Synthesis of oxapenam derivatives by silver induced cyclization.

Kobayashi, Takeyuki; Iwano, Yuji; Hirai, Koichi

doi:10.1248/cpb.26.1761

Cited by 11 publications

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“…The coupling constant observed between the enriched C-2 and C-3 sites was 1 J CC ) 32.6 Hz, in accord with the earlier successful incorporation of [2,3-13 C 2 ]proclavaminic acid (16). 6 To ensure that the observed incorporation of paired 13 C-labels from [2,3-13 C 2 ]clavaminic acid (32) was not due to trivial incorporation of unreacted [2,3-13 C 2 ]proclavaminic acid (16) carried along from the enzyme incubation, the integrity of the purified cyclization product was confirmed by analytical HPLC and 1 H-and 13 Cspectroscopy. The relatively low but specific incorporation of clavaminic acid was similarly observed in experiments to investigate the biosynthesis of clavulanic acid (1).…”

Section: Resultssupporting

confidence: 82%

“…29 Reduction of the mixed anhydride 30 of 24 gave the alcohol 25, which was readily oxidized 29 to the aldehyde 26. Labeled bromoacetic acid was converted to its benzhydryl ester 31 and reacted with 4-(phenylthio)azetidin-2-one (27) 32 to give 28, which was reduced with nBu 3 SnH and AIBN to 29. Deprotonation of 29 with LiHMDS at -78 °C and aldol reaction 29,[33][34][35] with 26 gave a mixture of the erythro-30 and threo-31 products, favoring the former.…”

Section: Resultsmentioning

confidence: 99%

“…Remaining [2,3-13 C 2 ]-(2S)-proclavaminic acid (16) and its unreactive 2Renantiomer were cleanly resolved from the 3S,5S-product 32 by preparative reversed-phase HPLC. [2,3-13 C 2 ]Clavaminic acid (32) was obtained as an off-white solid contaminated by small amounts of MOPS buffer, but no labeled proclavaminate 16.…”

Section: Resultsmentioning

confidence: 99%

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Probable Role of Clavaminic Acid as the Terminal Intermediate in the Common Pathway to Clavulanic Acid and the Antipodal Clavam Metabolites

et al. 1997

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Emerging chemical and genetic evidence suggests that separate biochemical solutions have evolved to synthesize the four known classes of β-lactam antibiotics. One of these classes contains clavulanic acid (1) and a family of structurally related but antipodal clavam metabolites 2−5, 7, and 8 which lack a carboxylate at C-3, have a different oxidation state, and exhibit stereochemical features at C-2. Previous work has demonstrated the incorporation of ornithine/arginine in the identical regiochemical sense in all of these natural products, and has established the common intermediacy of the monocyclic β-lactam proclavaminic acid (12) as well. In this paper the quite advanced bicyclic intermediate clavaminic acid (14) has been synthesized in doubly 13C-labeled form by preparative incubation of recombinant clavaminate synthase. The intact and equally efficient incorporation of 14 into valclavam (7) and 2-(2-hydroxyethyl)clavam (8), together with 18O2-incorporation experiments, has been interpreted to define clavaminic acid as the final intermediate shared in the biosynthesis of clavulanic acid and the antipodal clavams. A mechanistic rationale of this interrelationship and the late stages of the respective biosyntheses is proposed.

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Section: Resultssupporting

confidence: 82%

Section: Resultsmentioning

confidence: 99%

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Probable Role of Clavaminic Acid as the Terminal Intermediate in the Common Pathway to Clavulanic Acid and the Antipodal Clavam Metabolites

et al. 1997

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“…The possibility was entertained that dihydroclavaminate 26, free in solution, bearing an ent/o-aminoethyl side chain might undergo an intramolecular transamidation reaction (cf. 26a and analogous precedented reactions; Kobayashi et al, 1978; Bentley & Hunt, 1980) in competition with its return to the synthase and further oxidative conversion to clavaminate (2). Such a process could be envisioned to account for the formation of peak A.…”

Section: Resultsmentioning

confidence: 99%

Elucidation of the order of oxidations and identification of an intermediate in the multistep clavaminate synthase reaction

Salowe

Krol²,

Iwata‐Reuyl³

et al. 1991

Biochemistry

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The enzyme clavaminate synthase (CS) catalyzes the formation of the first bicyclic intermediate in the biosynthetic pathway to the potent beta-lactamase inhibitor clavulanic acid. Our previous work has led to the proposal that the cyclization/desaturation of the substrate proclavaminate proceeds in two oxidative steps, each coupled to a decarboxylation of alpha-ketoglutarate and a reduction of dioxygen to water [Salowe, S. P., Marsh, E. N., & Townsend, C. A. (1990) Biochemistry 29, 6499-6508]. We have now employed kinetic isotope effect studies to determine the order of oxidations for CS purified from Streptomyces clavuligerus. By using (4'RS)-[4'-3H,1-14C]-rac-proclavaminate, a primary T(V/K) = 8.3 +/- 0.2 was measured from [3H]water release data, while an alpha-secondary T(V/K) = 1.06 +/- 0.01 was determined from the changing 3H/14C ratio of the product clavaminate. Values for the primary and alpha-secondary effects of 11.9 +/- 1.7 and 1.12 +/- 0.07, respectively, were obtained from the changing 3H/14C ratio of the residual proclavaminate by using new equations derived for a racemic substrate bearing isotopic label at both primary and alpha-secondary positions. Since only the first step of consecutive irreversible reactions will exhibit a V/K isotope effect, we conclude that C-4' is the initial site of oxidation in proclavaminate. As expected, no significant changes in the 3H/14C ratio of residual substrate were observed with [3-3H,1-14C]-rac-proclavaminate. However, two new tritiated compounds were produced in this incubation, apparently the result of isotope-induced branching brought about by the presence of tritium at the site of the second oxidation. One of these compounds was identified by comparison to authentic material as dihydroclavaminate, a stable intermediate that normally remains enzyme-bound. On the basis of the body of information available and the similarities to alpha-ketoglutarate-dependent dioxygenases, a comprehensive mechanistic scheme for CS is proposed to account for this unusual enzymatic transformation.

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“…For the preparation of 14 C-labeled (•) proclavaminate 34 , the (−)-(4 S )-isomer 29 was coupled with benzyl [2- 14 C]bromoacetate, prepared from phenyl diazomethane and [2- 14 C]bromoacetic acid, to give the azetidinone 30 in 47% yield . Aldol condensation with N- Cbz-aminopropanal 22 provided the d -erythro diastereomer 31 in 33% yield after recrystallization.…”

Section: Introductionmentioning

confidence: 99%

β-Secondary Kinetic Isotope Effects in the Clavaminate Synthase-Catalyzed Oxidative Cyclization of Proclavaminic Acid and in Related Azetidinone Model Reactions

1999

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Clavaminate synthase is an Fe(II)/R-ketoglutarate-dependent oxygenase that catalyzes three mechanistically distinct reactions in the course of clavulanic acid biosynthesis. Clavulanic acid is of significant chemical importance as a potent inhibitor/inactivator of β-lactamase enzymes, a prominent means of bacterial resistance to, for example, penicillin. Primary and R-secondary T (V/K) kinetic isotope effects have been determined in earlier work for the clavaminate synthase-catalyzed oxidative cyclization of proclavaminic acid, one of the three reactions mediated by this enzyme. In this paper the β-secondary deuterium kinetic isotope effect for this reaction has been determined using remote 3 H and 14 C labels in an attempt to distinguish between radical or cationic intermediates in the reaction as suggested by the magnitudes of the primary and secondary R-effects. The presence of the adjacent azetidinone nitrogen and the intervention of an azetinone intermediate, formally antiaromatic in the resonance form of the amide, make interpretation of the low β-secondary effect (1.056 ( 0.002 for dideuteriation at C-3′) problematic. To assist interpretation of this result, a 4-chloroazetidinone model system has been constructed dideuteriated at C-3 identically to proclavaminic acid and bearing remote radiolabels. Reaction of this substrate at 25 °C under both radical and solvolysis conditions afforded β-secondary kinetic isotope effect data for direct comparison to the enzymic reaction. The measured effects are similarly small but strongly dependent on the polarity/acidity of the reaction medium. These results are discussed in terms of the commitment to catalysis and the extent to which amide resonance may be favored in the transition state of the oxidative cyclization.

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Synthesis of oxapenam derivatives by silver induced cyclization.

Cited by 11 publications

References 0 publications

Probable Role of Clavaminic Acid as the Terminal Intermediate in the Common Pathway to Clavulanic Acid and the Antipodal Clavam Metabolites

Probable Role of Clavaminic Acid as the Terminal Intermediate in the Common Pathway to Clavulanic Acid and the Antipodal Clavam Metabolites

Elucidation of the order of oxidations and identification of an intermediate in the multistep clavaminate synthase reaction

β-Secondary Kinetic Isotope Effects in the Clavaminate Synthase-Catalyzed Oxidative Cyclization of Proclavaminic Acid and in Related Azetidinone Model Reactions

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