Proanthocyanidins are oligomers of catechins that exhibit potent antioxidative activity and inhibit binding of oxidized low-density lipoprotein (OxLDL) to the lectin-like oxidized LDL receptor (LOX-1), which is involved in the onset and development of arteriosclerosis. Previous attempts aimed at developing proanthocyanidin derivatives with more potent antioxidative activity and stronger inhibition for LOX-1 demonstrated the synthesis of a novel proanthocyanidin derivative (1), in which the geometry of one catechin molecule in procyanidin B3 was constrained to a planar orientation. The radical scavenging activity of 1 was 1.9-fold higher than that of procyanidin B3. Herein, we synthesized another procyanidin B3 analogue (2), in which the geometries of both catechin molecules in the dimer were constrained to planar orientations. The radical scavenging activity of 2 was 1.5-fold higher than that of 1, suggesting that 2 may be a more effective candidate than 1 as a therapeutic agent to reduce oxidative stress induced in arteriosclerosis or related cerebrovascular disease.Download high-res image (155KB)Download full-size image

Two hallmarks of Alzheimer’s disease (AD) observed in the brains of patients with the disease include oxidative injury and deposition of protein aggregates comprised of amyloid-β (Aβ) variants. To inhibit these toxic processes, we synthesized antioxidant-conjugated peptides comprised of Trolox and various C-terminal motifs of Aβ variants, TxAβx–n (x = 34, 36, 38, 40; n = 40, 42, 43). Most of these compounds were found to exhibit anti-aggregation activities. Among them, TxAβ36–42 significantly inhibited Aβ1–42 aggregation, showed potent antioxidant activity, and protected SH-SY5Y cells from Aβ1–42-induced cytotoxicity. Thus, this method represents a promising strategy for developing multifunctional AD therapeutic agents.

Amyloid-β (Aβ) deposition and oxidative stress observed in the brains of patients with Alzheimer’s disease (AD) are important targets for therapeutic intervention. In this study, we conjugated the antioxidants caffeic acid (CA) and dihydrocaffeic acid (DHCA) to Aβ1–42 C-terminal motifs (Aβx–42: x = 38, 40) to synthesize CA-Aβx–42 and DHCA-Aβx–42, respectively. Among the compounds, CA-Aβ38–42 exhibited potent inhibitory activity against Aβ1–42 aggregation and scavenged Aβ1–42-induced intracellular oxidative stress. Moreover, CA-Aβ38–42 significantly protected human neuroblastoma SH-SY5Y cells against Aβ1–42-induced cytotoxicity, with an IC50 of 4 μM. These results suggest that CA-Aβ38–42 might be a potential lead for the treatment of AD.

Catechin analogue 1 with methyl substituents ortho to the catechol hydroxyl groups was synthesized to improve the antioxidant ability of (+)-catechin. The synthetic scheme involved a solid acid catalyzed Friedel–Crafts coupling of a cinnamyl alcohol derivative to 3,5-dibenzyloxyphenol followed by hydroxylation and then cyclization through an intermediate orthoester. The antioxidative radical scavenging activity of 1 against galvinoxyl radical, an oxyl radical, was found to be 28-fold more potent than (+)-catechin.A catechin analogue (1) with methyl groups ortho to the catechol hydroxyl groups was synthesized and exhibited 28-fold more potent radical scavenging activity than (+)-catechin.

Proanthocyanidin, an oligomer of catechin, is a natural antioxidant and a potent inhibitor of lectin-like oxidized LDL receptor-1, which is involved in the pathogenesis of arteriosclerosis. We synthesized proanthocyanidin analogue 1, in which the geometry of one catechin molecule in procyanidin B3, a dimer of (+)-catechin, is constrained to be planar. The antioxidant activities of the compounds were evaluated in terms of their capacities to scavenge galvinoxyl radicals, and results demonstrate that while procyanidin was 3.8 times more potent than (+)-catechin, the radical scavenging activity of proanthocyanidin analogue 1 was further increased to 1.9 times that of procyanidin B3. This newly designed proanthocyanidin analogue 1 may be a promising lead compound for the treatment of arteriosclerosis and related cerebrovascular diseases.