Allocholanic acids

J-Acetoxy- 14)3-hy droxy-14-isoetio-allocholanic acid, configuration, VIII, 267 structure and synthesis, VIII, 260 3/ -Acetoxy-17-isoetioallocholanic susid, optical rotation of methyl ester, VIII, 279... 

Fig. 1. Cholanic acid (5y3-choIanoic acid) (I) allocholanic acid (5a-cholanoic acid) (II).

Fig. 4. Cholanic acid (I) allocholanic acid (II) cholic acid (III) dehydrocholic acid (IV) coprostane (V) cholestane (VI).

Table I lists known allocholanic acids and some of their derivatives. Very few carbon-carbon unsaturated allocholanoic acids have been described (6, 9) several halogenated derivatives of the allo-acids and a number of 4,4,14a-trimethyl allocholanoic acids have been reported (10, 11) but they have not been included in this review. Of the monohydroxy derivatives, the 6-oxy derivative reported by Wieland in 1932 (12) without assignment of configuration was prepared by catalytic reduction of the 6-keto acid, and is probably the axial 6/3 derivative (13). From an inspection of the data in the table it is clear that the subject of this chapter covers a span of 50 years with a renewed interest in the subject evidenced about 38 years after the initial paper of Windaus on allocholanic acid in 1919. Also it is evident that investigations on allo-acids flourished for about 18 years, then lagged, and were revived with new vigor again about 38 years later.

A study of the chemistry and metabolism of the allo-acids has been inhibited by the inherent problem of separating these acids effectively from their 5/3-epimers. This is evident from the first experiments of Windaus with allocholanic acid, for a period of 16 years elapsed before the pure acid was obtained. With the advent of chromatography and newer methods of separation of closely similar molecules the purified allo-acids emerged as entities unto themselves. The efficiency of these methods was assessed readily with labeled compounds. 

Goto (88) obtained an allo-acid designated as 3a,7 -dihydroxy-5a-cholanoic acid in a manner somewhat analogous to the procedure of Anderson and Haslewood for the preparation of allocholic acid. Methyl 3 -cathyl-7,12-diketo-6a-bromo-5/3-cholanoate was allomerized with alkali to provide three ketolic acids. One of these designated as 3a,7/3-dihydroxy-6,12-diketo-5a-cholanoic acid, m.p. 235 °C, was reduced by the Wolff-Kishner procedure to provide equal quantities of allocholanic acid and alloursodeoxycholic acid, m.p. 223-224°C. 

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