Lactones, detection hydrolysis

Like in gangliosides, lactones might be found in some bacterial capsular polysaccharides containing 1-carboxyethylsubstituents. But their identification remains problematic due to the conditions of isolation and preparation of analytic samples. To facilitate their detection by NMR, and in order to determine if the formation or hydrolysis of lactones occurred during analytical procedures, synthetic model substances, 2,3- and/or 3,4-lactones based on gluco-12, manno-13, and galactopyranosides 14 were prepared and characterized by NMR spectroscopy (Fig. 2).20 The relative lactonisation rates in acetic acid-fi 4 and hydrolysis rates in buffered D20 were evaluated. 

In most cases, uronic acids are liberated from acidic polysaccharides by hydrolysis leading to irreproducible concomitant formation of lactones. Several methods to circumvent this problem have been published describing conversion of the uronic acid into methyl esters followed by reduction with borohydride or borodeuteride reagents and subsequent hydrolysis and GC-MS detection [129]. Other techniques are based on the liberation and quantification of carbon dioxide. Direct determination of uronic acid residues in hydrolyzates has frequently been performed according to colorimetric assays, which are rather insensitive and have thus mostly been replaced by high-performance anion exchange chromatography (HP-AEC) methods [130-132]. 

Where the second term in equation (4) is negligible but the water reaction is sufficiently large to be detected, the result is curve d. The important example is the decomposition of nitramide (Brpnsted and Pedersen, 23), and others are the hydrolysis of jS-lactones (Johansson, 29) and the halogenation of nitroparaffins (Pedersen, 30). 

Carthamoidinecic acid was studied in Adams laboratory, where Phillips (3) isolated the acid upon alkaline hydrolysis of carthamoidine. The acid proved to be dibasic. It lactonized readily and formed a diester when treated with diazomethane. The presence of a double bond was detected and it was assigned a position a,/8 to one of the carbomethoxy groups because of the exaltation in the molar refraction of dimethyl cartha-moidinecate (b.p. 135° (5 mm.) [a]f)4.3° (ethanol) ). Hydrogenolysis of the parent alkaloid, carthamoidine, produced a sirupy acid which was probably saturated. 

An enzyme inhibition assay capable of measuring total HMG-CoA reductase inhibitors in biological fluids has been described in the literature (1). The basis of this assay is the in vitro inhibition of the HMG-CoA reductase catalyzed conversion of Rc-HMG-CoA to C-mevalonic acid. The concentration of inhibitors can be measured before and after base hydrolysis of plasma samples. The measurement before hydrolysis gives the concentration of inherently active species (active inhibitors). Base hydrolysis irreversibly converts inactive but potentially active species (lactones and conjugates) to their corresponding active forms the inhibition assay of hydrolyzed samples thus provides the concentration of total inhibitors. The enzyme inhibition assay is sensitive (detection limit of ca. 5 ng/mL), but is not specific for lovastatin. 

Lactonizing Enzyme. The spontaneous hydrolysis of the lactone prevented its detection for many years, but is not fast enough to keep pace with the rate of formation of the lactone by naturally occurring levels... 

A simple detection procedure for esters is based on their hydrolysis. A drop of the tested ester is dissolved in 2—3 ml of ethanol and mixed with a solution of phenolphthalein and a drop of 0.1 n NaOH. If on heating the solution loses its color, the presence of an ester is indicated. The same reaction is also given by lactones. 

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