Terpenoids are diverse, widespread and exceedingly numerous class of natural products constructed from five carbon building units (isoprene units). It is synonymously termed as terpenoids, terpenes and isoprenoids. There is no agreement on basic nomenclature and various subgroups are often given the –oid and –ene suffixes interchangeably, e.g: monoterpenoids ≈ monoterpenes. However we use the –oid suffix for both general and subgroups and this logical system like alkaloids or flavonoids. The ene suffix represents unsaturated hydrocarbons of the family.
The name terpene is an inappropriate to include compounds such as alcohols, aldehydes and ketones. The general molecular formula for natural terpenoid is (C5H8)n. Terpenoids can be found in all living things. They occur widely in all parts such as seeds, flowers, fruit, root and wood of higher plants. These compounds as components of oil or in extracts of flavours, preservatives, perfumes, medicines, soaps and pigments etc.
Camphor easily obtainable virtually pure as crystalline and very fragrant solid was introduced in Europe in 11th century and by the late middle ages numerous essential oils from common herbs such as lavender, rosemary, thyme and wormwood were used as perfumes and in folk medicines. The terpenoids contribute to scent of eucalyptus, the flavours of cinnamon, cloves and ginger.
Terpenoids play important role in the traditional herbal remedies and are under investigations for antimalarial, anti-neoplastic and other pharmaceutical functions.
Well known terpenoids include citral, menthol, camphor etc.
The progress was slow on the isolation and characterization of natural products until the period 1950. After that period modern chromatographic techniques like Liquid Chromatography (LC), Thin Layer Chromatography (TLC), High Performace Liquid Chromatography (HPLC), Gas Chromatography (GC) were introduced to isolated the natural products. In addition spectroscopic techniques such as Infrared (IR), Ultraviolet-Visible (UV-Vis), Mass, Nuclear Magnetic Resonance (NMR) were evolved to characterize the isolated compounds.
The great number of naturally occurring terpenoids over 15000 have been isolated, characterized and dozens more reported weekly. Many of these compounds have been functionalized or derivatized in laboratories in hope of preparing compound with enhanced and desirable biological activities.