Fine tuning of folded conformation by change of substituents: H-1 NMR and crystallographic evidence for folded conformation due to arene interactions in pyrazolo[3,4-d]pyrimidine core based 'propylene linker' compounds

摘要

Proton NMR and X-ray crystallographic analysis of two newly synthesized 'trimethylene linker,' (Leonard linker) compounds 1,3-bis(4-ethoxy-6-methylsulfanyl-1H-pyrazolo [3,4-d]pyrimidin-1-yl)propane (4c) and 1,3-bis(4-isopropoxy-6-methylsulfanyl-1H-pyrazolo[3,4d]pyrimidin-1-yl)propane (4d) show intramolecularly stacked conformations both in solution and solid state. Robustness of the unusual U-motif formed due to intramolecular stacking in earlier related compounds (1, n = 3 and 3, n = 3) is not only confirmed but additional fine tuning is also achieved in new compounds (4) formed by replacement of remote 4-alkylsulfanyl group in la by 4-alkoxy substituents. (c) 2005 Elsevier B.V. All rights reserved.