Plant triterpenoids represent a large and structurally diverse class of natural products. A growing interest has been focused on triterpenoids over the past decade due to their beneficial effects on human health. We show here that these bioactive compounds are major constituents of several aerial parts (floral bud, leaf bud, stem, and leaf) of olive tree, a crop exploited so far almost exclusively for its fruit and oil. O. europaea callus cultures were analyzed as well. Twenty sterols and twenty-nine nonsteroidal tetra- and pentacyclic triterpenoids belonging to seven types of carbon skeletons (oleanane, ursane, lupane, taraxerane, taraxastane, euphane, and lanostane) were identified and quantified by GC and GC-MS as free and esterified compounds. The oleanane-type compounds, oleanolic acid and maslinic acid, were largely predominant in all the organs tested, whereas they are practically absent in olive oil. In floral buds, they represented as much as 2.7% of dry matter. In callus cultures, lanostane-type compounds were the most abundant triterpenoids. In all the tissues analyzed, free and esterified triterpene alcohols exhibited different distribution patterns of their carbon skeletons. Taken together, these data provide new insights into largely unknown triterpene secondary metabolism of Olea europaea. 1. Introduction Plant triterpenoids, which include sterols, steroids, and brassinosteroids, constitute a large and structurally diverse group of natural products, with over 100 different carbon skeletons [1, 2]. Oxidative modifications and glycosylations generate more chemical diversity . Sterols and nonsterol triterpenoids are synthesized via the cytoplasmic acetate/mevalonate pathway and share common biosynthetic precursors up to (3S)-2,3-oxidosqualene (OS). The conversion of OS to cycloartenol by the cycloartenol cyclase (CAS, EC 18.104.22.168) is the first committed step in sterol biosynthesis, but OS can be also cyclized by distinct OS cyclases (OSCs), also known as triterpene synthases, into a variety of triterpene skeletons including those of α- and β-amyrins, the most commonly occurring plant triterpenes. These nonsterol triterpenoids are then metabolized into multioxygenated compounds, the precursors of triterpene saponins . Thus, OS cyclization by the various triterpene synthases is a major branch point in the regulation of the carbon flux toward either the sterol pathway (primary metabolism) or the nonsterol triterpenoid pathway (secondary metabolism). During these last ten years, triterpenoids isolated from a large number of plant organs
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