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.