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The microsomal mixed function oxidase system contains the cytochrome P-450 oxidative drug metabolizing family of enzymes, The catalytic cycle of cytochrome P-450 is believed to involve the formation of an active iron-oxygen species which is responsible for oxygen transfer to the substrate. This assumption is supported by the fact that a number of peroxidative agents can replace NADPH, the reductase, and oxygen as co-reactants in most oxidative reactions of microsomal cytochrome P-450. We have found that a mixture of either ferrous or ferric ions with hydrogen peroxide (Fenton and Ruff reagents) can serve as biomimetic models for cytochrome P-450 in hydroxylation, exposidation, sulfoxidation, and N-demethylation of various drugs. The existance of an iron-oxo active species in both Fenton and Ruff type reactions has been postulated and provides reaction cycles similar to those of cytochrome p-450.Other model systems for the hepatic hydroxylation and epoxidation using transition metal complexes with porphyrin are also discussed.The present paper reviews the various biomimetic models of the heme cytochrome P-450 and emphasizes their simulation of hepatic drug metabolism and their potential medical and industrial applications.KEY WORDS Biomimetic models Cytochrome P-450 Drug metabolism
The microsomal mixed function oxidase system contains the cytochrome P-450 oxidative drug metabolizing family of enzymes, The catalytic cycle of cytochrome P-450 is believed to involve the formation of an active iron-oxygen species which is responsible for oxygen transfer to the substrate. This assumption is supported by the fact that a number of peroxidative agents can replace NADPH, the reductase, and oxygen as co-reactants in most oxidative reactions of microsomal cytochrome P-450. We have found that a mixture of either ferrous or ferric ions with hydrogen peroxide (Fenton and Ruff reagents) can serve as biomimetic models for cytochrome P-450 in hydroxylation, exposidation, sulfoxidation, and N-demethylation of various drugs. The existance of an iron-oxo active species in both Fenton and Ruff type reactions has been postulated and provides reaction cycles similar to those of cytochrome p-450.Other model systems for the hepatic hydroxylation and epoxidation using transition metal complexes with porphyrin are also discussed.The present paper reviews the various biomimetic models of the heme cytochrome P-450 and emphasizes their simulation of hepatic drug metabolism and their potential medical and industrial applications.KEY WORDS Biomimetic models Cytochrome P-450 Drug metabolism
Reactions of trans-stilbene, cis-stilbene, 5H-dibenzo [a,d] cyclo-heptene 5-one and 5H-dibenz [b,f] azepine (iminostilbene) with Fenton reagent [Fe (II)/H2O2] clearly simulate their hepatic metabolism. Expoxidation on the corresponding ethylenic linkage was found to be a common pathway of these compounds. Epoxides of trans-stilbene, cis-stilbene, and 5H-dibenzo[a,d]cycloheptene 5-one were further oxidized to dihydrodiols, alpha-hydroxyketones, diketones, and finally cleavage of the ethylenic bonds to the formation of the corresponding aldehydes. However, the unstable epoxide of iminostilbene gave 9-acridinecarbaldehyde that is further oxidized to 9-acridone. Reaction of both trans- and cis-stilbene with Ruff reagent [Fe III)/H2O2] gave the same oxidative products to that obtained from Fenton reagent. The radical scavenger 2,6 bis (1,1-dimethylethyl)-4-methyl phenol (BHT) decreases the total yield conversion and increases the formation ratio of both cis-epoxide and d,l-hydrobenzoin from cis-stilbene.
Das intermediare Auftreten von 4.5-Dehydro-2.3 ; 6.7-dibenzo-cycloheptatrienon (11) wird anhand kinetischer und praparativer Untersuchungen diskutiert. 11 l5Rt sich mit Dienen und nucleophilen Partnern in guten Ausbeuten abfangen. C = C-Dreifachbindungen in Siebenringen beanspruchen besonderes Interesse, da alle Versuche zur Isolierung von Cycbheptin bislang fehlschlugen, wiihrend das bereits merklich gespannte Cyclooctinz) noch in Substanz erhalten werden konnte. Wenn auch das siebengliedrige Cycloalkin als solches noch nicht gefaat wurde, so dad auf Grund der Arbeiten von G. WIITIG doch als gesichert angesehen werden, daB Cycloheptin3) und neuerdings auch Benzocycloheptenin4) sowohl bei der Oxydation des entsprechenden 1 .ZBis-hydrazons als auch bei der Enthalogenierung des 1.2-Dibrom-cycloheptens als kurzlebige Zwischenstufen auftreten.In diesem Zusammenhang interessieren ebenfalls die Arbeiten japanischer Autoren, die bei der Einwirkung von Basen auf 3-Halogen-tropolone ,,cine"-Substitutionen~) nachwiesen und j.q-Dehydro-rropolon6) diskutierten, wobei ein Vergleich mit Dehydrobenzol besonders reizvoll erscheint. Aus der uns zuganglichen Literatur geht jedoch nicht eindeutig hervor, inwieweit andere, in diesem besonderen Fall denkbare Mechanismen mit Sicherheit ausgeschlossen werden konnten7). Einfache Halogentropone durften dagegen wegen ihrer leichten Isomerisierbarkeit zu Benzoedurederivaten fur entsprechende Umsetzungen wenig geeignet sein7).Die vorliegende Arbeit, die sich mit dem Nachweis des 4.5-Dehydro-2.3; 6.7-dibenzo-cyclohepfafrienons (It) befafit, ergab sich ursprunglich aus einem synthetischen Problem, das beim 1)
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