Klaus Peter Latté

Antifungal effects of hydrolysable tannins and related compounds on dermatophytes, mould fungi and yeasts.

A series of hydrolysable tannins and related compounds was evaluated for antifungal activities against filamentous fungi ( Epidermophyton floccosum; Microsporum canis; Microsporum gypseum: Trichophyton mentagrophytes; Trichophyton rubrum; Trichophyton tonsurans; Trichophyton terrestre; Penicillium italicum; Aspergillus fumigatus; Mucor racemosus; Rhizopus nigricans) and opportunistic yeasts ( Candida albicans; Candida glabrata; Candidata krusei; Cryptococcus neoformans), using the agar dilution method. While all samples had no activity against the filamentous fungi in concentrations of 1.1 -5.9 μм (1000 [μg/ml), the phenolic compounds displayed significant potencies against all the opportunistic yeasts tested but C. albicans, with minimum inhibitory concentrations ranging from 0.02 to 0.1 μм ( 16 - 125 (μg/ml). Although the presence of galloyl groups in flavonoids did not necessarily produce activity, this structural element, an HHDP moiety or its oxidatively modified entity proved to be an important structural feature of hydrolysable tannins. Comparison of dilution methods provided strong evidence of dependence of MIC values on the test method. Employing the microdilution broth method, the ellagitannin corilagin (MIC 0.8 nм) was found to be similarly potentially active as amphotericin B (MIC 0.5 nм) and sertaconazole (MIC 0.9 nм) against Candida glabrata strains. The order of effectiveness observed being 64- and 4 -8-fold increased for corilagin and the reference compounds respectively, when compared with that of the agar dilution test.

Pelargoniins, new ellagitannins from Pelargonium reniforme

The range of natural ellagitannins is extended by identification of five new metabolites with 1C4 glucose core, designated as pelargoniins A-D and isocorilagin, and the new phyllanthusiin E methyl ester. They are accompanied in the aerial parts of Pelargonium reniforme by two known structurally related metabolites, corilagin and phyllanthusiin C, two phenolcarboxylic acids, brevifolincarboxylic acid and phyllanthusiin E, the gallotannin 1-O-galloyl-beta-D-glucopyranose, and the ellagitannins strictinin and isostrictinin having a 4C1-glucose core. The structures of these compounds were established from spectroscopic studies. This is the first example of the co-occurrence of ellagitannins with 4C1 and 1C4 glucopyranose core demonstrated for a member of the Geraniaceae.

Unusual Coumarin Patterns of Pelargonium Species Forming the Origin of the Traditional Herbal Medicine Umckaloabo

Abstract The coumarin patterns of Pelargonium sidoides DC. and Pelargonium reniforme CURT., forming the origin of the herbal medicine “umckaloabo”, were analysed and compared for therapeutic equivalence. For both species, members of tri- and tetraoxygenated coumarins almost exclusively were present in the respective metabolic pools. However, the roots of P. sidoides and P. reniforme expressed conspicuously distinct coumarin variations, with umckalin, its 7-O-methyl ether, 7-acetoxy-5,6-dimethoxycoumarin, 6,8-dihydroxy-7-methoxycoumarin, 6,8-dihydroxy-5,7-tetramethoxycoumarin, artelin and three unique coumarin sulfates as uncommon metabolites of this class of secondary products of P. sidoides. Furthermore, the highly oxygenated but known coumarins fraxinol, isofraxetin and fraxidin were associated with the new 8-hydroxy-5,6,7-trimethoxycoumarin as representatives of P. reniforme. Of the twelve identified coumarins only the two species shared the ubiquitous scopoletin and the unique 6,7,8-trihydroxycoumarin. From the oxygenation patterns it is evident that the majority of these Pelargonium coumarins match the recently established basic structural requirements for marked antibacterial activity, i.e. the presence of a methoxy function at C-7 and an OH group at either the C-6 or C-8 position. The current data on the coumarin profiles of each Pelargonium species also indicate a previous erroneous identification of the plant material claimed to be P. reniforme. Absence and presence of umckalin and its 7-O-methyl ether defines P. reniforme and P. sidoides, respectively.

Composition of the essential oils of Pelargonium sidoides DC. and Pelargonium reniforme Curt.

The essential oils of Pelargonium sidoides DC. and P. reniforme Curt. were obtained by hydrodistillation from the leaves of the plants in 0.52% and 0.71% yields, respectively, related to the dry weight. Their composition was analysed by GLC and GC–MS. About 230 components have been detected in each of the Pelargonium oils, of which 102 (P. sidoides) and 81 (P. reniforme) could be unambiguously identified, accounting for about 65% and 49% of the total peak area, respectively. For both species, sesquiterpenes (approximately 60%) were the dominating components, with caryophyllene (2.3%) and caryophyllene epoxide (13%) as the most abundant compounds of the sesquiterpene fraction of the oil of P. sidoides, and the sesquiterpene hydrocarbons δ-selinene (4.2%) and δ-cadinene (4.0%) as the main representatives of the oil of P. reniforme. Other major groups of the oil of P. sidoides comprised monoterpenes (16%) and phenylpropanoids (9%), the major compounds of the latter group being methyleugenol (4.3%) and elemicin (3.6%). By contrast, only monoterpenes were found in reasonable amounts (4.7%) in the related species P. reniforme. Detection of anacardic acids and furan-type constituents provide a rational explanation for insect deterrency by Pelargonium species.

Enhancement of Antimicrobial Activity of Tannins and Related Compounds by Immune Modulatory Effects

Tannins presumably represent the most ubiquitous group of all plant phenols, being commonly found in a large array of woody and some herbaceous higher plant species.1 Their presence in significant amounts in the wood, bark, leaves, and fruits of many plants of predominantly woody habit has suggested a crucial role of polyphenols at the ecological and evolutionary level.2–4 One of their proposed and now well-documented functions includes protecting plants against herbivores such as phytophagous insects and vertebrate herbivores. It should be noted that the impact of plant polyphenols on herbivores ranges from negative to positive interactions, indicating that the effects may be strongly dependent on the individual herbivore, but structure-function relationships have also been assumed to explain the observed contrasting impacts on plant-consuming animals.5 Recently, the action of polyphenols on herbivore-associated microbes has been suggested to mediate plant-herbivore interactions.6 The mode of action of tannins in protecting plants against herbivores is generally attributed to polyphenol-protein interactions.7 Polyphenols are also established as remarkable antimicrobials and potent inhibitors of viral infections in many ecological systems and in a number of in vitro experiments.8–10 Although there is good evidence for the adaptation of some herbivores and microbes to this constitutive chemical defense,11 plants may have benefited from accumulating large quantities of polyphenols in their tissues.