An alternative to ‘propylene/Leonard linker’ for studying arene interactions in flexible pyrazolo[3,4-d]pyrimidine core based models both at molecular and supramolecular levels

Abstract

An alternative C-3 linker to ‘propylene/Leonard linker’ is proposed for studying arene interactions in face-to-face (offset) mode. The two new flexible symmetrical compounds with an electron deficient pyrazolo[3,4-d]pyrimidine core and biologically important isomeric purine systems and one dissymmetrical compound with a pyrazolo[3,4-d]pyrimidine core and electron-rich carbazole residue at the termini of the new linker show folding due to intramolecular π–π interactions by both ¹H NMR in solution and X-ray crystallography in the solid state. Surprisingly, the replacement of the 4-methylsulfanyl group of the dissymmetrical compound by an electron donating methoxy group shows open conformation in the solid state by X-ray crystallography. The fifth symmetrical compound with an electron-rich carbazole residue at the termini of new linker, however, shows the normally expected open conformation.