Piotr Sałański

B–Z DNA reversible conformation changes effected by high pressure

There are numerous data showing that a DNA molecule with alternate pirymidine‐purine sequence can adopt a left‐handed, double‐helical Z‐DNA conformation. Such structural changes of DNA occur as a consequence of environmental conditions (e.g. 4 M NaCl) or chemical modification (e.g. methylation or bromination of bases). In this paper, we found for the first time that high pressure (several kilobars) can change the DNA conformation from the B to the Z form. When the pressure is reduced to an atmospheric one, DNA conformation returns back to the B‐form. The Z‐DNA structure formation was confirmed by circular dichroism (CD) and ultraviolet (UV) measurements. However, we found, that the values of the ratio of absorbance at the wavelenghts 295 and 257 nm in the range of 0.3–0.4 is not a fully conclusive proof for the Z‐DNA conformation. Although the ratio is typical for Z‐DNA form, it is not obvious that the negative band in CD spectrum will be observed. On the other hand, methylated DNA does not undergo B→Z DNA transitions at the high pressure. These conformational changes of DNA molecules could be interpreted as the effect of different hydration of various DNA forms.

A new method for the synthesis of diazacoronands via double-amidation reaction

Abstract α,ω-Diamino aliphatic ethers react under ambient conditions with dimethyl α,ω-dicarboxylates, in methanol as a solvent, to give the cyclic diamides in good yields. Their subsequent reduction with a borhoydride-dimethyl sulphide complex affords the respective diazacoronands.

APPLICATION OF STABILIZED SUGAR-DERIVED PHOSPHORANES IN THE SYNTHESIS OF HIGHER CARBON MONOSACCHARIDES. FIRST SYNTHESIS OF A C21-DIALDOSE

Abstract C21 Monosaccharide precursors 11 and 12 were synthesized by a coupling of a C12 aldehyde 1 with C9 stabilized phosphoranes 2 and 3 respectively. The “smaller” C19 sugar 13 was prepared from a C12 aldehyde 1 and C7 phosphorane 4. All reactions with phosphoranes were performed under high pressure (13 kbar). No reaction was observed under normal pressure even at high temperature (ca 140°C). The synthesis of C19 and C21 monosaccharides was accomplished also under normal pressure when phosphoranes were replaced with more nucleophilic phosphonates; however, partially eliminated products (M - benzyl alcohol) were isolated together with higher sugar enones 11, 12 and 13. Sugar α-hydroxy-aldehydes (14) did not react with a C9-phosphorane even under 13 kbar pressure, although reaction with a shorter analog - C7 phosphorane 15 proceeded under normal pressure in boiling benzene.

The use of the Mitsunobu reaction in preparation of chiral synthons for macrocyclic frameworks

Abstract The Mitsunobu reaction was used for the synthesis of chiral diesters 2 and 6 and chiral diamine 4 . Five new chiral macrocyclic bisamides were synthesized, starting from these precursors.

Stereoselectivity of 1,3-dipolar cycloadditions of L-valine-derived nitrones with methyl acrylate

Abstract Chiral nitrones derived from l -valine react with methyl acrylate to afford the corresponding diastereomeric 3,5-disubstituted isoxazolidines. The dibenzylsubstituted nitrone gave also 3,4-disubstituted isoxazolidine in 4% yield, additionally. The stereoselectivity was dependent on the steric hindrance of the nitrone and reaction conditions. High pressure decreased the reaction time of the cycloadditions. The major products were found to have the C-3/C-6 erythro and C-3/C-5 trans relative configuration. The major cycloadduct undergoes N–O cleavage and deprotection to a chiral diaminodiol derivative.

High-pressure approach to the synthesis of macrocyclic diamides

Abstract A versatile and efficient route to macrocyclic amides via high-pressure synthesis is described. Application of the high-pressure technique allows obtaining the title compounds under ambient conditions. The scope and limitations of this reaction are presented.

A general method for the synthesis of diazacoronands

α,ω-Diamino aliphatic ethers react under ambient conditions with dimethyl α,ω-dicarboxylates, in methanol as a solvent, to give the cyclic diamides in good yields, and their subsequent reduction with lithium aluminium hydride affords the respective diazacoronands.

High-pressure approach to the synthesis of novel chiral cryptands derived from methyl 4,6-O-benzylidene-α-D-manno-, -α-D-galacto-, and -α-D-gluco-pyranoside

Diaza crown ethers derived from sugars react under high pressure with bis-(2-iodoethyl) ether to give the quaternary salts in quantitative yield and their subsequent demethylation with triphenylphosphine affords chiral cryptands in high yield.

Native transfer RNA catalyzes Diels-Alder reaction.

In this paper we show that transfer ribonucleic acids (tRNAs) catalyze the Diels-Alder cycloaddition reaction. A new DNA oxidative damage product, 6-furfuryladenine (kinetin) or its riboside (diene), was transformed with dimethyl acetylenedicarboxylate or maleic anhydride (dienophile). The reaction proceeds in the presence of tRNA at high pressure but not at ambient condition. If so tRNA in prebiotic conditions (RNA world) had at least two functions: catalytic and a carrier of genetic information. It means that tRNA at high pressure shows catalytic properties and is a true Diels-Alderase.

Synthesis of macrocyclic tetraamides derived from α-amino acids and their investigations using ESI-MS technique

Abstract Chiral α,ω-diesters react under high-pressure conditions (10 kbar) with α,ω-diamines to give chiral cyclic tetraamides of C2-symmetry. The complexation properties of tetraamides towards alkali metal cations (Li+, Na+, K+, Rb+ and Cs+) were estimated on the basis of ESI-MS spectra.