Despite the introduction of newer triazoles and echinocandins, invasive fungal infections (IFI's) including invasive candidiasis (IC) remain very difficult to treat with currently available antifungals. The annual cost burden of treating nosocomial fungal infections exceeds $2.6 billion a year in the United States alone. Worldwide, the annual incidence of IC is about 300,000. Children suffering from the most common pediatric cancer, acute leukocytic leukemia have an approximate 5% mortality rate; however, if the patient develops invasive candidiasis, their mortality rate increases 4 to 8 times to 20-40%. Currently, only three classes of antifungal drugs are employed to treat IC, and no new class has been introduced to the market for thirteen years. It has been widely recognized that antifungal treatments which address mechanisms of drug resistance and could be combined with existing therapeutics would provide a tremendous advantage over currently available treatments. Unfortunately, unlike cancer chemotherapy, there are relatively few treatment regimens that productively combine different antifungals to achieve better therapeutic outcomes and address drug resistance without the added burden of drug toxicity. Work performed in the lab of our colleague, Prof. Joe Heitman and others has revealed the tremendous therapeutic potential of inhibiting the fungal protein, calcineurin. Calcineurin inhibition compromises the cell wall stress response of Candida albicans, NCAC's, Aspergillus fumigatus, Cryptococcus neoformans, and other pathogenic fungi. Furthermore, when combined with triazoles, echinocandins, or allylamines, calcineurin inhibitors are highly synergistic and can reduce the MIC value by a factor of 50 or more. It has also been observed that resistant clinical isolates of C. albicans, A. fumigatus, and other fungi become susceptible to antifungal therapeutics when combined with a calcineurin inhibitor both in vitro and in vivo. However, the lack of a potent, antifungal calcineuin inhibitor that does not cause immunosuppression has hindered progress in exploiting this novel target. Moreover, calcineurin inhibitors are typically are large, structurally complex (>700 Daltons) molecules and this has hindered the facile creation of analogues for testing. Employing newly developed chemistry and structural insight, we propose developing a potent, non-immunosuppressive fungal calcineurin inhibitor, building on progress from our Phase I project. Aim 1. Generate closely related analogs of hits resulting from screens from Phase I. Aim 2. Characterize compounds in vitro for advancement. Iterate library as required. Aim 3. Characterize compounds in vivo for pharmacokinetics and efficacy.