Antimicrobial properties

It is generally recognized that alkaloids have strong antimicrobial, antibacterial and antifungal biological properties329'383'386'387'388'389'390'391. Moreover, some studies have evidenced anti-parasitic activity in this group of compounds392 393. Caron et al.329 have investigated 34 quasi-dimeric indole alkaloids for antimicrobial activity using 8 different test micro-organisms. It was found that all of the studied alkaloids showed activity against Staphylococcus aureus and Bacillus subtilis, which are Gram-positive bacteria. Caron et al.329 found that 31 alkaloids showed biological activity against micro-organisms. The micro-organisms tested by Caron et al.329 were B. subtilis, S. aureus, Mycobacterium smegmatits, Escherichia coli, Pseudomonas aeruginosa, Candida albicans, Aspergilus niger. This study concluded that antimicrobial activity of alkaloids is connected with the stereochemistry of the carbon ring, its aromatic substitution and oxidation329.

The antimicrobial activity of pendulamine A, pendulamine B and penduline isolated from the root extract of Polyalthia longifolia var. pendula was studied by Faizi et al.388. All three alkaloids showed bioactivity, though the most active was found to be pendulamine A. In this study, the following Gram-positive organisms were used: B. subtilis, Corynebacterium hoff-manii, S. aureus, Streptococcus faecalis, Streptococcus pyogenes, Streptococcus viridans and Micrococcus lysodicklycus. The Gram-negative micro-organisms were E. coli, K. pneumoniae, P. aeruginosa, Proteus mirabilis, Salmonella paratyphi A., S. paratyphi B. and Salmonella typhi388. Antibacterial properties of the alkaloids isolated from Zanthoxylum rhifolium have also been noted in the study of Gonzaga et al.390. Significant bioactivity was displayed by 6-acetonyldihydronitidine, 6-acetonyldihydroavicine and zanthoxyline. Gonzaga et al.390 used the following Gram-positive bacteria in their research: S. aureus, Staphylococcus epidermilis, Micrococcus luteus. The Gram-negative bacteria were K. pneumoniae, Salmonella setubal and E. coli. Antifungal, antibacterial and anti-malarial properties are mentioned in the case of sampangine as a result of in vitro studies383. This alkaloid has also shown other bioactivities, especially a novel opportunity to be used as anticancer agent.

Figure 85 presents antibacterial activity by some alkaloids. There are clearly different minimum inhibitory amount of alkaloids for this activity. It is also clear that alkaloid antibacterial activity is selective.

Scutianine E

o

Condaline A

Pendulamine A

v

Penduline

Xanthoxyline

Berberine

Sparteine

o

Scutianine E

Condaline A

a

Pendulamine A

Xantoxyline

o

£

Klebsiella pneumoniae

Staphylococcus aureus

Klebsiella pneumoniae

Figure 85. Activity of some alkaloids on Gram-positive (Staphylococcus aureus, 1) and Gram-negative (Klebsiella pneumoniae, 2) bacteria. Explanations: Observe that the value for Scutianine E and Xanthoxyline is the same (12.5^g). Alkaloids indicated in 1 but not in 2 have values of more than 100 ^g. In the case of Penduline there is no data available (Refs [388, 389, 390, 394 ]).

Morel et al.389 reported on the antimicrobial activity of cyclopeptide alkaloids isolated from Scutia buxifolia Reiss (Rhamnaceae). The organisms used in this research were identical to those used in the study of Gonzaga et al.390. Condaline and scutianine have shown the widest range of bioactivity. It is necessary to mention that the antimicrobial activity of alkaloids is one of the many possible biological activities of these molecules. Recent studies provide vast amounts of new information about the status of marine environments as large reservoirs for biologically active alkaloids. The indole alkaloids from marine environments are a promising and active group of molecules. Their biological activity covers cytotoxic, antiviral, anti-parasitic, anti-inflammatory, serotonin and antagonistic realms395. Another alkaloid group from marine environments consists of the pyridoacridone alkaloids. They have been reported as having a wide range of biological properties386'387'391'393. These alkaloids have been known as having anti-tumourous and antifungal ability. Moreover, Sas-Piotrowska et al.231 addressed the fungistatic effects of the quinolizidine alkaloid fractions from extract of Lupinus spp. on potato pathogens. The alkaloid fractions had the strongest effect on the colonization of certain potato leaf fungi, such as Altenaria solani, Cladosporium herbarum, Colletotrichum coccodes and

Vertricillum albo-atrum. Moreover, this study has evidenced that alkaloids from Lupinus luteus L. strongly inhibited the growth of potato tuber fungi such as Rhizoctonia solani and Phoma exigua. This study also suggested that alkaloid influence is stronger in the case of facultative fungi than in the case of specialized fungi. However, the clearly different sensitivities of various potato pathogen species observed in the experiments carried out by Sas-Piotrowska et al.231 to alkaloid preparations have been explained by pathogenic cell structures and by the chemical structure of the alkaloids. On the other hand, it was also possible that the fungistatic action of the preparation was based on the influence of the different synergetic levels of various compounds found in fungi species.

Bringmann et al.396 have researched naphthylisoquinoline alkaloids isolated from the tropical lianas Ancistrocladus abbreviatus and Triphyophyllum peltatum. The most prominent naphthylisoquinoline alkaloid is dioncophylline A, which has a variety of bioactivities. It was evidenced that this alkaloid possesses high fungicidal and insecticidal properties. It has proven very active in limiting the fungus Botrytis cinerea and inhibiting the growth of the insect Spodoptera lit-toralis. Moreover, this alkaloid has anti-parasitic bioactivity against Plasmodium falciparum and larivicidal in the case of Anopheles stephensi. Bringmann et al.396 have studied naphthylisoquinoline alkaloids for their molluscicidal activity against the tropical snail Biomphalaria glabrata. This study indicated a strong molluscicidal activity by the alkaloid.

It is necessary to mention that the antimicrobial activity of alkaloids has been studied relatively extensively even during the 1940s-1980s. These studies have reported nearly 50 different steroid397-398-399-400-401-402-403-404-405-406-407-408-409 and over 100 different isoquinoliZidine402'404,407,410,411,412,413,414,415,416,417,418,419,420,421,422,423,424,425,426 and at least 90 different terpenoid indole alkaloids to have antimicrobial activity329-427-428-429-430,431-432-433-434-435-436,437-438-439-440-441-442 Research has reputed large diversity in antimicrobial activity against bacteria, yeasts and fungi. In the 1990s, the most known and widely used alkaloids were berberine and sanguinarine, due to their antimicrobial activity. Berberine has anti-diarrhoetic and sanguinarine anti-carries properties.

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