Zygmunt Kazimierczuk

Tautomerism of Isoguanosine and Solvent-Induced Keto-Enol Equilibrium

Abstract Ultraviolet and infrared absorption spectroscopy, in aqueous and non-aqueous media, have been employed to study the tautomerism of 9-substituted isoguanines, including the nucleoside iso guanosine. With the aid of a series of model compounds, it was shown that 9-substituted isogua nines, and isoguanosine, in aqueous medium are predominantly in the form N(1)H,2-keto-6-amino. In dioxane solution the tautomeric equilibrium is shifted in the direction of the enol form. The shift towards this form is accentuated for those analogues in which the exocyclic amino group is methylated. With the aid of N6,N6,9-trimethylisoguanine, and its 9-octyl analogue, the tautomeric constant was studied as a function of concentration, temperature, and solvent polarity, and the results applied to evaluate the tautomeric equilibria of 9-methylisoguanine and isoguanosine as a function of these variables. In general the enol form is favoured by a decrease in solvent polarity, by a decrease in concentration in dioxane, or an increase in temperature in chloroform solution. Syntheses are described for several N6-amino and methylamino derivatives of 2-methoxy-9-methylpurine, and 3-methyl-5-oxo-7,8-dihydroimidazo (2,1-i) purine, which served as an analogue of the unavailable 1,9-dimethylisoguanine.

Substrate/Inhibitor Properties of Human Deoxycytidine Kinase (dCK) and Thymidine Kinases (Tk1 And Tk2) Towards the Sugar Moiety of Nucleosides, Including O′-Alkyl Analogues

Nucleoside analogues with modified sugar moieties have been examined for their substrate/inhibitor specificities towards highly purified deoxycytidine kinase (dCK) and thymidine kinases (tetrameric high-affinity form of TK1, and TK2) from human leukemic spleen. In particular, the analogues included the mono- and di-O-methyl derivatives of dC, dU and dA, syntheses of which are described. In general, purine nucleosides with modified sugar rings were feebler substrates than the corresponding cytosine analogues. Sugar-modified analogues of dU were also relatively poor substrates of TK1 and TK2, but were reasonably good inhibitors, with generally lower Ki values vs TK2 than TK1. An excellent discriminator between TK1 and TK2 was 3-hexanoylamino-2,3-dideoxythymidine, with a Ki of approximately 600 microM for TK1 and approximately 0.1 microM for TK2. 3-OMe-dC was a superior inhibitor of dCK to its 5-O-methyl congener, consistent with possible participation of the oxygen of the (3)-OH or (3)-OMe as proton acceptor in hydrogen bonding with the enzyme. Surprisingly alpha-dT was a good substrate of both TK1 and TK2, with Ki values of 120 and 30 microM for TK1 and TK2, respectively; and a 3-branched alpha-L-deoxycytidine analogue proved to be as good a substrate as its alpha-D-counterpart. Several 5-substituted analogues of dC were good non-substrate inhibitors of dCK and, to a lesser extent, of TK2. Finally, some ribonucleosides are substrates of the foregoing enzymes; in particular C is a good substrate of dCK, and 2-OMe-C is an even better substrate than dC.

Synthesis of 2-Chloro-2′-Deoxyadenosine by Microbiological Transglycosylation

Abstract The title compound have been synthesized by an enzymatic trans-2′-deoxyribosylation of 2-chloroadenine using the whole cells of E. coli BMT-1D/1A as a biocatalyst and 2′-deoxyguanosine as a donor of glycosyl moiety.

Nucleosides, XLIV1 Synthesis, Properties and Biological Activity of Indazole Nucleosides

Abstract Various new haloindazole-1-β-D-ribofuranosides (10-17,20,21) and a 2-β-D-ribofuranoside (18) have been synthesized by the fusion method and by direct halogenations, respectively. The new nucleosides have been characterized by UV and 1H NMR spectra as well as pKa determinations. Indazole ribofuranosides behave in aqueous acid like purine and benzimidazole nucleosides showing the same mechanism of cleavage of the glycosidic bonds. Toxicity studies against various cell populations indicate only little biological activities.

Mechanism for Acid-Catalyzed Hydrolysis of Nucleoside and Acyclonucleoside Analogues of Benzimidazole

Abstract A study has been made of a broad series of nucleosides and acyclonucleosides of a variety of benzimidazole analogues. Quantitative kinetic data are presented, and the mechanism of the reactions described, taking into account steric, electronic and conformational effects. The overall results are also compared with those of purine nucleosides.

Activation of cyclic AMP-dependent protein kinases I and II by cyclic 3′,5′-phosphates of 9-β-D-ribofuranosylpurine and 1-β-D-ribofuranosylbenzimidazole

Abstract Analogs of cyclic AMP lacking the 6-amino group—9-β-D-ribofuranosylpurine cyclic 3′,5′-phosphate (I)—or the 1- and 3-nitrogens as well as the 6-amino group—1-β-D-ribofuranosylbenzimidazole cyclic 3′,5′-phosphate (II)—were effective activators of both type I (cAKI) and type II (cAKII) isozymes of cAMP-dependent protein kinase. An analog with a pyrimidine ring fused to the benzimidazole ring system of II—3-β-D-ribofuranosyl-8-aminoimidazo[4,5-g]-quinazoline cyclic 3′,5′-phosphate (III)—was equipotent to I or II as an activator of cAKII but only 1 10 as potent as I or II as an activator of cAKII. The results show that neither cAKI nor cAKII requires the 6-amino group and that they may have different sensitivities to the effects of alterations in the electron distribution in the pyrimidine ring.

Specific inhibition of hnRNA synthesis by 5,6-dichloro-1-β-d-ribofuranosylbenzimidazole. Requirement of a free 3′-hydroxyl group, but not 2′- or 5′-hydroxyls

Five structural analogues of 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB), all with modified sugar moieties, have been examined for their inhibitory activities on RNA transcription in salivary glands of Chironomus tentans. The well-known ability of the parent DRB at 65 microM concentration to selectively inhibit hnRNA/mRNA synthesis by approx. 90% was essentially abolished on methylation of the 3-OH; but, at an overdose the analogue suppressed labeling of all RNA classes examined (hnRNA/mRNA, rRNA, 4-5 S RNA) by 70-80%. By contrast, the 2-O-methyl derivative of DRB was almost as effective as DRB itself in blocking transcription of hnRNA/mRNA genes. Blocking of both the 2 and 3 hydroxyls (2,3-O-isopropylidene-DRB) completely abolished inhibitory activity, irrespective of the concentration employed. The 5-deoxy-5-chloro derivative of DRB was only slightly less effective than the parent DRB. An unusual aspect of the activities of 2-O-methyl-DRB and 5-deoxy-5-chloro-DRB was their ability to stimulate synthesis of 4-5 S RNA by 25-45%. Also investigated was the influence of the various analogues on the rate of formation of [3H]UTP from [3H]uridine used as an RNA precursor. The rate of such formation of [3H]UTP was suppressed 2-6-fold by treatment with 2-O-methyl or 3-O-methyl-DRB, but was unaffected by 5-deoxy-5-chloro-DRB or 5,6-dichloro-1-alpha-D-arabinofuranosylbenzimidazole. The overall data point to the importance of a free 3-OH in the ribose moiety of DRB for selective inhibitory activity. The alpha-D-arabinofuranosyl analogue, although less selective in inhibition of RNA transcription, still exhibits about 50% of the activity of DRB.

CONVERGENT SYNTHESES AND CYTOSTATIC PROPERTIES OF 2-CHLORO-2'-DEOXY-2'-FLUOROADENOSINE AND ITS N7-ISOMER

Glycosylation of trimethylsilylated 2,6-dichloropurine 2 with acetate 1 in anhydrous MeCN was investigated. In the presence of SnCl4, the reaction was regio- and stereoselective affording N7-β-glycoside 3 (86%). The use of TMS-Tfl instead of SnCl4 afforded a ≈ 9:1 mixture of the N9-β- and -α-glycosides 5 and 6 (90%, combined). The title nucleosides were tested for their cytotoxicity.

THE NOVEL PRODUCT OF CATHODIC REDUCTION OF PHTHALIMIDE ANION

Abstract Cathodic reduction of phthalimide anion in methanol was studied. The novel product, N-hydroxymethyl-3-hydroxyphthalimidine, was found. Full characterization of this new compound was carried out by means of NMR, FT-IR, MS, and X-ray crystallography. The mechanism of electrolytic formation of N-hydroxymethyl-3-hydroxyphthalimidine is proposed.

Preparation and properties of the 5,6- and 4,6(5,7)-dinitro derivatives of benzimidazole and their 1-β-D-ribofuranosides

Abstract Nitration of benzimidazole leads to the formation of the two isomeric 5,6- and 4,6(5,7)-dinitrobenzimidazoles, which may be isolated by fractional crystallization. The chloromercury salts of these were employed to synthesize the corresponding 1-β-D-ribofuranosides, unequivocally characterized by 1H NMR spectroscopy. Reference is made to the biological significance of these results.