Antioxidant Activity of Planar Catechin Conjugated with Trolox

Abstract

Planar catechin (PCat), a natural antioxidant with a fixed 3D catechin structure on a plane, exhibits radical-scavenging activity approximately five times stronger than the conventional catechin. We synthesized a compound, PCat-TrOH, by binding Trolox (TrOH), an α-tocopherol analog, to PCat to enhance its antioxidant effect against oxidative stress, such as lipid peroxidation. TrOH shows radical-scavenging activity about 6.5 times greater than PCat, and PCat-TrOH exhibited a similar level of radical-scavenging activity to TrOH. Additionally, PCat-TrOH demonstrated twice the radical-scavenging activity against reactive oxygen species compared to PCat or TrOH. This compound is also expected to exhibit an excellent antioxidant effect against lipid peroxidation caused by radical chain reactions, through interactions with vitamin C, similar to that in the case of α-tocopherol.

Keywords: antioxidant activity; catechin; tocopherol; trolox.

Figure 1

Structures of (+)-catechin, PCat, α-tocopherol, TrOH, and PCat-TrOH.

Figure 2

Synthesis of PCat-TrOH. Regents and conditions: (a) ethyl levulinate, TMSOTf, THF, −30 °C; (b) tert-butyldimethylchlorosilane, imidazole, DMF, 0 °C → rt; (c) LiAlH₄, THF, 0 °C → rt; (d) di-tert-butyliminodicarboxylate, Ph₃P, DEAD,THF, 0 °C → rt; (e) TFA, CH₂Cl₂, 0 °C → rt; (f) TrOH, DIPEA, HATU, DMF, 0 °C → rt; (g) TBAF, CH₂Cl₂, 0 °C → rt.

Figure 3

Spectral change (interval: 1 s) observed during the reaction of PCat-TrOH (7.2 × 10⁻⁵ M) with GO^• (5.6 × 10⁻⁶ M) in MeCN at 298 K. The arrow denotes the direction of absorbance changes. Inset: The first-order plot of the absorbance at 428 nm.

Figure 4

Plots of pseudo-first-order rate constants (k_obs) vs. concentrations of TrOH (green circles), PCat-TrOH (red circles), PCat (blue circles), and Cat (black circles) in MeCN at 298 K.

Figure 5

Spectral change observed upon addition of PCat-TrOH (0, 4.4 × 10⁻⁷, 8.7 × 10⁻⁷, 1.3 × 10⁻⁶, 1.7 × 10⁻⁶, 2.2 × 10⁻⁶ M) to GO^• (7.8 × 10⁻⁶ M) in MeCN at 298 K. The arrows denote the direction of absorbance changes.

Figure 6

Plots of the absorbance at 428 nm vs. the concentration ratios of antioxidants (TrOH (green circles), PCat-TrOH (red circles), and PCat (blue circles)) to GO^•, [antioxidants]/[GO^•], in MeCN.