Ursodeoxycholic acid structure

The tertiary bile acids are formed in the liver as well as in the gut. (s. fig. 3.3) Intestinally absorbed lithocholic acid is enzymatically converted to sulpholitho-cholic acid in the liver. Ketolithocholic acid is transformed to (hypercholeretic) ursodeoxycholic acid in both the intestine and the liver. When passing through the canaliculi, UDC is partly reabsorbed by epithelial cells and returned to the liver via the blood circulation (= cholehepatic shunt). (41) The latter is chemically and structurally identical to chenodeoxycholic acid, of which it is deemed to be the 7P-epimer ... 

Solid-state NMR has been used extensively for characterizing the structures of N-desmethylnefopam HC1 (38), patellin (39), erythromycin A dihydrate (40), and the amorphous nature of ursodeoxycholic acid (41). The conformations of 3 -amino-3 -deoxythymidine (42), gramicidin A (43), and amiodarone HC1 (44) have been confirmed by solid-state NMR. 

Other precursors of the muricholates via 6)8-hydroxylation include 5)8-cholanic acid [78], lithocholic acid [84-86], 7-oxolithocholic acid [95,96], and ursodeoxycholic acid (3a,7j6-dihydroxy-5/3-cholanic acid) [97], The rat metabolized 12a-hydroxy-5/S-cholanic acid to 6/S,12a-dihydroxy-5)S-cholanic acid [83] and a small amount of 6)3,7a,12a-trihydroxy-5 -cholanic acid [98]. 3a,6)8,12a-Trihydroxy-5)8-cholanic acid was isolated from urine of surgically jaundiced rats after administration of de-oxycholate [99]. A series of bile acids from rat bile of unconfirmed structures but containing the 6/3,7/3-diol will be reviewed in Section II1.3. 

Several other atypical acids were eventually isolated from various species. Ursodeoxycholic acid, first isolated in crystalline form from bear bile in 1927 (58), was identified as the 7/S-epimer of chenodeoxycholic acid. The so-called /3-hyodeoxycholic acid (3 3,6a), which Kimura obtained in small amounts from pig bile (59), was structurally identified in the course of a thorough investigation of the four possible 3,6-dihydroxycholanic acids (60). The lagodeoxycholic acids isolated from rabbit bile by Kishi (61) were not characterized until the recent studies of Danielsson et al. (62) identified one of these compounds as allodeoxycholic acid. The contention that one of them may have been the 12 -epimer of deoxycholic acid was placed in doubt by Koechlin and Reichstein (63), who prepared that acid and found that it did not exhibit the physical properties of the natural material. 

The most prominent BA present in human are cholic acid (C), chenodeoxy-cholic acid (CDC), deoxycholic acid (DC), lithocholic acid (LC), and ursodeoxycholic acid (UDC), as derivatives of 5p-cholan-24-oic acid. Primarily they are present as glycine and taurine conjugates, with the conjugation occurring at carbon 24 of the structure. In addition to the above major BA, a wide array of minor components has been identified. 

Bile acids contain hydroxyl groups, which are usually substituted at positions, C-3, C-7, or C-12 of the steroid nucleus. The three major bile acids found in man are 3a,7a,12a-trihydroxy-5P-cholan-24-oic acid 3a,7a-dihydroxy-5p-cholan-24-oic add and 3a,12a-dihydroxy-5p-cholan-24-oic acid. Because of the complexities of steroid nomenclature, bile acids are nearly always referred to by trivial names. 11108, the three major human bile acids are named cholic acid, chenodeoxycholic acid, and deoxycholic acid, respectively, and their chemical structures are shown in Fig. 1. Human bile does, however, contain small amounts of other bile acids, such as lithocholic acid (3a-hydroxy-5P-cholan-24-oic add) and ursodeoxycholic add (3a,7p-dihydroxy-5p-cholan-24-oic acid) (see Fig. 1). 

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