Novel High Energy Intermediate Analogues with Triazasterol-Related Structures as Potential Inhibitors of the Ergosterol Biosynthesis II [1]. Optimization of the Synthesis of 1,6,7,11b-Tetrahydro-2Hpyrimido[4,3-a] isoquinolin-4-amines as Parent Compounds of Novel 8,13,15-Triazasteroids

Summary.

Various routes for an effective synthesis of 1,6,7,11b-tetrahydro-2H-pyrimido[4,3-a]isoquinolin-4-amine and its 9-methoxy derivative, which were designed as tricyclic triaza-analogues with stable positive charge to mimic carbocationic high energy intermediates (HEI) of the ergosterol biosynthesis, were investigated. Starting from β-phenylethylamines the corresponding 3-chloro-N-phenethylpropionamides were prepared and transformed into N-phenethyl-3-phthalimidopropionamides. These amides were cyclized via Bischler-Napieralski reaction to yield after hydrolytic deprotection 1-(aminoethyl)tetrahydroisoquinolines. The 1,6,7,11b-tetrahydro-2H-pyrimido[4,3-a]isoquinoline ring system was then built up by condensation of the bicyclic diamines with various carbonic acid derivatives (carbon disulfide, nitroguanidine, tetraethyl orthocarbonate). Along with the applied reaction sequences unexpected side reactions took place. The structures of all isolated compounds were proven and completely assigned on the basis of homo- and heteronuclear correlated 1D and 2D NMR experiments. The in vitro antifungal susceptibility tests with a standard panel of eight pathogenic fungi revealed only weak antimycotic effects of the pyrimidoisoquinolinamine salts, but strong inhibitory activity of the intermediate 1-(aminoethyl)-3,4-dihydroisoquinoline.