Search

Isohexenylnaphthazarins are commonly found in the root periderm of several Boraginaceous plants and are known for their broad range of biological activities. The work described herein concerns the biological activity of compounds from the roots of Echium plantagineum L. and Echium gaditanum Boiss (Boraginaceae) collected from field sites in southern Spain and Australia. Bioactivity was assessed using etiolated wheat coleoptile bioassay and in vitro growth inhibitory activity in HeLa and IGROV-1 cells. The quantification of four isohexenylnaphthazarins (shikonin/alkannin, deoxyshikonin/deoxyalkannin, acetylshikonin/acetylalkannin and dimethylacrylshikonin/dimethylacrylalkannin) was performed by LC-MS/MS using juglone as internal standard. Correlation coefficient values for the activities and concentrations of these four analytes were in the linear range and were greater than 0.99. Acetylshikonin/acetylalkannin and dimethylacrylshikonin/dimethylacrylalkannin were present in the highest concentrations in extracts of both species. The results reveal that greatest overall inhibition was observed in both bioassays with E. gaditanum extracts. Strong correlations between time of collection, sampling location and bioactivity were identified.

Four previously undescribed sucrose diester of aryldihydronaphthalene-type lignans, named echiumins A-D, were isolated from the butanol fraction of Echium angustifolium Mill, in addition to a known compound, trigonotin A, which is reported for the first time from the title plant. The structures of isolated compounds were elucidated using spectroscopic methods such as HRESIMS and 1D and 2D NMR spectroscopy. The isolated compounds displayed strong to weak antitumor activity against HepG2 and MCF7 cancer cell lines, with echiumins A and D showed the most potent activity.

Nineteen species of the genus Echium (Fam. Boraginaceae) collected in Macaronesia were surveyed in a search for new sources of γ-linolenic acid (GLA, 18:3ω6). High amounts of this acid were found in all of them, ranging from 9.15% (E. plantagineum) to 26.31% (E. callithyrsum) of total seed fatty acids. The amounts of GLA related to total seed weight were also significant, ranging from 1.77% (E. sventenii) to 5.02% (E. nervosum). In addition, considerable amounts of stearidonic acid (SA, 18:4ω3) were detected, ranging from 3.03% (E. auberianum) to 12.94% (E. plantagineum) of total fatty acids. These data allow us to consider the members of the genus Echium from Macaronesia as one of the richest sources of γ-linolenic acid found so far in nature. The results obtained from multivariable data analysis and the taxonomic relationships among the species is discussed.

The methanolic extract of the whole plant of Echium glomeratum Poir. (Boraginaceae) has afforded five pyrrolizidine alkaloids, three that were (7S, 8R)-petranine (1), (7S, 8S)-petranine (2), and (7R, 8R)-petranine (3a) or (7R, 8S)-petranine (3b), comprising a tricyclic pyrrolizidine alkaloids subclass; and two that were known but to the species: 7-angeloylretronecine (4) and 9-angeloylretronecine (5). All compounds were tested against a human tumor panel for cytotoxicity; no activity was observed (EC50 values > 20 µg/ml).

Fourteen species of the genus Echium (Fam. Boraginaceae) collected in the Macaronesia were surveyed in a search for high levels of γ-linolenic acid (GLA, 18:3ω6) in the seed oil. High amounts of this fatty acid were found in all of them, ranging from 18.85% (E. pitardii var. pitardii ) to 27.42% ( E. gentianoides ) on total seed fatty acids. The GLA content related to total seed weight was also significant, ranging from 1.26% ( E. handiense ) to 8.22% ( E. gentianoides ). In addition, considerable amounts of stearidonic acid (SA, 18:4ω3) were detected, ranging from 3.78% ( E. bonnetii var. bonnetii ) to 8.81% ( E. pininana ) on total fatty acids. Besides all the perennial species, the four herbaceous Echium taxa endemic to the Macaronesia also showed high GLA percentages. This is in contrast to the low GLA level found in continental Echium species, all of them bearing an herbaceous habit. These results are in good agreement with the available genetic data and show the ability of GLA to discriminate between Macaronesian and continental Echium species. The analysis of five other Macaronesian species belonging to plant families rich in GLA are also reported.

Leaves from 25 Macaronesian Echium (Boraginaceae) species have been surveyed for hydrocarbon compounds. These plants were previously reported as the major source of γ-linolenic acid so far found in nature. In addition, six European Echium species and the common Borago officinalis have been analysed for comparative purposes. High squalene amounts were found in all Echium plants from the Macaronesia, ranging from 3.73% in E. simplex to 20.11% in E. fastuosum . Squalene was almost absent from all European Echium species, and the same is true for B. officinalis . The relatively high oil content (2.27%) in leaves of E. fastuosum raises the total squalene amount to about 0.46% within this tissue. The main fatty acid component in the leaf was α-linolenic acid (ALA, 18:3ω3), ranging in the Macaronesian Echium from 9.32% in E. acanthocarpum to 54.45% in E. simplex . Possible utilisation of these plants as a commercial source of squalene and hypotheses about its physiological role in the plant are discussed.

Callus cultures of Echium lycopsis were shown to produce a large amount of a mixture of red pigments consisting of five esterified derivatives of 5,8-dihydroxy-2-(1-hydroxy-4-methyl-3-pentenyl)-1,4-naphthoquinone. Examination of the absolute configuration of these compounds revealed that the cultures produced both the R -form (shikonin) and the S -form (alkannin) in various ratios depending upon the esterified derivative, although the overall ratio for the total derivatives was ca 1:1. On the other hand, all the corresponding derivatives produced by Lithospermum cultures were primarily of the R -form. It was also demonstrated that pigment formation in Echium cultures was inhibited by either white or blue light as well as by the synthetic auxin 2,4-D as in the case of Lithospermum cultures.

Two new quinones, echinone and echinofuran, have been isolated from callus cultures of Echium lycopsis along with several acyl esters of shikonin. The structures of both quinones have been established by spectroscopic methods and by chemical degradations.