Four cyclopentanoid monoterpenes were isolated from Teucrium marum; they are the two [(A) and (B)] C2-epimers of a-(2-formyl-3-methy1cyclopentyl)acrylaldehyde and two new [(C) and (D)] isomeric unsaturated lactones. Structures were established by spectral (u.v., i.r., n.m.r., m.s.) evidence and chemical transformations.

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The crystal and molecular structures of agerol diepoxide (3) and ageratriol (2), which have been determined by direct methods and refined by least-squares to R 0.060 and 0.069 respectively, confirm the previously suggested biogenetic scheme from agerol (1 ). Theoretical calculations by a molecular mechanics method ( G E M 0 program) show that the conformers observed in the crystals have the lowest strain-energy. N.m.r. measurements indicate that agerol diepoxide adopts this conformation also in solution.AGEROL (1) and ageratriol (2) are the main sesquiterpene configurations have been determined by chemical components of Achzillea ageratum, and their absolute methods.lP2 Chemical transformation of the diepoxide