Shinobu Kobayashi

Fourier transform infrared and circular dichroism spectroscopic studies of hydrogen bonding in micacocidin A and micacocidin in dilute CH2Cl2 or CHCl3 solution

Abstract FTIR spectra of micacocidin A ( I ), which is a Zn complex antibiotic, the metal-free ligand micacocidin ( II ), its derivatives and their related compounds were measured in dilute CH 2 Cl 2 solution in order to elucidate the conformations of I and II in solution. Curve analysis of the spectra to separate overlapping absorption bands showed that I forms dimers due to two strong intermolecular hydrogen bonds between a hydroxy group and the phenolate anion and II exists in a folded conformation with three rings formed by intramolecular hydrogen bonds between phenolic, aliphatic and carboxylic OH groups and the N atoms of thiazoline, another thiazoline and thiazolidine, respectively. The concentration and temperature dependencies of CD spectra of I were measured in CHCl 3 and CH 3 OH solutions and CH 3 CN solution, respectively, in order to confirm the formation of the dimers of I in these solvents. The variation of the CD band by addition of ZnCl 2 to II was also measured in CH 3 OH solution. II was shown to be more easily transformed to I by Zn 2+ ion in the solution.