Three new diterpenoids, a neoclerodane and two labdane derivatives, have been isolated from an acetone extract of Plectranthus ornatus. The structures of these compounds (plectrornatins A-C, 1-3, respectively) were established mainly by spectroscopic means, particularly by 1D and 2D NMR studies and, in the case of the neoclerodane 1, by an X-ray diffraction analysis. Compounds 1 and 3 showed moderate antimicrobial activity against five Candida species and selected Gram negative and Gram positive bacteria strains.

From an acetone extract of Staehelina dubia, large quantities of the previously known germacranolide artemisiifolin were isolated. The conformations of the 10-membered germacra-1(10)E,4Z-diene ring system of this compound and those of its derivatives 11,13-dihydroartemisiifolin, isabelin and 6alpha-hydroxy-15-oxogermacra-1(10)E,4Z,11(13)-trien-12,8alpha-olide were studied by NMR spectroscopic methods. Low-energy conformations were obtained by quantum mechanical calculations. An x-ray diffraction analysis of artemisiifolin established that, in the crystalline state, it possesses a unique conformation that corresponds to the majority one existing in acetone-d6 solution.

Substituted 2,7‐dimethyl‐3‐thioxo‐3,4,5,6‐tetrahydro‐2H‐[1,2,4]triazepin‐5‐one reacts as a dipolarophile with several N‐aryl‐C‐ethoxycarbonylnitrilimines, in equimolar quantities, to give, in all cases, two types of products: diethyl 3‐(p‐aryl)‐2‐[N′‐(p‐aryl)‐N′‐(2′,7′‐dimethyl‐5′‐oxo‐5′,6′‐dihydro‐2H‐[1,2,4]triazepin‐3′‐yl)‐hydrazino]‐2,3‐dihydro[1,3,4]thiadiazole‐2,5‐dicarboxylate (3a–3c in 20–25% yield) and ethyl 4‐(p‐aryl)‐5‐imino‐1,4‐dihydro[1,3,4]thiadiazole carboxylate (4a–4c in 45–50% yield). When 1:2 stoichiometry was used, the formation of product 3 (50%) was favoured. The reaction is entirely chemo‐ and regioselective. The structures of the compounds obtained, where aryl stands for p‐chloro‐phenyl (3b) in the first type and for tolyl (4a) in the second type, were determined by X‐ray crystallography and analysed by spectral methods (NMR and mass spectroscopy). The global and local electrophilicity/nucleophilicity have been analysed to rationalize the chemical reactivity of the reactants. Copyright © 2005 John Wiley & Sons, Ltd.