Thiolate additions to bicyclomycin and analogues: a structurally novel latent Michael-acceptor system

Williams, Robert M.; Tomizawa, K.; Armstrong, Robert W.; Dung, Jen Sen

doi:10.1021/ja00308a059

Cited by 11 publications

(9 citation statements)

References 4 publications

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“…The mechanism, structural requirements and biological relevance of this reaction has been carefully studied in our laboratories. 18,19 Careful inspection of the bicyclomycin structure and consideration of the regiochemistry of the mercaptan addition led to the SCHEME 10 suggested20 mechanistic pathway depicted in Scheme 10. Tautomeric ring opening of 1 was envisioned to produce the monocyclic eight-membered ring a,/?-unsaturated ketone 51, which should function as a reactive Michael-type acceptor.…”

Section: Mechanism Of Actionmentioning

confidence: 99%

Bicyclomycin: synthetic, mechanistic, and biological studies

Williams¹,

Durham²

1988

Chem. Rev.

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Section: Mechanism Of Actionmentioning

confidence: 99%

Bicyclomycin: synthetic, mechanistic, and biological studies

Williams¹,

Durham²

1988

Chem. Rev.

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“…Studies of the mechanism of action of bicyclomycin ( 1 ) have focused on the role of the C(5)−C(5a) exomethylene group. − The pioneering investigations of Iseki and co-workers showed that methyl mercaptan reacted at the C(5a) site in 1 at basic pH values − These findings led to proposals that bicyclomycin expresses its activity by reacting with nucleophilic species necessary for bacterial function upon hemiaminal ring-opening to enone 2 (Scheme ). , The importance of these transformations for bicyclomycin antibiotic activity remains unresolved.…”

mentioning

confidence: 99%

Role of the C(5)−C(5a) Exomethylene Group in Bicyclomycin: Synthesis, Structure, and Biochemical and Biological Properties

Park

Zhang

et al. 1996

J. Org. Chem.

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Thirty-two C(5)-C(5a) exomethylene-modified bicyclomycin derivatives were prepared to determine the effect of structural modification of this unit on bicyclomycin (1) function. The compounds were grouped into three categories: the C(5)-unsaturated bicyclomycins, the C(5a)-substituted C(5)-C(5a)-dihydrobicyclomycin derivatives, and the C(5)-modified norbicyclomycins. An efficient three-step procedure was developed to synthesize C(5a)-substituted C(5),C(5a)-dihydrobicyclomycins. Bicyclomycin was converted to bicyclomycin C(2'),C(3')-acetonide (36) and then treated with a nucleophile in 50% aqueous methanol ("pH" 10.5) to give the C(5a)-substituted C(5),C(5a)-dihydrobicyclomycin C(2'),C(3')-acetonide. Removal of the acetonide group (trifluoroacetic acid in 50% aqueous methanol) in the final step provided the desired bicyclomycin derivative. All the compounds were evaluated using the rho-dependent ATPase assay and their antimicrobial activities determined using a filter disc assay. Most of the compounds were also tested in the transcription termination assay. We observed that many of the C(5)-unsaturated bicyclomycins effectively inhibited ATP hydrolysis at 400 &mgr;M and inhibited the production of rho-dependent transcripts at 100 &mgr;M. The biochemical activities of C(5a)-bicyclomycincarboxylic acid (5), methyl C(5a)-bicyclomycincarboxylate (6), ethyl C(5a)-bicyclomycincarboxylate (7), and bicyclomycin C(5)-norketone O-methyloxime (11) were all similar to 1. Compounds 6, 7, and 11 exhibited diminished antibiotic activity compared to 1, and 5 displayed no detectable activity. Several C(5a)-substituted C(5),C(5a)-dihydrobicyclomycins showed significant inhibition of rho-dependent ATPase and transcription termination activities. The inhibitory properties of C(5),C(5a)-dihydrobicyclomycin C(5a)-methyl sulfide (18), C(5),C(5a)-dihydrobicyclomycin C(5a)-phenyl sulfide (23), and C(5)-C(5a)-dihydrobicyclomycin-5,5a-diol (31) approached those of 1. Compounds 18, 23, and 31 did not exhibit antibiotic activity. Two of the four C(5)-modified norbicyclomycin adducts showed moderate inhibitory activities in the ATPase assay, and none showed significant antibiotic activity. Our findings showed that the C(5)-C(5a) exomethylene unit retention in 1 was not essential for inhibition of in vitro rho activity. The structure-activity relationship data indicated that bicyclomycins that contained a small unsaturated C(5) unit or C(5),C(5a)-dihydrobicyclomycins that possessed a small, nonpolar C(5a) substituent effectively inhibited rho function in in vitro biochemical assays. We concluded that the C(5)-C(5a) unit in 1 was not a critical structural element necessary for drug binding to rho and that irreversible, inactivating units placed at this site would permit the bicyclomycin derivative to bind efficiently to rho.

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“…Early reports on the 1 inhibition pathway suggested that the antibiotic irreversibly modified its receptor(s) [27][28][29][30][31][32][33]. Indeed, our chemical studies showed that 1 covalently reacted with thiols and amines under moderate conditions [39][40][41][42][43], so we asked if a comparable process occurred with rho.…”

Section: Bicyclomycin Inhibits Rho By a Reversible Pathwaymentioning

confidence: 93%

“…Bicyclomycin was reported by several researchers to affect bacterial outer-membrane synthesis [27][28][29][30][31][32][33]. First, administering 1 to E. coli modified cell wall synthesis but had little effect on DNA, lipid, or cell-free protein synthesis [28].…”

Section: Early Proposals Of Bicyclomycin Function: Insights Into Bicymentioning

confidence: 99%

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The Molecular Basis for the Mode of Action of Bicyclomycin

Kohn

Widger

2005

CDTID

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Bicyclomycin (1) is a clinically useful antibiotic exhibiting activity against a broad spectrum of Gram-negative bacteria and against the Gram-positive bacterium, Micrococcus luteus. Bicyclomycin has been used to treat diarrhea in humans and bacterial diarrhea in calves and pigs and is marketed by Fujisawa (Osaka, Japan) under the trade name Bicozamycin. The structure of 1 is unique among antibiotics, and our studies document that its mechanism of action is novel. Early mechanistic proposals suggested that 1 reacted with nucleophiles (e.g., a protein sulfhydryl group) necessary for the remodeling the peptidoglycan assembly within the bacterial cell wall. We, however, showed that 1 targeted the rho transcription termination factor in Escherichia coli. The rho protein is integral to the expression of many gene products in E. coli and other Gram-negative bacteria, and without rho the cell losses viability. Rho is a member of the RecA-type ATPase class of enzymes that use nucleotide contacts to couple oligonucleotide translocation to ATP hydrolysis. Bicyclomycin is the only known selective inhibitor of rho. In this article, we integrate the evidence obtained from bicyclomycin structure-activity studies, site-directed mutagenesis investigations, bicyclomycin affinity labels, and biochemical and biophysical measurements with recent X-ray crystallographic images of the bicyclomycin-rho complex to define the rho antibiotic binding site and to document the pathway for rho inhibition by 1. Together, the structural and functional studies demonstrate how 1, a modest rho inhibitor, can disrupt the rho molecular machinery thereby leading to a catastrophic effect caused by the untimely overproduction of proteins not normally expressed constitutively, thus leading to a toxic effect on the cells.

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Thiolate additions to bicyclomycin and analogues: a structurally novel latent Michael-acceptor system

Cited by 11 publications

References 4 publications

Bicyclomycin: synthetic, mechanistic, and biological studies

Bicyclomycin: synthetic, mechanistic, and biological studies

Role of the C(5)−C(5a) Exomethylene Group in Bicyclomycin: Synthesis, Structure, and Biochemical and Biological Properties

The Molecular Basis for the Mode of Action of Bicyclomycin

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