Allocholic acid structure

FI GURE 4.3 Structures of allocholic acid (petromyzonol sulfate is identical apart from replacement of the carboxyl group with sulfate), taurine-conjugated bile acid, and geosmin. 

Yun, S-S., Scott, A. P., and Li, W. (2003). Pheromones of the male sea lamprey, Petromyzon marinusL. structural studies on a new compound, 3-keto allocholic acid, and 3-keto petromyzonol sulfate. Steroids 68,297-304. 

In a study by Ali and Elliott it was shown that 5a-cholestane-3 ,7a-diol was an even better substrate for the 12a-hydroxylase in rabbit liver microsomes than 7a-hydroxy-4-cholesten-3-one (156%) [104]. This reaction is probably of importance in the formation of allocholic add. The high specificity of the 12 -hydroxylase towards the coplanar 5a-sterol nucleus is also evident from the finding that allochenodeoxycholic acid can be converted into allocholic acid in rats, both in vivo and in vitro [105,106, Chapter 11]. Based on the known structural requirements of the 12a-hydroxylase, Shaw and Elliott prepared competitive inhibitors with different substitutions in the C,2 position [107]. The best inhibitor of those tested was found to be 5a-cholest-ll-ene-3a,7 ,26-triol. Theoretically, such inhibitors may be used to increase the endogenous formation of chenodeoxycholic acid in connection with dissolution of gallstones. 

Noma et al. found 2 keto bile alcohols in unconjugated form in bullfrog bile [42]. Their structures were determined as 24-dehydro-26-deoxy-5a-ranol and its 5 isomer by comparison with synthetic 3a,7a,12a-trihydroxy-27-nor-5a- and 5/8-choles-tan-24-ones, prepared from allocholic acid and chohc acid, respectively [41]. 

Fig. 1. Comparison of structures of 5a- and 5/8-bile acids. Allocholic acid (3a,7a,12a-trihydroxy-5a-cholanic acid) cholic acid (3a,7a,12a-trihydroxy-5 -cholanic acid).

Bile salts with a steroid structure appear to be confined to vertebrates (76). In some evolutionarily more primitive vertebrates, the major bile salts are sulfate esters of polyhydroxy C27- and C26-steroids and/or taurine-conjugated C27-steroid acids. In other primitive vertebrates, C24 bile acids, usually cholic acid and/or allocholic acid, or mixtures of primitive bile salts (bile alcohols and C27 bile acids) and modern bile salts (C24 bile acids) occur. Most of the work concerning the structure and occurrence of primitive bile salts has been carried out in the laboratories of G. A. D. Haslewood and T. Kazuno, and Haslewood and collaborators have accumu-... 

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