Barbiturate guest molecule

The synthesis of bis(triazine) molecules capable of acting as synthetic receptors for barbiturate guest molecules has been described <06EJO1444>. 

Often designated briefly as Hamilton receptor , this barbiturate receptor niche (Fig. 6.12) consists of an isophthaloyl spacer flanked by two acylated 2,6-diaminopyridine moieties. Macrocyclisation with a rigid diphenylmethane unit generates a non-collapsing host cavity suitable for selective complexation of barbiturate guest molecules via formation of six hydrogen bonds. 

Fig. 6.12 Macrocyclic Hamilton receptor for barbiturate guest molecules (left-hand side). A non-cyclic Hamilton host compound with...

Fig. 6.13 POPAM dendrimer with peripheral Hamilton receptor niches (red) and docking of barbiturate guest molecules (green schematic)...

Figure 9 shows the examples of separations of racemic mixtures of methylphenobarbital and mephenytoin performed under optimal conditions available (37). It has been found that ( -CD complexation resuTts in a distinct enantioselectivity in the case of mephenytoin and barbiturates which have a chiral center in the pyrimidine ring. The resolution of barbiturate enantiomers is due to the different stabilities of their diastereo-isomeric -CD complexes, while the separation of mephenytoin enantiomers results from the difference in their adsorption on the RP phase. The latter case should be considered further. It has been already suggested (18) that the adsorption of CD complexes in which guest molecules are entirely immersed in the CD cavity is low on RP phases. The distinct adsorption arises from the part of the molecule which is outside the cavity. Taking into account this fact and the remarkable difference in the adsorption of -CD mephenytoin diastereoisomers one may conclude that a significant difference must exist between immersion of mephenytoin enantiomers in the -CD cavity. 

Of those functional crystalline assemblies with structures that conform to polyhedra, it is the prisms that have, thus far, been most studied. In particular, Rein-houdt has described a 3D assembly with a structure that conforms to the simplest prism namely, a trigonal prism.53 Specifically, three calix[4]arenes functionalized at the upper rim with two melamine units have been shown to assemble with six barbituric acid molecules via 36 hydrogen bonds to form a nine-component assembly with a structure that approximated a trigonal prism (Fig. 31). Although the cavity of the assembly was too small to accommodate a guest, the assembly packed to produce voids that included toluene molecules as guests. 

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