Fig. 2.

Schematic representation of retinoid-based amines and their biologic activities. (A) Retinal analogs. For QEA, R₁ and R₄ represent H or methyl; R₂ and R₃ are H, hydroxyl; R₅ is H, methyl, t-butyl, benzyl, or p-methoxy benzyl; R₆ corresponds to H, methyl, or t-butyl; and X could be C, O, or N. When X is O, there is no R₃ group. For QEA-D and QEA-G-001, R₅ represents a -(CH₂)₃- bridge connecting C7 and C9. For TEA, R₁ and R₄ can be H or methyl, whereas R₂ and R₃ are H or hydroxyl; R₅ is H or t-butyl; R₆ can be H, methyl, t-butyl, or benzyl; and R₇ corresponds to H or methyl. For PEA, R₁ and R₂ are H or hydroxyl. These compounds were converted to primary amines prior to the tests. (B) Schematic representation of the experimental design used to test the biologic activity of amines. The black arrows represent the chemical conversions of tested compounds, whereas blue arrows represent the candidate compound selection. (C) Fraction of tested compounds that serve as substrates of LRAT. (D) Extent of inhibition displayed by tested amines against RPE65 enzymatic activity.