Synthesis and Inhibition Studies of Sulfur-Substituted Squalene Oxide Analogues as Mechanism-Based Inhibitors of 2,3-Oxidosqualene−Lanosterol Cyclase

• Published in: Journal of medicinal chemistry 1997-01, Vol.40 (2), p.201-209
• Main Authors: Stach, Dirk, Zheng, Yi Feng, Perez, Alice L, Oehlschlager, Allan C, Abe, Ikuro, Prestwich, Glenn D, Hartman, Peter G
• Format: Article
• Language: English
• Subjects: Analytical, structural and metabolic biochemistry; Animals; Biological and medical sciences; Enzyme Inhibitors - chemical synthesis; Enzyme Inhibitors - pharmacology; Enzymes and enzyme inhibitors; Fundamental and applied biological sciences. Psychology; Intramolecular Transferases; Isomerases - antagonists & inhibitors; Kinetics; Liver - drug effects; Liver - enzymology; Molecular Conformation; Rats; Squalene - analogs & derivatives; Squalene - chemical synthesis; Squalene - pharmacology; Sulfur - chemistry; Swine; Transferases
• ISSN: 0022-2623; 1520-4804
• DOI: 10.1021/jm960483a

The synthesis and biological evaluation of three new sulfur-substituted 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 sulfur position in the OS skeleton was chosen to disrupt one or more key processes involved in cyclization:  (a) the folding of the B-ring into 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 oxidosqualene cyclases (OSC) were also examined for the previously reported S-19 analogue 4. The four analogues were potent inhibitors of mammalian OSCs (IC50 = 0.05−2.3 μM for pig and rat liver OSC) and fungal cell-free Candida albicans OSC (submicromolar IC50 values). In particular, the S-18 analogue 3 showed the most potent inhibition toward the rat liver enzyme (IC50 = 50 nM) and showed potent, selective inhibition against the fungal enzyme (IC50 = 0.22 nM, 10-fold more potent than the S-19 analogue 4). Thus, 3 is the most potent OSC inhibitor known to date. The K i values ranged from 0.5 to 4.5 μM for pig OSC, with 3 and 4 showing about 10-fold higher potency for rat liver OSC. Interestingly, the S-18 analogue 3 showed time-dependent irreversible inhibition with homogeneous pig liver OSC (k inact = 0.06 min-1) but not with rat OSC.