New antimycotic diprenylindoles and rosane-type diterpenoids from as teranthe asterias and hugonia casteneifolia

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University of Dar es Salaam
This thesis reports on new antimycotic diprenylindoles and rosane-type diterpenoids from Asteranthe asterias (S. Moore) Engl. & Diels which belongs to the family Annonaceae and Hugonia casteneifolia Engl. Which is a member of the family Linaceae. Phytochemical investigations of theethanol extract from the stem and root barks of Asteranthe asterias collected from Handeni (Tanga Region), Chalinze, and Pugu Forest (Coast Region), in Tanzania yielded two new diprenylated indoles, 1’,3’-epoxyyasteranthine and 2’,3’-dihydroxyasteranthine. Each of the two compounds was obtained in an enantiomeric ratio of 3:1 (S/R) and showed a remarkable antimycotic activity against Saprolegnia asterophora and Rhizoctonia solani, this activity being comparable with that of the standard antimycotic agent naftifine. The activity of the two compounds against Botrytis cineria was only 20% of that of naftifine. Both compounds were found to be inactive against the trypanosomiasis causing parasites, Trypanosoma brucei rhodesiense in vitro. The enantiomeric purity of the two compounds was established by HPLC analysis on a chiral adsorbent (Chiralcel OD) which was also used to separate the two enantiomers of the diol. The absolute configuration of the separated enantiomeric diols was established by CD measuments, on comparison with CD spectra for related compounds (the hexalobines). Failure to open the epoxide ring under acidic conditions similar to the situation during chromatographic workup indicated that the diol was a true natural product, and not an arterfact of the epoxide. Diprenylated indoles, such as the hexalobines have been isolated as natural products only recently and almost exclusively from plants of the family Annonaceae. The previous isolations of these compounds from Hexalobus, Isolona and Uvaria species and now from Asteranthe asterias represent the only reported isolation of such compounds from natural sources. Three new rosane diterpenoids have been isolated from the root bark of Hugonia casteneifolia Engl. These diterpenes have been named hugorosenone, 19-hydroxyhugorosenone and 19-hydroxyhugorosene. These cpmpounds belong to the rare rosane class of diterpenes that have an exocyclic viny1 group similar to pimaranes and isopimaranes. The dichloromethane extracts of the root bark of H. casteneifolia also yielded two new bis nor-diterpenoids which have been named hugonone A and hugonone B. the hugonones are related to maytenone, which is a bis nor-diterpene that was isolated from Maytenus dispermum. Maytenone can be considered to be a Diels-Alder type dimerisation product of 13-hydroxyabieta-8(14),9(11)-dien-12-one, which is an abiatane-type diterpenoid. The hugonones on the other hand are the Diels-Alder adducts of nor-diterpenoids of the isopimarane skeleton, in which the exocyclic vinylic unit has been degraded. So far dimeric nor-diterpenoids similar to hugonones have not been reported. The crude root bark extract exhibited strong activity in the brine shrimp test and hugorosenone was found to be the active principle.
Available in print form, EAF Collection, Dr. Wilbert Chagula Library, (THS EAF QK861.M44)
Botanical chemistry, Asterias
Mdee, L.K (1997) New antimycotic diprenylindoles and rosane-type diterpenoids from as teranthe asterias and hugonia casteneifolia, Masters dissertation, University of Dar es Salaam, Dar es Salaam.