Substrate selectivity in epoxidation by metalloporphyrin and metallosalen catalysts carrying binding groups

Breslow, Ronald; Brown, Alan B.; McCullough, Richard D.; White, Peter W.

doi:10.1021/ja00194a067

Cited by 54 publications

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“…Furthermore this result is in line with our observation of reduced selectivity and conversion to product whenever a singly binding substrate was used in the epoxidation of alkenes (8) or in the hydroxylation of steroids by cyclodextrin based catalysts (11).…”

Section: Figsupporting

confidence: 89%

“…In an obvious extension of our previous work on epoxidation (8), we tried to oxidize steroid nicotinates. Unfortunately the FIG.…”

Section: Resultsmentioning

confidence: 99%

“…Now we are focusing our attention on the possibility of using metal coordination as the recognition element. Previous work from this laboratory showed that an olefin carrying auxiliary metal ligands is oxidized preferentially over a nonbinding one by an iron porphyrin with appended metal ligand groups in the presence of Cu 2+ ions (8). We decided to extend this approach to the selective hydroxylation of steroids by using a new manganese porphyrin carrying metal coordinating groups.…”

Section: Introductionmentioning

confidence: 99%

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Regioselective Oxidation of Steroids by a Manganese Porphyrin Carrying Metal Coordinating Groups

Belvedere

Breslow

2001

Bioorganic Chemistry

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Section: Figsupporting

confidence: 89%

“…In an obvious extension of our previous work on epoxidation (8), we tried to oxidize steroid nicotinates. Unfortunately the FIG.…”

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Regioselective Oxidation of Steroids by a Manganese Porphyrin Carrying Metal Coordinating Groups

Belvedere

Breslow

2001

Bioorganic Chemistry

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“…[35][36][37][38] An artificial enzyme system which perfectly illustrates the possibility to achieve high selectivity is the manganese porphyrin 7, which possesses four covalently linked peripheral -CDs (Figure 1c). [39][40][41][42][43] In the presence of iodosyl benzene, this tetramer is capable of selectively epoxidizing or hydroxylating stilbene derivatives. Its superior selectivity is best illustrated by the fact that it can regio-and stereoselectively oxidize the unactivated 6-CH 2 position in the B-ring of steroid derivative 8.…”

Section: Covalent Systemsmentioning

confidence: 99%

Self‐Assembled Nanoreactors

et al. 2005

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“…In our first study (21), metal binding groups were attached to the porphyrin or salen system, so that substrates carrying metal binding groups at both ends could coordinate to the catalysts through bridging metal ions. When two such coordinations occurred, to stretch the substrate across the central metal ion of the metalloporphyrin or metallosalen, a substrate double bond was catalytically epoxidized with turnover.…”

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confidence: 99%

An artificial cytochrome P450 that hydroxylates unactivated carbons with regio- and stereoselectivity and useful catalytic turnovers

Breslow

Huang

Zhang

et al. 1997

Proc. Natl. Acad. Sci. U.S.A.

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A catalyst has been synthesized comprising a manganese porphyrin carrying four beta-cyclodextrin groups. It catalyzes the hydroxylation of substrates of appropriate size carrying tert-butylphenyl groups that can hydrophobically bind into the cyclodextrin cavities. In one example as many as 650 catalytic turnovers are seen before the catalyst is oxidatively destroyed, and with a rate comparable to that of typical cytochrome P450 enzymes. In another example, a steroid derivative is regio-and stereoselectively hydroxylated at a single unactivated carbon atom, but more slowly and with fewer turnovers. The carbon attacked is not the most chemically reactive, and the selectivity is determined by the geometry of the catalyst-substrate complex. Nonbinding substrates are not reactive under the conditions used, and substrates with more f lexible binding geometries give more than a single product.Enzymes are remarkably selective catalysts. They bind a particular substrate out of a sea of available compounds in solution, then they perform a reaction at a particular position of the bound substrate (thus showing regioselectivity), often with stereoselectivity as well. The geometric control in the enzyme-substrate complex can completely dominate the normal reactivity of the substrate. For example, enzymes in the class cytochrome P450 can hydroxylate unactivated carbons in steroids while leaving much more reactive substrate positions, such as those in or next to double bonds, untouched (1-3). In these enzymes an oxygen atom becomes attached to the iron atom in the metalloporphyrin, and is then transferred to the substrate within the enzyme-substrate complex.Although it is of interest to learn how to mimic the great rate accelerations achieved in enzymatic catalysis, imitating the selectivity is even more important. For this reason, we have carried out studies over many years to learn how to use the geometric control typical of enzyme reactions in selectively functionalizing steroids and other substrates. In the earliest work, a benzophenone attached to a steroid was shown to perform selective photochemical functionalization of the substrate (4-11). In later work, a template attached to the substrate was able to direct free radical reactions to specific carbons because of the geometry of the template-substrate species; see refs. 12-14 for reviews. However, there were limitations to these methods.For one, the reagent or template was covalently attached to the substrate, so catalytic turnover was not possible. As a corollary of this, relatively simple reagents or templates were used-attached by a single flexible link-so the geometric control was not perfect. have shown that organization in a bilayer can be used to achieve hydroxylation of a steroid by a metalloporphyrin catalyst, but catalytic turnover was blocked by strong binding of the product. Grieco and colleagues (18-20) have also shown that a metalloporphyrin can hydroxylate a steroid in an intramolecular reaction if it is covalently attached, but again, this is no...

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Substrate selectivity in epoxidation by metalloporphyrin and metallosalen catalysts carrying binding groups

Cited by 54 publications

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Regioselective Oxidation of Steroids by a Manganese Porphyrin Carrying Metal Coordinating Groups

Regioselective Oxidation of Steroids by a Manganese Porphyrin Carrying Metal Coordinating Groups

Self‐Assembled Nanoreactors

An artificial cytochrome P450 that hydroxylates unactivated carbons with regio- and stereoselectivity and useful catalytic turnovers

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