X-14885A: An ionophore closely related to calcimycin (A-23187). NMR, thermodynamic, and kinetic studies of cation selectivity - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue Journal of the American Chemical Society Année : 1989

X-14885A: An ionophore closely related to calcimycin (A-23187). NMR, thermodynamic, and kinetic studies of cation selectivity

A.M. Albrecht-Gary
  • Fonction : Auteur
D.W. Boyd
  • Fonction : Auteur
G. Dauphin
  • Fonction : Auteur
G. Jeminet
  • Fonction : Auteur
J. Juillard
  • Fonction : Auteur
C. Tissier
  • Fonction : Auteur

Résumé

X-14885A is an open-chain carboxylic ionophore, recently isolated from a Streptomyces strain. NMR data have shown that the free acid form adopts a pseudocyclic conformation in chloroform, while in the neutral A 2Mg complex a rotation of the benzoxazole arm is achieved to accommodate the cation in a sandwich system. The replacement of the -NHMe by an -OH function and of a methyl group by H in position 15 for X-14885A does not lead to a large modification in the conformation of the new microbial metabolite in solution. The acid-base equilibria and the thermodynamics of association with alkali and alkali-earth cations are determined in methanol, from potentiometric and spectrophotometric measurements. Divalent cations M 2+ form strong complexes of 1:1 (AM +) and 2:1 (A 2M) stoichiometries, following the sequence Ca 2+ > Mg 2+ > Sr 2+ > Ba 2+. For AM + + A - ⇄ A 2M, log K A2M are, respectively, 8.0, 7.3, 6.9, and 6.2 (I = 0). A complete kinetic study is carried out in methanol for the A 2Mg and A 2Ca complexes, with use of a stopped-flow system. This work shows that the rate-limiting steps of the formation and dissociation mechanisms are associated with the charged complex AM +, the addition or loss of the second ligand being faster. As for the closely related ionophore A-23187 (calcimycin), the selectivity calcium/magnesium has predominantly a kinetic origin, with faster formation and dissociation rates of the calcium complexes. The replacement of the -NHMe group in calcimycin by an -OH group in X-14885A has a drastic effect in the acid-base properties of X-14885A and on the acid-catalyzed dissociation pathway of its complexes.

Domaines

Chimie

Dates et versions

hal-01457203 , version 1 (06-02-2017)

Identifiants

Citer

A.M. Albrecht-Gary, Sylvie Blanc, D.W. Boyd, G. Dauphin, G. Jeminet, et al.. X-14885A: An ionophore closely related to calcimycin (A-23187). NMR, thermodynamic, and kinetic studies of cation selectivity. Journal of the American Chemical Society, 1989, 111 (23), pp.8598-8609. ⟨10.1021/ja00205a007⟩. ⟨hal-01457203⟩
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