0-Glucosiduronates, acid hydrolysis

Garton, Robinson and Williams66 have studied the rate of acid hydrolysis of phenyl D-glucosiduronic acid as compared with phenyl acid sulfate. The ester acid sulfate was hydrolyzed completely by N hydrochloric acid at 93-95° in 10 minutes, 50 times as rapidly as the D-glucosiduronic acid. After 20 minutes, only 40% of the latter was hydrolyzed. On refluxing... 

Hydrolysis of the xylenyl D-glucosiduronic acids by 5N sulfuric acid for 1.5 hours in a boiling water bath results in a variable loss of D-glucuronic acid.67... 

Since hydrolysis in N hydrochloric acid in the autoclave at a pressure of 20 lb. per sq. in. was needed to hydrolyze the conjugate, it might be presumed that a glucosiduronic acid was formed. 

Fig. 2.—Hydrolysis of 0.00125 M Phenolphthalein /8-D-Glucosiduronic acid by Partially Purified Mouse-liver /3-Glucuronidase at Various pHs (in 0.125 N acetate (X), 0.125 N citrate ( ), and 0.125 N phthalate (O) buffer).

Dissociation Constants (Kx) for Various ff-o-Glucosiduronic Acids Treated as Competing Substrates in the Hydrolysis of Phenolphthalein fi-o-Glucosiduronic Acid by Mammalian and Non-mammalian fi-Glucuronidase... 

Thus, as the first approach to kinetic studies of the action of /8-D-glu-cosiduronase toward synthetically prepared 1-O-acyl-a- and -/3-D-glu-copyranuronic acids, a reliable method that would permit monitoring of the rate of enzymic hydrolysis was needed. For this purpose, To-masic and Keglevic268 developed an analytical procedure, involving the colorimetric reaction of D-glucuronic acid with benzidine in the presence of acetic acid,269 that proved to be fully applicable to enzymic, kinetic studies performed with 1-esters of D-glucuronic acids and with D-glucosiduronic acids as the substrates. 

Harborne compared the behavior of flavonoid glycosides and of several C-glycosyl compounds in a 1 1 solution of ethanol in 2 V hydrochloric acid at 100°, and found that the former are invariably hydrolyzed, whereas the latter are not. Thus, even apigenin 7-D-glucosiduronic acid, which is resistant to acid hydrolysis, is completely cleaved in 4 hours, whereas no C-glycosyl compound tested liberates sugar under these conditions. This procedure provides a convenient method for distinguishing between the two types of compound. 

The sulfates of saturated ketosteroids are readily split under the conditions of acid hydrolysis described above (Section III,1) which were found effective for the cleavage of glucosiduronates. However, their cleavage may also be accomplished under very much milder conditions, as was shown by Lieberman and Dobriner (79) and subsequently confirmed by Buehler et at. (14) (Table III, method A). Continuous extraction with ether at pH 0.7 for 24 to 48 hours gives a quantitative recovery of the free steroid. The hydrolysis of the sulfate esters takes place without inversion of stereochemical configuration (82). 

As far as is known at the present time, the enzymatic hydrolysis of steroid glucosiduronic acids leads to the release of the free steroids without concomitant formation of transformation products. 

Tlie chemical reactions catalyzed by /3-glueuronidase are of the general type indicated in reaction (1), hydrolysis of glucosiduronic acid. To this we can add glucofuranosiduroiiic acid and the various nerver glucosiduronic acids such as enolic and A4iydroxyglucuronide. 

---