Tess De Bruyne

Triterpenoid saponins from Maesa lanceolata

Six new homologous triterpenoid saponins were isolated from the methanol extract of the leaves of Maesa lanceolata and characterized as 3 beta-O-[alpha-L-rhamnopyranosyl(1 --> 2)-beta-D-galactopyranosyl (1 --> 3)]-[beta-D-galactopyranosyl(1 --> 2)]-beta-D-glucuronopyranosides alpha-diol, 22 alpha-angeloyloxy-16 alpha-butanoyloxy-13 beta,28-oxydoolean-21 beta,28 alpha-diol, 16 alpha,22 alpha-diangeloyloxy-13 beta,28-oxydoolean-21 beta,-28 alpha-diol, 22 alpha-angeloyloxy-13 beta,28-oxydo-16 alpha-(2-methyl-butanoyloxy)-olean-21 beta,28 alpha-diol, 21 beta-acetoxy-22 alpha-angeloyloxy-13 beta,28-oxydo-16 alpha-propanoyloxyolean-28 alpha-ol, 21 beta-acetoxy-22 alpha-angeloyloxy-16 alpha-butanoyloxy-13 beta,28-oxydoolean-28 alpha-01. The structures were established on the basis of chemical and spectral evidence.

Unambiguous assignments for free dimeric proanthocyanidin phenols from 2D NMR

Characterization of proanthocyanidin oligomers proceeds commonly through investigation of NMR data of their peracetates or methyl ether acetates, in conjunction with FAB-mass spectrometry and circular dichroism. Since such an approach is unsuitable in bioassay-guided isolations, we applied two-dimensional NMR techniques for the identification of dimeric proanthocyanidins. This afforded not only a powerful probe for distinction between the different procyanidin isomers, but also allowed full assignments, even for both major rotameric forms, whenever present, without the need for derivatisation. Moreover, discrimination between the crucial 6- and 8-protons and carbons was achieved after addition of traces of cadmium nitrate, resulting in the separation of the broad phenolic signals into sharp singlets. As an example of the general strategy followed in the assignment and combination of data of the different spectra available, complete analysis of underivatised procyanidin B3 or catechin-(4α→8)-catechin is discussed for the first time.

Chemical Composition and Antifungal Activity of Essential Oils of Some Aromatic Medicinal Plants Growing in the Democratic Republic of Congo

Abstract The chemical composition and the antifungal activity of essential oils from 15 aromatic medicinal plant species growing in the Democratic Republic of Congo have been studied. More than 15 constituents in an amount ≥ 0.1% were identified in each oil. 1,8-Cineole, α- and β-pinene, P-cymene, α-terpineol, camphene and limonene were prevalent constituents. The antifungal activity of these oils (5 μL per disc) was evaluated by the diffusion method. Results indicate that all oils from fresh plant materials exhibited an antifungal activity at different levels against Candida albicans, Candida tropicalis, Aspergillus niger, Trichophyton mentagrophytes and Microsporum canis. A high antifungal activity was found in the leaf oil of E. tereticornis (15–22 mm) followed by the leaf oils of Eucalyptus alba (14–17 mm), E. camaldulensis, E. citriodora, E. globulus, Cymbopogon citratus and Monodora myristica seed oil (11–17 mm) against selected yeasts, fungus and dermatophytes. The leaf oils of E. deglupta, E. robusta, Ocimum gratissimum and Aframomum stipulatum also showed a good activity against selected microorganisms (10–12 mm). The less active oils were those from E. saligna, E. propinqua and O. americanum leaves. No correlation between the amount of some major constituents and the antifungal activity was observed.

New acylated triterpenoid saponins from Maesa lanceolata

Ten new acylated triterpenoid saponins were isolated from the leaves of Maesa lanceolata. For their structure elucidation extensive use was made of homo- and heteronuclear 2D NMR techniques such as COSY, NOESY, HSQC and HMBC. All saponins identified contained the same tetraglycosidic side chain, but the triterpenoid moiety showed a variable esterification pattern. Monoester, diester and triester derivatives were present. Maesasaponin I was a 21-monoester derivative, i.e. ¿3 beta-O-[alpha-L-rhamnopyranosyl-(1-->2)-beta-D-galactopyranosyl- (1-->3)]-[beta-D-galactopyranosyl-(1-->2)]-beta-D-glucuronopyranosyl+ ++¿-21 beta-angeloyloxy-13 beta, 28-oxidoolean-16 alpha, 22 alpha, 28 alpha-triol. Maesasaponins III, IV3, V3 and VI2 had an additional acetyl, propanoyl, n-butanoyl and angeloyl substituent, respectively, in position 22. Maesasaponins II, IV2, V2, VI3 and VII1 were characterised as the 16-acetyl derivatives of maesasaponins I, III, IV3, V3 and VI2, respectively. Structures of saponins previously reported in M. lanceolata had to be revised.

Oligomeric proanthocyanidins possessing a doubly linked structure from Pavetta owariensis

Abstract Pavetannins B7 and B8, two new trimeric proanthocyanidins, have been isolated from the stem bark of Pavetta owariensis , along with the known tetramers cinnamtannin B2 and its positional isomer, pavetannin C1, and the pentamer pavetannin D1. NMR and mass spectral data established the structure of the pavetannins as epicatechin-(4 β → 8, 2 β → O → 7)- ent -epicatechin-(4 α → 8, 2 α → O → 7)- ent -catechin, epicatechin-(4 β → 8, 2 β → O → 7)-epicatechin-(4 β → 8, 2 β → O → 7)- ent -catechin, epicatechin-(4 β → 6)-epicatechin-(4 β → 8, 2 β → O → 7)-epicatechin-(4 β → 8)-epicatechin and epicatechin-(4 β → 8)-epicatechin-(4 β → 8, 2 β → O → 7)-epicatechin-(4 β → 8)-epicatechin-(4 β → 8)- epicatechin, respectively. The naming of cinnamtannin B2 is revised to epicatechin-(4 β → 8)-epicatechin-(4 β → 8,2 β → O → 7)-epicatechin-(4 β → 8)-epicatechin, according to its structural presentation.

Study of potential systemic oxidative stress animal models for the evaluation of antioxidant activity: status of lipid peroxidation and fat‐soluble antioxidants

Although many compounds have already been tested in‐vitro to determine their antioxidant profile, it is necessary to investigate the in‐vivo effect of potential antioxidants. However, representative models of systemic oxidative stress have been poorly studied. Here, different potential systemic oxidative stress animal models have been investigated. These included a vitamin E‐deficient rat, a diabetic rat and an atherosclerotic rabbit model. Plasma/serum malondialdehyde was measured as a parameter of oxidative damage. Plasma/serum fat‐soluble antioxidants were determined as markers of antioxidant defence. We demonstrated that vitamin E‐deficient rats were not suitable as a model of systemic oxidative stress, whereas diabetic and atherosclerotic animals showed increased systemic oxidative damage, as reflected by significantly augmented plasma/serum malondialdehyde. Moreover, plasma coenzyme Q9 increased by 80% in diabetic rats, confirming systemic oxidative stress. In view of these observations and economically favouring factors, the diabetic rat appeared to be the most appropriate systemic oxidative stress model. These findings have provided important information concerning systemic oxidative stress animal models for the in‐vivo study of antioxidants.

Tetrameric proanthocyanidins containing a double interflavanoid (A-type) linkage from Pavetta owariensis☆

Abstract Pavetannins C-2 to C-6, five new tetrameric proanthocyanidins containing one or two double interflavanoid (A-type) linkages have been isolated from the stem bark of Pavetta owariensis . Spectroscopic investigations and partial acid-catalysed degradation established their structure as epicatechin-(4 β → 8,2 β → O → 7)- ent -catechin-(4 β → 8)-epicatechin-(4 β → 8)-epicatechin, epicatechin-(4 β → 8,2 β → O → 7)- ent -epicatechin-(4 α → 8)- ent -epicatechin-(4 α → 8)-epicatechin, epiafzelechin-(4 β → 8,2 β → O → 7)-epicatechin-(4 β → 8)-epicatechin-(4 β → 8)-epicatechin, epiafzelechin-(4 β → 8,2 β → O → 7)- ent -afzelechin-(4 α → 8)- ent -epicatechin-(4 α → 8,2 α → O → 7)- ent -catechin and epiafzelechin-(4 β → 8,2 β → O → 7)- ent -catechin-(4 α → 8)- ent -epicatechin-(4 α → 8,2 β → O → 7)- ent - catechin, respectively. While aesculitannin F is being reported from a plant source for the second time, the remaining tetramers are new natural metabolites.

Flavonoid glucuronides from Picria fel-terrae

Abstract Three flavonoid glucuronides are reported from a n-BuOH extract of Picria fel-terrae (Scrophulariaceae). The structures were established by UV, one- and two-dimensional NMR and mass spectrometry as apigenin 7-O-β-glucuronide, luteolin 7-O-β-glucuronide and apigenin 7-O-β-(2″-O-α-rhamnosyl)glucuronide, the latter one being a new compound.

Low-molecular weight compounds with complement activity

The complement system is one of the major effector pathways in the process of inflammation. Along with the clotting, fibrinolytic and kallikrein-kinin systems, complement represents one of the complex enzyme systems of blood which can be activated in specific cascade reactions upon a triggering stimulation. Activated com-plement components mediate various biological effects, each with its specific func-tion in the defence reactions against noxious stimulants. These effects, being bene-ficial to the host under normal conditions, may also cause adverse reactions depen-ding on the site, extent and duration of complement activation. Pharmacological modulation of the complement system could be of potential interest for the treatment and control of immune-pathological reactions linked with complement activation [1].

NMR Characterization and Biological Evaluation of Proanthocyanidins: A Systematic Approach

Condensed tannins or proanthocyanidins constitute an important group of secondary plant metabolites and are in many cases the active compounds of the medicinal plants from which they are isolated. Reports of several in vitro assays demonstrate potentially significant interactions with biological systems, such as antiviral, antibacterial, molluscicidal, enzyme-inhibiting, antioxidant, and radical scavenging properties.1 Their anticipated interference with biological systems is, at least in part, due to their characteristic ability to form complexes with macromolecules, combined with their polyphenolic skeleton.1,2