A novel class of 2-(4-heterocyclylphenyl)-1,4-dihydropyridines (2-38) possessing antagonist activity against platelet activating factor (PAF) was prepared by the Hantzsch synthesis from a variety of ethyl 4'-heterocyclic-substituted benzoylacetates, aryl or heteroaryl aldehydes, and substituted 3-aminocrotonamides or 3-aminocrotonate esters. Structure-activity relationships were evaluated where PAF antagonist activity was measured in vitro by determining the concentration of compound (IC50) required to inhibit the PAF-induced aggregation of rabbit washed platelets, and in vivo by determining the oral dose (ED50) which protected mice from a lethal injection of PAF. The nature of the substituent at the dihydropyridine 2-position was found to be important for both in vitro and in vivo activity, whereas there was greater flexibility for structural variation at the 4- and 5-positions. The most potent compound was 4-(2-chlorophenyl)-1,4-dihydro-3-(ethoxycarbonyl)-6-methyl-2-[4-(2- methylimidazo[4,5-c]pyrid-1-yl)phenyl]-5-[N-(2- pyridyl)carbamoyl]pyridine (17, UK-74,505), IC50 = 4.3 nM, ED50 = 0.26 mg/kg po, which was found to be approximately 33 times more potent in vitro (rabbit platelet aggregation) and about 8 times more potent in vivo (murine lethality) than WEB2086. Compound 17 also exhibited a long duration of action in the dog (inhibition of PAF-induced whole blood aggregation ex vivo was maintained for greater than 24 h following a single oral dose of 75 micrograms/kg) and was highly selective as a PAF antagonist, showing only weak affinity (IC50 = 6600 nM) for the [3H]nitrendipine binding site. As a result of its high oral potency, selectivity, and duration of action, UK-74,505 has been selected for clinical evaluation.

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The therapeutic potential of UK-49,858, a difluorophenyl bis-triazole derivative, has been assessed by evaluating its activity against systemic infections with Candida albicans in normal mice and rats and in mice with impaired defence mechanisms, against vaginal infections with C. albicans in mice, and against dermal infections with Trichophyton mentagrophytes in guinea pigs. Orally administered ketoconazole was used as a comparative agent throughout, and parenterally administered amphotericin B was included in the study of C. albicans systemic infection in normal mice. The activity of UK-49,858 given orally to mice or rats infected systemically with C. albicans was far superior to that of ketoconazole. In addition, UK-49,858 showed activity comparable to that of amphotericin B when given parenterally, although the latter gave more prolonged protection. UK-49,858 was also effective orally in curing experimental candidal vaginitis in mice and trichophytosis in guinea pigs, against which it was approximately 10 times more active than ketoconazole. These data suggest that UK-49,858 may be of value in the treatment of both C. albicans and dermatophyte fungal infections in man.

UK-49,858 (fluconazole), a new, orally absorbed bis-triazole derivative, has been evaluated against systemic infections with Candida albicans in normal and immunosuppressed mice and against an intestinal infection with C. albicans in immunosuppressed mice. Orally administered ketoconazole was used as a comparison agent throughout, and orally administered amphotericin B was included for comparative in the experimental intestinal infection. In a 10-day dosage regimen, UK-49,858 was far more active than ketoconazole against systemic infections with C. albicans in normal and immunosuppressed mice. In normal mice, extension of UK-49,858 dosing to 30 days resulted in prolongation of survival to over 90 days, and up to 60% of treated animals had no detectable C. albicans in their kidneys. In addition, over 90% of mice with intestinal candidiasis had culture-negative feces after a 3-day treatment with UK-49,858, but only 62 and 23% of mice gave this response after amphotericin B and ketoconazole therapy, respectively. These data suggest that UK-49,858 may be of value in the treatment of systemic and gastrointestinal infections due to C. albicans in humans.The high morbidity and mortality caused by opportunistic systemic fungal infections (10, 12), their increasing incidence (2, 3), and the lack of safe, effective therapy (4, 11, 18) has prompted a search for safer and more effective drugs. UK-49,858 (fluconazole) is a new bis-triazole derivative, developed at Pfizer Ltd., which has been reported (15) to exhibit superior efficacy to that of ketoconazole in fulminating systemic candidiasis (107 CFU per animal) of normal and immunosuppressed animals as well as in superficial infections (15). Candida albicans is the most common opportunistic fungal pathogen (9,12,22), and so we have examined UK-49,858 in comparison with ketoconazole in less rapidly progressing but still lethal systemic infections (104 to 105 CFU per animal) and with ketoconazole and amphotericin B in a gastrointestinal infection in mice.MATERIALS AND METHODS Fungi. C. albicans Y0102 from the Pfizer culture collection (Pfizer Central Research, Sandwich, Kent, England) was stored freeze-dried or under liquid nitrogen, and when needed fresh cultures were grown on Sabouraud dextrose agar for 24 h at 28°C. This isolate is a standard test strain used in our laboratory and responds to azoles in a manner typical of other isolates (9, 15). Inocula for the in vivo models were prepared from washed blastospores in saline, standardized by turbidimetry with an absorptiometer (Evans Electroselenium Ltd., Halstead, England), and checked by hemocytometer counts.

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