Tetracyclic indole alkaloids with antinematode activity from <i>Uncaria rhynchophylla</i>

<p>A new tetracyclic indole alkaloid, 17-<i>O</i>-methyl-3,4,5,6-tetradehydrogeissoschizine, together with seven known ones, were isolated from the aerial part of <i>Uncaria rhynchophylla</i>. Their structures were unambiguously elucidated by spectroscopic methods and comparing with the literature data. Among them, compounds <b>1</b>, <b>3</b>, <b>4</b> and <b>6</b>–<b>8</b> showed potent to moderate antinematode activities against <i>Panagrellus redivevus</i> at a concentration of 250 μg/mL.