C-labeled Compounds

The most widely used synthetic routes follow on closely from those adopted for syntheses - a small number of key precursors such as C02, CHsI, CN , and H CHO are sufficient to label a wide range of compounds. 

The synthesis of [ C]-labeled esters using a C-alkylation of diethyl malonate under microwave-enhanced solid-liquid phase transfer catalysis (PTC) conditions and a subsequent microwave-enhanced decarboalkoxylation (Krapcho reaction) [167] indicates that an alternative approach to the preparation of [ C]-labeled fatty acids/esters [168] with less harsh conditions may be possible. 

reactions with less reactive substrates can be achieved by increasing the polarity of the reaction medium through the addition of various salts. 

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B. M. McDougall. and A. D. Rovira, Sites of exudation of C-labelled compounds from wheat roots. New Phyiol. 69 999 (1970). 

In Fischer-Tropsch synthesis the readsorption and incorporation of 1-alkenes, alcohols, and aldehydes and their subsequent chain growth play an important role on product distribution. Therefore, it is very useful to study these reactions in the presence of co-fed 13C- or 14 C-labeled compounds in an effort to obtain data helpful to elucidate the reaction mechanism. It has been shown that co-feeding of CF12N2, which dissociates toward CF12 and N2 on the catalyst surface, has led to the sound interpretation that the bimodal carbon number distribution is caused by superposition of two incompatible mechanisms. The distribution characterized by the lower growth probability is assigned to the CH2 insertion mechanism. 

Sullivan et al. [69] studied the loss of phthalic acid esters and chlorinated biphenyls from seawater whilst stored in glass containers. Equilibrium was essentially reached in 12 h at 25 °C. Labelled compounds were used in some of the studies. Table 1.10 shows that between 2.2 and 49.9% of the organic solutes were lost from the spiked solutions. 

The effect of 6-mercaptopurine on the incorporation of a number of C-labelled compounds into soluble purine nucleotides and into RNA and DNA has been studied in leukemia L1210, Ehrlich ascites carcinoma, and solid sarcoma 180. At a level of 6-mercaptopurine that markedly inhibited the incorporation of formate and glycine, the utilization of adenine or 2-aminoadenine was not affected. There was no inhibition of the incorporation of 5(or 4)-aminoimidazole-4(5)-carboxamide (AIC) into adenine derivatives and no marked or consistent inhibition of its incorporation into guanine derivatives. The conversion of AIC to purines in ascites cells was not inhibited at levels of 6-mercaptopurine 8-20 times those that produced 50 per cent or greater inhibition of de novo synthesis [292]. Furthermore, AIC reverses the inhibition of growth of S180 cells (AH/5) in culture by 6-mercaptopurine [293]. These results suggest that in all these systems, in vitro and in vivo, the principal site at which 6-mercaptopurine inhibits nucleic acid biosynthesis is prior to the formation of AIC, and that the interconversion of purine ribonucleotides (see below) is not the primary site of action [292]. Presumably, this early step is the conversion of PRPP to 5-phosphoribosylamine inhibited allosterically by 6-mercaptopurine ribonucleotide (feedback inhibition is not observed in cells that cannot convert 6-mercaptopurine to its ribonucleotide [244]. 

We then studied group 5 metals, especially tantalum-for which the laboratory already had great experience. Because of the studied reaction, alkyl or hydride-type compounds such as those developed in the laboratory could not be employed. Consequently, we became interested in alkoxo-type derivatives, either synthesized by reaction of the grafted complex with an alcohol or obtained by direct synthesis starting from an alkoxy-tantalum compound grafted on silica. In all cases, resulting complexes have been characterized by surface organometallic chemistry techniques, especially EXAFS and solid-state NMR (ID and 2D with C-labeled compounds). Indeed various compounds bonded by one, two or three surface bonds have been prepared and characterized. 

The zonate lesions produced by cynodontis greatly resemble those caused by bipolaroxin. Mode of action studies on bipolaroxin may be facilitated by the use of the C-labeled compound. Recently, we have learned that [ C] mevalonate administered to cultures of the fungus serves as an excellent precursor to both IX and X. 

In 1990, Nakamura et al. reported for the first time the complete biosynthetic origin of the whole carbon skeleton of carbazomycin B isolated from lower plants (378). Based on feeding experiments with and C-labeled compounds, followed by measurement of radioactivity and C-NMR spectroscopy, it was shown that L-tryptophan (408) contributes to C-3 and C-4 of the hexasubstituted aromatic ring, in addition to the indole ring, indicating tryptophan as the progenitor of carbazomycin B (261), in contrast to Chakraborty s proposal of 2-methylcarbazole. The indole part of L-tryptophan (408) is formed by incorporation of two carbons from phosphor-ibosyl diphosphate (430), with loss of the anthraniiic acid (397) carboxyl. The... 

B 16% sodium salicylate (w/v) in ddH20 C radioactive ink mix some kBq of any C-labeled compound with a litde amount of refill and refresh a pen with it. Handle this pen with care and avoid contaminations. ... 

Nitrogen NMR data have been obtained using both the low-abundance, spin = 1/2 N and the predominant spin = 1 N nuclei. Several different references have been used for nitrogen NMR including aqueous ammonia, ammonium salts, acetonitrile, nitric acid, and nitrates. Current opinion favors neat nitromethane, and the compilation of the known data for 1,4-oxazines (Table 6) is expressed with respect to this reference and arranged in order of the observed chemical shift. For the C-labeled compound 87, carbamate rotamers lead to two separate signals and the value of 7c n can be determined -283.98 (d, J 9) and -284.46 (d, 7 11) <2001JOC8010>. 

Enander, I., Sundwall, A., and Sorbo, B. Metabolic studies on N-methylpyrldinlum-2-aldoxime. III. Experiments with the l C-labelled compound. Biochem. Pharmacol. 11 377-382, 1962. 

The feces was the major route of elimination of 2,2, 4,4, 5-pentaBDE in rats administered a single dose of the " C-labeled compound (Hakk et al. 1999). Over a 72-hour period, <1% of the administered dose was recovered in the urine and approximately 42% in the feces. In rats with cannulated bile ducts, <0.4% was detected in the urine and about 87% in the feces over the same period of time. 

Preparation of the C-labelled compound 65 was accomplished in a manner analogous to Scheme 14. Friedel-Crafts acylation of 44 was conducted with [2- C]-chloroacetyl chloride under aluminum trichloride catalysis to give the radiolabelled intermediate 64 (48 mCi/mmol). The carbonyl group of 64 was reduced with triethylsilane and the resulting alkyl chloride was reacted with piperazine 40 to provide C-labelled ziprasidone (65). The HCI salt of 65 was formed resulting m a final compound with a specific activity of 9.6 mCi/mmol. 

In rats receiving a single oral dose of bis(2-chloro-l-methylethyl)ether of 0.0002-300 mg/kg bw, peak blood levels of radioactivity were reached at about 2-4 h. Following administration of a dose of 30 mg/kg bw, elimination was biphasic in rhesus monkeys, with half-lives of 5 h and two days, and monophasic in rats, with a half-life of two days. In rats, total recovery of radioactivity was 75% of an oral dose of the l- C-labelled compound and 90% after an intraperitoneal dose with the 2-i<-labelled compound approximately 20% of the oral dose was exhaled as CO2 in 48 h. Also in rats, urinary excretion of radioactivity accounted for 48% of a 90 mg/kg bw oral dose of the 1- relabelled compound within 48 h and for 60% of a 30 mg/kg bw intraperitoneal dose of the 2- rC-labelled compound within 24 h. Urinary metabolites identified after administration of an oral dose of 90 mg/kg bw of the I - ( -kibcllcd compound to rats were 2-(2-chloro-1-methylethoxy)propanoic acid (17% of the dose) and N-acetyl-5 -(2-hydroxypropyl)-cysteine (approximately 9% of the dose) following an intraperitoneal dose of the 2- 4C-labelled compound, metabolites identified were l-chloropropan-2-ol, propylene oxide and 2-(2-chloro-l-methylethoxy)propanoic acid (lARC, 1986). 

These formatted outputs are stored on a flexible disk exactly the same as printed. Later the data on the disk are stored by sample number and project. All raw and reduced data for a project are stored on a single flexible disk. After the data have been stored on a flexible disk, it is a simple matter for the computer to make summaries or do trend analyses. An example of one of these summaries is shown in Figure 5. In this example, the percent of 1 C remaining in the peel and fruit at various time periods after spraying apples with a 1 C labeled compound, was analyzed by a curve fit program. 

Estimated BCF value of C-labeled compound in bluegiU simfish (0.35 g initial weight) after 28 d [367b]. 

Underhill, E.W., Chisholm, M.D. and Wetter, L.R. (1962) Biosynthesis of mustard oil glucosides administration of C-labelled compounds to horseradish, nasturtium and watercress. Can.. Biochem. Physiol., 40,1505-14. 

Classical biosynthetic studies with C-labeled compounds and later with stable isotopes established that nonactic acid is derived from two acetates (or malonates), succinate and propionate (Fig. 3d) (21). Feeding studies with 36 (Fig. 3e) has shown that the first committed step of macrotetrolide biosynthesis is the coupling of the succinate unit with an acetate (or malonate) to give a-ketoadipate 40 (22). The late steps of non-actate biosynthesis (Fig. 3 g) were shown to involve the cycliza-tion of 42a into (-)-nonactate and 42b into (-l-)-nonactate, which... 

Figure 12.7. Preparation of C-labelled compounds (example, acetic acid) from Ba C03.

The infrared spectra of cyclopropenones have been assigned using C-labeled compounds A strong band at 1850 cm" arises from coupling of the two double bonds. Another characteristic band at 880 cm " Ms a symmetrical stretching interaction of the ring carbon-carbon bonds. It is interesting that no hydrate can be detected by infrared spectroscopy in aqueous solution ". ... 

IR spectroscopy on C-labeled compounds revealed the coordinatively unsaturated intermediate of Scheme 1 [viz., A in reaction (a)] is obtained by methyl migration to one of the cis-carbonyl groups ... 

Phosgene is a versatile reagent for the isotopic labelling of organic molecules and its use for the preparation of a variety of radiopharmaceuticals is well established. In particular, the synthesis of C-labelled compounds is possible owing to the frequently rapid reactions... 

The incorporation of 14C into compounds at a suitable site often requires extensive and complicated syntheses and thus a relatively long time. This usually means that 14 C-labeled compounds are unsuitable for studies to be carried out during discovery. There are, however, very rapid methods for incorporating 3H into compounds. The newer methods, generally involving metal-catalyzed exchange reactions [15-18], in our experience, mean that suitable labels can often be prepared in 2 or 3 weeks. These timescales make the approach viable for discovery support. Additionally, and importantly, these methods can lead to specific incorporation of tritium. 

Robinson s original suggestion that the natural pyrrolizidine bases are derived in vivo from two molecules of ornithine (149) has been supported by studies using C-labeled compounds. Ornithine has been shown to be a specific precursor for the pyrrolizidine nucleus present in a variety of alkaloids. The feeding experiments carried out to date are listed in Table I. Three groups of workers have obtained labeled alkaloids after feeding C-labeled ornithines.Hydrolysis of the alkaloid to yield the free base, retronecine (127), has established that almost all the radioactivity is in the base portion. It is likely that ornithine is incorporated into retronecine after decarboxylation to putrescine (150) [Eq. (40)] since labeled putrescine is also specifically incorporated into retronecine (Table I). 

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