Stephan A. Jonker

Aporphinoid alkaloids and other constituents from Lettowianthus stellatus.

Two new aporphinoid alkaloids, f1ttowianthine and 11-methoxylettowianthine were isolated from the root bark of Lettowianthus stellatus, together with the new sesquiterpene 11-hydroxyguaia-4,6-diene and the known compounds liriodenine, (Z)-7-octadecen-9-ynoic acid, methyl (2E,6E,10R)-10,11-epoxy-3,7,11-trimethyl-2,6-dodecadienoate, methyl (2E,6E,10R)-10,11-dihydroxy-3,7,11-trimethyl-2,6-dodecadienoate , and 3,4,5-trimethoxyphenol. The structure elucidation was achieved by spectroscopic methods.

Oxygenated pyrenes, their potential biosynthetic precursor and benzylated dihydroflavones from two African Uvaria species

Two new oxygenated pyrenes, 2,7-dihydroxy-1,8-dimethoxypyrene and 2-hydroxy-1,7,8-trimethoxypyrene, have been isolated, from the stem bark of Tanzanian Uvaria lucida spp. lucida, along with the benzylated dihydroflavones chamanetin, isochamanetin, dichamanetin, uvarinol and isouvarinol, and the carotenoid lutein. 2,7-Dihydroxy-1,8-dimethoxypyrene was also isolated from Ghanaian U. doeringii, together with a potential biogenetic precursor of the pyrenes, 1,2-dihydro-2,9-dihydroxy-10-methoxy-furo[2,3-a]phenanthrene, and most of the benzylated flavanones, which were found in U. lucida spp. lucida.

Prenylindoles from Tanzanian Monodora and Isolona Species

6-(3-Methyl-but-2-enyl)-1,3-dihydro-indol-2-one, annonidine F [3-[6-(3-methyl-but-2-enyl)-1H-indolyl]-6-(3-methyl-but-2-enyl)-1H-indole], 1H-indole-5-carbaldehyde, 6-(3-methyl-2-butenyl)-1H-indole, 6-(3-methylbuta-1,3-dienyl)-1H-indole, 6-(4-oxo-but-2-enyl)-1H-indole and 3-geranylindole were isolated from Monodora angolensis (Annonaceae) while 3-(1,1-dimethyl-but-2-enyl)-5-(3-methyl-but-2-enyl)-1H-indole (caulidine A), 4-[3-(1,1-dimethyl-but-2-enyl)-1H-indol-5-yl]-but-3-en-2-one (caulidine B), 5-(3-methyl-2-butenyl)-1H-indole and 5-(3-methylbuta-1,3-dienyl)-1H-indole were obtained from Isolona cauliflora (Annonaceae); structural determination by spectroscopic analysis. Some of the prenylindoles had antifungal and antimalarial activities.

New Diprenylated Indoles from Asteranthe Asterias (Annonaceae)

Abstract Two new diprenylated indoles, 2′,3′-epoxyasteranthine and 2′,3′-dihydroxyasteranthine, were isolated from the stem bark and the root bark of Asteranthe asterias (Annonaceae). Their structures were elucidated by spectroscopic methods. Each of the two compounds was obtained in an enantiomeric ratio of 3:1 (S/R) and exhibited antimycotic activity against Saprolegnia and Rhizoctonia species.

A Novel Phenanthrenolide and C-Benzyl Dihydrochalcones from Uvaria Puguensis

Two new natural products, the phenanthrenoid puguenolide (6-hydroxy-3-methoxy-4-oxapyren-5-one) and isoangoletin were isolated from the stem bark of the newly described Uvaria species, U. puguensis D.M. Johnson, together with the sesquiterpene guaiol and the usual C-benzyldihydrochalcones previously found in the genus Uvaria , viz . uvaretin, diuvaretin, chamuvaritin and a mixture of triuvaretin and isotriuvaretin. Structural elucidation was achieved through a combination of spectroscopic methods.

Ophrypetalin and Other Annonaceous Acetogenins From Ophrypetalum Odoratum

Abstract Ophrypetalin, a new bis-tetrahydrofuran acetogenin, was isolated from Ophrypetalum odoratum (Annonaceae) together with the known acetogenins desacetyluvaricin, rolliniastatin-1, dieporeticenin and a mixture of dieporeticanin-1, dieporeticanin-2, and diepoxyrollin. the structures were elucidated by spectroscopic methods. the absolute configurations were established by Moshers method and by CD measurements.

C18 tetraynoic fatty acids and essential oil composition of Mkilua fragrans

The fatty acids 17,18-dihydroxyoctadeca-9,11,13,15-tetraynoic acid (mkiluaynoic acid A) and 18-hydroxyoctadeca-9,11,13,15-tetraynoic acid (mkiluaynoic acid B), 5,7,3′,4′-tetrahydroxyflavanol, 3,4-dihydroxybenzoic acid and a mixture of stearic and oleic acids were isolated from fruits and stem barks of Mkilua fragrans (Annonaceae). Mkiluaynoic acid A exhibited antifungal activity against Candida albicans comparable with that of the standard antifungal agent Ketoconazole. Structural determination was achieved by analysis of spectroscopic data. The flower stalks yielded essential oils that mainly consisted of sesquiterpenoids as revealed by GC–MS analysis, whereby 14 sesquiterpenes and four other compounds were identified.

A new Coumarin and Polyhydroxysqualenes from Ekebergia Benguelensis

Abstract A new coumarin, 4-methoxy-5-hydroxymethylcoumarin was isolated from the root bark of Ekebergia benguelensis, together with the polyhydroxysqualenes, 2,22,23-tetrahydroxy-2,6,10,15,19,23-hexamethyl-6,10,14,18-tetracosatetraene and 2-hydroxymethyl-2,3,22,23-tetrahydroxyl-6,10,15,19,23-pentamethyl 1-6,10,14,18-tetracosatetraene, besides a mixture of 3α-hydroxy-12-oleanen-28-oic and 3-oxo-12-oleanen-28-oic acids. Structural determination was achieved by spectroscopic analyses.

Diprenylated Indole Alkaloids from Fruits of Hexalobus monopetalus

New hexalobine type alkaloid, 5-(2″,3″-epoxy-3″-methylbutyl)-3-(3′-hydroxy-3′-methyl-1′-acetyloxy-but-2′-yl)indole (1) alongside the known hexalobines 3-(2′,3′-dihydroxy-3′-methylbutyl)-5-(3″-methylcrotonoyl) indole (2), 3,5-hexalobine C (3) and 3,5-hexalobine D (4) were isolated from fruits of Hexalobus monopetalus. Compounds 3 and 4 exhibited antifungal activity against Candida albicans.