C. Triterpenoids
37
position in the chain of the sodium hydrogen sulfate. This finding no doubt
has bearing on the reported unusual physiological properties of holotoxin,
as pointed out by Shimada (1969).
The first two asterosaponins have now been fully characterized (Turner
et al, 1971) and surprisingly turn out to be not triterpenoidal but steroidal
glycosides. These compounds will therefore be discussed in Chapter 2.
3. KNOWN TRITERPENOIDS
a. Friedelin
So far only two triterpenoids that are known constituents of terrestrial
plants have been isolated from marine sources. The first such compound,
friedelin (89) was identified by Tsuda and Sakai (1960) after its isolation
89
from a blue-green alga Monostroma nitidum. Although it was first isolated
from cork (Friedel, 1892) in the last century, its structure was not fully
elucidated until 1955 (Corey and Ursprung, 1955a,b; Dutler et al, 1955).
b. Taraxerol
Another triterpenoid, taraxerol (90), which is widely known from terrestrial
sources, was recently isolated from the green alga Caulerpa
lamourouxii
by Santos and Doty (1971). Its constitution was deduced by Beaton and coworkers (1954), who also partially synthesized it from ß-amyrin (91) (Beaton
et al, 1955a,b).
90
91