Cyclopentenosine, Major Trifunctional Crosslinking Amino Acid Isolated from Acid Hydrolysate of Elastin

A trifunctional crosslinking amino acid named cyclopentenosine (CP) was isolated from the hydrolysate of bovine nuchal ligament elastin. CP and its derivatives were identified by spectroscopic methods. CP was found to consist of a 2-cyclopenten-1-one structure and its imine–enamine tautomers with enantiomers in H2O. A model reaction for the formation of the CP crosslink using model compounds for allysine (propanal) and lysine (n-butylamine) demonstrated that CP is composed of 2-cyclopenten-1-one and α, β, γ, δ-unsaturated aldehyde derived from three allysine residues. An ion-paired high-performance liquid chromatographic method for the determination of CP was developed. Among various bovine tissues the nuchal ligament had the highest concentration of CP. The age-related changes in the concentration of CP were examined in the aorta from rat (short-lived species) and bovine (long-lived species). The CP content was very low in the newborn rat but increased markedly with growth. After maturity, the CP content remained nearly the same or slightly decreased. In bovine aorta, the CP content scarcely changed from 7 months to 16 years.