Novel high energy intermediate analogues with triazasterol-related structures as inhibitors of ergosterol biosynthesis. III. Synthesis and antifungal activity of N4-alkyl-1,6,7,11b-tetrahydro-2H-pyrimido[4,3-a]isoquinolin-4-amine salts.

A series of N4-alkyl-1,6,7,11b-tetrahydro-2H-pyrimido[4,3-a]isoquinolinamine hydroiodides with triazasterol-related structures was designed and synthesized to mimic, as stable analogues, native high energy intermediates (HEI) of ergosterol biosynthesis. The title compounds can be regarded as 8,13,15-triaza-13,17-secosteroids with aromatic ring A bearing the positive charge in the guanidinium moiety. Hence, these compounds present structural similarities with corresponding carbocationic intermediates occurring during the enzyme catalyzed transformation of squalene into ergosterol. The N4-alkylaminopyrimidoisoquinolinium salts were prepared by reaction of respective S-methylthiotetrahydropyrimidoisoquinoline hydroiodides with octylamine, and appropriately methyl-branched alkyl- and alkenylamines. In order to prepare (3R)-6-isopropyl-3-methyl-6-hepten-1-amine several synthetic routes were investigated. The structures of all reported compounds were proved and completely assigned on the basis of homo- and heteronuclear correlated 1D and 2D NMR spectroscopy. The in vitro antifungal susceptibility tests of the title compounds with a standard panel of eight pathogenic fungi revealed especially against the used dermatophytes and yeasts with MICs in the range of 1-32 microg/ml moderate to good antimycotic effects. Depending on the nature of the N4-alkyl substituents structure-activity relationships were found with a maximum of antifungal efficacy of the N4-3,7-dimethyloctylaminopyrimidoisoquinolinium iodide.

Novel high energy intermediate analogues with a triazasterol structure as potential ergosterol biosynthesis inhibitors IV: antimicrobial activity of mono-, bi-, and tricyclic 8, 13, 15-triazasteroid analogues including the synthesis of novel 4-alkylamino- and 4-alkenylamino-9-hydroxypyrimidoisoquinolines.

4-alkylamino-and 4-alkenylamino-9-hydroxy-1, 6, 7, 11b-tetrahydro-2H-pyrimido[4, 3-a]isoquinolines were designed as inhibitory tricyclic triaza-analogues of carbocationic high energy intermediates (HEI) of enzymes involved in fungal ergosterol biosynthesis. Various routes for effective synthesis of 9-hydroxypyrimidoisoquinolines from 9-methoxythiones were investigated. The ether cleavage of 9-methoxy-pyrimidoisoquinolines, a key step in the synthesis, was carried out using various protocols. The structures of the obtained 9-hydroxy compounds were confirmed using homo- and hetero-nuclear correlated 1D and 2D NMR experiments. In vitro antifungal susceptibility tests of the alkylaminohydroxypyrimidoisoquinolines revealed weak to good antimycotic effects. The maximum antifungal efficacy was found for 4-[(3R)-6-isopropyl-3-methyl-6-heptenylamino]-9-hydroxypyrimidoisoquinoline. Furthermore, the in vitro activities of the newly synthesized 9-hydroxypyrimidoisoquinolines and of a series of prepared 8, 13, 15-triazasteroid analogues (N-alkyl-N'-(phenethyl- and cyclohexenylethyl)guanidines, N(2) -and N(2), 4-substituted imidazolin-2-amines, and N(4)-alkylaminopyrimidoisoquinolines) against representatives of gram-positive and gram-negative bacteria were investigated. The compounds showed significant antibacterial effects against gram-positive bacteria.