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Review
, 105 (12), 4730-56

A Case Study in Biomimetic Total Synthesis: Polyolefin Carbocyclizations to Terpenes and Steroids

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Review

A Case Study in Biomimetic Total Synthesis: Polyolefin Carbocyclizations to Terpenes and Steroids

Ryan A Yoder et al. Chem Rev.

Figures

Figure 1
Figure 1
Robinson and Bloch proposals for pre-cholesterol squalene organization (x=acetate carboxyl, o=acetate methyl), and Bloch labeling outcome
Figure 2
Figure 2
Carbenium ion additions to olefins: mechanistic possibilities and their stereochemical outcomes
Figure 3
Figure 3
Construct relating stereospecific π-cation biscyclization to decalin configuration
Figure 4
Figure 4
Acid catalyzed cyclohexannulation: stereochemistry and mechanism
Figure 5
Figure 5
Stork and Burgstahler hypothesis. Reprinted with permission from ACS publications.
Figure 6
Figure 6
Eschenmoser, Ruzicka, Jeger, and Arigoni hypothesis correlating diene conformation to cyclization diastereoselection, and its application to chair-chair-chair-boat (‘Scheme 4’) and chair-boat-chair-boat (‘Scheme 7’) squalene conformations in the biosynthesis of triterpenes. Reprinted with permission from Verlag Helvetica Chimica Acta AG.
Figure 7
Figure 7
Hoshino's mnemonic illustrating primary and secondary residues known to play a role in squalene-hopene cyclase (Reproduced by permission of The Royal Society of Chemistry)
Figure 8
Figure 8
X-Ray crystal structure of 2-azasqualene-bound SHC illustrating residues necessary for activation (protonation)
Figure 9
Figure 9
X-Ray crystal structure of 2-azasqualene-bound SHC illustrating residues necessary for charge stabilization during polycyclization
Figure 10
Figure 10
X-Ray crystal structure of 2-azasqualene-bound SHC illustrating residues necessary for charge stabilization during polycyclization
Figure 11
Figure 11
Johnson's theory of point-charge stabilization by the oxidosqualene cyclase to control regio- and stereoselection
Figure 12
Figure 12
Comparison of Schulz (X-ray) and Hess (calculation) distances for AB-ring formation from squalene. Reprinted with permission from ACS publications.
Figure 13
Figure 13
Yamamoto's LBA catalysts
Figure 14
Figure 14
Corey's working hypothesis for the enzymatic π-cation cyclization of oxidosqualene to lanosterol
Figure 15
Figure 15
X-Ray crystal structure of lanosterol-bound OSC illustrating residues necessary for activation (protonation)
Figure 16
Figure 16
X-Ray crystal structure of lanosterol-bound OSC illustrating residues necessary for charge stabilization during polycyclization
Figure 17
Figure 17
X-Ray crystal structure of lanosterol-bound OSC illustrating residues necessary for charge stabilization during polycyclization
Figure 18
Figure 18
A few of the landmarks in the stories of terpene biosynthesis and total synthesis
Scheme 1
Scheme 1
General outline of the biosynthesis pathways involving squalene and oxidosqualene cyclases
Scheme 2
Scheme 2
Brønsted Acid catalyzed 1,5-diene cyclization
Scheme 3
Scheme 3
Acid catalyzed cyclohexannulation: Linstead's stereoselective decalin formation
Scheme 4
Scheme 4
Schinz and Stork cyclization of farnesic acid, and correction of product stereochemical assignment
Scheme 5
Scheme 5
Stork's cyclization of farnesyl acetic acid
Scheme 6
Scheme 6
Stork's cyclization of farnesyl acetic acid
Scheme 7
Scheme 7
Schinz-Eschenmoser evidence for anti-carbenium ion addition to an olefin ('nonclassical carbonium ion intermediate')
Scheme 8
Scheme 8
Mechanism of polycyclization supported by AM1* calculations (Gao)
Scheme 9
Scheme 9
Johnson's synthesis of rac-sophoradiol using a biomimetic pentacarbocyclization
Scheme 10
Scheme 10
Johnson's biomimetic polyolefin electrophilic cyclization towards 11α-hydroxyprogesterone
Scheme 11
Scheme 11
Johnson's diastereoselective biomimetic polyolefin electrophilic cyclization towards d-4β-hydroxyandrostan-17-one
Scheme 12
Scheme 12
Yamamoto's enantioselective olefin protonation-initiated polycyclization
Scheme 13
Scheme 13
Yamamoto's enantioselective synthesis of (5S,10S)-54
Scheme 14
Scheme 14
Yamamoto's enantioselective synthesis of (5S,10S)-61
Scheme 15
Scheme 15
Models for oxidosqualene cyclase: relative rates for epoxide ring opening
Scheme 16
Scheme 16
Product formation from oxidosqualene cyclases using nonnatural substrates
Scheme 17
Scheme 17
Eschenmoser's rationale to predict α-C18 configuration
Scheme 18
Scheme 18
Lanosterol biosynthesis: oxidosqualene cyclization and group migrations
Scheme 19
Scheme 19
van Tamelen's epoxysqualene tricyclization/migration sequence catalyzed by SnCl4
Scheme 20
Scheme 20
Janda's antibody catalyzed cyclization carbocyclization using a sulfonate initiator
Scheme 21
Scheme 21
Janda's antibody catalyzed cyclization of substrate 91 to afford decalin products
Scheme 22
Scheme 22
Cyclization of an oxidosqualene-like substrate by an antibody elicited to a steroidal hapten
Scheme 23
Scheme 23
van Tamelen's tetracyclization favoring 6- and 5-membered C- and D-rings
Scheme 24
Scheme 24
Corey's total synthesis of dammarenediol
Scheme 25
Scheme 25
Corey's total synthesis of scalarenedial
Scheme 26
Scheme 26
Corey's total synthesis of hexacyclic sedimentary triterpene 123
Scheme 27
Scheme 27
Corey's total synthesis of tetracyclic sedimentary diterpene 129
Scheme 28
Scheme 28
Overman's total synthesis of the adociasulfate from an epoxysqualene-like polycyclization
Scheme 29
Scheme 29
Demuth's formation of a steroid skeleton using a diastereoselective PET strategy
Chart 1
Chart 1
Substrate analogue 20-oxaoxidosqualene and products formed upon cyclization by oxidosqualene cyclase

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