Tibor Timar

Precocene derivatives and aphid morphogenesis

The precocenes have notable effects on insect development, in particular they can induce specific destruction of corpora allatal cells and thus prevent the synthesis of juvenile hormones. As juvenile hormones have wide-ranging physiological roles in insects, from metamorphosis to reproduction, the effects of precocenes are also diverse. It has been suggested that high juvenile hormone titres in aphids induce the development of wingless adult forms while low titres promote the development of winged forms. The morphogenetic effects of precocene derivatives on aphids are complex. They can affect wing dimorphism in some species, both promoting wing development and inhibiting wing development, depending upon experimental strategy, and can exhibit the classical induction of precocious adult development indicating destruction of the corpus allatum. The morphogenetic effects promoted by a series of precocenes and 2,2-dimethylchromene derivatives have been investigated in the pea aphid, Acyrthosiphon pisum (Harris), and structure-activity relations determined for wing induction, wing inhibition, and precocious metamorphosis. These experiments show that compounds which promote wing development are not, or not so, effective in wing inhibition and that the compounds that inhibit wing formation are more closely aligned with those that induce precocious metamorphosis. Substitution of alkylthio for alkoxy groups at C7 alters the morphogenetic activity profile while 2,2-dimethylchroman derivatives have no morphogenetic activity.

Structural effects on the enantioselective acetylation of 4-hydroxychromans catalyzed by microbial lipases

Abstract Kinetic resolutions of a series of racemic 4-hydroxychromans by the Candida cylindracea lipase catalysed acetylation are described. Correlation between structure (conformation) and enantioselectivity is discussed.

Hypervalent iodine in carbon-carbon bond forming reactions. A new reaction of hypervalent iodine compounds and organolithium reagents

Abstract Hypervalent iodine compounds react with organolithium reagents instantaneously even at −80°C resulting in the formation of hydrocarbons. Our findings indicate that the carboncarbon bond formation is the result of ligand exchange and second displacement on the carbon bonded to iodine.

Synthesis of 2,2-dimethylbenzoxazepinones by the schmidt reaction of 2,2-dimethyl-4-chromanones

2,3-Dihydro-2,2-dimethyl-1,4-benzoxazepin-5(4H)-ones and 2,3--dihydro-2,2-dimethyl-1,5-benzoxazepin-4(5H)-ones have been synthesized by the Schmidt reaction of 2,2-dimethyl-4-chromanone. 2,2-Dimethylbenzoxazepinthiones have been prepared by the reaction of 2,2-dimethylbenzoxazepinones with Lawessons Reagent

A novel synthesis of 4-halo-2H-chromenes

Abstract substituted 4-halo-2H-chromenes were synthesized from the corresponding 4-chromanones and phosphorus trihalides.

Selective syntheses of analogues of the natural precocenes: synthesis and regioselective O-alkylation of 6-chloro- and 6-tert-butyl-7,8-dihydroxy-2,2-dimethyl-4-chromanones

The synthesis of novel benzopyran compounds analogues of the natural precocenes is described. These derivatives are obtained via novel synthesis and regioselective O-alkylation of 6-chloro- and 6-tert-butyl-7,8-dihydroxy-2,2-dimethyl-4-chromanones

On the Reaction of Substituted Phenols and 3-Methylbut-2-enoic Acid. A Comparative Study

A systematic and comparative study of the reaction of a series of substituted phenols and 3-methylbut-2-enoic acid in zinc chloride/phosphorus oxychloride and aluminum chloride/phosphorus oxychloride reveals that the formation of phenolic esters and 2,2-dimethyl-4-chromanones is strongly influenced by the substituents, their position on the aromatic ring of the starting phenols. Based on our study, a mixed Friedel-Crafts and Fries rearrangement mechanism is in operation in these reactions

Effects of precocene analogs on the nematode Caenorhabditis remanei (var. Bangaloreiensis). I. Structure/activity relations.

Precocenes (PI and PII) and 114 of their analogs (PAs) were synthetized and tested on C. remanei embryos for their precocene-like (P-like) activities resulting in unusual development at sublethal doses. The P-like activity was quantitated by plotting the probit of the percentage of the developmentally affected survivors against the (log) dose to obtain the EC plot and the half effective concentration (EC50). All five PAs (PI, PII, 7-ethoxy-PII, 7-(prop-2-ynyloxy)-PI, and 6-methoxy-7-(prop-2-ynyloxy)-PII) which exert both antiallatal activity in insects and P-like activity in nematodes are 7-alkoxy-substituted 2,2-dimethylchromenes. Both activities can be enhanced by an additional 6-MeO-substitution or by an asymmetric 6,7-dialkoxy-substitution, on condition that R-7 is longer than R-6. There are many more similarities than dissimilarities in the structural requirements needed for antiallatal and P-like activities. All but three nonantiallatal PAs effective in nematodes are 7-prop-2-ynyloxy-subsituted; two are symmetrically 6,7-disubstituted, and one is heterosubstituted (thio-PI). All PAs with antiallatal but without P-like activity are 7-monosubstituted with a relatively long alkoxy group. Certain substitutions favor antiallatal activity and others P-like activity. The severe nematocidal effect of 6,7-methylenedioxy-2,2-dimethylchromene (inert in insects) is not accompanied by P-like activity. The present findings lend some indirect support to the supposition that JH-producing cells and/or JH-dependent function(s) might exist in the nematodes.

Synthesis of 2,2-dimethylbenzoxazepinones by the Beckmann rearrangement of 2,2-dimethyl-4-chromanone oximes

2,3-Dihydro-2,2-dimethyl-1,4-benzoxazepin-5(4H)-ones and 2,3-dihydro-2,2,6-trimethyl-1,5-benzoxazepin-4(5H)-ones have been synthesized by the Beckmann rearrangement of 2,2-dimethyl-4-chromanone oximes

Effects of precocene analogs on the nematode Caenorhabditis remanei (var. Bangaloreiensis). II. Competitions with a juvenile hormone analog (methoprene)

Fourteen 7-alkoxy-2,2-dimethychromenes were synthetized and studied in JH competition experiments: precocenes (Ps) PI and PII, and synthetic analogs (PAs) including (i) three with both antiallatal and P-like activities: 7-ethoxy-PII (7-EPII); 7-(prop-2-ynyloxy)-2,-2-dimethylchromene (PPI); and 6-methoxy-7-(prop-2-ynyloxy)-2,2-dimethylchromene (PPIII); (ii) six without antiallatal activity, exerting P-like activity in nematodes; and (iii) three without either antiallatal or P-like activity, but with a strong nematocidal effect. Within the dose range 8-1000 micrograms/ml, different concentrations of each PA were applied to nematode growth medium which did or did not contain 1000 micrograms methoprene (a juvenile hormone analog JHA)/ml. Plates inoculated with Caenorhabditis embryos were incubated and scored for developmentally affected survivors. The JHA did not compete with any PA mentioned as (iii). It competed moderately with some nonantiallatal PAs (8-Me-PPI, 8-MeO-PPI, and 3,4-diCl-PPI) with strong P-like and nematocidal activities. The JHA competed most efficiently with all Ps, antiallatal PAs, and two nonantiallatal PAs (PPII and thio-PI) which exerted severe P-like activities in nematodes. Parameters assumed to be indicators of the P-like (rather than nematocidal) activity of the PAs proved more sensitive to the JHA than those of nematocidal activity. Whether the JH-compensable P-like activity of some PAs can be regarded as a real anti-JH action needs further clarification.