Diterpenoids from the stem bark of Croton zambesicus

Three clerodane diterpenoids, crotozambefurans A, B and C were isolated from the stem bark of Croton zambesicus together with the known clerodane crotocorylifuran and two trachylobanes: 7 beta-acetoxytrachyloban-18-oic acid and trachyloban-7 beta, 18-diol. Betulinol, lupeol, sitosterol and its 3 beta-glucopyranosyl derivative were also obtained. The structures of crotozambefurans A, B and C were determined, respectively, as: 15,16-epoxy-1,3,13(16),14-clerodatetraen-20,12-olide-18,19-dioic acid dimethylester, 15,16-epoxy-1,3,13(16),14-clerodatetraen-18,19,20-trioic acid trimethylester and 15,16-epoxy-3,13(16),14-clerodatrien-19,1 alpha:20,12-diolide-18-oic acid methylester, using spectroscopic analysis, especially, NMR spectra in conjunction with 2D experiments, COSY, HSQC, HMBC and TOCSY.     

7β-Acetoxytrachyloban-18-oic acid from the stem bark of Xylopia quintasii

A novel diterpene has been isolated from the stem bark of Xylopia quintasii and identified as 7β-acetoxytrachyloban-18-oic acid. The taxonomic si     

Endiandric acid derivatives from the stem bark of Beilschmiedia anacardioides

Three new endiandric acid derivatives, beilschmiedic acids D, E and beilschmiedin were isolated from the stem bark of Beilschmiedia anacardioides together with the known compounds bisabolene and tricosanoic acid. Their structures were determined on the basis of spectroscopic analysis.     

Antifungals and acetylcholinesterase inhibitors from the stem bark of Croton heliotropiifolius

The ethanolic extract of the stem bark of Croton heliotropiifolius Kunth (Euphorbiaceae) showed significant in vitro inhibition of acetylcholinesterase using a dilution spectrophotometric assay and antifungal activity against Candida albicans with a thin layer chromatography (TLC) bioautographic assay. In order to isolate the active compounds, bioassay-guided fractionation was undertaken using HPLC to localize the active compounds. Different zones of the HPLC-UV chromatogram were linked to acetylcholinesterase inhibition or to antifungal activities. In parallel to this HPLC-based activity profiling, HPLC-PDA-ESI-MS and HPLC-TOF-HRMS were used for the early identification of some of the compounds present. The targeted isolation of the active compounds was performed by medium pressure liquid chromatography (MPLC-UV) and further semi-preparative HPLC. Using this approach, nine compounds were isolated, one of them being a new indole alkaloid derivative. The structures of the isolated compounds were elucidated by spectroscopic methods including UV, NMR, MS and HRMS.     

Cembranolides from the stem bark of the southern African medicinal plant,Croton gratissimus (Euphorbiaceae)

The stem bark of Croton gratissimus (Euphorbiaceae) yielded four cembranolides, including the first reported example of a 2,12-cyclocembranolide, (+)-[1R*,2S*,7S*,8S*,12R*]-7,8-epoxy-2,12-cyclocembra-3E,10Z-dien-20,10-olide, whose structure was confirmed by means of single crystal X-ray analysis. This compound showed moderate activity against the PEO1 and PEO1TaxR ovarian cancer cell lines.     

8β-hydroxypimar-15-en-19-oic acid from Taxodium mucronatum

A new diterpenoid has been isolated from the leaves and fruits of Taxodium mucronatum. Its structure, 8β-hydroxypimar-15-en- 19-oic acid, was established by chemical and spectroscopic means.     

Ellagic acid rhamnosides from the stem bark of Eucalyptus globulus

Four ellagic acid rhamnosides were isolated from the stem bark of Eucalyptus globulus. Their structures have been established on the basis of the analysis of their 1H NMR, 13C NMR, HMBC, IR and MS spectral data. The HMBC data of these compounds were most useful for their structure determinations, with these bring determined to be 3-O-methylellagic acid 3'-O-alpha-rhamnopyranoside, 3-O-methylellagic acid 3'-O-alpha-3'-O-acetylrhamnopyranoside, 3-O-methylellagic acid 3'-O-alpha-2'-O-acetylrhamnopyranoside, 3-O-methylellagic acid 3'-O-alpha-4'-O-acetylrhamnopyranoside, respectively. Their antioxidant activities were evaluated by measuring the inhibition of lipid peroxidation using rat liver microsomes, with IC50 values of 10.0-14.0 microg/ml.     

A new ent-kaur-16-en-19-oic acid from the aerial parts of Inula bifrons

The phytochemical study of the chloroform extract of the aerial parts of Inula bifrons (L.) L. led to the isolation of one new ent-kaurane diterpenes acid along with twelve known compounds (two ent-kaurane diterpenoids, an eudesmane acid, five sesquiterpene lactones, three triterpenoids and β-sitosterol). All known compounds are found for the first time in I. bifrons. Their structures were elucidated by using spectral methods (NMR, HRESIMS and IR). The distribution of these compounds in the genus Inula and their chemotaxonomic significance is discussed.     

Acutifloric acid: A diterpene dimer from the stem bark of Xylopia acutiflora

In addition to four kaurane and kaurene diterpenes, the stem bark of Xylopia acutiflora yielded a dimeric diterpene derived via Diels-Alder condensation of kaurene and labdane monomers. The structure of the dimer, which has been given the trivial name acutifloric acid, was assigned on the basis of detailed spectroscopic analysis.     

Limonoids from the stem bark of Cedrela odorata

Four nomilin/obacunol derivatives and a swietenolide derivative, together with seven known limonoids, were isolated from stem bark of Cedrela odorata and their structures established by spectroscopic methods. Antifeedant activity of the isolated compounds was also tested.     

Xanthones from the stem bark of Garcinia nigrolineata

Nine xanthones, nigrolineaxanthones A-I, together with nine known xanthones, were isolated from the crude methanol extract of the stem bark of Garcinia nigrolineata; two of which have previously been reported as synthetic xanthones. The structures were elucidated by analysis of spectroscopic data, especially using 1D and 2D NMR spectroscopic data.     

Flavonoids from the stem bark of Millettia hemsleyana

The stem bark of Millettia hemsleyana has yielded six simple flavonoids of which three are novel. Dihydromilletenone methyl ether and dihydroisomilletenone methyl ether represent the two keto—enol tautomers of the known β-hydroxychalcone milletenone, trapped by methylation and reduction, and the third new compound, 3′,4′-methylenedioxy-7-methoxyflavone, is the cyclized form of a demethylated milletenone. All compounds were identified on the basis of detailed spectral analysis.     

Flavonoids from the stem bark of Bolusanthus speciosus

Three flavonoids (bolusanthols A-C), viz an isoflavan and two prenylated isoflavanones, were isolated from the stem bark of Bolusanthus speciosus in addition to four known flavonoids, 5,7,3'-trihydroxy-4'-methoxy-5'-methoxy-gamma,gamma-dimethylallylisoflavanone, 5,7,2'-trihydroxy-4'-methoxy-6,5'-di(gamma,gamma)-dimethylallyl)isoflavanone, 3,5,7,3',4'-pentahydroxy-6-gamma,gamma-dimethylallylflavone and 5,7,2',4'-tetrahydroxy-8,3'-di(gamma,gamma-dimethylallyl)-isoflavanone. The structure of the new compounds were determined to be 4,2',3',4'-tetrahydroxy-6,7-methylenedioxyisoflavan (bolusanthol A), 5,7,3',4'-tetrahydroxy-5'-gamma,gamma-dimethylallylisoflavanone (bolusanthol B), and 5,7,4'-trihydroxy-6,3'-di(gamma,gamma-dimethylallyl)isoflavanone (bolusanthol C) by spectroscopic methods.     

Flavonoids from the stem bark of Lonchocarpus xuul

The stem bark of Lonchocarpus xuul (Leguminosae) has yielded four flavonoids which have been identified by spectroscopic methods as the novel 4beta,5-dimethoxy-6",6"-dimethyl-2H-pyrano-(2",3":7,6)-fl avan (xuulanin), 3beta,4beta,5-trimethoxy-6",6"-dimethyl-2H-pyrano-(2",3":7,6 )-flavan (3beta-methoxyxuulanin). 4beta-ethoxy-5-methoxy-6",6"-dimethyl-2H-pyrano-(2",3":7,6)- flavan (4beta-demethylxuulanin-4beta-ethyl ether), and the known 5,7-dihydroxy-6,8-di(3-methylbut-2-enyl)flavanone (spiniflavanone-B). The ethyl derivative is considered likely to be an artefact.     

Limonoids from the stem bark of Khaya grandifoliola

Three limonoids, deacetylkhayanolide E (1), 6S-hydroxykhayalactone (2), and grandifolide A (3), along with three known ones, were isolated from stem bark of the Nigerian medicinal plant Khaya grandifoliola. Their structures were characterized on the basis of the application of spectroscopic methods. In vitro antimicrobial and cytotoxic activities of the isolates were also tested, but were all found to be inactive.     

Alkaloids from the stem bark of Strychnos icaja

A comprehensive phytochemical study of the stem bark of Strychnos icaja was done for the first time and led to the isolation of two new monoindole alkaloids 15-hydroxyvomicine (1) and 12-methoxyicajine (2) along with 13 known alkaloids: the monoindoles N-methyl-sec-iso-pseudostrychnine (3), vomicine (4), icajine (5), 19,20-α-epoxy-12-methoxyicajine (6), 19,20-α-epoxy-12,15-dihydroxy-11-methoxyicajine (7), 19,20-α-epoxy-15-hydroxynovacine (8), 15-hydroxyicajine (9), 12-hydroxystrychnine (10), strychnine (11) and the tertiary bisindoles sungucine (12), isosungucine (13), strychnogucine C (14) and bisnordihydrotoxiferine (15). Apart from 10 and 11, the other alkaloids were isolated for the first time from the stem bark of this plant. The hemisynthetic derivative, N_b-chloromethosungucine (16) and the previously reported synthetic compound 3 were isolated from a natural source for the first time. Fractions and some isolated compounds were tested against the chloroquine-sensitive 3D7 strain of Plasmodium falciparum. The bisindole alkaloids were most active with IC₅₀ ranging from 0.72 to 3.41 μg/ml whilst the monomers 1 and 3 were slightly active (IC₅₀ 39.92 and 40.27 μg/ml respectively) and 6 inactive. The structures of the compounds were determined based on the analysis of their spectral data. The full ¹H and ¹³C NMR data of compounds 3, 6 and 7 are also reported in the present work for the first time.