Isolation of Seven Verrucosane Diterpenoids from the Liverwort Scapania bolanderi

Liverworts (Hepaticae) form a special group consi­ dered to be an early stage in the evolution of terrest­ rial plants, and produce terpenoids and/or aromatic compounds characteristic to the species as their ma­ jor lipophilic constituents. During the last two de­ cades many types of sesquiterpenoids have been ob­ tained from the liverworts and most of the liverwort sesquiterpenoids are the enantiomeric forms corres­ ponding to antipodes of those from higher plants [1—5]. However, few investigations have been con­ ducted on diterpenoids of the liverworts: about twen­ ty kinds of diterpenoids with acyclic [3, 6], labdane [7—9], pimarane [10], kaurane [11 — 15], clerodane [16], and dolabellane [17, 18] frameworks have been isolated from several liverworts. All of these carbon skeletons are known in other kinds of organisms. In general, the diterpenoids, distributed widely in plants, are classified by difference of the initial step in biogenetical cyclization of geranylgeranyl py­ rophosphate: the first group is formed by a protoninitiated reaction at the double bond of the distal unit, in a manner similar to those for triterpenoids and steroids. Alternative path of diterpenoid biosyn­ thesis has a similarity to that observed in sesquiter­ penoids. Recently, several diterpenoids consisting of the new carbon skeletons, sacculatane [19—21], ver­ rucosane [22—25], and neoverrucosane [26], have been isolated from the liverworts. In continuing our study on the diterpenoid constituents of liverworts, using as the diagnostic components to chemotax­ onomy of the liverworts, we here isolated eight kinds of diterpenoids including two new compounds from