Novel macrocyclic uracil derivatives: Structure in solid and solution

Abstract

Isomeric pyrimidinophanes containing uracil moieties and nitrogen atoms in bridges have been synthesized and characterized by a variety of methods both in solid and in solution. Unambiguous assignment of mutual arrangement of C(4) pyr O groups at different pyrimidine rings in isomers is made by X-ray diffraction. In solutions the arrangement of C(4) pyr O groups of the isomeric pyrimidinophanes results in different dipole moments. Based on dipole moments simulations mutual orientation of uracil units in isomers is analysed. UV-data are discussed in terms of hypo-or hyperchromic effect.

Unusual Reaction of Macrocyclic Uracils with Paraformaldehyde

“…Isomers 1c/1d and 1e/1f were separated by column chromatography; trans-pyrimidinophanes were the first to elute and the cis isomer was eluted in the second fractions. [19] The yields of the macrocycles proved to be slightly less than those of isomers 1a,b. [17,19] The methyl group is introduced either at the C 5 atom or at the C 6 atom of the pyrimidine ring to permit or to prohibit any electrophilic substitution at the C 5 position.…”

“…[19] The yields of the macrocycles proved to be slightly less than those of isomers 1a,b. [17,19] The methyl group is introduced either at the C 5 atom or at the C 6 atom of the pyrimidine ring to permit or to prohibit any electrophilic substitution at the C 5 position. As a result, the reaction of pyrimidinophanes 1e,f with paraformaldehyde can occur only with 6-methyluracil but not with the thymine fragments of the compounds, whereas in macrocycles 1c,d both 6-methyluracil moieties can react with paraformaldehyde to afford methylene bridges connecting the C 5 atoms of the pyrimidine rings.…”

“…As excellent starting monomeric pyrimidinophanes for their cross-linking into multipyrimidinophanes, we considered isomeric pyrimidinophanes 1a,b previously developed [17,19] and distinguished from one another by mutual arrangement, trans (pyrimidinophanes 1a) or cis (pyrimidinophanes 1b) to the C 4 =O groups at the pyrimidine cycles, as shown in Figure 1. It was assumed that reaction of one or both uracil moieties in isomers 1a,b with paraformaldehyde might afford linearly arranged multipyrimidinophanes 2a,b, which are schematically represented in Figure 2.…”

Interplay of thermochemistry and Structural Chemistry, the journal (volume 17, 2006) and the discipline

“…A study by Semenov et al [223] follows on the synthesis of a series of new pyrimidinophanes with polymethylene bridging chains of different length (n = 3, 4, 5) and nitrogen atom incorporated into the bridges and cis and trans-isomers isolated. According to dipole moments data uracil units of cis-isomer are situated either in one plane or in parallel planes while uracil moieties of trans-isomer in solution are twisted respective to each other by 40°C in contrast to their mutual arrangement in crystal.…”

The twentieth year in Structural Chemistry

“…X-ray diffraction played an important role in the structure determination of novel macrocyclic uracil derivatives [6]. Semenov et al used a combination of experimental techniques (X-ray diffraction, IR, UV, NMR spectroscopy, and dipole moment measurements), and their investigation revealed the characteristic twist of the macrocyclic ring upon solvent effects with respect to the solid-phase structure.…”