KONRAD BLOCK 



ring closure need not be preceded by oxidation. Of some in- 

 terest in this connection is the structure of ambrein (Figure 5), a 

 terpene alcohol which is a pathological excretion product of the 

 sperm whale, and undoubtedly originates from squalene by 

 partial cyclization. The linkage of the hydroxyl group of this 

 interesting compound to the carbon corresponding to Cg of the 

 steroids may be taken as evidence that oxidation occurred after 

 rings A and B had been established. In view of the obscure 

 circumstances which attend the origin of this alcohol, it would be 



AMBREIN TETRACYCLOSQUALENE 



Fig. 5. Transformations ot squalene. 



hazardous to say that ambrein, though it is derived from a bio- 

 logical source, is actually the product of an enzymatic action. 

 In any event, it is questionable that much can be deduced from 

 the structure of either tetracyclosqualene or ambrein regarding 

 the stage at which the oxidation step occurs in steroid biogenesis. 

 It must also be borne in mind that in the chemical cyclization 

 the reagent attacks the symmetrical squalene chain at two 

 equivalent points. One would suspect, on the other hand, that 

 in the analogous biological reaction one of the two sensitive 

 double bonds must be shielded so that the aliphatic portion 

 which becomes the isooctyl side chain of the sterol can be pre- 

 served. Conceivably, the squalene molecule is rendered asym- 



484 



