ABSTRACT
Terpenoids are naturally-occurring compounds, most of which are syn thesized through a mevalonic acid pathway. Their carbon backbones can be regarded as consisting of isoprene (C5) units. Depending on the number of isoprene units, they are classified as monoterpenoids (C10), sesquiterpenoids (C15), diterpenoids (C2o), sesterterpenoids (C25), and triterpenoids (C30). Sponges are a major source of terpenoids, ranging from sesquiterpenes to triterpenes as shown in Table 11.1 which gives the approximate numbers of marine terpenoids recorded by the end of 1993 (Higa, unpublished data). A total of some 2000 terpenoids had been reported from various marine organisms by that time. We have no accurate count at present, but the number could well have doubled. The major sources of diterpenoids, which amounted to more than a half of the 1993 count, were octocorals and brown algae. Although sponges contain all types of terpenoids except for monoterpenes, the inverte brates could best be characterized by the wealth of sesterterpenes, vide infra. Marine monoterpenes are virtually confined to certain species of red algae.
