Labelling carboxylic acid derivatives

To make as much carboxylic acid derivative as possible available to the nucleophile at all stages of the reaction, the nucleophile is added dropwise to the carboxylic acid derivative and not the other way around. In Figure 6.41, the approach to chemoselective acylations of hydride donors and organometallic compounds, which we have just described, is labeled as strategy 2 and compared to two other strategies, which we will discuss in a moment. 

He reacted water with carboxylic acid derivatives RCOX that had been labelled with an isotope of oxygen, 180. 

He then reacted these derivatives with water to make labelled carboxylic acids. However, he added insufficient water for complete consumption of the starting material. At the end of the reaction, he found that the proportion of labelled molecules in the remaining starting material had decreased significantly in other words, it was no longer completely labelled with lsO some contained normal 160. 

Recent trend in biosensor manufacturing is to use synthetic procedures to incorporate a label indicative of a change in a physicochemical property upon binding to biomolecule. An example is the preparation of a novel, fluorescently active, carboxylic acid derivative of 2-pyridylazo compounds (PAR) [186]. 

We don t expect you to be satisfied with the bland statement that tetrahedral intermediates are formed in these reactions of course, you wonder how we know that this is true. The first evidence for tetrahedral intermediates in the substitution reactions of carboxylic acid derivatives was provided by Bender in 1951. He reacted water with carboxylic acid derivatives RCOX that had been labelled with an isotope of oxygen,... 

M14. Mayer, A., Schmidt, E., Kinkel, T., Molz, P., Neuenhofer, S., and Skrzipezyk, H. J., Hydrophilic acridinium 9-carboxylic acid derivatives used as labels in luminescence immunoassays. In Bioluminescence and Chemiluminescence Current Status (P. E. Stanley and L. J. Kricka, eds.), pp. 99-102. Wiley, Chichester, 1991. 

A review of the synthesis and chemistry of nitroxide spin labels includes a number of steroid derivatives. Novel spin-labelled steroids have been prepared by esterification with the nitroxyl carboxylic acid derivative (17),for use in spin immunoassays (SIA) as an alternative to radioactive labelling. The prednisolone ester (18), for example, exhibits an e.s.r. spectrum with narrow lines when it is in a free state in solution, but when bound to antibody the rate of tumbling is reduced, and linewidths are broad. Signals from bound and unbound derivatives are easily distinguished and measured, so SIA of antibody-bound prednisolone provides a potentially useful serum assay method. 

Detailed hydrolysis studies of the carboxylic acid derivatives by Bender (1960) and others (Samuel and Silver, 1965) provided the initial evidence for formation of the tetrahedral intermediate. These investigators found that when hydrolysis studies were conducted in 0-labeled water, incorporation of 0 into unhydrolyzed substrate occurred. 

The microwave spectrum of bicydo [2,1,0] pentane and six deuterium-labelled species has led to a complete structural analysis resulting in the parameters shown in (5) and an Y -ray analysis of the l-phenyl-exo-5-carboxylic acid derivative confirms the earlier n.m.r. assignments made by Schaffher. Gas-phase electron diffraction data on anti-tricyclo[3,l,0,0 ]hexanef show that the four-membered ring is planar with the three-membered rings canted out of the plane by 113°. 

Probably the most widely cited evidence for the existence of a tetrahedral intermediate comes from isotopic exchange reactions. For example, in the reaction of a carboxylic acid derivative, such as an ester, the two OH groups in the tetrahedral intermediate are equivalent (examine the T.L in Scheme 10.22). If the reaction were performed in 0-labeled water, one of these OH groups would be isotopically labeled. Reversal of the nucleophilic addition step would exchange the 0 into the carbonyl oxygen 50% of the time. As the reaction proceeds... 

Cyanide salts are available with either inorganic or organic cations, and a cyanide group can be conveniently prepared with radioactive " C-labeled atoms. The cyanohydrin reaction serves for the preparation of more complex " C-labeled carboxylic acids and their derivatives intended for pharmacological studies. 

Figure 11.43 Application of Meyers bislaaam methodology to the synthesis of labeled a,a-dialkylated carboxylic acid derivatives of high enantiomeric purity...

The Derivative, 5-(biotinamido)pentylamine, contains a 5-carbon cadaverine spacer group attached to the valeric acid side chain of biotin (Thermo Fisher). The compound can be used in a carbodi-imide reaction process to label carboxylate groups in proteins and other molecules, forming amide bond linkages (Chapter 3, Section 1). However, the main use of this biotinylation reagent is in the determination of factor XHIa or transglutaminase enzymes in plasma, cell, or tissue extracts. 

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