The biochemistry and medical significance of the flavonoids.

In recent years, the use of essential oils (EOs) derived from aromatic plants as low-risk insecticides has increased considerably owing to their popularity with organic growers and environmentally conscious consumers. EOs are easily produced by steam distillation of plant material and contain many volatile, low-molecular-weight terpenes and phenolics. The major plant families from which EOs are extracted include Myrtaceae, Lauraceae, Lamiaceae, and Asteraceae. EOs have repellent, insecticidal, and growth-reducing effects on a variety of insects. They have been used effectively to control preharvest and postharvest phytophagous insects and as insect repellents for biting flies and for home and garden insects. The compounds exert their activities on insects through neurotoxic effects involving several mechanisms, notably through GABA, octopamine synapses, and the inhibition of acetylcholinesterase. With a few exceptions, their mammalian toxicity is low and environmental persistence is short. Registration has been the main bottleneck in putting new products on the market, but more EOs have been approved for use in the United States than elsewhere owing to reduced-risk processes for these materials.

Essential oils in insect control: low-risk products in a high-stakes world.

https://chemistry.mdma.ch/hiveboard/rhodium/pdf/piper.phytochemistry.pdf

Phytochemistry of the genus Piper

A review of botanical phytochemicals with mosquitocidal potential.

An in vitro evaluation of human cytochrome P450 3A4 inhibition by selected commercial herbal extracts and tinctures.

Insecticidal and growth-reducing properties of extracts of 14 species of American neotropical Piperaceae were investigated by inclusion in diets of a polyphagous lepidopteran, the European corn borer,Ostrinia nubilalis. Nutritional indices suggested most extracts acted by postdigestive toxicity.Piper aduncum, P. tuberculatum, andP. decurrens were among the most active species and were subjected to bioassay-guided isolation of the active components. Dillapiol was isolated from the active fraction ofP. aduncum, piperlonguminine was isolated fromP. tuberculatum, and a novel neolignan fromP. decurrens. The results support other studies on Asian and AfricanPiper species, which suggest that lignans and isobutyl amides are the active defence compounds in this family.

Insecticidal defenses of Piperaceae from the neotropics.

2,3-Dihydro-2-(4'-hydroxyphenyl)-3-methyl-5(E)-propenylbenzofuran (conocarpan) (1), 2-(4'-hydroxy-3'-methoxyphenyl)-3-methyl-5(E)- propenylbenzofuran (eupomatenoid-5) (2), and 2-(4'- hydroxyphenyl)-3-methyl-5(E)-propenylbenzofuran (eupomatenoid-6) (3), three known neolignans found for the first time in a species of the Piperaceae, were isolated from Piper decurrens via insecticidal bioassay-guided fractionation, along with a small quantity of a new related compound, 2,3-dihydro-5-formyl-2-(4'-hydroxyphenyl)-3-methylbenzofuran (decurrenal) (4), and 3,7,11,15-tetramethyl-2(E)-hexadecen-1-ol (trans-phytol).

Insecticidal Neolignans from Piper decurrens

Effect of lignans and other secondary metabolites of the asteraceae on the mono-oxygenase activity of the european corn borer

XThe CHCl3-soluble extract of Piper guanacastensis (Piperaceae) was found to have noteworthy insecticidal activity to Aedes atropalpus mosquito larvae (LC50 80.5 Ig/mL). Bioassay-guided fractionation afforded methyl 4-hydroxy-3-(3′-methyl-2′-butenyl)benzoate (1) as the major bioactive constituent (LC50 20.5 Ig/mL). The separation of compound 1 from its transesterification artifact (2), ethyl 4-hydroxy-3-(3′-methyl-2′-butenyl)benzoate, was achieved by recycling reversed-phase HPLC. The flavonoids acacetin, chrysin, and pinostrobin were also isolated from the active fraction but did not display insecticidal properties. The Piperaceae or pepper family is widely used in tropical regions throughout the world as medicines, condiments in regional cuisine, and pest-control agents. 1 As a part of a program aimed at the development of potentially useful phytochemicals as insect control agents (“green insecticides”) and because of our interest in the chemical ecology of the American neotropical Piperaceae, we now report the isolation and identification of a novel prenylated phenolic from Piper guanacastensis C. DC., an endemic species of Costa Rica in Central America. The insecticidal and growth-reducing properties of this plant material, as well as the activity of 13 additional species in the Piperaceae, were established previously using as model insect the European corn borerOstrinia nubilalis(Lepidoptera: Pyralidae). 2 This investigation confirmed that tropical American Piper species, including P. guanacastensis, have insecticidal activities comparable to previously studied African and Asian species. Bioactivity-guided fractionation of selected active crude extracts indicated the importance of phenyl propanoids (Piper aduncum), amides (Piper tuberculatum), and lignans (Piper decurrens) as the chemical defenses of the Piperaceae. 2,3 In the present study, the EtOH extract of P. guanacastensis aerial parts was found to be toxic to mosquito larvae, Aedes atropalpus L. (Diptera: Culicidae), the model insect used during bioactivity-guided fractionation of the crude total extract (LC50 ) 127.5 Ig/mL) for isolation of the active principle. The insecticidal activity was traced to the CHCl3-soluble fraction. Further fractionation on a silica gel column yielded a fraction rich in a mixture of prenylated benzoic acids derivatives, which had most of the insecticidal activity. HPLC separation furnished esters 1 (LC50 ) 20.5 Ig/ mL) and 2 (LC50 ) 25.7 Ig/mL) in pure form as the major active components. The structure of compound 1 was elucidated as methyl 4-hydroxy-3-(3′-methyl-2′butenyl)benzoate on the basis of spectral analysis. Derivative2represents the ethyl ester analog of natural product1and, therefore, an artifact of extraction formed by prolonged storage of the plant material in EtOH. The flavonoids acacetin, chrysin, and pinostrobin were also isolated from the CHCl3-soluble fraction but did not have pronounced insecticidal activity. These compounds have been found in other medicinally important Piper species, especially in those native to the Middle and Far East. 4

http://repositorio.fciencias.unam.mx:8080/xmlui/bitstream/handle/11154/2882/Methyl%204-hydroxy-3-(3'-methyl-2'-butenyl)benzoate,%20major%20insecticidal%20principle%20from%20Piper%20guanacastensis.pdf?sequence=2

Methyl 4-Hydroxy-3-(3'-methyl-2'-butenyl)benzoate, Major Insecticidal Principle from Piper guanacastensis

The phenylpropanoid, dillapiol, a compound capable of inhibiting the activity of cytochrome P-450 epoxidase in microsomal preparations of midguts of the European corn borer (ECB), Ostrinia nubilalis Hubner (Lepidoptera), did not enhance the toxicity of two insecticidal allelochemicals from the Asteraceae: the sesquiterpene lactone, tenulin or the phenylacetylene, phenylheptatriyne, when ingested simultaneously. Dillapiol alone was toxic to ECB larvae, and inhibited their growth. Possible reasons for the lack of synergism or potentiation by dillapiol of the insecticidal activity of the other allelochemicals are considered.



Resume

Effets in vitro des mixtures de substances allelochimiques sur le cycle biologique de la pyrale du mais, Ostrinia nubilalis



Le dillapiolc, un phenylpropanoide monomere d'un lignait et contenant un groupement methylenedioxyhphenyl (MDP), a la capacite d'inhiber in vitro les enzymes d'oxydations multiples a cytochrome P-450 (PSMO) utilisees par la pyrale du mais (ECB), Ostrinia nubilalis, pour dctoxifier les substances allelochimiques. Les composes contenant un groupe MDP comptent parmi les plus nombreux et puissants synergistes d'insecticides. Cependant, aucun synergisme n'est observe lorsque le dillapiole est ingere par la pyrale en association avec l'une ou l'autre ou les deux substances secondaires insecticides des Asteraceae, la lactone sesquiterpene tenuline ou/et le polyacetylene phenylheptatriyne (PHT). Plutot, le dillapiole est une toxine qui diminue la prise de poids des larves et retarde leur developpement. Les effets toxiques sont plus importants avec le dillapiole seul que lorsque celui-ci est associe a la tenuline ou/et au PHT. Les expications possibles de ces resultats sont discutees.

C.-B. Bernard

Papers

Insecticidal defenses of Piperaceae from the neotropics.

Insecticidal Neolignans from Piper decurrens

Effect of lignans and other secondary metabolites of the asteraceae on the mono-oxygenase activity of the european corn borer

Methyl 4-Hydroxy-3-(3'-methyl-2'-butenyl)benzoate, Major Insecticidal Principle from Piper guanacastensis

In vivo effect of mixtures of allelochemicals on the life cycle of the European corn borer, Ostrinia nubilalis