Flavone and isoflavone derivatives of terrestrial plants as larval settlement inhibitors of the barnacle Balanus amphitrite

Abstract

To determine whether they could serve as non-toxic or less damaging alternative antifouling (AF) agents, 17 flavone and isoflavone derivatives were isolated from terrestrial plant extracts, purified and examined for their ability to inhibit the settlement of barnacle (Balanus amphitrite) cyprids. In larval bioassays, eight compounds showed strong anti-larval settlement activities, with EC₅₀ values <10 μg ml⁻¹. Through an analysis of the structure-activity relationship of these compounds, it was found that (1) the structural difference between flavones and isoflavones did not affect their AF activities; (2) the 5-hydroxyl group on the skeletons played a key role in AF activities; and (3) the presence of hydroxyl group or bulky group on C3 significantly reduced AF activities. A hydrolysis experiment using genistein, a typical active compound in this study, indicated that it was decomposed in the marine environment by hydrolysis reaction and that the degradation speed was significantly affected by pH. In a field AF test, genistein inhibited the attachment of B. amphitrite on panels coated with genistein-paint mixtures.

Keywords:

• antifoulant
• flavone and isoflavone derivatives
• structure-activity relationship
• Balanus amphitrite
• hydrolysis
• antifouling field test

Acknowledgement

This study was supported by a grant from the Chinese Ocean Mineral Resources Research and Development Association (COMAR06/07.SC02), and the CAS/SAFEA International Partnership Program for Creative Research Teams as well as a RGC grant (CA04/05.SC01) to P.-Y. Qian.