Zev Lidert

An x-ray crystallographic, mass spectroscopic, and NMR study of the limonoid insect antifeedant azadirachtin and related derivatives

Abstract The limonoid insect antifeedant azadirachtin (1) may be partially hydrogenated at the C22-C23 position and subsequently treated with an excess of sodium periodate and potassium permanganate in the presence of a base to give detigloyldihydroazadirachtin (4). This compound was examined by X-ray crystallographic techniques which revealed key structural fragments and together with detailed n.m.r. and mass spectroscopic studies allowed the complete unambiguous structure assignment to the parent azadirachtin molecule. Two further compounds, 3-deacetyl-11-desoxyazadirachtin (2), and 3-acetoxy-7-tigloyl-vilasinin lactone (3) were also isolated and characterised from a Senegal sample of neem seed.

Insect antifeedants from azadirachta indica (part 5): Chemical modification and structure-activity relationships of azadirachtin and some related limonoids

Abstract Chemical modification of the potent insect antifeedant and growth-disruption agent azadirachtin (1) and the related limonoids 3-tigloyl azadirachtol (6) and salannin (27) have permitted an exploration of the biological activity of these compounds. General comments are made regarding the structural dependency of the antifeedant effect.

3′-formyl-2′,4′,6′-trihydroxydihydrochalcone from Psidium acutangulum

Abstract Twig and leaf extracts of the Peruvian plant Psidium acutangulum were shown to have antifungal properties against the fungi Rhizoctonia solani, Helminthosporium teres and Pythium ultimum . Chemical investigation of these extracts resulted in the isolation of the new compound, 3′-formyl-2′,4′,6′-trihydroxychalcone, which demonstrated activity against the fungi R. solani and H. teres .

Chemistry of insect antifeedants from azadirachta indica (part 3): reactions on the C-22,23 enol ether double bond of azadirachtin and conversion to 22,23-dihydro-23-β-methoxyazadirachtin.☆

Abstract Azadirachtin (1) can be converted to the natural product 22,23-dihydro-23β-methoxyazadirachtin (2) via selective bromomethoxylation of the C-22,23 enol ether double bond and tri-n-butyltin hydride reduction; the corresponding acetic acid adduct on pyrolysis affords (1) in high yield. The antifeedant effects of the addition compounds were assessed.

Synthesis of 2-(2,6-dichloro-4-pyridyl)-3-propargyl-5-ethyl-6-methyl-4(3H)-pyrimidinone, a promising new herbicide

Abstract A novel synthesis of the promising new herbicide 2-(2,6-dichloro-4-pyridyl)-3-propargyl-5-ethyl-6-methyl-4(3 H )-pyrimidinone (12) is reported which features (1) regioselective carbon, followed by nitrogen, dialkylation of an intermediate dianion, and (2) a tandem “one-pot” sequence of reactions involving sigmatropic sulfoxide elimination, lithium chloride-induced demethylation of a carbomethoxy grouping, decarboxylation, and isomerization/aromatization.

Structural reappraisal of the limonoid insect antifeedant azadirachtin

Based upon a detailed 250 MHz 1H n.m.r. study an alternative structure for the limonoid antifeedant azadirachtin has been determined.

1,4-Bis-(2,3-epoxypropylamino)-9,10-anthracenedione and related compounds as potent antifungal and antimicrobial agents

1,4-Bis-(2,3-epoxypropylamino)-9,10-anthracenedione (1) and related derivatives were assayed for antifungal, antimicrobial, and plant growth regulatory activity. Compound 1 was extremely potent against several strains of fungi, bacteria, and algae (MIC <2 ppm) and controlled two types of downy mildew by 90–100% at a dose of 12 ppm.

Synthesis of a monocyclic analogue of bipolaroxin, a phytotoxin of fungal origin

A sequence of three reactions leads to an efficient synthesis of compound 5, a model for a newly discovered phytotoxic metabolite from a plant-pathogenic fungus Bipolaris cynodontis.

A new synthesis of the tricyclic [10]annulene 7b-methyl-7bH-cyclopent [cd]indene

In a new versatile synthesis of the tricyclic [10]annulene, 7b-methyl-7bH-cyclopent[cd]indene, the third ring is formed by an intramolecular aldol condensation rather than a cycloaddition reaction.

5-Hydroxy-7b- methyl-7bH-cyclopent[cd]indene, a stable annulenol

5-Hydroxy-7b-methyl-7bH-cyclopent[cd]indene (1), the diester (6), and dialdehyde (11a) exist in the stable enol form and are thus the first isolable higher annulenols.