Subject Antifungal activity

Comparison of these reactivities and antifungal activities of phytoalexin derivatives is an interesting future subject. 

A convenient procedure for the lactonization of alkenols has been recently revealed by Borhan and coworkers [19]. This methodology was successfully applied in the total synthesis of (+)-tanikolide (7-37), a natural product of marine origin which exhibits antifungal activities. Thus, when alkenol 7-36 is subjected to soluble oxone and a catalytic amount of 0s04, a smooth domino oxidative cleavage/lactonization process takes place which leads, after debenzylation, to the desired product in good overall yield (Scheme 7.12). 

Siderophores are low molecular weight compounds that chelate Fe3+ and transport it into the cell. Competition for iron appears to occur between pseudomonads and the rhizosphere bacteria and fungi. Three unusual siderophores with antifungal activity have been described from fluorescent pseudomonads, pyochelin (9), S-dihydroaeruginoic acid (10) and aeruginoic acid [13]. The importance of siderophores in biological control has been the subject of some debate [14]. 

In conclusion, these studies have indicated that chemical modification of the basic podocarpic acid structure can produce new compounds with antifungal activity. The results derived from this study represent preliminary findings irtiich are subject to further investigation. We anticipate that more detailed studies will reveal information concerning the mechanism and mode of action of many of these compounds. In the meantime, we continue to develop new antifungal agents using selected natural products as model compounds. 

This article will review the antifungal activity of plant steroids but it should be noted that not all steroids act in an inhibitory capacity towards fungi. Certain sterols have a stimulatory effect on fungal development promoting growth, the differentiation of reproductive structures, and fertilisation in species of Pythium and Phytophthora which lack the ability to synthesize sterols (9). This subject is considered elsewhere in this volume. 

The exact mechanism of antifungal activity is still unknown, and is currently the subject of many researches. There is three suggested qualitative concepts DNA association, cell wall damage and deactivation of enzymes. On the molecular level it is known that silver is enable to form a bond with S, N, and O atoms, and also to catalyze the formation of disulfide bonds. 

Many Hj antihistamines are metabolized by CYPs. Thus, inhibitors of CYP activity such as macrolide antibiotics (e.g., erythromycin) or imidazole antifungals (e.g.,ketoconazole) can increase Hj antihistamine levels, leading to toxicity. Some newer antihistamines, such as cetirizine, fexofenadine, levocabastine, and acrivastine, are not subject to these drug interactions. 

Ketoconazole (KC) as the first systemlcally-active azole antifungal has been the subject of a number of reviews including the general management of fungal disease,and its efficacy in superficial and systemic infections 0 it was the subject of a number of papers at a recent symposium, The use of KC in the treatment of coccidioidomycosis has been recently reviewed in detail, 2 gjid parallel reviews of the indications for coccidioidomycosis treatment in general, 5 and the use of AMB and miconazole (MC) 5 in particular have been presented. 

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