600
W. SANDERMANN
postulated. Wenkert assumes an intermediate spiran compound, from
which totarol and also podocarpic acid are formed (35).
The biogenesis of the triterpenes was elucidated above all by
Ruzicka's group of investigators (2-5). Stork and Burgstahler independently arrived at the same results (40). The parent compound of
all triterpenes is all-frans-squalene, which, with the help of enzymes,
undergoes a specific manner of folding. This enzymatic folding is the
prerequisite for a subsequent nonstop reaction; thereby, a sequence of
stereospecific 1,2-rearrangements of hydrogen atoms and methyl groups
takes place, with the final loss of a proton (or addition of an anion). In
this manner, for example, by means of chair-chair-chair-boat-boat
(CCCBB) folding, a lupanyl cation arises, from which through appropriate rearrangements the known types of pentacyclic terpenes are
formed. The various foldings in the biogenesis are seen in Fig. 5. The
Sterols
Onocerin
CCSCC
Lanosterol
CBCBS
Ambrein -*-CCSS(C)
Hydroxyhopanone
CCCB
Euphol
2 Dammarendiols
Tirucallol
Lupeol
Bauerenol
Taraxasterol
Ψ-Taraxasterol
a - Amy r in
ß-Amyrin
δ-Amyrin
Germanicol
Friedelin
Glutinone
Tarax'erol
FIG. 5. Biogenetic folding of the rings in the triterpenes. C = chair form;
B = boat form; S = straight form.