Karel Bláha

Cyclic Enamines and Imines

Publisher Summary This chapter reviews the properties, methods of preparation, and reactions of heterocyclic compounds possessing the so-called enamine grouping. It also discusses the reactions of enamines obtained from aliphatic or alicyclic carbonyl compounds and those from secondary heterocyclic bases, which are very interesting from the preparative point of view. The chapter begins with the structure and physico-chemical properties of enamines. The existence of an enamine grouping in a molecule makes possible several interconvertible isomeric structures. This fact is responsible for the high reactivity of these compounds. Furthermore, unsaturated amines in which the double bond is separated from the nitrogen atom by at least one saturated carbon atom show a behavior typical to saturated amines and non-conjugated olefins. A double bond in the position α, β to the nitrogen atom leads, by contrast, to the formation of a new reactive grouping in which the free electron pair of nitrogen is conjugated with the π-electrons of the double bond. The character of both the original structural elements is considerably changed.

Verbaskine, a macrocyclic spermine alkaloid of a novel type from Verbascum pseudorobile Stoj. et Stef. (Scrophulariaceae)☆

Abstract On the basis of chemical degradation and spectral data (UV, IR, NMR and MS) the structure 1 was deduced for the macrocyclic spermine alkaloid verbaskine from Verbascum pseudonobile Stoj. et Stef. of Bulgarian origin. (E)-Cinnamamide was also isolated from the same plant material.

Basic polypeptides as histone models: circular dichroism of complexes of model polypeptides with DNA.

Circular dichroism (CD) was used to study the complexes of DNA (in 0.15M NaCl) with two polypeptides considered as models of the histone molecules. CD spectra in the region of DNA absorption were studied with respect to the concentration used for annealing and to the molecular weight and composition of the DNA used. The properties of supernatants after centrifugation of aggregated complexes were examined. The effect of selectively bound antibiotics (actinomycin D and netropsin) on CD sprectra of complexes was investigated. The induced CD of proflavine molecules bound to DNA in the various complexes was also studied. It was concluded that changes in the CD spectra of DNA in complexes with the polypeptides are due to the formation of chiral superstructures, even if some conformational changes of DNA molecules themselves may also be decisive in some cases. The superstructure is affected by the composition of DNA, the role of (G + C) rich segments being particularly important.

Thermal melting and circular dichroism of DNA complexes with (Lys-Ala-Ala)10 and (Lys-Ala-Ala)n: effect of polypeptide chain length

Abstract DNA complexes with polypeptides (Lys-Ala-Ala) 1 )] and (Lys-Ala-Ala) 34 have been studied using the methods of thermal melting and circular dichroism. Derivative melting curves of (Lys-Ala-Ala) 10 DNA differed substantially from those of (Lys-Ala-Ala) 34 prepared either by salt gradient dialysis or by direct mixing. Melting curves of the former complex were unimodal or bimodal with T m increasing continuously withn input lysin-to-DNA phosphate ratio ( r ); those of the latter complex consisted of three separate transitions with T m values almost independent of r . Complete reversibility of binding in the (Lys-Ala-Ala) 10 -DNA system but a slow redistribution of (Lys-Ala-Ala) 34 on DNA at low temperature were found in the redistribution experiments Much faster redistribution from denatured to native DNA occurs at the temperature of melting, contributing to the unusual trimodal melting pattern. Circular dichroism curves are very similar for both complexes and indicate little change of DNA conformation upon polypeptide binding.

THERMAL MELTING OF DNA COMPLEXED WITH POLYPEPTIDES CONTAINING BASIC AND NEUTRAL ALIPHATIC AMINO ACID RESIDUES

ABSTRACT Complexes of DNA with sequential polytripeptides of the type (Lys-X-Gly)n and (Lys-X-Ala)n where X is neutral aliphatic amino acid residue, and with (A2bu-Leu-Gly)n and (A2bu-Leu-Ala)n have been studied by the method of thermal denaturation. The melting temperature of polypeptide-bound DNA strongly depends on the amino acid side chain structure. In the case of polypeptides containing amino-acid residues with linear side chain, melting temperature of complexes decreases with increasing length of side chain. Branching on B carbon is without influence in the case of valine-containing polypeptides but substantially lowers the thermal stability of complexes in the case of isoleucine-containing polymers. The decrease in thermal stability caused by both factors is probably due to sterical reasons. Complexes of DNA with leucine-containing polypeptides are more stable than other complexes, probably due to stabilization by hydrophobic forces. However, the stabilization is strongly reduced when lysine is replaced by diaminobutyric acid.

NATURE OF PROTEIN – DNA INTERACTIONS REVEALED BY MODEL POLYPEPTIDE COMPLEXES

Publisher Summary Generally, two types of DNA - binding proteins can be recognized: (1) specific binding proteins, for example, repressors and other regulatory proteins and (2) nonspecific binding proteins, for example, histones or protamines. The primary and higher structures of the entire protein molecule may affect the binding to DNA. It is assumed that the binding is largely determined by the structure of the binding polypeptide segment. Basic polypeptides are designed and synthesized with controlled amino acid composition and sequence to study the effect of polypeptide primary structure and conformation on the binding to DNA. The affinity of polypeptides to DNA and the mechanism of binding are substantially affected by two factors in the polypeptide primary structure: the nature, content, and distribution of basic residues and, the presence of strongly hydrophobic residues.