Compounds, labeled acid esters

Procedures for shipping boric acid esters depend on the particular compound. Aryl borates produce phenols when in contact with water and are therefore subject to shipping regulations governing such materials and must carry a Corrosive Chemical label. Lower alkyl borates are flammable, flash points of methyl, ethyl, and butyl borates are 0, 32, and 94°C, respectively, and must be stored in approved areas. Other compounds are not hazardous, and may be shipped or stored in any convenient manner. Because borate esters are susceptible to hydrolysis, the more sensitive compounds should be stored and transferred in an inert atmosphere, such as nitrogen. 

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. 

Carbon-11 labelled calcium channel antagonists C-nifedipine, C-nisoldipine, C-nitrendipine and C-CFj-nifedipine possessing vasodilating and hypotensive properties have been synthesized using a modified Hantzsch-type cyclocondensation proce-dure . Condensation of aldehydes 242, 243 and 244 with 3-aminocrotonic acid esters 245, 246, 247 and with acetoacetic ester 248 produced in one pot after 12 hours reflux in dry ethanol the methyl sulphonylethyl protected dihydropyridines 249-252. Deprotection of the carboxylic acids by alkaline hydrolysis followed by conversion into the dihydropyridine monocarboxylic acids 253-256 gave potassium salts in situ, and subsequent methylation with CH3I produced the corresponding labelled title compounds 257-260 (equation 102),... 

Compounds, labeled) a-aminocarboxylic acids from acylaminomalonic acid esters 21, 115 aziridine ring from ketoximes 21, 538 Di. . . s. a. Bi. . . ... 

The synthesis of F-labeled stilbenes [ F]2g, [ F]3g, and [ F]4e ( -isomers) by the FIorner-Wadsworth-Emmons reaction was accomplished [83]. This carbonyl-olefination reaction was performed via a multistep/one-pot reaction by the coupling of benzylic phosphonic acid esters (3,5-bis-methoxymethoxybenzyl)-phosphonic acid diethyl ester, (4-methoxymethoxybenzyl)phosphonic acid diethyl ester, and (4-dimethylaminobenzyl)phosphonic add diethyl ester with 4-[ F]fluor-obenzaldehyde. The radiochemical yields ranged from 9 to 22%. Three new polyfluorinated compounds ([( )-4-(4-bromostyryl)-2,3,5,6-tetrafluorobenzonitrile]x-[( )-4-(4-bromo-2,3,5,6-tetrafluorostyryl)benzonitrile]i K) were obtained by the Homer-Wadsworth-Emmons approach to study intermolecular interactions in the crystal state and the formation of cocrystals [84]. 

Incorporation of labelled mavalonic acid esters into the defensive mono- and diterpenes of Nasutitermes oatopilis suggests that these compounds are biosynthesised de novo by the soldiers themselves, rather than being supplied as precursors by the work-... 

A variety of compounds cannot be prepared by direct nucleophilic F-fluorination. When high specific activity is required and electrophilic fluorination thus is impossible, labeling is often carried out by a multistep route using small reactive intermediates, often named secondary labeling precursors or prosthetic groups. A whole battery of these F-labeled intermediates was investigated and prepared, such as amines, alcohols, aldehydes, ketones, carboxylic acids, esters, and halides. Since a quantitative overview about these synthons is outside the scope of this chapter, only some examples are discussed. 

Without additional reagents w.ax. Boronic and halogenohoronic acid esters B,0-Heterocyclics s. 16, 156 Bisboric acid esters s. 16, 157 Diacoxystannanes from stannanes > SnHg > Sn(OAc)2 s. 17,689 Phosphorylation of hydroxy compounds OH OPO3H2 Simplified procedure—Labeled compounds s. 17, 164 Dithiophosphoric acid esters -e- via dithiophosphoric acid 0,0-diesters—P-Lebeled compounds s. 17, 165 ... 

Bodroux reaction—Garboxylic acid esters from carboxylic acids—Labeled compounds s. 11, 451... 

Useful but rarely exploited is the use of [ " C]acetic anhydride as an active methylene compound with aromatic aldehydes to produce labeled cinnamic acids (Perkin reaction, Figure 6.18). This adol-type reaction is limited to aromatic aldehydes, and in many cases malonic acid ester methods are superior, being more flexible and giving higher yields. The reaction of [l- " C]acetic anhydride with o-nitrobenzaldehyde is one of the very few examples published in the literature". ... 

Depending on the respective reaction partner, acetic acid esters can react either as C-H acidic compounds or as acylating agents. Both are illustrated by the self-condensation of ethyl [ 1 acetate in the presence of 0.5 equivalent of sodium ethoxide or triphenymethyl sodium to give ethyl [1,3- C2]acetoacetate (Claisen condensation). In the first case, however, because of the relatively low radiochemical yields (40-45%) obtained by this procedure, it is of minor importance for the preparation of labeled ethyl acetoacetate. The deprotonation of alkyl acetates with LiHMDS followed by acylation with unlabeled or labeled acyl halides to labeled give /3-keto esters is discussed in Section 6.4. Claisen condensation of alkyl [ CJacetates with esters lacking a-hydrogens (i.e. ethyl formate, diethyl oxalate, aromatic/heteroaromatic carboxylic acid esters) proceed unidirectionally and are valuable pathways in the synthesis of ethyl [ C]formyl acetate (521. diethyl [ C]-oxaloacetate (53) and ethyl 3-oxo-3-pyrid-3-yl[2- C]acetate (54). The last example... 

One of the standard methods for preparing enantiomerically pure compounds is the enantioselective hydrogenation of olefins, a,/3-unsaturated amino acids (esters, amides), a,/3-unsaturated carboxylic acid esters, enol esters, enamides, /3- and y-keto esters etc. catalyzed by chiral cationic rhodium, ruthenium and iridium complexes ". In isotope chemistry, it has only been exploited for the synthesis of e.p. natural and nonnatural H-, C-, C-, and F-labeled a-amino acids and small peptides from TV-protected a-(acylamino)acrylates or cinnamates and unsaturated peptides, respectively (Figure 11.9). This methodology has seen only hmited use, perhaps because of perceived radiation safety issues with the use of hydrogenation procedures on radioactive substrates. Also, versatile alternatives are available, including enantioselective metal hydride/tritide reductions, chiral auxiliary-controlled and biochemical procedures (see this chapter. Sections 11.2.2 and 11.3 and Chapter 12). 

A suspension of NaH in abs. tetrahydrofuran stirred and treated portionwise at 0° with diethyl methoxycarbonylmethylphosphonate, after completion of the Hg-evolution a soln. of cortexone in abs. tetrahydrofuran added whereupon the temp, rises to 40-50° then drops to ca. 30°, the product isolated after 35 min. stirring crude butenolide. Y 90.1%. F. e. s. W. Fritsch, U. Stache, and H. Ruschig, A. 699, 195 (1966) a, -ethylenecarboxyiic acid esters from ketones, labeled compounds, s. W. M. Walter, Jr., J. Labelled Compds. 3, 54 (1967) a,/ -ethylenephosphonic from methylenediphosphonic acid esters s. T. L. Hular, Tetrah. Let. 1967, 4921 a,y -ethylenealdehydes from oxo compounds by Horner synthesis cf. W. Nagata and Y. Hayase, Tetrah. Let. 1968, 4359. 

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