Tobacco isoprenoids - precursors of important aroma constituents
Much of the aroma of tobacco can be viewed as arising by way of biodegradation of tobacco isoprenoids, predominantly of the cembranoid, labdanoid and carotenoid groups. The oxygenation patterns and relative abundance of these diterpenoids imply that most of them are derivedfrom (Z)-abienol and two cembratrienediol epimers ( I and 2) by a series of reactions often initiated by singlet oxygen andlor analogous enzymatic systems assumptions veriJied by biomimetic synthesis of a large number of them. Further transformations of these C20 tobacco constituentsfirnish a series of degraded diterpenoids having 19 to 8 carbon atoms, many of which contribute to the characteristic aroma of tobacco. Here, the interest will be focused on the transformations of the cembranoids. Evidence for the presence of several new cembrane-derived tobacco constituents and of their stereostructures will be presented along with the major biogenetic pathways adopted to enplain the formation of most cembranic compounds known in tobacco to date.