ABSTRACT
The terpenoids occur in abundance in the plant world, where they possess many different kinds of functions. They are all derived from the basic 5-carbon isoprene unit, biosynthetically as isopentenyl pyrophosphate, which is itself derived from acetate via mevalonic acid. They may be classified into discrete groups according to the number of isoprene units, e.g., monoterpenes; sesquiterpenes; diterpenes; triterpenes and sterols, saponins, cardiac glycosides and carotenoids. The virus titrations of key tissues are important in the case of triterpenoids because the compounds can induce interferon and augment immune responses in mice; thus their activities in vivo may be indirectly antiviral. The mixed terpenoid delta-9-tetrahydro-cannabinol exerts its antiviral effect via membrane-mediated events, while the few mono- and diterpenoids examined are clearly virucidal to membrane-containing viruses. There have been reports of the beneficial effects of the two synthetic triterpenoids: carbenoxolone and cicloxolone, in helping to control herpes simplex oral and genital lesions and to promote healing.
