88 II. DIGESTION AND ABSORPTION OF FATS 



The alcoholic groups in general have an a-orientation. 481 The hydroxyl 

 on C 3 is not in the correct position to be precipitated by digitonin. Data 

 on the melting point, specific rotation, and configuration of the hydroxyl 

 groups are summarized in Table 1 1 . 



d. Synthesis of the Bile Acids. As is evident from Table 11, an in- 

 creasing number of cholanic acids, related to the natural bile acids, have 

 been obtained synthetically. One of the successful procedures has been 

 the reduction of the corresponding diketo compounds. Thus, when 

 Tukamoto 482 applied the Meerwein-Pondorf reduction 483,484 to 3,6-diketo- 

 cholanic acid, he was able to prepare the following amounts of the four 

 possible dihydroxycholanic acids 482 : 3a, 6a- (hyodesoxycholic acid), 485 

 15%; 3a,6/3-, 2%; 3/3,6a-("/3" hyodesoxycholic acid), 1.5%; and 3/3, 

 6/3-, 8%. Tukamoto 486 prepared 3a,6/3- and 3/3,6/3-dihydroxyallocholanic 

 acids by the application of the same reduction procedure to 3,6-diketo- 

 allocholanic acid. 



Although Iwasaki 405 was able to prepare only 3a,7a-dihydroxycholanic 

 acid (chenodesoxycholic acid) by catalytic' hydrogenation of 3,7-diketo- 

 cholanic acid, Miyaji 423 reported the production of the two C 7 isomers on 

 hydrogenation of 3a-hydroxy-7-ketocholanic acid, namely chenodesoxy- 

 cholic acid (3a,7a-dihydroxycholanic acid) and ursodesoxycholic acid 

 (3a,7/3-dihydroxycholanic acid). Tukamoto, 486 likewise, was able to syn- 

 thesize the 3a, 7a- and 3a,7/3-dihydroxycholanic acids by reduction of the 

 corresponding diketone. 



The production of four enantiomorphs of the 3,6-dihydroxycholanic 

 acids has been carried out readily by the use of the 3a- or 3/3-hydroxy acid 

 having a keto group in position 6. Tukamoto 487 obtained 3a,6a-(hyodes- 

 oxycholic acid), and 3a,6/3-dihydroxycholanic acids in 30 and 9.3% yield, 

 respectively, by reduction of 3a-hydroxy-6-ketocholanic acid; similarly, 

 3/3,6/3- and 3/3,6a-dihydroxycholanic acids were prepared in yields of 33 and 

 10%, respectively, when the 3/3-hydroxy 6-ketone was reduced. 



e. Interrelations of the Bile Acids. The fact that certain specific bile 

 acids are characteristic of the bile of different species of animals would 



481 The terminology "a" and "/3" is in accordance with a system proposed by L. F. 

 Fieser and M. Fieser, Natural Products Related to Phenanthrene, 3rd ed., Reinhold, New 

 York, 1949, which is based upon the configuration of cholestanol. 



482 M. Tukamoto, J. Biochem. (Japan), 32, 451-460 (1940). 



483 H. Meerwein and R. Schmidt, Ann., 444, 221-238 (1925). 



484 H. Meerwein, R. v. Rock, R. Kirschnick, W. Lenz, and A. Migge, ./. prakt. Chem., 

 147, 211-225(1037). 



485 A. Windaus and A. Rohne, Ann., 433, 278-287 (1923). 



486 M. Tukamoto, ./. Biochem. {Japan), 32, 4G1-4G5 (1940). 



487 M. Tukamoto, ./. Biochem. (Japan), 32, 407-172 (1940). 



