Effect of changing pH upon the kinetic <sup>13</sup>C-isotope effect in the decarboxylation of 4-methoxyanthranilic acid

Dunn, G. E.; Buccini, J.

doi:10.1139/v68-092

Cited by 6 publications

(6 citation statements)

References 4 publications

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“…Commun., 72 (1970). (11) While the crystal used to collect data was rather larger than desirable, it was clearly the best among the very few crystals of this complex available to us as regards having well-developed faces and no satellites.…”

Section: Methodsmentioning

confidence: 99%

Crystal and molecular structure of the barium salt of an antibiotic containing a high proportion of oxygen

Johnson¹,

Herrin²,

Liu³

et al. 1970

J. Am. Chem. Soc.

128

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The molecular structure of an antibiotic X-537A, C34H54O8, from an unidentified streptomyces has been determined by the X-ray structure analysis of a barium salt. Two molecules of the barium salt monohydrate, Ba(CS4H53Os)2 H20, crystallize in the space group P2i with a = 14.59, b = 17.95, c = 13.99 A, and ß = 105°17'. The structure has been refined to an R factor of 0.11 on 4753 structure amplitudes measured by film methods. The two crystallographically independent antibiotic molecules wrap themselves around the barium, with eight oxygen atoms and the water molecule of crystallization in the range 2.6-3.1 Á from the metal ion. Eighteen years ago, three hitherto unknown, crystalline antibiotics were obtained from three unidentified streptomyces, designated X-206, X-464, and X-537A.3 All three antibiotics are optically active organic acids, containing a high proportion of oxygen. These antibiotics are capable of forming a variety of salts with Ag+, Na+, K+, and Ba2+.3 More recently, another antibiotic, monensic acid, was isolated from Streptomyces cinnamonensis, and showed similar high oxygen content and capability to form metal salts.4The structure of monensic acid has been determined by a combination of chemical studies and an X-ray structural analysis of the monosilver salt.4The antibiotic X-537A produced by X-537A has the molecular formula C34H54O8.5 Nmr studies indicate that, while mainly aliphatic, it has two protons in a region indicative of a tetrasubstituted aromatic group, and that there is a methyl group ( = 2.18) which is either bound to an aromatic ring or to a C=C double bond.6 There is no evidence for a methoxyl group;6 monensic acid contains one methoxyl group.4 Mass spectra also provided evidence for the presence of an aromatic ring or of a structure which could readily form such a ring.6 The infrared spectra of the piperidine salt and the free acid both have a band at 1700 cm-1, suggestive of a saturated ketone.6In view of the limited structural evidence available, an X-ray structure analysis of a suitable metal salt was proposed as the most convenient means of structure determination of the antibiotic from X-537A. Furthermore, the conformation of the antibiotic when bound to a metal will be of interest when compared to that of monensic acid. Since the inception of this study, two independent X-ray studies of a related antibiotic, nigericin, have appeared7-8 and chemical studies have shown that nigericin and X-464 are identical.9 A

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Section: Methodsmentioning

confidence: 99%

Crystal and molecular structure of the barium salt of an antibiotic containing a high proportion of oxygen

Johnson¹,

Herrin²,

Liu³

et al. 1970

J. Am. Chem. Soc.

128

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“…This rather complex rate expression can be simplified to a straight-line equation in three separate regions of acidity. At low acidity (pH greater than 1) there is no appreciable '3~-carboxyl kinetic isotope effect in the decarboxylation of anthranilic (8) or 4-methoxyanthranilic acids (2). Consequently, the right-hand fraction in eq.…”

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confidence: 98%

“…In previous papers (1,2) it was proposed that the general mechanism for decarboxylation of substituted anthranilic acids is as shown in eq. 1, where HA can be either unionized acid, as shown, or zwitterion and for which the overall rate constant is given by eq.…”

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confidence: 99%

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Mechanism of decarboxylation of substituted anthranilic acids at high acidity

Dunn¹,

Dayal²

1970

Can. J. Chem.

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The rates of decarboxylation of 4-methyl-, 4-methoxy-, and unsubstituted anthranilic acids have been determined in aqueous buffers over the p H range 2.5-3.8. Electron-releasing substituents increase the rates of ring-protonation about equally for an acid and its anion, and decrease the ratio of decarboxylation to deprotonation of the protonated acid. Rates, 13C-carboxyl kinetic isotope effects, and deuterium solvent isotope effects have been determined for the decarboxylation of anthranilic acid in aqueous sulfuric acid up to 10 M. N o evidence for decarboxylation by cleavage of the unionized carboxyl group was obtained.

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“…The apparatus and method used to follow the kinetics of the reaction have been described previously (I), as k have the methods of sample collection and calculation of R a c o o A RQ + co, the isotope effects (2).…”

Section: Methodsmentioning

confidence: 99%

Mechanism of decarboxylation of substituted salicylic acids. II. Kinetics and ¹³C-carboxyl kinetic isotope effects in nitrobenzene–quinoline mixtures

Bourns¹,

Buccini²,

Dunn³

et al. 1968

Can. J. Chem.

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The decarboxylation of 4-methylsalicylic acid in dilute solutions of quinoline in nitrobenzene at 200 OC is first order with respect to the salicylic acid and first order with respect to quinoline. The pscudo-firstorder rate constant reaches a maximum a t 0.25 M quinoline, then decreases as the quinoline concentration increases. The 13C-carboxyl kinetic isotope effect, 100(k,z/k,3 -l), is 2.2% in pure quinoline and 0.7% in 0.02 M quinoline. It is therefore concluded that the mechanism proposed in Part I of this series involves three steps: ionization of the salicylic acid to a quinolinium salicylate ion pair, reversible protonation by quinolinium ion of the salicylate ion at carbon 1 of the aromatic ring, and loss of carbon dioxide from the protonated salicylate ion. I n dilute quinoline solution the second step is slow, while in pure quinoline the third step becomes rate determining.Canadian Journal of Chemistry, 46, 3915 (1968) In Part I of this series (1) it was proposed that more negative than o (applicable to step l), so a number of 4-and 5-substituted salicylic acids that for these substituents cancellation is not decarboxylate in quinoline solution by the follow-complete. ing mechanismThe evidence did not permit a decision as to COOH COOwhether steps 2 and 3 are sequential, as shown, or. QH+ concerted. It was, therefore, the object of the OH present investigation to study the kinetics of decarboxvlation and the '3C-carboxvl kinetic H isotope effect in the "inert" solvent nitrobenzene. ExperimentalThe apparatus and method used to follow the kinetics of the reaction have been described previously (I), as OH OHThis mechanism was designed to account for 3 major experimental observations. (a) Although the decarboxylation in nitrobenzene solution is second order with respect to salicylic acid, in quinoline it is first order, so that the quinoline must be a reactant in the decarboxylation. (b) Most 4-and 5-substituents have little effect on the rate, so that their influence on one process (step 1) must be cancelled by that on another (step 2). (c) The rate is sharply increased by those substituents for which o+ (applicable to step 2) is distinctly Results and DiscussionThe decarboxylation of salicylic acid has been shown to be second order with respect to the acid in nitrobenzene solution (1). However, in nitrobenzene containing quinoline the decarboxylation of 4-methylsalicylic acid is now found to be first order with respect to the acid to more than 3 half lives, even when the concentration of the acid is in considerable excess over that of the quinoline. This, of course, is in agreement with the proposed mechanism since, according to it, Can. J. Chem. Downloaded from www.nrcresearchpress.com by 34.213.178.48 on 05/10/18For personal use only.

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Effect of changing pH upon the kinetic ¹³C-isotope effect in the decarboxylation of 4-methoxyanthranilic acid

Cited by 6 publications

References 4 publications

Crystal and molecular structure of the barium salt of an antibiotic containing a high proportion of oxygen

Crystal and molecular structure of the barium salt of an antibiotic containing a high proportion of oxygen

Mechanism of decarboxylation of substituted anthranilic acids at high acidity

Mechanism of decarboxylation of substituted salicylic acids. II. Kinetics and ¹³C-carboxyl kinetic isotope effects in nitrobenzene–quinoline mixtures

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Effect of changing pH upon the kinetic 13C-isotope effect in the decarboxylation of 4-methoxyanthranilic acid

Cited by 6 publications

References 4 publications

Crystal and molecular structure of the barium salt of an antibiotic containing a high proportion of oxygen

Crystal and molecular structure of the barium salt of an antibiotic containing a high proportion of oxygen

Mechanism of decarboxylation of substituted anthranilic acids at high acidity

Mechanism of decarboxylation of substituted salicylic acids. II. Kinetics and 13C-carboxyl kinetic isotope effects in nitrobenzene–quinoline mixtures

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Effect of changing pH upon the kinetic ¹³C-isotope effect in the decarboxylation of 4-methoxyanthranilic acid

Mechanism of decarboxylation of substituted salicylic acids. II. Kinetics and ¹³C-carboxyl kinetic isotope effects in nitrobenzene–quinoline mixtures