48
1, Isoprenoids
119
A mixture of acetylenic carotenoids that are related to, and were previously
believed to be identical with, astaxanthin (103) had been isolated from the
sea star Asterias rubens and was known in the literature as asterinic acid.
Recent reinvestigation by the Norwegian group (Sorensen et al, 1968;
Liaaen-Jensen, 1969) showed asterinic acid to be mono- and diacetylenic
analogs of astaxanthin (103) of structures 116 and 117.
°
„<Α/
Ο
117
Naturally occurring allenic substances are far fewer in number than are
acetylenes. The first authentic example is that of mycomycin (118), a linear
Ci3 compound that is an antibiotic isolated from a fungus (Celmer and
Solomons, 1952a,b). Almost all naturally occurring aliènes have been isolated
from microorganisms and they have unbranched carbon skeletons (Jones,
1966). In view of this backdrop it is rather amazing that the principal carotenoid of brown algae (Phaeophyceae) and perhaps the most abundant natural
=
~~ ~~
=
\ = ^^ / CO a H
118
OH
°
AC