Potential Allelopathic Activity of Natural Plant Heliannanes: A Proposal of Absolute Configuration and Nomenclature

Proposals for the biogenesis and absolute configuration of 12 heliannanes (based on modified Mosher methodology) are presented. The proposal of biogenesis is discussed for both possible origins—terrestrial or marine. Due to the different skeleton types that have been found, a systematic nomenclature based on the different heterocycle ring size is proposed. Phytotoxicity of compounds 5–11 suggests that these new bioactive sesquiterpenes may be involved in sunflower defense against dicotyledon species, and they could be used as natural herbicide templates.