Aliphatic and Cyclohexanoid Monoterpenes

Monoterpenes are aliphatic or cyclic isoprenoid Cjo-compounds. They usually contain one or two isolated double bonds, but may also be saturated or aromatic. Often hydroxy, keto, aldehyde, carboxylic acid, or ester groups are present (Fig, 99). Most compounds are volatile and lipophilic. 

Monoterpenes are typical products of higher plants. They are synthesized, however, also in animals and in a few microorganisms. 

Aliphatic or cyclohexanoid monoterpenes originate from geranyl pyrophosphate (D 6) and/or neryl pyrophosphate probably formed by different prenyltrans-ferases. Of significance are the following types of reactions  

Geraniol Geranic acid Nerolic acid Citral 

8-Cineole (-a-Terpi neol Linalool Fig. 99. Structural formulas of monoterpenes 

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