Structural Elucidation and Chemistry of a Novel Family of Bioactive Sesquiterpenes: Heliannuols
作者:Francisco A. Macias、Jose M. G. Molinillo、Rosa M. Varela、Ascension Torres、Frank R. Fronczek
DOI:10.1021/jo00105a052
日期:1994.12
From the moderately polar active fractions of leaf aqueous extract of Helianthus annuus L. var. SH-222 and VYP, we have isolated three new sesquiterpenes which contain a previously unknown skeleton, heliannuols B-D (2-4). The structural elucidation of heliannuols was based on extensive spectral studies, including H-1-H-1 COSY, H-1-C-13 HETCOR, and NOE difference experiments, X-ray diffraction analysis of 4, and chemical correlation between 1, 2, and 4. A biosynthetic pathway that involves an oxirane ring opening is proposed for heliannuols A (1) and D (4), while a phenonium ion intermediate is proposed for heliannuol C (3). The oxirane ring opening and the formation of this intermediate have been evaluated using the semiempirical method PM3. Allelopathic activity bioassays of compound 1-4 suggest that those members of a new class of bioactive sesquiterpenes may be involved in the cultivar sunflower defense against dicotyledon species.
Enantioselective total synthesis of heliannuols D and A †
Heliannuols D and A, which exhibit allelopathic activity, were synthesized enantioselectively via a base-mediated intramolecular cyclisation of a phenolic epoxide for the first time, and the absolute structures were established by total synthesis.