A high field proton magnetic resonance study of the solution conformation of thromboxane B2

Abstract

The solution conformation of thromboxane B2 (TXB2) was studied using high-field NMR techniques. In CDCl3, both anomers are present in solution with 76% 11.alpha.-OH TXB2 and 24% 11.beta.-OH TXB2. In CD3OD, the predominant anomer is 11.beta.-OH TXB2 (80%) while the concentration of 11.alpha.-OH TXB2 is 20%. The proton resonances were assigned at 400 MHz using double resonance techniques. The analysis of the vicinal coupling constants indicates that the 6-membered ring is present in solution in a chair conformation with both of the aliphatic side chains equatorial. Proton longitudinal relaxation times were measured at 25.degree. C in CDCl3 for H-2, H-11.beta., H-12, H-13, H-14 and H-17 to H-19, both at 200 and 400 MHz. From the frequency dependence of these dipolar relaxation times, the rotational correlation times were evaluated. Within experimental error, all values are similar in magnitude (.apprx. 2.0 .times. 10-10 s); this is the molecular rotational correlation time.