Wesley G. Taylor

Triterpenoid saponins synergize insecticidal pea peptides: effect on feeding and survival of Sitophilus oryzae (Coleoptera: Curculionidae)

Abstract The triterpenoid saponins soyasaponin I, dehydrosoyasaponin I, echinocystic acid 3-glucoside, &bgr;-escin, glycyrrhizic acid, hederacoside C, and &agr;-hederin were tested alone and in combination with insecticidal PA1b peptide mixtures isolated from peas for their effects on the feeding and survival of a stored-product insect, the rice weevil, Sitophilus oryzae (L.). There were two sources of peptides: a purified extract composed primarily of PA1b peptides and a partially purified extract (C8 extract) that contained mainly peptides and lesser amounts of soyasaponin I, dehydrosoyasaponin I, and other compounds. Dehydrosoyasaponin I, echinocystic acid 3-glucoside, &agr;-hederin, and &bgr;-escin were active (causing reduced feeding and increased mortality) when used alone. Soyasaponin I, hederacoside C, and glycyrrhizic acid were inactive when used alone. Purified peptides and C8 extract were active when used alone. The mixtures of the inactive soyasaponin 1 and the active peptides were as active as peptides alone, even when peptides composed only 10% of the mixture. Similar trends were seen with the mixtures of &bgr;-escin and PA1b. In general, the mixtures of saponins and peptides were synergistic. Possible modes of synergistic action are discussed.

Synthesis and Mosquito Repellent Properties of 2,2‐Dialkyl‐ and 2‐Alkyl‐4,4‐dimethyl‐N‐acetyloxazolidines

Nineteen novel N-acetyl-2,2-dialkyloxazolidines (2) and N-acetyl-2-alkyl-4,4-dimethyloxazolidines (3) were synthesized from commercially available carbonyl compounds and ethanolamine or 2-amino-2-methyl-1-propanol. Their bioactivity against laboratory-reared mosquitoes was compared in patch tests to known N-acetyl-2-alkyloxazolidines (1) and N,N-diethyl-m-toluamide (deet insect repellent). Isomeric composition measurements by [ 13 C]NMR spectroscopy favoured the Z rotational isomer for samples of 2 (91-96% Z) and the E rotational isomer for samples of 3 (66-71% E), in agreement with molecular mechanics calculations on rotational isomers of model oxazolidines. Samples of 1 were previously shown to exist in solution mostly as the Z isomer (60-70% Z). Within the optimal molecular weight range for these experimental chemicals, the duration of repellency against Aedes aegypti (L.), Anopheles quadrimaculatus Say and Anopheles albimanus Wiedemann generally followed the order : 1 > 2 > deet > 3. Bioassay data are discussed in relation to the equilibrium populations of rotational isomers for substituted N-acetyloxazolidines.

Soyasaponins and Related Glycosides of Desmodium canadense and Desmodium illinoense

Seed extracts of Desmodium canadense (L.) DC., a native Canadian legume, were examined by HPLC and electrospray ionization mass spectrometry (LC/MS) for the presence of triterpenoid saponins of the oleanene type. An aqueous methanol extract, fractionated by use of a Diaion™ HP-20 macroporous resin, was found to possess soyasaponin III (soyasaponin Bb´) and the 2,3-dihydro-2,5-dihydroxy-6-methyl-4H-pyran-4-one conjugate of soyasaponin III (DDMP S-III) as major saponin components. Minor components were identified by LC/MS as C-24 aldehyde (sandosapogenol) derivatives, S-III al and DDMP S-III al. Soyasaponin I (soyasaponin Bb), soyasaponin VI (soyasaponin  g) and dehydro- soyasaponin I (soyasaponin Be) were also found as minor components. These components were also detected in extracts obtained by Soxhlet extraction with water followed by partitioning into n-butanol. Extracts from foliage of greenhouse and field origins were essentially free of these saponins. Soyasaponin VI was the main seed saponin of Desmodium illi- noense A. Gray whereas soyasaponin III and DDMP S-III were found as minor components. Components corresponding in molecular mass to C-22 glycosides of soyasaponin I and soyasaponin III were also detected in saponin-enriched ex- tracts. Neither species was a good source of alkaloids.

Capillary gas chromatographic determination of permethrin insecticide by transesterification

A sensitive method was developed to determine permethrin extracted from phosphate buffer and cattle plasma by potassium cyanide catalyzed transesterification of this insecticide with refluxing ethanol and detection of the resulting ethyl esters by capillary gas chromatography with an electron capture detector. With a reflux time of 2 h and with 3-phenoxybenzyl 2-chlorobenzoate as an internal standard, linear calibration curves from buffer (5-250 ng) and plasma (5-100 ng) were obtained. Precision and accuracy of the method were < or = 15%. The limit of detection was approximately 2.5 ng/ml (cis) and 1 ng/ml (trans) from buffer. In cattle sprayed along the back at 2 mg/kg, the concentration of cis- and trans-permethrin in plasma was below the detection limit (5 ng/ml).