Siegfried E. Drewes

Antimicrobial acylphloroglucinols and dibenzyloxy flavonoids from flowers of Helichrysum gymnocomum

From the dichloromethane extract of the flowers of Helichrysum gymnocomum (Asteraceae) two known flavonoids, 4 and 5, and a known acylphloroglucinol, 3B, were isolated. In addition to 1 and 2, the 4,6-dibenzyloxy-2-hydroxy derivative of 2,4,6-trihydroxychalcone and 5,7-dibenzyloxy derivative of pinocembrin, respectively, are reported in Nature for the first time. A compound 3A, related to 3B has the structure 2-methyl-1-[2,4,6-trihydroxy-3-(2-hydroxy-3-methyl-3-butenyl)phenyl]-1-propanone. Compounds 1, 2, 3A, 3B, 4 and 5 have MIC values below 64microg/ml against a selection of pathogens, with 3B having the highest sensitivity (6.3-45microg/ml) for eight of the ten pathogens tested, including Staphylococcus aureus (6.3microg/ml) and methicillin and gentamycin resistant strain of S. aureus (7.8microg/ml). With the exception of 2, the other compounds had notable activity (45-63microg/ml) towards Pseudomonas aeruginosa.

The chemical structures, plant origins, ethnobotany and biological activities of homoisoflavanones

This work reviews the four basic structural types of homoisoflavanones. The relationships between the various structures of homoisoflavanones and their plant origins, ethnobotany and biological activities are put into perspective.

Total Synthesis of the Pyranoisoflavone Kraussianone 1 and Related Isoflavones

The first total synthesis of the pyranoisoflavone kraussianone 1 (1) is described. The key steps involved the Suzuki-Miyaura reaction for the construction of the isoflavone core and the regioselective formation of the dimethylpyran scaffolds to the phloroglucinol (ring A) and resorcinol (ring B) moieties of kraussianone 1 (1). This route also provided access to the related isoflavones eriosemaone D (2) and genistein (3) via simple structural modifications.

Experimental and theoretical studies of a naturally occurring non-oligomeric steroidal supramolecular zipper

Methanol extraction of the bulbs of Ornithogalum tenuifolium afforded a novel crystalline steroidal sapogenin (25R)-5β-spirostane-1β,3α-diol (compound 1). The structure and stereochemistry, but not the enantiomer, of this compound was unambiguously assigned using X-ray diffraction and multidimensional 1H and 13C NMR data. The crystal structure of 1 (monoclinic space group P21) is both novel and remarkable in that the extended lattice or “supramolecular” structure comprises an unusual one-dimensional hydrogen-bonded polymer with 21 symmetry (the polymer axis is co-linear with the b-axis of the unit cell). Each ladder-like hydrogen-bonded polymer stacks in an interlocking fashion with a neighbouring polymer along the c-axis of the unit cell. The self-recognition by hydrogen-bonding that leads to the formation of the polymer is characterized by discrete 10-membered supramolecular rings. Moreover, the steroid units of the one-dimensional polymer interlock perfectly to form a supramolecular zipper. The newly-discovered supramolecular synthon of the zipper has been elaborated on due to its possible use in crystal engineering applications. The supramolecular zipper system has also been simulated in vacuo using semi-empirical (AM1) quantum mechanics techniques, which correctly reproduce not only the experimental conformation but also the hydrogen-bonded extended structure of the compound. The simulations showed that formation of the supramolecular zipper structure of 1 most likely reflects charge-complementarity of its hydrogen-bonded hydroxy groups and that the electrostatically driven process is characterized by a favourable and cooperative in vacuo enthalpy of association. A further hallmark of the self-assembly of 1 was the lowering of the mean vibrational frequency of the hydrogen-bonded hydroxy groups upon formation of the zipper.

In vitro 5-lipoxygenase and anti-oxidant activities of Warburgia salutaris and drimane sesquiterpenoids

The purpose of this investigation was to determine the in vitro 5-lipoxygenase inhibitory and anti-oxidant activities of Warburgia salutaris . Aqueous and methanol extracts of the leaves of W . salutaris were obtained and subjected to the 5-lipoxygenase assay and the 2,2- diphenyl-1-picrylhydrazyl (DPPH) assay to determine their anti-inflammatory and anti-oxidant activities, respectively. Furthermore, drimane sesquiterpenoids, mukaadial and warburganal, isolated from the same plant, were subjected to the same biological tests. The methanol extract of the leaves of W . salutaris displayed promising in vitro anti-inflammatory activity with an IC 50 value below 33xa0μgxa0ml -1 , while the aqueous extract of the same plant exhibited no activity in the same assay. The aqueous and methanol extracts of W . salutaris displayed promising anti-oxidant activities with IC 50 values of 34.43xa0+xa00.74xa0μgxa0ml -1 and 15.38xa0±xa00.20xa0μgxa0ml -1 , respectively. The compounds mukaadial and warburganal displayed 5-lipoxygenase inhibitory activity and contribute to the in vitro anti-inflammatory activity of the crude extract of the same plant. Anti-oxidant activity of W . salutaris did not appear to be confined to the drimane sesquiterpenoids tested.

Enolic iridolactone and other iridoids from Alberta magna

From fresh leaves of Alberta magna two new iridoids and a known cyclopentene dialdehyde have been identified. One of the new compounds has the less-common irido-lactone structure and has an enolic hydrogen on C-4. Two of the compounds show short term mosquito-repellent effects.

Hypoglycaemic effect of Eriosema kraussianum N. E. Br. [Fabaceae] rootstock hydro-alcohol extract in rats

Erectile dysfunction (ED) is a common medical condition in men with cardiovascular disorders such as ischaemic heart disease, hypertension and peripheral vascular diseases. It is also common in men with diabetes mellitus, probably because of the shared factors that impair haemodynamic mechanisms in the penile and ischaemic vasculature. In an attempt to scientifically appraise the efficacy, ethnomedical significance and contribution of Eriosema kraussianum rootstock to its Zulu folkloric use as “uBangalala” and “Viagra substitute”, the present study was undertaken to investigate the hypoglycaemic effect of E. kraussianum rootstock hydro-alcohol extract in normoglycaemic (normal) and hyperglycaemic (diabetic) rat experimental paradigms, using glibenclamide, a ‘second-generation’ sulphonylurea, as the reference oral hypoglycaemic drug for comparison. E. kraussianum rootstock hydro-alcohol extract (EKE, 40–320xa0mg/kg p.o.) produced dose-dependent, significant (Pxa0<xa00.05–0.001) hypoglycaemia in the normoglycaemic and diabetic rats used. Glibenclamide (10xa0mg/kg p.o.) also induced marked, significant reductions (Pxa0<xa00.001) in the blood glucose concentrations of the normoglycaemic and diabetic rats used. The contribution of this hypoglycaemic activity to the folkloric use of the plant’s rootstock as a remedy for the management and/or treatment of ED among Zulu men of South Africa still remains an unresolved scientific nightmare.