As part of an effort to develop general probes for radical reactions involving DNA bases, several uracil derivatives were synthesized. The rates of the cyclopropyl carbinyl rearrangement in these systems were evaluated by means of competition experiments. The results indicate that when a cyclopropyl group is substituted in the 5-position of uracil, the rearrangement occurs very slowly-with a rate constant of <2.5 x 10(4) s(-1). On the other hand, the analog of the 5-hexenyl radical cyclization onto the 5,6-double bond of uracil derivatives occurs with rates which were similar to the parent process: (4.0-8.9) x 10(4) s(-1). The experimental results along with semiempirical calculations show that radicals 23 and 25 are unusually stable species. These results explain why no rearrangements are observed when a cyclopropyl-substituted thymine dimer is cleaved by reductive single electron transfer.
As part of an effort to develop general probes for radical reactions involving DNA bases, several uracil derivatives were synthesized. The rates of the cyclopropyl carbinyl rearrangement in these systems were evaluated by means of competition experiments. The results indicate that when a cyclopropyl group is substituted in the 5-position of uracil, the rearrangement occurs very slowly-with a rate constant of <2.5 x 10(4) s(-1). On the other hand, the analog of the 5-hexenyl radical cyclization onto the 5,6-double bond of uracil derivatives occurs with rates which were similar to the parent process: (4.0-8.9) x 10(4) s(-1). The experimental results along with semiempirical calculations show that radicals 23 and 25 are unusually stable species. These results explain why no rearrangements are observed when a cyclopropyl-substituted thymine dimer is cleaved by reductive single electron transfer.
5-Cyclopropyluracil and cyclopropylcytosine were prepared by the Pd(0)-catalyzedcouplingreaction of 5-bromo-2,4-di(trimethylsilyloxy)pyrimidine and 5-bromo-2,4-O,N-bis-trimethylsilylcytosine with tributylstan-nylcyclopropane. The reactions also gave dehalogenated pyrimidine bases as by-products. Attempts to use 2,4-O,N-bis-trimethylsilyl-5-iodocytosine as the halide gave complete dehalogenation.
The Synthesis of Some 5-Substituted and 5,6-Disubstituted 2′-Deoxyuridines
作者:I. Basnak、A. Balkan、P. L. Coe、R. T. Walker
DOI:10.1080/15257779408013234
日期:1994.3
5-Alkyl(cycloalkyl)-2'-deoxyuridines VIa-VIf were synthesised in high yields by condensation of the corresponding silylated bases with 2-deoxy-3,5-di-O-p-toluoyl-D-erythro-pentosyl chloride in chloroform and subsequent deblocking with sodium methoxide in methanol. The beta-configuration, anti-glycosidic conformation and C2'-endo (S) sugar pucker of all of these compounds has been established from their H-1 NMR, C-13 NMR, UV and mass spectra. Under the same conditions, the condensation of silylated 5,6-trimethyleneuracil, resulted in 1:2/alpha:beta anomeric mixture (overall yield 71%) and syn-conformation of the 5,6-trimethylene-2'-deoxyuridine [Xg]. The results of the condensation of the silylated 5,6-dimethyluracil are discussed as well. No significant antiviral activity has been found in testing the synthesised compounds against a range of herpes, influenza and HIV-1 viruses.
The Synthesis of Some 5-Alkyl (Cycloalkyl)-Substituted 2′ -Deoxy-4′-Thiouridines
作者:I. Basnak、M. Sun、P. L. Coe、R. T. Walker
DOI:10.1080/07328319608002375
日期:1996.1
The silylated pyrimidine bases IIa-d were condensed with the benzyl 3,5-di-O-benzyl-2-deoxy-1,4-ditkio-D-erythro-pentofuranoside III in acetonitrile under activation by N-iodosuccinimide, giving ca 1.5 : 1/alpha: beta anomeric mixtures of the blocked nucleosides IVa-d and Va-d. in yields of 55-88%. After the separation on a silica column the pure anomers were deprotected by BCl3 or TiCl4, providing the free nucleosides VIa-d and VIIa,c,d in moderate to good overall yields. The beta- or alpha-anomeric configuration, anti-glycosidic conformation and prevailing C2'-endo(S) thiosugar pucker in the synthesized compounds were established by the combined use of the H-1, C-13 NMR and X-ray crystallography.
Basnak, Ivan; Farkas, Jiri; Zajicek, Jaroslav, Collection of Czechoslovak Chemical Communications, 1986, vol. 51, # 8, p. 1764 - 1771