursor suitable for carbon-11 (and therefore probably tritium or carbon-14) labeling . 

A brief review on the preparation of -labeled compounds is given in the following pages. The methods of isotopic analysis of both organic and inorganic compounds are discussed in Section V. 

---