Solution structure of mesobiliverdin XIII alpha bridged between the propionic acid substituents

摘要

The solution structure of two intramolecular diesters (methylene and 1,3-propylidene) of mesobiliverdin-XIII alpha was studied and compared with that of the corresponding dimethyl ester. The UV/Vis absorption spectra, chiral discrimination with ethyl (S)-(-)-lactate, and the H-1 NMR spectra (ROESY) show that the cyclization of the propionate substituents of biliverdins does not significantly affect the helix structure or its (P) reversible arrow (M) interconversion. The internal methylene diester does not show conformational heterogeneity of the propionate substituents and probably exists only in one diastereomeric form. In this case, the results point to a simultaneous racemization of the tetrapyrrole helix and the bridge cycle. The methylene diester of mesoprotoporphyrin was also synthesized. In this case, the geometry of the propionate chains is probably similar to that present in some hemoproteins. [References: 43]