Quinonemethide biosynthesis

Corsino et al. [22] reported that friedelane and quinonemethide biosynthesis is compartmentalized in Maytenus aquifolium and Salacia campestris, indicating cyclase activity in the leaves but not in the root bark. In order to confirm the possible translocation of friedelin derivatives, from the leaves to root bark, a solution of ( )5-3H-mevalonolactone was administered to the leaves of M. aquifolium seedlings. No labeled friedelin was detected in the root bark but, nevertheless, label quinonemethides were found. 

Corsino et al. [22] reported that friedelane and quinonemethide biosynthesis is compartmentalized in Maytenus aquifolium and Salacia campestris, indicating cyclase activity in the leaves but not in the root... 

The biosynthesis process, which consists essentially of radical coupling reactions, sometimes followed by the addition of water, of primary, secondary, and phenohc hydroxyl groups to quinonemethide intermediates, leads to the formation of a three-dimensional polymer which lacks the regular and ordered repeating units found in other natural polymers such as cellulose and proteins. 

N-Acetyldopamine A -[2-(3,4-dihydroxyphenyl)ethyl]-acetamide and N-P-alanyldopamine (3-amino-A -[2-(3,4-dihydroxyphenyl)ethyl]propanamide) occur in insects where they serve to form the sclerotized cuticle required for the exoskeleton. They are transformed by enzymatic oxidation to the corresponding o-quinones and p-quinonemethides which cross-link structural proteins with each other and with chitin. The biosynthesis of N-acetyldopamine starts from dopamine and acetyl-CoA by way of arylamine-A acyltransferase (EC 2.3.1.5). In contrast to the biosynthesis of (/f)- noradrenaline, the p-quinonemethides, generated non-selectively by enzymatic oxidation from N-ace-tyldopamine or )V-)3-alanyldopamine, undergo addition of water to furnish the racemic side-chain hydrox-ylated derivatives N-acetylnoradrenaline ()V-[2-(3,4-dihydroxyphenyl)-2-hydroxyethyl]acetamide) or, respectively N- alanylnoradrenaline (3-amino-)V-[2-(3,4-dihydroxyphenyl)-2-hydroxyethyl]propan-amide). 

---