syn-Oxidative Polycyclization of Hydroxy Polyenes: A New Approach to Polyether Synthesis

McDonald, Frank E.; Towne, Timothy B.

doi:10.1021/ja00096a069

Cited by 49 publications

(13 citation statements)

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“…Our hypothesis on the spiroketalization step involved into the conversion of 20 to 10 well agrees with the McDonald et al 48 and Schlecht et al 49 mechanistic proposals. This transformation is strongly reminiscent of the oxidative spirocyclization of cyclic enolethers mediated by rhenium (VII) oxides reported by Boyce and Kennedy 50 and would represent the first example of the PCC-induced formation of a cyclic spiroketal involving an enolether double bond.…”

Section: Methodssupporting

confidence: 92%

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Pyridinium chlorochromate chemistry. New insight into oxidation of tetrahydrofurans

Zaccaria¹,

Borbone²,

Oliviero³

et al. 2017

Arkivoc

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A thorough investigation of the minor oxidation products of two penta-tetrahydrofuran compounds with pyridinium chlorochromate has been carried out. Isolation of ring-B oxygenated spiroketal and degradation products, including polycyclic mono-and bis-lactone compounds, supports the previously postulated involvement of cyclic enolether intermediates in the oxidation of THF and poly-THF substances with PCC. Based on the collected evidence, a new mechanistic route for the PCC-mediated oxidative cleavage of -hydroxy-THF compounds to -lactones has been postulated. The proposed mechanism well agrees with the one reported for the oxidative cleavage of 8-hydroxy-neoisocedranol oxide by RuO4, a fact that further supports our previous observation on the similar oxidizing behaviour shown by PPC and RuO4 towards THFcontaining compounds.

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Section: Methodssupporting

confidence: 92%

“…[47][48][49] It is worth noting that such a cycloaddition step also explains the observed cis relationship between the ring-F spiroketal oxygen and the C-8 hydroxyl group (Figure 1).…”

Section: Methodsmentioning

confidence: 80%

Pyridinium chlorochromate chemistry. New insight into oxidation of tetrahydrofurans

Zaccaria¹,

Borbone²,

Oliviero³

et al. 2017

Arkivoc

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“…[84,85] According to this hypothesis, monensin A may be produced from an all-Z triene precursor (an all-Z isomer of 26) through a series of oxidative cyclizations proceeding via a [2+2] mechanism that involves the action of an iron-containing monooxygenase ( Figure 4). Synthetic studies by Townsend himself [84] and work on model systems closely related to the proposed all-Z premonensin triene by McDonald [86,87] provided further support for this hypothesis. The issue of stereochemistry of the alkenes in the monensin A precursor was also raised by Leadlay et al Speculating that the cascade of epoxide opening may be initiated by activation of the methyl ketone electrophile, Leadlay proposed that a Z,Z,Ealkene would be required en route to monensin A.…”

Section: Polyether Ionophoresmentioning

confidence: 92%

Epoxide‐Opening Cascades in the Synthesis of Polycyclic Polyether Natural Products

2009

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The group of polycyclic polyether natural products is of special interest due to the fascinating structure and biological effects displayed by its members. The latter includes potentially therapeutic antibiotic, antifungal, and anticancer properties, as well as extreme lethality. The polycyclic structural features of this family can, in some cases, be traced to their biosynthetic origin, but in others that are less well understood, only to proposed biosynthetic pathways that feature dramatic, yet speculative, epoxide-opening cascades. In this review we summarize how such epoxide-opening cascade reactions have been used in the synthesis of polycyclic polyethers and related natural products.

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“…More recently an alternative biosynthetic pathway has been proposed by Townsend [84]. The formation of 51 and 52 from the (Z)-hydroxydiene, and 53 and 54 from the (E)-hydroxydiene provide support for the syn-oxidative cyclisation mechanism.…”

Section: Scheme 21mentioning

confidence: 97%

The Biosynthesis of Aliphatic Polyketides

Staunton

Wilkinson²

1998

Biosynthesis

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Aliphatic polyketides are a large family of natural products which exhibit an impressive range of biological activities. They are synthesised by a common pathway in which units derived from acetate, propionate and butyrate are condensed onto a growing chain, which is initiated from a range of structurally varied carboxylic acid starter units, in a process closely resembling fatty acid biosynthesis. The intermediates remain bound to the polyketide synthase (PKS) throughout multiple rounds of chain extension, and to a variable degree, reduction of the newly formed b-keto functionality. It is the manner in which each different PKS controls the number and type of extender units added, and the extent and stereochemistry of reduction at each cycle which gives rise to the diverse structural variation seen in this family of natural products. Furthermore, the aglycone product of the PKS may be modified by post-PKS enzymes, including glycosidases, methyltransferases, acylases and oxidative enzymes, to produce still greater diversity. In this article the development of the field will be exemplified by a detailed discussion of the archetypal example of erythromycin A biosynthesis. This will then be followed by further discussion of other relevant areas of research in this field.

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syn-Oxidative Polycyclization of Hydroxy Polyenes: A New Approach to Polyether Synthesis

Cited by 49 publications

References 0 publications

Pyridinium chlorochromate chemistry. New insight into oxidation of tetrahydrofurans

Pyridinium chlorochromate chemistry. New insight into oxidation of tetrahydrofurans

Epoxide‐Opening Cascades in the Synthesis of Polycyclic Polyether Natural Products

The Biosynthesis of Aliphatic Polyketides

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