Metabolism of 24,25-dihydrolanosterol analogs by partially purified cytochrome P-450(14DM) from rat liver microsomes

27-Nor-24,25-dihydrolanosterol (27-nor-DHL), 26,27-dinor-24,25- dihydrolanosterol (26,27-dinor-DHL), and 25,26,27-trinor-24,25-dihydrolanosterol (25,26,27-trinor-DHL), analogs of 24,25-dihydrolanosterol (DHL) which have no C-27 carbon, C-26,27 carbons and C-25,26,27 carbons, were converted to the corresponding 14-demethylated products using a reconstituted monooxygenase system from rat liver microsomes which contained cytochrome P-450(14DM) catalyzing lanosterol 14-demethylation and reduced nicotinamide adenine dinucleotide phosphate (NADPH)-cytochrome P-450 reductase in the presence of NADPH and molecular oxygen. Each metabolite showed a relative retention time (RtR) of 0.72 with respect to each substrate in high-performance liquid chromatography (HPLC) on a reversed-phase column. Comparison of each gas chromatography-mass spectrum and RtR value with those of the metabolite of DHL, 4,4-dimethyl-5 alpha-cholesta-8,14-dien-3 beta-ol, indicated that the metabolites could be inferred to be 27-nor-4,4-dimethyl-5 alpha-cholesta-8,14-dien-3 beta-ol, 26,27-dinor-4,4- dimethyl-5 alpha-cholesta-8,14-dien-3 beta-ol, and 25,26,27-trinor-4,4-dimethyl-5 alpha-cholesta-8,14-dien-3 beta-ol. However, 24,25,26,27-tetranor- and 23,24,25,26,27-pentanor analogs of DHL and 20-iso-24,25-dihydrolanosterol were not metabolized by the reconstituted enzyme system.     

Effects of 32-oxygenated lanosterol derivatives on 3-hydroxy-3-methylglutaryl coenzyme A reductase activity and cholesterol biosynthesis from 24,25-dihydrolanosterol.

The effects of 32-oxygenated lanosterol derivatives on 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase activity and cholesterol biosynthesis from [24,25-3H]24,25-dihydrolanosterol were studied. Among the derivatives, 3 beta-hydroxylanost-7-en-32-oic acid was the most active in depressing HMG-CoA reductase activity (IC50: 0.7 microM) and cholesterol biosynthesis (IC50: 0.4 microM) from 24,25-dihydrolanosterol.     

Synthesis of 15alpha-fluoro-24,25-dihydrolanosterol as a potential inhibitor and/or mechanistic probe for lanosterol 14alpha-demethylase

As a potential inhibitor and/or mechanistic probe for lanosterol 14alpha-demethylase, 15alpha-fluoro-24,25-dihydrolanosterol was prepared by fluorination of 15alpha-hydroxy-24,25-dihydrolanost-7-en-3beta-yl benzoate with diethylaminosulfur trifluoride, followed by hydrogen chloride-catalyzed isomerization of the delta7 to delta8 and reductive cleavage of the benzoate.     

Detection of the enzymatic activity of cytochrome P-450 enzymes by high-performance liquid chromatography.

The reactions catalysed by the various cytochrome P-450 enzymes are reviewed with respect to the analysis of products by high-performance liquid chromatography (HPLC). Especially biotransformation reactions of purified cytochrome P-450 enzymes in a reconstituted system and in microsomes mainly of rat liver origin are considered. Emphasis is put on the specificity of product formation due to the individual isozymes of cytochrome P-450. It is shown that the presence of eight cytochrome P-450 isozymes can be monitored and determined by specific product formation after HPLC analysis, which is an important parameter in toxicological studies.     

Inhibitory effect and interaction of stanozolol with pig testicular cytochrome P-450 (17 alpha-hydroxylase/C17,20-lyase)

The inhibitory effect of an anabolic steroid, stanozolol, on testicular microsomal cytochrome P-450 (17 alpha-hydroxylase/C17,20-lyase) (P-450(17 alpha/lyase] and the nature of the interaction were compared with those of other anabolic steroids, furazabol and mestanolone. Stanozolol markedly inhibited delta 16-C19-steroid synthesizing activity, 17 alpha-hydroxylase and C17,20-lyase activities, which were mediated by oxygenase activities of testicular microsomal cytochrome P-450(17 alpha/lyase). In addition, stanozolol was a competitive inhibitor of 17 alpha-hydroxylase (Ki = 6.31 microM) and C17,20-lyase (Ki = 1.30 microM) activities in the reconstituted enzyme system. The interaction of cytochrome P-450&17 alpha/lyase) with stanozolol induced a type I difference spectrum (peak at 387 nm and trough at 418 nm) with a dissociation constant (Ks) of 1.47 microM.     

1,2,3-Triazole incorporated coumarin derivatives as potential antifungal and antioxidant agents

A series of novel ethyl-7-((1-(benzyl)-1H-1,2,3-triazol-4-yl)methoxy)-2-oxo-2H-chromene-3-carboxylates 8a-h as potential antifungal agents were synthesized via click chemistry. The antifungal activity was evaluated against five human pathogenic fungal strains, such as Candida albicans, Fusarium oxysporum, Aspergillus flavus, Aspergillus niger and Cryptococcus neoformans. Compound 8c, 8d, 8e and 8h were found to be equipotent against C. albicans when compared with miconazole and compound 8f was found to be two-fold more active compared with miconazole and equipotent to fluconazole against C. albicans. The coumarin-based triazole derivatives were also evaluated for antioxidant activity and compound 8a was found to be potent antioxidant when compared with standard drug. Furthermore, molecular docking study of the newly synthesized compounds was performed and results showed good binding mode in the active site of fungal C. albicans enzyme P450 cytochrome lanosterol 14α-emethylase. Moreover, the synthesized compounds were also analyzed for ADME properties and showed potential to build up as good oral drug candidates.     

Oxidative transformations of labdane diols. III. Preparation of acids with a strobane skeleton from larixol

It has been shown that the oxidation of larixol with chromic acid mixture forms methyl 6-oxo-8α,13α-epoxystroban-14β-oate, methyl 6-oxo-8α,13α-epoxystroban-14α-oate, and 6,13-dioxo-14,15-bisnorlabd-7-en-17-oate.     

Alkene epoxidation catalyzed by cytochrome P450 BM-3 139-3

We recently reported conversion of cytochrome P450 BM-3, a medium-chain (C₁₂-C₁₈) fatty acid monooxygenase, into a highly efficient alkane hydroxylase by directed evolution [Nat. Biotechnol. 2002, 20, 1135]. P450 BM-3 mutant 139-3 exhibited high activity towards a variety of fatty acid and alkane substrates, including C₃-C₈ alkanes. We report here that mutant 139-3 is also active on benzene, styrene, cyclohexene, 1-hexene, and propylene. Benzene is converted to phenol, while styrene is converted to styrene oxide. Propylene oxidation generates only propylene oxide, but cyclohexene oxidation produces a mixture of cyclohexene oxide (85%) and 2-cyclohexene-1-ol (15%), and 1-hexene is converted to the allylic hydroxylation product, 1-hexene-3-ol. Initial rates of NADPH oxidation for 139-3 in the presence of the substrates greatly (17- to >100-fold) surpass the wild-type in all cases. However, NADPH consumption is only partially coupled to product formation (14-79%). This cytochrome P450 epoxidation catalyst is a suitable starting point for further evolution to improve coupling and activity.     

Two-step purification of cytochrome P-450 from rat liver microsomes using high-performance liquid chromatography

Cytochrome P-450 from rat liver microsomes treated with phenobarbital (PB) was separated into six fractions, as was cytochrome P-450 treated with 3-methylcholanthrene (MC), by high-performance liquid chromatography (HPLC) with an anion-exchange column. PB and MC induced three forms and one form of cytochrome P-450, respectively. The major forms induced by PB and by MC were further purified to apparent homogeneity based on sodium dodecyl(lauryl)sulphate--polyacrylamide gel electrophoresis by HPLC using a hydroxyapatite column. These new HPLC techniques are simple, rapid and useful for the purification of major forms of cytochrome P-450 from solubilized microsomes.     

Biocatalytic asymmetric hydroxylation of hydrocarbons with the topsoil-microorganism Bacillus megaterium

A Bacillus megaterium strain was isolated from topsoil by a selective screening procedure with allylbenzene as a xenobiotic substrate. This strain performed the hydroxylation chemoselectively (no arene oxidation and overoxidized products) and enantioselectively (up to 99% ee) in the benzylic and nonbenzylic positions of a variety of unfunctionalized arylalkanes. Salycilate and phenobarbital, which are potent inducers of cytochrome P-450 activity, changed the regioselectivity of the microbial CH insertion, without an effect on the enantioselectivity. The biotransformation conditions were optimized in regard to product yield and enantioselectivity by variation of the oxygen-gas supply and the time of the substrate addition. The different product distributions (alpha- versus beta-hydroxylated product) that are obtained on induction of cytochrome P-450 enzyme activity demonstrate the involvement of two or more hydroxylating enzymes with distinct regioselectivities in this biotransformation. An oxygen-rebound mechanism is assumed for the cytochrome P-450-type monooxygenase activity, in which steric interactions between the substrate and the enzyme determine the preferred face of the hydroxy-group transfer to the radical intermediate.     

24-亚甲基胆甾-5-烯-3β,19-二醇的合成

从豆甾醇出发,通过10步反应,合成得到具有显著细胞毒活性的24-亚甲基胆甾-5-烯-3β,19-二醇(1),总产率为16%.目标产物1的熔点、[α]值和波谱数据与天然产物一致.化合物1的合成是首次报道,它对人体鼻咽癌(CN2)和胃癌(Mgc803)细胞有显著抑制活性.     

Photooxidative dehydrogenation of Δ8-drimen-and Δ8-11-homodrimen-7-ones into α,α ′-dienones

An efficient two-step procedure for photooxidative dehydrogenation of drimane and 11-homodrimane compounds containing an 8-en-7-one structural unit into α,α′-dienones was elaborated. The method is based on the transformation of ketones into the respective enol acetates followed by photosensitized oxygenation. Methyl 7-oxo-11-homodrima-5,8-dien-12-oate, 5,6-dehydro-7-ketoisodrimenine, 11-acetoxydrima-5,8-dien-7-one and 11,12-diacetoxydrima-5,8-dien-7-one were prepared in high yields starting from methyl 7-oxo-11-homodrim-8-en-12-oate, 7-oxoisodrimenine, 11-hydroxydrim-8-en-7-one and 11,12-diacetoxydrim-8-en-7-one, respectively. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 678–682, April, 2006.     

Triazole antifungals. II. Synthesis and antifungal activities of 3-acyl-4-methyloxazolidine derivatives

Triazole compounds with an oxazolidine ring were designed and synthesized as a potential inhibitor of the fungal cytochrome P450 14 alpha-demethylase. In testing for antifungal activity against a mouse systemic Candida albicans infection, (4R,5R)-3-acyl-4-methyloxazolidine derivatives 4 exhibited remarkably high efficacy after oral or parenteral dosing. The potent activity of 4 is hypothesized to be a consequence of a structural similarity between 4 and lanosterol, a target molecule of the cytochrome P450 14 alpha-demethylase. Highly stereoselective synthesis of these oxazolidines is also described.     

Three-dimensional quantitative structure-activity relationship (QSAR) and receptor mapping of cytochrome P-450(14 alpha DM) inhibiting azole antifungal agents

Molecular modeling was performed by a combined use of conformational analysis and 3D-QSAR methods to distinguish structural attributes common to a series of azole antifungal agents. Apex-3D program was used to recognize the common biophoric structural patterns of 13 diverse sets of azole antifungal compounds demonstrating different magnitudes of biological activity. Apex-3D identified three common biophoric features significant for activity: N1 atom of azole ring, the aromatic ring centroid 1, and aromatic ring centroid 2. A common biophore model proposed from the Apex-3D analysis can be useful for the design of novel cytochrome P-450(14 alpha DM) inhibiting antifungal agents.     

Engineering cytochrome P-450s

Cytochrome P-450 isozymes represent a critical component of nature’s spectrum of detoxification catalysts that could be exploited for bioremediation. The ethanol-inducible human cytochrome P-450 2E1 serves as a model eukaryotic P-450 that complements the bacterial P-450 cam in dehalogenation and detoxification of environmental pollutants. We explored the construction of novel chimeric P-450s using cytochrome P-450 camC and 2E1 genes. For construction of chimera 1 (478 amino acids, 55.14 kDa), 145 amino acids from the N-terminus of P-450 2E1 protein (493 amino acids, 56.84 kDa) were replaced with 130 amino acids from the N-terminus of P-450 camC protein (415 amino acids, 46.66 kDa). In chimera 2 (525 amino acids, 60.24 kDa) the strategy involves replacement of 28 amino acids in the C-terminus of chimera 1 with 75 amino acids from the C-terminus of P-450 camC gene. Homology models of both the chimeric proteins were developed using SWISS-MODEL based on the known crystal structure of cytochrome P-450 camC, BM-3, 1DT6A, and 2C17A. The models indicated that the proposed heme-binding site was intact, which is inevitable for catalytic activity of cytochrome P-450s. The expression of chimera 1 and 2 genes in Escherichia coli DH5α was evident from light-pink cell pellets, protein band in sodium dodecyl sulfate polyacrylamide gel electrophoresis, and diagnostic carbon monoxide-difference spectra. Our studies show that strategies can be developed to exploit the natural diversity of the P-450 superfamily to generate chimeric biocatalysts that would provide new templates amenable to directed evolution.     

Chemie der Pleuromutiline,IX. Konfigurationsumkehr der Methylgruppe am Kohlenstoff 6 im tricyclischen Gerüst des Diterpens Pleuromutilin

The contact of pleuromutilin derivatives with the protein moiety of cytochrome P-450 as well as its orientation towards the heme iron is mainly dependent on the steric environment of the hydrindanone-part of the tricyclus. The apparent affinity between substrate and enzyme, which is correlated with the rate of metabolism can be reduced by inversion of configuration at carbon 6. This inversion is achieved by equilibrating the diastereomeric ketones12 and13 followed by a selective reduction of the keto group at position 7. The 6-methylgroup of14 was assigned α-configuration on the basis of spectroscopic data in comparison to those of the naturally configurated compound14a.     

Tyrosine phosphatase and cytochrome P450 activity are critical in regulating store-operated calcium channels in human fibroblasts

Diverse signaling pathways have been proposed to regulate store-operated calcium entry (SOCE) in a wide variety of cell types. However, it still needs to be determined if all of these known pathways operate in a single cell type. In this study, we examined involvement of various signaling molecules in SOCE using human fibroblast cells (HSWP). Bradykinin (BK)-stimulated Ca2+ entry, previously shown to be via SOCE, is enhanced by the addition of vanadate, an inhibitor of tyrosine phosphatases. Furthermore, SOCE is regulated by cytochrome P-450, as demonstrated by the fact that the products of cytochrome P-450 activity (14,15 EET) stimulated SOCE while econazole, an inhibitor of cytochrome P450, suppressed BK-stimulated Ca2+ entry. In contrast, Ca2+ entry was unaffected by the guanylate cyclase inhibitor LY83583, or the membrane permeant cyclic GMP analog 8-bromo-cyclic GMP (8-Br-cGMP). Neither nitric oxide donors nor phorbol esters affected BK-stimulated Ca2+ entry. SOCE in HSWP cells is primarily regulated by tyrosine phosphorylation and the cytochrome P-450 pathway, but not by cyclic GMP, nitric oxide, or protein kinase C. Thus, multiple pathways do operate in a single cell type leading to the activation of Ca2+ entry and some of these signaling pathways are more prominently involved in regulating calcium entry in different cell types.     

An NH2-terminal truncated cytochrome P450 CYP3A4 showing catalytic activity is present in the cytoplasm of human liver cells

Cytochrome P450 3A4 (CYP3A4), is the dominant human liver hemoprotein enzyme localized in the endoplasmic reticulum (ER), and is responsible for the metabolism of more than 50% of clinically relevant drugs. While we were studying CYP3A4 expression and activity in human liver, we found that anti-CYP3A4 antibody cross-reacted with a lower band in liver cytoplasmic fraction. We assessed the activities of CYP3A4 and its truncated form in the microsomal and cytoplasmic fraction, respectively. In the cytoplasmic fraction, truncated CYP3A4 showed catalytic activity when reconstituted with NADPH-cytochrome P-450 reductase and cytochrome b5. In order to determine which site was deleted in the truncated form in vitro, we transfected cells with N-terminal tagged or C-terminal tagged human CYP3A4 cDNA. The truncated CYP3A4 is the N-terminal deleted form and was present in the soluble cytoplasmic fraction. Our result shows, for the first time, that N-terminal truncated, catalytically active CYP3A4 is present principally in the cytoplasm of human liver cells.     

Regio- and stereoselective introduction of 15β-hydroxy group and side chains to steroids by the palladium-catalyzed reaction of 1,3-diene monoepoxide

The Pd-catalyzed reaction of 1,3-diene monoepoxides with carbonucleophiles is applied to the regio- and stereoselective introduction of 15β-hydroxy group and side chains to steroid nuclei. 3β-Hydroxyandrost-5-en-17-one (15) was converted to 15,16β-epoxy-Δ¹⁷⁽²⁰⁾ isoheptylidene steroid 20 and ethylidene steroid 21. The former was subjected to the Pd-catalyzed reaction with dimethyl malonate and then converted to 15β-hydroxycholesterol (29). Similarly, 15β-hydroxyisocholesterol (32) was obtained from the ethylidene steroid 21 using the Pd-catalyzed reaction of methyl 3-oxo-5-methylhexanoate (24) as a key reaction.     

Chemiluminescence detection of haem-containing microsomal proteins

In the purification and characterization of cytochrome P-450 isoenzymes from rat liver microsomes, a luminol-mediated chemiluminescence in microsomes after addition of peroxides was discovered. The pH dependence of the kinetics of the chemiluminescence reaction was investigated and the reactions conditions were optimized with respect to the peroxide and luminol concentrations. The detection limits appear to be a factor of 10³ lower than those obtained with other techniques. The speed of detection was also improved substantially. The nature of the strong chemiluminescence was further investigated by (partial) purification of the cytochrome P-450 isoenzymes. It appeared that the chemiluminescence activity was closed related to the presence of cytochrome P-450.