Acta Crystallographica Section B

Structural Science

Volume 58, Part 2 (April 2002)

research papers

Acta Cryst. (2002). B58, 300-315 [ doi:10.1107/S0108768101021607 ]

Amino-substituted O⁶-benzyl-5-nitrosopyrimidines: interplay of molecular, molecular-electronic and supramolecular structures

A. Quesada, A. Marchal, M. Melguizo, M. Nogueras, A. Sánchez, J. N. Low, D. Cannon, D. M. M. Farrell and C. Glidewell

Abstract: The structures of eight 2,4,6-trisubstituted-5-nitrosopyrimidines (one of which crystallizes in two polymorphs) have been determined, including seven O⁶-benzyl derivatives which are potential, or proven, in vitro inhibitors of the human DNA-repair protein O⁶-alkylguanine-DNA-transferase. In the derivatives having an amino substituent at the 4-position, an intramolecular N-HO hydrogen bond with the nitroso O as an acceptor leads to an overall molecular shape similar to that of substituted purines. There is a marked propensity for these nitroso compounds to crystallize with Z' = 2. The structure of an analogue with no nitroso group is also reported for comparative purposes. Compounds containing the N-alkyl substituents -NHCH₂COOEt, -NHCH₂CH₂COOEt and -NHCH(CH₂Ph)COOEt, derived from amino acid esters, exhibit a rich variety of conformational behaviour, and in all of the nitroso compounds the bond lengths provide strong evidence for a highly polarized electronic structure. Associated with this polarization is extensive charge-assisted hydrogen bonding between the molecules, leading to supramolecular aggregation in the form of finite (zero-dimensional) aggregates, chains, molecular ladders, sheets and frameworks.

Keywords: supramolecular structures; charge-assisted hydrogen bonding; polymorphism.


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