On the basis of our study on the structure-activity relationships of 1,3,7-alkylxanthines and condensed-purines on cAMP-phosphodiesterase 4 (PDE 4) isoenzyme inhibitor, we investigated the synthesis and the inhibitory activity of 3-phenylxanthine and 4-phenyl[i]condensed-purine derivatives. Xanthines and condensed-purines with the phenyl group exhibited potent and selective PDE 4 inhibitory act...

1. Community level oak–tannin–insect patterns have been largely unexplored since Paul Feeny’s ground-breaking research. Two hypotheses were tested for Quercus velutina and Q. alba in the Missouri Ozarks: abundance and richness of leaf-chewing herbivores are negatively correlated with foliar condensed tannin concentrations and variation in condensed tannin concentrations explains variation in he...

The physical location of the rDNA repeating units (25 S, 18 S and 5.8 S rRNA genes and the intergenic spacer sequences) was investigated in rye (Secale cereale L.) and wheat (Triticum aestivum L.) root tip meristematic cells by in situ hybridization using light and electron microscopy. The rDNA sequences are organized differently in the two related and intercrossable species. In rye (2n = 14, o...

The importance of caterpillar trees in the topological theory of benzenoid systems lies in the following. Let B be a non-branched cata-condensed benzenoid hydrocarbon (that is a hydrocarbon containing linearly and angularly condensed rings). If we associate a symbol L to each linearly condensed ring (and also to the two terminal ones) and a symbol A to each angularly condensed ring, then the so...