29-Methylidene-2,3-oxidosqualene: a potent mechanism-based inactivator of oxidosqualene cyclase

Various (1E,3E)- and (1Z,3E)-conjugated methylthio derivatives of oxidosqualene (OS) and conjugated and non-conjugated phenylthio derivatives of OS were obtained. These compounds, designed as inhibitors of pig liver and Saccharomyces cerevisiae 2,3-oxidosqualene-lanosterol cyclases (OSC) (EC 5.4.99.7) and of Alicyclobacillus acidocaldarius squalene-hopene cyclase (SHC) (EC 5.4.99.-), contain the reactive function adjacent to carbons involved in the formation of the third and the fourth cycle during OS cyclization. All the new compounds are inhibitors of OSC and SHC, with various degrees of selectivity. The conjugated methylthio derivatives behaved as potent inhibitors of S. cerevisiae OSC, whereas most of the phenylthio derivatives were especially active toward SHC.

Section: Resultsmentioning

confidence: 90%

Conjugated methyl sulfide and phenyl sulfide derivatives of oxidosqualene as inhibitors of oxidosqualene and squalene‐hopene cyclases

Rocco

Bosso

Viola

et al. 2003

“…The inhibitors listed in Table 2 are derivatives of different length, bearing a vinylic function at position C-19 or C-2. The (18Z)-29-MOS 7 (10,14) and the (18E)-hexanor-29-MOS 9 (14), were effective time-dependent inhibitors of pig liver and yeast OSC. Abe and Prestwich (9), using [ 3 H]-(18Z)-29-MOS 7, have been able to label rat OSC, and Corey et al (11), using a mixture of the two E and Z isomers 9 and 10 succeeded in labeling yeast OSC.…”

Section: Resultsmentioning

confidence: 97%

Rationally designed inhibitors as tools for comparing the mechanism of squalene‐hopene cyclase with oxidosqualene cyclase

Viola

Ceruti

Cattel

et al. 2000

The inhibition of squalene-hopene cyclase (SHC) (E.C. 5.4.99.-), an enzyme of bacterial membranes catalyzing the formation of pentacyclic sterol-like triterpenes, was studied by using different classes of compounds originally developed as inhibitors of oxidosqualene cyclase (OSC) (E.C. 5.4.99.7), the enzyme of eukaryotes responsible for the formation of tetracyclic precursors of sterols. The mechanism of cyclization of squalene by SHC, beginning with a protonation of the 2,3 double bond by an acidic residue of the enzyme, followed by a series of electrophilic additions of the carbocationic intermediates to the double bonds, is similar to the mechanism of cyclization of 2,3-oxidosqualene by OSC. The inhibitors studied included: (i) analogs of the carbocationic intermediates formed during cyclization, such as aza-analogs of squalene and 2,3-oxidosqualene; (ii) affinity-labeling inhibitors bearing a methylidene reactive group; and (iii) vinyldioxidosqualenes and vinylsulfide derivatives of the substrates. Comparison of the results obtained with the two enzymes, SHC and OSC, showed that many of the most effective inhibitors of OSC were also able to inhibit SHC, while some derivatives acted as specific inhibitors. Differences could be easily explained on the basis of the different substrate specificity of the two enzymes.

“…The closure of the last ring and the rearrangement are probably differently controlled in different OSC, as the 19-aza-derivative is very active only against pig liver OSC. The 29-methylidene derivatives 4-7, previously shown to be time-dependent inhibitors (16,22), similarly lack specificity.…”

Section: Discussionmentioning

confidence: 94%

“…Basically, three types of inhibitors were studied: analogs of the carbocationic intermediates, as the azasqualenes (15,18); oxidosqualene derivatives bearing a conjugated methylidene group, designed as affinity-labeling inhibitors (16,22); and vinyl sulfide, and conjugated vinyl sulfide derivatives of oxidosqualene, very effective inhibitors of yeast OSC (17,19,20), (Fig. 2).…”

mentioning

confidence: 99%

Analogs of squalene and oxidosqualene inhibit oxidosqualene cyclase of Trypanosoma cruzi expressed in Saccharomyces cerevisiae

Oliaro‐Bosso

Ceruti

Balliano

et al. 2005

ABSTRACT:Recently, a number of inhibitors of the enzyme oxidosqualene cyclase (OSC; EC 5.4.99.7), a key enzyme in sterol biosynthesis, were shown to inhibit in mammalian cells the multiplication of Trypanosoma cruzi, the parasite agent of Chagas' disease. The gene coding for the OSC of T. cruzi has been cloned and expressed in Saccharomyces cerevisiae. The expression in yeast cells could be a safe and easy model for studying the activity and the selectivity of the potential inhibitors of T. cruzi OSC. Sterols are eukaryotic membrane components that are necessary to support cell growth and differentiation. Sterol biosynthesis is a well-established chemotherapeutic target in pathogenic eukaryotes, such as fungi (1,2). The final product of the sterol biosynthetic pathway in fungi is the 24-alkyl sterol ergosterol. Ergosterol or similar 24-alkyl sterols are also the final products of the sterol synthetic pathway of some pathogenic protozoa including Trypanosoma species. These organisms cannot completely substitute these sterols with the cholesterol biosynthesized in host mammalian cells and need to synthesize at least some of their own distinctive sterols (3-5). This dependence on sterols suggests that sterol biosynthesis inhibitors may be useful antiprotozoal drugs. The sterol biosynthetic pathway ( Fig. 1) offers many potential targets for therapeutic purposes. Many effective antifungal drugs already in use act by inhibiting different enzymes of sterol biosynthesis; the allylamine antifungal drug terbinafine inhibits squalene epoxidase (6), and azole drugs such as ketoconazole and itraconazole are inhibitors of lanosterol C 14 -demethylase (7). The activity of these inhibitors can be explained as a consequence either of depletion of the ergosterol or of accumulation of toxic intermediates or side products. In addition to the antifungal activity, some of these compounds Acetyl-CoAwere shown to inhibit the growth of Trypanosoma and other kinetoplastid parasites (8). Kinetoplastid parasites have also been shown recently to be susceptible to inhibitors of squalene synthase (9,10) and oxidosqualene cyclase (11,12). The enzyme oxidosqualene cyclase (OSC; EC 5.4.99.7), which catalyzes the formation of the first cyclic precursor of sterols, is considered a good target for the inhibition of sterol biosynthesis in both humans and fungi. Many inhibitors, designed on the basis of the complex cyclization mechanism of OSC (13), are active on the enzyme and have been investigated as potential cholesterol-lowering or antifungal drugs (1,2,13). The recent crystallization of human OSC as a complex with the potent inhibitor RO48-8071 opens the way to new structurebased studies of the cyclization mechanism (14).We have designed and tested against mammalian and fungal OSC many acyclic substrate analogs modified either to mimic the high-energy carbocationic intermediates (compounds 1-3 of Fig. 2) or to bear reactive functions able to interact with the active site residues, as the methylidene (compounds 4-8), vinyl sulfide (compounds 9...