Phenanthrene Derivatives from <i>Asarum heterotropoides</i> Showed Excellent Antibacterial Activity against Phytopathogenic Bacteria

Abstract

<i>Asarum heterotropoides</i> extracts showed strong antibacterial activity against selected phytopathogenic bacteria. Bioguided isolation was conducted to obtain 11 phenanthrene derivatives (<b>1</b>-<b>11</b>), 4 phenylpropanoids (<b>12</b>-<b>15</b>), a flavonoid (<b>16</b>), and a steroid (<b>17</b>), including a new phenanthrene derivative (<b>1</b>). <i>In vitro</i> bioassay results showed that phenanthrene derivatives are the main active components of <i>A. heterotropoides</i> extracts. The new compound aristoloxazine C (<b>1</b>) was found to exhibit outstanding antibacterial activity against <i>Ralstonia solanacearum</i>, <i>Xanthomonas oryzae</i>, <i>Erwinia carolovora</i>, <i>Pseudomonas syringae</i>, and <i>Xanthomonas axonopodis</i>, with MIC values of 0.05, 2.5, 2.5, 5, and 6.25 μg/mL, respectively. These values were significantly higher than that of the positive control, streptomycin sulfate. Aristoloxazine C (<b>1</b>) also demonstrated an excellent control effect on tobacco bacterial wilt. Physiological and biochemical experiments combined with electron microscopy showed that the antibacterial activity of aristoloxazine C (<b>1</b>) was primarily related to the destruction of the bacterial cell wall structure. Thus, aristoloxazine C (<b>1</b>) may have the potential to be used as a template for the development of new bactericides or as a probe for the discovery of new antimicrobial targets.