Chemistry of Natural Products
CHEMISTRY OF NATURAL PRODUCTS
Terpenoids
Sameena Bano Department of Chemistry Faculty of Science Jamia Hamdard New Delhi-110062
(24.09.2007) CONTENTS Introduction Classification of Terpenoids Isolation of mono and sesquiterpenoids General properties of Terpenoids General methods of structure elucidation Terpenoids Citral Menthol Camphor Eugenol
Keywords Terpenes, isoprene, citral, menthol, camphor and eugenol
1
Introduction There are many different classes of naturally occurring compounds. Terpenoids also form a group of naturally occurring compounds majority of which occur in plants, a few of them have also been obtained from other sources. Terpenoids are volatile substances which give plants and flowers their fragrance. They occur widely in the leaves and fruits of higher plants, conifers, citrus and eucalyptus. The term ‘terpene’ was given to the compounds isolated from terpentine, a volatile liquid isolated from pine trees. The simpler mono and sesqui terpenes are chief constituent of the essential oils obtained from sap and tissues of certain plant and trees. The di and tri terpenoids are not steam volatile. They are obtained from plant and tree gums and resins. Tertraterpenoids form a separate group of compounds called ‘Carotenoids’ The term ‘terpene’ was originally employed to describe a mixture of isomeric hydrocarbons of the molecular formula C10H16 occurring in the essential oils obtained from sap and tissue of plants, and trees. But there is a tendency to use more general term ‘terpenoids’ which include hydrocarbons and their oxygenated derivatives. However the term terpene is being used these days by some authors to represent terpenoids. By the modern definition: “Terpenoids are the hydrocarbons of plant origin of the general formula (C5H8)n as well as their oxygenated, hydrogenated and dehydrogenated derivatives.” Isoprene rule: Thermal decomposition of terpenoids give isoprene as one of the product. Otto Wallach pointed out that
Terpenoids
Sameena Bano Department of Chemistry Faculty of Science Jamia Hamdard New Delhi-110062
(24.09.2007) CONTENTS Introduction Classification of Terpenoids Isolation of mono and sesquiterpenoids General properties of Terpenoids General methods of structure elucidation Terpenoids Citral Menthol Camphor Eugenol
Keywords Terpenes, isoprene, citral, menthol, camphor and eugenol
1
Introduction There are many different classes of naturally occurring compounds. Terpenoids also form a group of naturally occurring compounds majority of which occur in plants, a few of them have also been obtained from other sources. Terpenoids are volatile substances which give plants and flowers their fragrance. They occur widely in the leaves and fruits of higher plants, conifers, citrus and eucalyptus. The term ‘terpene’ was given to the compounds isolated from terpentine, a volatile liquid isolated from pine trees. The simpler mono and sesqui terpenes are chief constituent of the essential oils obtained from sap and tissues of certain plant and trees. The di and tri terpenoids are not steam volatile. They are obtained from plant and tree gums and resins. Tertraterpenoids form a separate group of compounds called ‘Carotenoids’ The term ‘terpene’ was originally employed to describe a mixture of isomeric hydrocarbons of the molecular formula C10H16 occurring in the essential oils obtained from sap and tissue of plants, and trees. But there is a tendency to use more general term ‘terpenoids’ which include hydrocarbons and their oxygenated derivatives. However the term terpene is being used these days by some authors to represent terpenoids. By the modern definition: “Terpenoids are the hydrocarbons of plant origin of the general formula (C5H8)n as well as their oxygenated, hydrogenated and dehydrogenated derivatives.” Isoprene rule: Thermal decomposition of terpenoids give isoprene as one of the product. Otto Wallach pointed out that