Neue Diterpenoide aus Blattdrüsen einerPlectranthus sp.aus Rwanda

Abietane Diterpenes of the Genus Plectranthus sensu lato

Plectranthus (Lamiaceae), which—according to the latest systematic revision—includes three separate genera (Coleus, Plectranthus sensu stricto, and Equilabium), is a genus widely used in traditional medicine—mainly in the treatment of various ailments of the digestive tract, respiratory tract, and skin. Many species of Plectranthus s.l. have been shown to produce phenolic compounds and terpenes. Diterpenes, especially those of the abietane class, are the most studied group of secondary metabolites found in Plectranthus s.l., which is characterized by a significant structural diversity arising from the oxygenation and further rearrangement of the basic tricyclic abietane skeleton to a complete aromatization of the ring system. This review summarizes the known information on abietane diterpenes, showing their structures, sources, and biosynthesis. A classification of these compounds into nine groups, according to the arrangement of their ring C, is used. Royleanones, spirocoleons, and hydroquinones are the largest classes of abietane diterpenes, covering more than 70% of all the compounds reviewed.

Diterpenoids from Leaves of Cultivated Plectranthus ornatus

Two new diterpenoid derivatives 7α,12β,17-triacetoxy-6β,19-dihydroxy-13β,16-spirocicloabiet-8-ene-11,14-dione ( 1: ) and 6β-acetoxy-3β,7α,12α-trihydroxy-13β,16-spirocicloabiet-8-ene-11,14-dione ( 2: ) along with 11 ( 3: - 13: ) miscellaneous compounds were isolated from the leaves of Plectranthus ornatus Codd. Their structures were elucidated by spectroscopic analysis and gauge independent atomic orbitals ¹³C NMR calculations. The isolated compounds were screened for their effects on intestinal motility using guinea-pig ileum and duodenum and by their cytotoxicity against 4 human cancer cell lines (HCT-116, SF-295, PC-3, and HL-60). Compounds 6: and 9: were moderately cytotoxic against HL-60, whereas 6: and 13: were more active on SF-295 and HCT-116.

Chemistry of the Genus Plectranthus

This review presents the phytochemical constituents of the genus Plectranthus reported up to 1999. Only a tetrameric derivative of caffeic acid was isolated from P. japonicus, but a group of long-chain alkylphenols, of possible taxonomic significance in the genus, was also isolated. As a genus of the subfamily Nepetoideae, Plectranthus is free from iridoid glycosides and rich in essential oil (i.e. > 0.5% volatile oil on a dry weight basis). Diterpenoids are the more common secondary metabolites in Plectranthus. The majority of them are highly modified abietanoids. This seems to be similar to the pattern of diterpenoids observed for Salvia, but no clerodane diterpenoids were found in Plectranthus.

Rearranged abietane diterpenoids from Clerodendrum mandarinorum

Five new abietane derivatives which have a commonly rearranged abietane skeleton contained a 17(15-->16),18(4-->3)-diabeo-abietane framework, mandarones D-H, were isolated from the stem of Clerodendrum nmantarinorum Diels (Verbenaceae). The structures were characterized as (16S)-12,16-epoxy-11-hydroxy-17(15-->16), 18(4-->3)-diabeo-abieta-3,5,8,11,13-pentaene-7-one (mandarone D, 1), 12,16-epoxy-11,14-dihydroxy-17(15-->16),18(4-->3)-diabeo-abieta-3,5,8,11, 13,15-hexaene-7-one (mandarone E, 2), 12,16-epoxy-6,11,14-trihydroxy-17(15-->16),18(4-->3)-diabeo-abieta-3,5,8,11,13,15-hexaene-7-one (mandarone F, 3),12,16-epoxy-11,14-dihydroxy-6-methoxy-17(15-->16),18(4-->3)-diabeo-abieta-3,5,8,11,13,15-hexaene-2,7-dione (mandarone G, 4) and 12,16-epoxy-11,14-dihydroxy-17(15-->16),18(4-->3)-diabeo-abieta-3,5,8,11,13,15-hexaene-1,7-dione (mandarone H, 5) respectively, mainly based on the spectral analysis and by comparison with those of closely related compounds.

Biological screening of traditional medicinal plants from Papua New Guinea

Based on ethnopharmacological literature, 17 species of medicinal plants used in the traditional medicine in Papua New Guinea were collected. Extracts of different polarities were tested in a preliminary biological screening for their antimicrobial (Escherichia coli, Bacillus subtilis, Micrococcus luteus and Penicillium oxalicum) and molluscicidal activity against Biomphalaria glabrata as well as for their toxicity to brine shrimp. The pretreated plant extracts were also investigated for their ability to inhibit protein kinase C and tyrosine-specific protein kinase of epidermal growth factor receptor. Furthermore, all plants were screened for the presence of alkaloids.