José M. G. Molinillo

Bioactive terpenoids from sunflower leaves cv. Peredovick.

The CH(2)Cl(2) extract of dried leaves of Helianthus annuus L. cv. Peredovick(R) has yielded, in addition to the known sesquiterpene lactones annuolide E and leptocarpin, and the sesquiterpenes heliannuols A, C, D, F, G, H, I, the new bisnorsesquiterpene, annuionone E, and the new sesquiterpenes heliannuol L, helibisabonol A and helibisabonol B. Structural elucidation was based on extensive spectral (one and two-dimensional NMR experiments) and theoretical studies. The sesquiterpenes heliannuol A and helibisabonol A and the sesquiterpene lactone leptocarpin inhibited the growth of etiolated wheat coleoptiles.

Allelochemicals from sunflower leaves cv. Peredovick

Abstract Isolation, structural elucidation and allelopathic bioassays of 13 compounds, isolated from sunflower cultivar cv. Peredovick are described. Two new sesquiterpene lactones, helivypolide D and helivypolide E and the bisnorsesquiterpene, annuionone D, which is reported at the first time as natural product, are described. The effects of a series of aqueous solutions at 10−4–10−9 M of these compounds were studied on the root and shoot lengths of Lactuca sativa, Lepidium sativum seedlings (dicotyledons) and Hordeum vulgare and Allium cepa (monocotyledons).

Bioactive flavonoids from Helianthus annuus cultivars

Abstract Isolation, structure elucidation and allelopathic bioassay of five flavonoids (the flavonol tambulin, the chalcones kukulcanin B and heliannone A, and the flavanones heliannones B and C) from the sunflower cultivar VYP® are described. Heliannones A–C are reported in the literature as natural products, for the first time. The effects of a series of aqueous solutions at 10−4–10−9 M of the flavonoids on the root and shoot length of Lycopersicon esculentum and Hordeum vulgare has been studied. They influence, principally, the shoot growth of seedlings, but germination and radical length can be affected by chalcones. The effects of very similar compounds, kukulcanin B and heliannone A, varied. The reason for this variation could be related to the number and position of free hydroxy groups.

Potential allelopathic guaianolides from cultivar sunflower leaves, var. SH-222

Abstract The leaf aqueous extracts of cultivar sunflower ( Helianthus annuus L.) var. SH-222® afforded, from the medium polar fractions, five new guaianoli

Plant biocommunicators: their phytotoxicity, degradation studies and potential use as herbicide models

The development of new bioactive molecules with potential application in pharmacology and agriculture by using natural products as templates has been a widely used approach in the recent years. Focusing our attention in phytochemicals with potential application in agriculture, allelochemicals (natural plant toxins) have been deeply researched with the main purpose of finding phytotoxic substances to use as new herbicidal templates. The development of new analytical methodologies, improved bioassay techniques and a complete understanding of the allelopathic phenomenon will provide new tools for natural herbicide models development, in the context of the new approaches to integrated pest management. A deeper knowledge of the release and assimilation of allelochemicals, and the degradation phenomena associated to them will aid to discover new chemical structures with potential utility, in addition to a better understanding on the ecological interactions mediated by phytochemicals. The research on these topics, made with promising allelochemicals such as benzoxazinones and their degradation derivatives, the improvements on analytical design, the degradation mechanisms elucidation and the novel bioassay techniques recently developed, are revised herein.

Rediscovering the bioactivity and ecological role of 1,4-benzoxazinones

Compounds of the (2H)-1,4-benzoxazin-3(4H)-one class have attracted the attention of phytochemists since the first isolation of 2,4-dihydroxy-2H-1,4-benzoxazin-3(4H)-one (DIBOA) and 2,4-dihydroxy-7-methoxy-(2H)-1,4-benzoxazin-3(4H)-one (DIMBOA). Extensive research has been carried out on the isolation and synthesis of these materials as well as on the dynamics of their degradation in different systems. This has led to the discovery of a wide variety of compounds that are of high interest from the point of view of phytotoxic, antifungal, antimicrobial, and antifeedant effects among others. The potential application of benzoxazinones and their derivatives as leads for natural herbicide models is a topic of current interest. Furthermore, the importance of degradation on the ecological behaviour of benzoxazinone-producing plants is also being realised, and proposals concerning the role of the degradation products in chemical defence mechanisms have been put forward. There is also increasing interest in the improvement of analytical methodologies, and ecotoxicologic effects, toxicity on target and non-target organisms, and degradation kinetics are also being addressed. The development of new phytotoxicity bioassay techniques represents one of the most important breakthroughs in this respect. Moreover, benzoxazinones and some of their derivatives have been employed in the development of pharmaceuticals. The versatility of the benzoxazinone skeleton, in addition to its relative chemical simplicity and accessibility, makes these chemicals amongst the most promising sources of bioactive compounds that are natural in origin.

Dehydrozaluzanin C: a potent plant growth regulator with potential use as a natural herbicide template.

The natural product dehydrozaluzanin C (former DHZ) is a sesquiterpene lactone obtained from different weeds of the Compositae family. Its potential as a plant growth regulator has been evaluated by using a phytotoxic allelopathic bioassay, where the commercial herbicide Logran is used as internal reference. The evaluation is made based on their effects on germination and growth over several dicotyledon and monocotyledon species. The activity was tested in the range of 1000-0.001 microM. In almost all cases, DHZ was more active than the internal reference at 1000 microM, and its activity fell below the level of the internal reference at 100 microM. These results confirm DHZ as a potent plant growth regulator and a good candidate for the development of new herbicide models.

Bioactive steroids from Oryza sativa L.

Rice is one of the most interesting crops in the world from both the social and the economic point of views. The monoculture practices along with the heavy use of herbicides are characteristic of modern agriculture and are inducing the appearance of tolerant and/or herbicide resistant weed biotypes. This is the case the worlds main weed of rice barnyardgrass (Echinochloa crus-galli). Alternative strategies for weed suppression consist of the use of chemicals from rice due to necessity of obtaining new herbicides with new modes of action that could prevent resistance phenomena. In order to carry out a study that guides to the isolation of the most active compounds from rice, different extracts were achieved, and their activities evaluated. So, all the plant material was divided into three parts: fresh plant, dried plant, and fresh plant from Pluviotron. The aerial part was separated from roots in all cases and extracted in water, in organic solvents as well as with the Pluviotron device. The activity of the 12 extracts obtained was evaluated using a generalist bioassay, wheat etiolated coleoptiles bioassay, and a phytotoxic bioassay on barnyardgrass as target species. The bioactive extracts were fractionated and 15 compounds were isolated and identified by spectroscopic methods. Eight of these compounds were isolated for the first time in Oryza sativa. The most phytotoxic compounds on E. crus-galli were ergosterol peroxide and 7-oxo-stigmasterol. In the case of ergosterol peroxide the activity was higher than the commercial herbicide Logran. This is the first report of potential allelopathic activity of steroids on weeds based on their phytotoxicity.

Isolation and Phytotoxicity of Terpenes from Tectona grandis

A study was carried out on the allelopathic potential of four forest species, Tectona grandis, Aleurites fordii, Gliricidia sepium, and Maytenus buxifolia. The most active species, T. grandis, was selected to perform a phytochemical study. A new compound, abeograndinoic acid, was isolated, and elucidation of its structure showed that this compound has an unusual carbon skeleton. A further 21 known terpenoids—including 4 sesquiterpenoids, 8 diterpenes and 9 triterpenes—also were isolated. A biosynthetic scheme for the presence of the new compound is proposed. Bioactivity profiles that used etiolated wheat coleoptiles and phytotoxicity bioassays on the isolated compounds were conducted. The compounds that presented the highest phytotoxic activity are the diterpenes 9 (2-oxokovalenic acid) and 12 (19-hydroxyferruginol).

Bioactive apocarotenoids from Tectona grandis

The bioactive fractions of Tectona grandis have yielded seven apocarotenoids, two of which have been isolated for the first time as natural products (tectoionols A and B). The chemical structures were determined through 1D and 2D nuclear magnetic resonance experiments. The absolute configuration of tectoionol A was determined using a modified Mosher methodology. Some NMR assignments for the compounds 9(S)-4-oxo-7,8-dihydro-beta-ionol and 3beta-hydroxy-7,8-dihydro-beta-ionone have been corrected on the basis of g-HSQC and g-HMBC experiments. The general bioactivities of isolated compounds have been studied using etiolated wheat coleoptiles. Those compounds that presented higher levels of activity were assayed on standard target species (Lactuca sativa, Lycopersicum esculentum, Lepidium sativum and Allium cepa).