Synthesis and analysis of the enantiomers of calmidazolium, and a 1H NMR demonstration of a chiral interaction with calmodulin.
Calmidazolium [R24571, 1-[bis(4-chlorophenyl)methyl]-3-[2-(2,4-dichlorophenyl)-2-[(2,4- dichlorophenyl)methoxy]ethyl]-1H-imidazolium chloride] is a potent calmodulin inhibitor. This paper describes the synthesis and properties of the enantiomers of calmidazolium from the enantiomers of miconazole [1(N)-(2-(2,4-dichlorobenzyloxy)-2-(2,4 dichlorophenyl))-ethyl imidazole], prepared from the racemate by chiral preparative scale high performance liquid chromatography. Overlap between ligand and protein resonances in the aromatic region of the 1H NMR spectrum of the calmidazolium-calmodulin complexes has been obviated by preparation of the protein with all of its nine phenylalanine rings deuterated (Phe-d5 calmodulin). This has been accomplished by the overexpression of calmodulin derived from Trypanosoma brucei rhodiesiense in E. coli in a medium supplemented with ring-deuterated phenylalanine. The kinetics of binding of each enantiomer are slow on the 1H NMR time scale as judged by the behaviour of the H2 resonance of Histidine-107, which is clearly visible under the sample conditions used. The aromatic spectral regions of the protein-bound (+) and (-) enantiomers contrast strikingly, reflecting differences in bound environment and/or conformation.
Edwards
A J
AJ
SmithKline Beecham Pharmaceuticals, The Frythe, Welwyn, Herts., United Kingdom.
Sweeney
P J
PJ
Reid
D G
DG
Walker
J M
JM
Elshourbagy
N
N
Egwuagu
C E
CE
Young
J F
JF
Patton
C L
CL
D002147:Calmodulin / Q000737:chemistry*; D004791:Enzyme Inhibitors / Q000032:analysis / Q000138:chemical synthesis* / Q000737:chemistry*; D007093:Imidazoles / Q000032:analysis / Q000138:chemical synthesis* / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D011522:Protons; D013237:Stereoisomerism; D017186:Titrimetry
D002147:Calmodulin; D004791:Enzyme Inhibitors; D007093:Imidazoles; D011522:Protons; C031938:calmidazolium