| Summary: | Pterocarpans and related polyphenolics are known as promising neuroprotective agents. We used models of rotenone-, paraquat-, and 6-hydroxydopamine-induced neurotoxicity to study the neuroprotective activity of polyphenolic compounds from <i>Lespedeza bicolor</i> and their effects on mitochondrial membrane potential. We isolated 11 polyphenolic compounds: a novel coumestan lespebicoumestan A (<b>10</b>) and a novel stilbenoid 5’-isoprenylbicoloketon (<b>11</b>) as well as three previously known pterocarpans, two pterocarpens, one coumestan, one stilbenoid, and a dimeric flavonoid. Pterocarpans <b>3</b> and <b>6</b>, stilbenoid <b>5</b>, and dimeric flavonoid <b>8</b> significantly increased the percentage of living cells after treatment with paraquat (PQ), but only pterocarpan <b>6</b> slightly decreased the ROS level in PQ-treated cells. Pterocarpan <b>3</b> and stilbenoid <b>5</b> were shown to effectively increase mitochondrial membrane potential in PQ-treated cells. We showed that pterocarpans <b>2</b> and <b>3</b>, containing a 3’-methyl-3’-isohexenylpyran ring; pterocarpens <b>4</b> and <b>9</b>, with a double bond between C-6a and C-11a; and coumestan <b>10</b> significantly increased the percentage of living cells by decreasing ROS levels in 6-OHDA-treated cells, which is in accordance with their rather high activity in DPPH<sup>•</sup> and FRAP tests. Compounds <b>9</b> and <b>10</b> effectively increased the percentage of living cells after treatment with rotenone but did not significantly decrease ROS levels.
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