FTIR spectral study of intramolecular hydrogen bonding in thromboxane A2 receptor antagonist S-145 and related compounds. Part 2

Abstract

The FTIR spectra of thromboxane A₂ receptor antagonists, a S-145 analogue (1),‡ ONO-3708 (2), a 13-APA analogue (3), SQ-29548 (4), and EP-045 (5), and related compounds have been measured in dilute CCl₄ and CHCl₃ solutions. The spectra were subjected to curve analysis in order to separate overlapping absorption bands. For (1)–(5), intramolecular hydrogen bonds involving twelve-, fourteen-, twelve-, thirteen-, and thirteen-membered rings are found between a carboxy group of the α-side chain and a functional group of the ω-side chain, respectively. In (3)–(5), these hydrogen bonds are also found to be of a zwitterion form. The formation ratio (ρ) of the intramolecular hydrogen bond in CCl₄ solution show high values of 85 for (1), 78 for (2), 75 for (3), 89 for (4), and 96% for (5). On the basis of these findings on the intramolecular hydrogen bonds, the conformations of (1)–(5) have been identified and are found to be similar.