14C-labeled

Evidence for this mechanism comes from the observation that the rearrangement takes place with an inversion of the allyl group. That is, allyl phenyl ether containing a 14C label on the allyl ether carbon atom yields o-allylphenol in which the label is on the terminal vinylic carbon (green in Figure 18.1). It would be very difficult to explain this result by any mechanism other than a pericyclic one. We ll look at the reaction in more detail in Section 30.8. 

C-labeled D-glucose (34) [87, 88] and D-ribose [87] were efficiently incorporated... 

In vitro and ex vivo studies have shown that FATPs transport LCFAs and very long-chain fatty acids (VLCFAs) but no medium-chain fatty acids, fatty acid esters, or lipid-soluble vitamins [4]. LCFA transport is inhibited by prior protease treatment. Synthetic substrates for FATPs include 14C-labeled fatty acids and the fluorescently labeled fatty acid analogue C1 -BODEP Y-Cl 2. Using the latter substrate, differences in fatty acid uptake kinetics between FATP expressing 3T3 LI adipocytes and 3T3 LI fibroblasts, which are devoid of FATPs, can be readily appreciated (Fig. 2). 

Experiments with 14C-labelled substrates also demonstrated conclusively the intramolecularity of the rearrangement. The generally accepted scheme involves the formation of the dienone LXXXV which can lose a hydrogen atom if R = H, to form the ortho product or if R H further rearrangement to LXXXVI occurs with subsequent formation of the para product, viz. 

Some years ago, comparative investigations into the biodegradation of secondary alkanesulfonates using 14C-labeled preparations [106] and radiometric studies of the biodegradation of secondary alkanesulfonates in a sewage plant model [107] are published (Fig. 42). 

The inhibition of Streptococcus mutans adherence to hydroxyapatite with combinations of alkyl phosphates and nonionic surfactants was tested. Seven alkyl phosphate derivatives and three nonionic surfactants were examined for their ability to inhibit the adherence of 3H-labeled cells of S. mutans to hydroxyapatite treated with buffer or parotid saliva. No compound by itself effectively hindered binding of bacteria to hydroxyapatite. A combination of certain of the alkyl phosphates, notably a disodium phosphate of 1-octadecanol, and nonionic surfactant at a 1 1 molar ratio gave a strong inhibition of S. mutans adherence. Treatment with this combination resulted in 98% reduction of adherence. Adsorption of the two types of surface-active agents alone and in combinations was studied using 14C-labeled agents. Electrophoretic measure-... 

Lichtenstein EP, Katan J, Anderegg BN. 1977. Binding of "persistent" and "nonpersistent" 14C-labelled insecticides in an agricultural soil. J Agric Food Chem 25 43-47. 

The occurrence of a symmetrical intermediate has also been demonstrated by 14C labeling in the case of a-chlorocyclohexanone.89... 

Witschi and colleagues19 identified the requirement for metabolic activation of BHT in determining that radioactivity from 14C-labeled BHT became covalently bound to proteins in mouse lung. Both toxicity and protein binding were prevented when mice were treated with cytochrome P450 inhibitors, thereby indicating the... 

Albemarle) has shown unique resistance to extraction from polyolefins. No radioactivity was detected in water run through a MDPE pipe stabilised with 14C-labelled Ethanox 330 for 10 months at ambient conditions, or in an accelerated 3-month test at 80 °C (limit of detection 25ppb). 

Based on a single-dose study and tissue blood concentration ratios, diisopropyl methylphosphonate is taken up by the lungs of mice, rats, and dogs (Hart 1976). The lung blood concentration ratios are 4.5 for mice, 3.6 for rats, and 2.0 for dogs. There is also some uptake of the [14C]-label by the testes where the testes blood concentration ratios are 2.7 for mice, 2.3 for rats, but only 1.1 for dogs. 

Mineral Oil Hydraulic Fluids. Absorption of a mineral oil in an emulsion was apparently very slow in female rats injected subcutaneously with 0.1 mL and in squirrel monkeys injected intramuscularly with 0.3 mL (Bollinger 1970). The emulsion contained 1 volume mannide monoleate, 9 volumes mineral oil, and 9 volumes water [14C]labeled hexadecane, a major component of the mineral oil, was added to the emulsion as a radiotracer. At 1 week and 10 months after treatment, radioactivity remaining at the sites of injection accounted for 85-99% and 25-33%, respectively, of the administered radioactivity. 

Patterns of excretion in rats differed among [14C]labeled tricresyl phosphate isomers administered by gavage at dosage levels ranging from 0.5 to 200 mg/kg (NTP 1988). Radioactivity from tn-ortho-cresy phosphate was excreted within 24 hours predominately in urine at all dosage levels ( 70% of applied doses). Radioactivity from trww-cresyl phosphate was excreted predominately in feces at all dosage levels. 

Bollinger JN. 1970. Metabolic fate of mineral oil adjuvants using 14C-labeled tracers. I. Mineral Oil. J Pharm Sci 59 1084-1088. 

As an example for the synthesis of a 14C-labeled depsipeptide from 14C-glycine and serine by the imidazolide method, see reference [78]. 

The following carbamoylimidazole, which was prepared from 14C-labeled methyl-ammonium chloride and CDI, was not isolated. It was instead fragmented by heating in vacuo into the isocyanate, which was then reacted with an alcohol to give the labeled carbamate [220]... 

This reaction was also carried out with 14C-labeled formic acid, leading to the radiochemically labeled s,-triazolo[4,3-a][ 1,4]benzodiazepine (58% yield).[153]... 

Degradation of 5 and 57 revealed that both skeletons are built from two C6-C2 units derivable from tyrosine (81,82). Many 14C-labeled isoquinolines, which on biogenetic grounds could be possible late precursors of both alkaloids, were prepared and fed to Stephania japonica plants, after which the labeled alkaloids were isolated. Isoquinolines 59-64, lacking the... 

Methylene insertion into C—H bonds is believed to be concerted for the singlet species and stepwise for the triplet.<164,156) The C—H insertion of methylene into the 14C-labeled isobutylene shown below results in 92% unrearranged isopentenes and 8% rearranged isopentene [Eq. (11.22)]. Assuming that an additional 8% of the unrearranged isopentene arises from the stepwise addition, it is clear that 84% of the insertion products result from insertion by singlet methylene and 16% by triplet methylene ... 

Further confirmation of the two-fold shift, and of the double inversion of the position of the 14C label, is provided by trapping (cf. p. 50) the first dienone intermediate (55a) with maleic anhydride in a Diels-Alder reaction. An exactly analogous rearrangement is found to occur in allyl ethers of aliphatic enols, e.g (58) ... 

Reactions over chromium oxide catalysts are often carried out without the addition of hydrogen to the reaction mixture, since this addition tends to reduce the catalytic activity. Thus, since chromium oxide is highly active for dehydrogenation, under the usual reaction conditions (temperature >500°C) extensive olefin formation occurs. In the following discussion we shall, in the main, be concerned only with skeletally distinguished products. Information about reaction pathways has been obtained by a study of the reaction product distribution from unlabeled (e.g. 89, 3, 118, 184-186, 38, 187) as well as from 14C-labeled reactants (89, 87, 88, 91-95, 98, 188, 189). The main mechanistic conclusions may be summarized. Although some skeletal isomerization occurs, chromium oxide catalysts are, on the whole, less efficient for skeletal isomerization than are platinum catalysts. Cyclic C5 products are of never more than very minor impor-... 

Analogous studies of the chemisorption of 14C-labeled benzene on copper powder and on platinum powder showed no chemisorption on the former, and the establishment of a low surface coverage over a range of temperature on the latter (Fig. 1). Again the surface coverage of hydrogen on platinum appeared to be about three times that achieved by benzene. 

Furthermore, there are clear disparities between this work and that of Tetenyi concerning (i) the fraction of the chemisorbed 14C-labeled... 

Leaf discs from rapidly expanding V.faba leaves incorporated 14C-labeled palmitic acid into cutin. After removal of the soluble lipids and other materials, the insoluble residue was subjected to LiAlH4 hydrogenolysis and the labeled reduction products of cutin monomers were identified by chromatography as hexadecane-... 

---