ortho-Quinone amines and derivatives: the influence of structure on the rates and modes of intramolecular reaction

Abstract

The influence of N-substituents and chain length on the mode and rate of intramolecular reaction of ortho-quinone amines is reviewed. These reactions have been the subject of a series of studies over the last decade using a combination of pulse radiolysis, enzyme oximetry and preparative chemistry. Alternative reactions are cyclisation, spirocyclisation and para-quinomethane formation. The observed mode of reaction is determined by both the length of the ortho-quinone side chain and the nature of the N-substituents. The rates of the competing reactions are discussed and compared with rates determined by other workers using cyclic voltammetry. Formation of a para-quinomethane is relatively slow and only occurs when cyclisation is unfavourable due to steric, entropy or electronic effects. Spirocyclisation is rapid and usually reversible but in one case a stable spirocyclic product has been isolated.

Mollusk Glue Inspired Mucoadhesives for Biomedical Applications

“…Around 50% HCA was left in the hydrogel after 2 h. This difference in the release profile may be due to the difference in ionization status of the catechol compounds. DA and DOPA are cationic, while HCA is anionic at pH 5.5. , Therefore, only HCA can interact electrostatically with the positively charged CH at pH 5.5. Such electrostatic interactions are responsible for the slower release of HCA.…”

“…DA and DOPA are cationic, while HCA is anionic at pH 5.5. 41,42 Therefore, only HCA can interact electrostatically with the positively charged CH at pH 5.5. Such electrostatic interactions are responsible for the slower release of HCA.…”

A melanin-inspired pro-oxidant system for dopa(mine) polymerization: mimicking the natural casing process

“…However, it is possible that the relative stability of the intermediate quinones generated on the CD-melanin surface also plays a role, in accord with the faster intramolecular cyclization rate constants reported for DOPA quinone (k = 3.8 s À1 at pH 7.4) versus NE quinone (k = 0.37 s À1 at pH 7.0) and DA quinone (k = 0.04 s À1 at pH 7.0). 11 Rate acceleration varied in a non-linear manner with the amount of CD-melanin (Fig. 2, panel b), reflecting likely non-linear changes in the total surface area of the heterogeneous redox system with concentration, due to aggregation phenomena.…”

Dopamine quinone chemistry: a study of the influence of amide, amidine and guanidine substituents [-NH-CX-Y] on the mode of reaction

“…We have previously described investigations of the reactions of a variety of dopamine ortho-quinone derivatives 4. 1,2 In these studies we have generated the ortho-quinones 4 by (i) tyrosinase oxidation of phenols 1 or catechols 2, 3-7 (ii) pulse radiolytic oxidation of catechols 2, 3-6,8 and (iii) chemical oxidation of catechols 2. [9][10][11] We have found that cyclisation to the 5-position to give the bicyclic products 5 (Scheme 1) is usually fast but that faster transient formation of the less stable spirocyclic compounds 3 is sometimes observed.…”