Jørgen Lam

Mosquito larvicidal activity of polyacetylenes from species in the Asteraceae

Twenty-four polyacetylenes isolated from species in the Asteraceae were screened for their near-UV-mediated larvicidal properties to the mosquito, Aedes aegypti. Dosage resonse lines for three of the most active compounds were prepared. One of these, σ-terthienyl from Tagetes was more toxic than DDT when near-UV radiation was provided. A scaled up trial with this compound in a simulated field situation demonstrated its potential as a larvicide. The effects of the radiation dose on larval survival were studied and the action spectra for the phototoxic effects of three compounds on larvae were obtained with narrowband interference filters. Because of the close agreement between the action and absorption spectra, it appears most probable that the polyacetylene is the primary absorbing compound. The potential of polyacetylenes as larvicides and their role in plant herbivore relations are discussed.

Acetylenes and related compounds in heliantheae

Abstract In this review acetylenes and related compounds, such as thiophenes, alkamides, unsaturated alkyl ketones and hydrocarbons, which have been isolated from the tribe Heliantheae (Asteraceae) are listed. Some of these compounds are widely distributed in Asteraceae, especially in the tribes Anthemideae, Cynareae, Helenieae and Inuleae. On the basis of their distribution in Heliantheae, the chemotaxonomy of this tribe is discussed. Furthermore the biosyntheses of some of the isolated compounds are evaluated.

Photosensitization of invertebrates by natural polyacetylenes

Fourteen polyacetylenes or their thiophene derivatives, isolated from species in the Asteraceae were screened for their biological activity to mosquito larvae (Aedes aegypti), blackfly larvae (Simulium vittatum) and adult nematodes (Caenorhabditis elegans). Toxicity of the compounds was found to be enhanced greatly by irradiation with near-UV radiation or natural sunlight. Only wavelengths less than 400 nm were effective in promoting photosensitization. The results are discussed in relation to herbivore-plant interactions.

Acetylenes and related compounds in astereae

Abstract In this review an attempt has been made to list all acetylenes and related compounds such as polyenes, unsaturated hydrocarbons and thiophenes, which have been isolated from the tribe Cynareae (Asteraceae). Some of these compounds are widely distributed in Asteraceae and others are characteristic natural products of this tribe. On the basis of their distribution in Cynareae, the chemotaxonomy of this tribe is discussed. Furthermore the biosynthesis and biological activities of some of the isolated compounds are evaluated.

Light-mediated allelochemical effects of naturally occurring polyacetylenes and thiophenes from asteraceae on herbivorous insects.

Polyacetylenes and their thiophene derivatives, characteristic secondary metabolites of the Asteraceae, were examined for their effects on herbivorous insects. Three thiophenes (a monothiophene, a bithiophene, and α-terthienyl) and four polyacetylenes (phenylheptatriyne, phenylheptadiynene, phenylheptadiyene acetate, and matricaria lactone) were studied for their phototoxicity and light-independent toxicity to (1) a polyphagous lepidopteran,Ostrinia nubilalis, whose host range includes a number of phototoxic Asteraceae, (2) a polyphagous lepidoteran,Euxoa messoria, whose host range includes very few species of Asteraceae, and (3) an oligophagous lepidopteran,Manduca sexta, which is a specialist on Solanaceae. Several compounds were phototoxic toM. sexta andE. messoria even at very low irradiance levels, but behavioral adaptations, including spinning silk and boring into diet, allowedO. nubilalis to avoid photosensitization. Light-independent activity of the compounds to all three species involved feeding deterrence increasing in the orderO. nubilalis, E. messoria, andM. sexta, and longterm metabolic toxicity in the form of impaired nutrient utilization. The biosynthetically derived thiophenes were more toxic than their acetylenic precursors, and toxicity increased with increasing number of thiophene rings. The results are discussed in terms of plant-insect coevolution.

THE ROLE OF OXYGEN IN PHOTOSENSITIZATIONS WITH POLYACETYLENES AND THIOPHENE DERIVATIVES

Abstract— The mechanism of photosensitization by polyacetylenes and biosynthetically derived thiophenes from species of the plant family Asteraceae was examined. With thiophenes photosensitization of yeast and E. coli occurred under aerobic but not anaerobic conditions. For similar experiments with polyacetylenes, both photodynamic and non‐photodynamic mechanisms were observed. While the relative toxicities of thiophenes and polyacetylenes under near UV radiation was in general similar, the in vitro generation of singlet oxygen was considerably less for polyacetylenes than thiophenes, which is additional evidence for the existence of an alternate mechanism of action in polyacetylene photosensitization. Rates of photodegradation of polyacetylenes are higher than for thiophenes suggesting that bond breaking/formation processes are more favored relative to energy transfer to oxygen for polyacetylenes than thiophenes.

Visualization reagents for sesquitterpene lactones and polyacetylenes on thin-layer chromatograms

Vanillin and p-dimethylaminobenzaldehyde were found to be the most useful of several benzaldehyde and benzoic acid derivatives for the detection of sesquiterpene lactones and polyacetylenic compounds on thin-layer chromatography (TLC). Colors produced with these two reagents and with 70 sesquiterpene lactones and 25 polyacetylenes were of all shades of the spectrum and were specific for individual compounds. Therefore these reagents can be used as an aid in the identification of these compounds on TLC. These spray reagents are the most sensitive of all reagents which have so far been used for the detection of sesquiterpene lactones or polyacetylenes on TLC.

Phototoxicity of naturally occurring and synthetic thiophene and acetylene analogues to mosquito larvae

Abstract Naturally occurring and synthetic analogues and derivatives of polyacetylenes and thiophenes of the Asteraceae were investigated for their phototoxic effects on mosquito larvae, iodination, dimethylation in the 3′,4′-position or substitution of the middle ring of α-terthienyl reduced phototoxicity. Methylation at the 2′-position increased activity. In the acetylene series, retention of a triacetylene-furan chromophore was necessary for optimal activity.

Phototoxic polyacetylenes and their thiophene derivatives [Effects on human skin]

Polyacetylenes and their thiophene derivatives were tested for their effects on human skin. Topically applied α‐terthienyl evoked bi‐phasic phototoxic dermatitis and the appearance of ‘sunburn’ cells in human epidermis. None of 11 polyacetylenes had the same effect although they mimicked α‐terthienyl in their phototoxic effects on Candida albicans and certain pathogenic microorganisms. The UV‐mediated antibiotic activity of the compounds and their apparent lack of phototoxicity towards the skin suggest a potential topical therapeutic role for them in yeast, fungal and bacterial infections and light‐responsive dermatoses. Their topical sensitizing capacity, however, has not yet been studied.

Flavonoids and polyacetylenes in Dahlia tenuicaulis

Abstract 5,7,4′-Trimethoxyflavanone, 5-hydroxy-7,4′-dimethoxyflavanone, 2′-hydroxy-4,4′,6′-trimeth-oxychalcone, and a new naturally occurring compound, 5,7,4′-trimethoxyflavan-4-ol have been isolated from the leaves of Dahlia tenuicaulis Sorensen. Two chalcones, 4,2′,4′-trihydroxychalcone and 3,2′,4′-trihydroxy-4-methoxychalcone, and 5-hydroxy-7,4′-dimethoxyflavanone have been isolated from the flower heads. Minute amounts of the polyacetylene 1,3-diacetoxy-tetradeca-4,6-diene-8,10,12-triyne have been found in both leaves and flower heads, whereas 1-acetoxy-tetradeca-4,6-diene-8,10,12-triyne was present only in the flower heads.