SYNTHESIS AND INHIBITION STUDIES OF SULFUR-SUBSTITUTED SQUALENE OXIDEANALOGS AS MECHANISM-BASED INHIBITORS OF 2,3-OXIDOSQUALENE-LANOSTEROLCYCLASE

The synthesis and biological evaluation of three new sulfur-substitute d oxidosqualene (OS) analogues (1-3) are presented. In these analogues , C-11, C-15, or C-18 in the OS skeleton was replaced by sulfur. The s ulfur position in the OS skeleton was chosen to disrupt one or more ke y processes involved in cyclization: (a) the folding of the B-ring int o a boat conformation, (b) the anti-Markovnikov cyclization leading to the C-ring, or (c) the formation of the D-ring during the lanosterol biosynthesis. Enzyme inhibition kinetics using homogeneous mammalian o xidosqualene cyclases (OSC) were also examined for the previously repo rted S-19 analogue 4. The four analogues were potent inhibitors of mam malian OSCs (IC50 = 0.05-2.3 mu M for pig and rat liver OSC) and funga l cell-free. Candida albicans OSC (submicromolar IC50 values). In part icular, the S-18 analogue 3 showed the most potent inhibition toward t he rat liver enzyme (IC50 = 50 nM) and showed potent, selective inhibi tion against the fungal enzyme (IC50 = 0.22 nM, 10-fold more potent th an the S-19 analogue 4). Thus, 3 is the most potent OSC inhibitor know n to date. The K-i values ranged from 0.5 to 4.5 mu M for pig, OSC, wi th 3 and 4 showing about 10-fold higher potency for rat liver OSC. Int erestingly, the S-18 analogue 3 showed time-dependent irreversible inh ibition with homogeneous pig liver OSC (h(inact) = 0.06 min(-1)) but n ot with rat OSC.