A diversity of alkylation/acylation products of uracil and its derivatives: synthesis and a structural study

tert-Butyl dicarbonate (Boc2O) and ethyl iodide (EtI) reactions with uracil (U), thymine (T) and 6-methyluracil (6-MU) were performed following routine procedures in pyridine/DMF solvents and with DMAP as the catalyst. Among 20 synthesized compounds, a derivative of 6-methyluracil substituted by the Boc-pyridine moiety at the C5 position appeared unexpectedly. The NMR spectra confirmed the molecular structure of all uracil derivatives. Parallel quantum mechanical DFT calculations supported the experimental findings.

Potential bioisosteres of β-uracilalanines derived from 1H-1,2,3-triazole-C-carboxylic acids

The 1H-1,2,3-triazole-originated derivatives of willardiine were obtained by: (i) construction of the 1H-1,2,3-triazole ring in 1,3-dipolar cycloaddition of the uracil-derived azides and the carboxylate-bearing alkynes or α-acylphosphorus ylide, or (ii) N-alkylation of the uracil derivative with the 1H-1,2,3-triazole-4-carboxylate-derived mesylate. The latter method offered: (i) reproducible results, (ii) a significant reduction of amounts of auxiliary materials, (iii) reduction in wastes and (iv) reduction in a number of manual operations required for obtaining the reaction product. Compound 6a exhibited significant binding affinity to hHS1S2I ligand-binding domain of GluR2 receptor (EC₅₀ = 2.90 µM) and decreased viability of human astrocytoma MOG-G-CCM cells in higher extent than known AMPA antagonist GYKI 52466.

Iodine monochloride facilitated deglycosylation, anomerization, and isomerization of 3-substituted thymidine analogues

The reaction of thymidine, 3-mono-, and 3,3',5'-trialkylsubstitued thymidine analogues with iodine monochloride (ICl) was investigated. Treatment with ICl resulted in rapid deglycosylation, anomerization, and isomerization of thymidine and 3-substituted thymidine analogues under various reaction conditions leading to the formation of the nucleobases as the major products accompanied by minor formation of α-furanosidic-, α-pyranosidic-, and β-pyranosidic nucleosides. On the other hand, 3,3',5'-trisubstitued thymidine analogues were only deglycosylated and anomerized. These results are similar to those observed for the acidic hydrolysis of the glycoside bond in nucleosides, but were presumably caused by the Lewis acid character of an iodine electrophile.

Synthesis, in vitro aerobic and hypoxic cytotoxicity and radiosensitizing activity of novel metronidazole tethered 5-fluorouracil

Background and the purpose of the study

Several 2, 4-dinitrophenyl and 2,4-dinitrophenylamine tethered 5-FU (5-fluorouracil) compared to their components have shown minimal or no cytotoxicity to HT-29 cell line under aerobic conditions but high cytotoxicity and radiosensitizing effects under hypoxic conditions. In the present study the cytotoxicity and radiation potentiation of three novel analogues of these compounds by replacing 2,4-dinitrophenyl moiety with 2-methyl-5-nitroimidazole, a known radiosensitizer and cytotoxic agent was investigated.

Methods

Tethered compounds 7–9 were prepared by the reaction of 1-(t-butoxycarbonyl)-5-fluorouracil 6 with metronidazole esters 2–4 followed by removal of the t-butoxycarbonyl protecting group. Cytotoxicity of compounds in HT-29 cells with or without radiation were determined by 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), propidium iodide (PI)-digitonin and clonogenic assays.

Results

Tethered compounds 7–9 induced time-and concentration–dependent cytotoxicity under hypoxia but had no significant effect under aerobic conditions. These compounds also showed selective and concentration- dependent radiosensitization effects under hypoxic conditions.

Conclusion

Tethered compounds 7–9 compared to 5-FU 5 showed minimal cytotoxicities under aerobic and selective radiosensitizing activities under hypoxic conditions. Also effects of these compounds were higher than those of metronidazole 1 which is a known cytotoxin and radiosensitizer under hypoxic conditions.

Cytotoxicity and radiosensitising activity of synthesized dinitrophenyl derivatives of 5-fluorouracil

BACKGROUND AND THE PURPOSE OF THE STUDY

Dual functional agents in which nitroaromatic or nitroheterocyclic compounds are attached through a linker unit to mustards and aziridines have shown higher cytotoxicities than the corresponding counterparts to both aerobic and hypoxic cells and enhanced radiosensitizing activity. In the present investigation cytotoxicity and radiosensitizing activity of 2,4-dinitrobenzyl, 2,4-dinitrobenzoyl, and 2,4-dinitrophenacetyl derivatives of 5-fluorouracil which was assumed to release cytotoxic active quinone methidide and 5-fluorouracil under hypoxic conditions on HT-29 cell line under both aerobic and hypoxic conditions was investigated.

METHODS

5-fluorouracil derivative X-XIII were prepared by the reaction of the corresponding di-nitro substituted benzyl, benzoyl and phenacetyl halides with 5-fluorouracil protected at N-1 with di-t-butoxydicarbonate (BOC) in dimethyl formamide (DMF) in the presence of the potassium carbonate followed by hydrolysis of the blocking group by potassium carbonate in methanol. Cytotoxicity of fluorouracil VIII and tested compounds X-XIII against HT-29 cell line under both aerobic and hypoxic conditions after 48 hrs incubation were measured by determination of the percent of the survival cells using 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and percent of the dead cells using propidium iodide(PI)-digitonine assay and results were used to calculate the corresponding IC(50) values. Radiosensitization experiments were carried out by irradiation of the incubations with a (60)Co source and clonogenic assay was performed to determine the cell viabilities following treatment with the tested compounds and/or radiation. Sensitization Enhancement Ratio (SER) of each tested compound was obtained from the radiation survival curves in the absence and presence of each sensitizer for 37% survival respectively.

RESULTS AND MAJOR CONCLUSION

Findings of the present study showed that alkylation or acylation of 5-fluorouracil result in compounds which have little or no cytotoxicity and radiosensitizing activity under aerobic conditions, but have high cytotoxicity and radiosensitizing effects under hypoxic conditions. Furthermore radiosensitizing activities of compounds under hypoxic conditions increased by increase in their concentrations and SER of the tested 5-FU derivatives at concentrations higher than 50 μmol were equal or higher than 1.6 which is the minimum effective SER of a radiosensitizer in an in vitro assay.

Synthetic strategies toward carbocyclic purine-pyrimidine hybrid nucleosides

The blending of key structural features from the purine and pyrimidine nucleobase scaffolds gives rise to a new class of hybrid nucleosides. The purine-pyrimidine hybrid nucleosides can be viewed as either N-3 ribosylated purines or 5,6-disubstituted pyrimidines, thus recognition by both purine- and pyrimidine-metabolizing enzymes is possible. Given the increasing reports of the development of resistance in many enzymatic systems, a drug that could be recognized by more than one enzyme could prove highly advantageous in overcoming resistance mechanisms related to binding site mutations. In that regard, the design, synthesis and results of preliminary biological activity for a series of carbocyclic uracil derivatives with either a fused imidazole or thiazole ring are presented herein.

Efficient N-Arylation and N-Alkenylation of the Five DNA/RNA Nucleobases

A general approach to N-arylation and N-alkenylation of all five DNA/RNA nucleobases at the nitrogen atom normally attached to the sugar moiety in DNA or RNA has been developed. Various protected or masked nucleobases engaged readily in the copper-mediated Chan-Lam-Evans-modified Ullmann condensation with a range of different boronic acids at room temperature and were subsequently converted to the corresponding deprotected or unmasked adducts. Different N(3)-protecting groups were examined in the case of thymine, where the benzoyl group afforded the highest yields. A 4-alkylthio-substituted pyrimidin-2(1H)-one served as both a cytosine and a uracil precursor and was N-arylated and N-alkenylated in high yields. Adenine was efficiently and selectively N-arylated and N-alkenylated at the N(9) position by employing a bis-Boc-protected adenine derivative, while a bis-Boc-protected 2-amino-6-chloropurine served as guanine precursor and could also be selectively N(9)-arylated and N(9)-alkenylated.

Benzhydryl as an efficient selective nitrogen protecting group for uracils

Regioselective N-substitution of the less active nitrogen within uracil analogues has been achieved following preliminary N-protection at the more active N-position with a benzhydryl protecting group. This protecting group is stable to concentrated HCl (aqueous) at reflux temperature, TFA at room temperature, and Pd-C-catalyzed normal pressure hydrogenation at room temperature; the benzhydryl group can be removed quantitatively and selectively with a 10% triflic acid solution in TFA at 0 degree C.

Synthesis, pharmacology and pharmacokinetics of 3-(4-aryl-piperazin-1-ylalkyl)-uracils as uroselective alpha1A-antagonists

Predominance in the urethra and prostate of the alpha(1A)-adrenoceptor subtype, which is believed to be the receptor mediating noradrenaline induced smooth muscle contraction in these tissues, led to the preparation of alpha(1A)-selective antagonists to be tested as uroselective compounds for the treatment of benign prostatic hyperplasia. Thus, a number of selective alpha(1A)-adrenoceptor antagonists were synthesized and assayed in vitro for potency and selectivity. Dog pharmacokinetic parameters of 12 (RO700004) and its metabolite 40 (RO1104253) were established. The relative selectivity of intravenously administered 12, 40 and standard prazosin to inhibit hypogastric nerve stimulation-induced increases in intraurethral prostatic pressure versus phenylephrine-induced increases in diastolic blood pressure in anesthetized dogs was 76, 71 and 0.6, respectively.